Table of contents

Enhancing the carrier or mass transport and establishing intimate electronic contact at the catalyst-electrode interface are critical for developing high-performance glucose biofuel cells (GBFCs). Here, we demonstrate that engineering of the electrical synergy between the electrode and graphene acid (GA)-based

catalysts can lead to an efficient, nonenzymic, membrane-free GBFC. Our studies suggest that GA is a bifunctional catalyst with high oxygen reduction reaction (an onset potential of 0.8 V) and good glucose oxidation activities. The glucose oxidation capability of GA is further enhanced by tuning the GA's band structure through forming a heterostructure between GA and samarium oxide (Sm₂O₃) nanoparticles. The GA based GBFC (with Sm₂O₃/GA heterostructure as bioanode and GA as biocathode) produced a power density of 1.55 µW·cm⁻² (in saliva). While the interdimensional Sm₂O₃/GA heterostructure showed excellent nonenzymic amperometric glucose sensing performance, the GBFC-based self-powered sensors showed a limit of detection of 70 nM for glucose. Our comparison between GA and reduced graphene oxide as catalyst substrates for glucose oxidation revealed that the higher carboxylic acid content on GA enhances its overall electron affinity and coupled with improved conductivity, leads to GA's better glucose sensing performance. Finally, through a detailed theoretical exploration, we establish that the superiority of Sm₂O₃/GA is due to the synergistic effects between Sm₂O₃ and GA in the heterostructure, leading to an increased number of catalytic sites with stronger glucose binding affinity. The study presents the potential of GA as a highly tunable platform for a broad range of electrochemical applications, especially in future self-powered biosensors.

Nanosensors consisting of carbon-based nanostructures (CNS) enable the study of physical, chemical, and biological phenomenon occurring in microdomains. One approach for producing such sensors employs template-based nanomanufacturing processes, where carbon nanostructures are formed inside nanoporous templates. In this work, template-based nanomanufacturing was utilized as the foundation to produce two distinct sensors at the tips of pulled glass capillaries: a nanoscale thermocouple and self-contained electrochemical nanosensor. The initial manufacturing steps were the same for both sensors. Briefly, pulled quartz theta capillary templates were prepared, carbon was deposited on the templates via chemical vapor deposition (CVD), and templates were wet-etched at their tips to expose CNS. The resulting device consisted of two distinct CNS within a sub-500 nm tip connected to conductive carbon conduits running the length of the pulled glass capillary. To form the thermocouple, gold and nickel were electroplated onto the CNS scaffold. The configuration and material selection provided a thermoelectric power of 14.9 μV·K-1, a significant improvement over other micropipette-based thermocouples. To form the electrochemical sensor, one of the two CNS was electroplated with silver and chlorinated to serve as a pseudoreference electrode. With the working and reference electrodes positioned within 50 nm of each other, the overall sensor footprint was minimized in order to perform self-contained electrochemistry inside aqueous microdroplets. These CNS sensors were designed to readily integrate into standard laboratory equipment, promoting broad utilization.

Figure 1

The development of self-contained analytical devices for accurate and rapid quantification of molecular analytes in unprocessed biological fluids holds great promise for next-generation precision medicine [1]. Since reagentless electrochemical approaches are ideal candidates for building fully integrated testing devices with optimal user-friendliness, several sensors based on redox-active enzymes, and affinity-binding assays with different configurations containing recognition elements have been applied broadly to biomolecular detection. These advancements have addressed a variety of challenging problems, including in vivo sensing of small molecules and single-step, quantitative detection of multiple antibodies, however, most of the existing affinity-based sensors are fundamentally limited to recognition agents based on small molecules, peptide epitopes, and small proteins. Moreover, their compromised sensitivity (sub-nanomolar to hundreds of nanomolar) in unprocessed biofluids greatly limits their clinical usability [2].

Recently, we have developed a new class of biomolecular sensors using molecular pendulum (MP) [3], which is a general approach for the development of reagentless sensors to monitor physiologically relevant proteins directly in body fluids. The sensing strategy is based on the motion of an inverted MPs tethered to an electrode surface that exhibits field-induced transport modulated by the presence of a bound analyte.This powerful and versatile sensing strategy, using antibody as the bioreceptor unit, demonstrated to detect as low as 1 pgml−1 (~40 fM) of a target protein, cardiac troponin I (cTnI), in several bio-fluids including blood and saliva. Since aptamers, in addition to having the molecular recognition properties of antibodies, such as high affinity and selectivity [4], have unique compelling features for high-throughput applications in diagnostics including small physical size, quick chemical production with low cost and minimum batch-to-batch variability, high stability and long shelf-life [5], we sought out to theoretically investigate and experimentally explore the feasibility to employ aptamers to develop novel and robust MP aptasensors. Here we describe novel reagent-free MP aptasensors that quantify different heart failure biomarkers including BNP and NT-pro BNP directly in whole human blood using only a sensor-modified electrode chip by leveraging and upgrading the MP approach. The electrode-tethered aptasensors (Fig. 1a) are constructed by anchoring a negatively charged double stranded DNA linker on to an electrode; one of the DNA strands is extended to form an analyte-binding aptamer and the other strand features a tethered redox probe. Using chronoamperometry, which enables the sensor transportation to the electrode surface, the presence of an analyte bound to our sensor complex can be detected and subsequently quantified as these species increase the hydrodynamic drag on the sensor. To explore the feasibility of this approach, we modeled the behavior of an MP aptasensor, and thanks to the intrinsic negative charge and small size of aptamers, our model yielded a higher Δτ, which is difference in the fall time of the sensors to the electrode surface between its unbound and bound state to its target analyte, for the aptasensors compared to its antibody-based counterpart; and a similar trend was observed when we explored these phenomena experimentally (Fig. 1b). We then systematically investigated the analytical strength of the MP aptasensors in lab buffer and in whole human blood, and the results show excellent performance matrices, such as a wide dynamic range (10 fg/mL to 10 ng/mL of BNP), a LOD of ~0.67fM BNP, and high specificity, and long-term stability of the sensors (Fig 1c-f).

The performance of the MP aptasensors to quantify BNP and NT-pro BNP in whole human blood has been evaluated and the data warrant potential applicability of these new class of sensors for earlier identification and better risk stratification of patients with chronic heart failure.

References:

1. Shrivastava, S. et al Chem. Soc. Rev. (2020) 49, 1812-1866

2. Clifford, A. et al J. Am. Chem. Soc. (2021), 143, 14, 5281–5294

3. Das, J., Gomis, S., et al. Nat. Chem. (2021) https://doi.org/10.1038/s41557-021-00644-y

4. Bunka, D., Stockley, P. Nat Rev Microbiol (2006) 4, 588–596

5. Zhou, J., Rossi, J. Nat Rev Drug Discov (2017) 16, 181–202

Figure 1

There is a great demand for a fast, on-site screening test, especially during the COVID-19 pandemic. However, most point-of-care (POC) sensors usually suffer from insufficient sensitivity and selectivity. Often these devices have a very high rate of false positives and false negatives. The incorrect data could result in low customer usage (both the patient and the doctor) due to decreased confidence in the results. Portable ELISA-based kits can have low rates of false-positive and false negatives. However, ELISA is inherently complicated and often requires a specialist on-site to ensure the success of each sample's high costs and time.

Here we show a new electrochemical platform called ESSENCE. ESSENCE is an Electrochemical Sensor that uses a Shear-Enhanced, flow-through Nanoporous Capacitive Electrode. ESSENCE can overcome current electrochemical sensors' selectivity and sensitivity limitations. The ESSENCE sensor architecture is a microfluidic channel sandwiched between two gold micro-electrode glass slides, formed a non-planar interdigitated porous electrode that improved electric field penetration compared with the traditional planar interdigitated electrode. The porous electrode structure used in this research has a high Zeta potential compared to the bare glass surface. This results in a significantly smaller Debye double-layer (EDL) length than in a clear channel. Due to a smaller EDL length, the relaxation frequency increases, which shifts the EIS signal to a higher frequency range (1kHz to 100MHz) and results in a fast response with a higher signal-to-noise ratio in Electrochemical Impedance Spectroscopy(EIS) measurements.

Further, the modular fabrication of the ESSENCE chip allows ESSENCE to target different biomolecules from DNAs to protein cancer biomarkers by simply changing the packed transducer material. However, the packing material's conductivity represents a significant challenge to the electrochemical response of ESSENCE. The high conductivity of the transducer material shorts the system leading to a pure resistive response. Impedance spectroscopy (EIS) response of ESSENCE cannot be distinguished enough to determine if the sensor is working. ESSENCE has a switchable electrode system for usage in multiple configurations like a material electrode, clear electrode, and working electrode to overcome these limitations. For carbon nanotube (CNT) transducers with functionalized oligos on the CNT, a 20-fold jump in the signal is noticed from the working electrode configuration compared to the other configurations. It is worthwhile to note that depending on the biomolecule (DNA or Protein), the surface charge transfer resistance (Rct) in the EIS signal of ESSENCE can either show a decrease (DNA) or increase (protein) on the binding of the target bio-molecule (target DNA to DNA or target protein to protein). The change in the Rct depends on the charge of the molecule. It has been seen that on the binding of a target protein, the active area of the electrode surface decreased, leading to a reduction in current and a concomitant increase in Rct. On binding of the target DNA, the capture-target DNA pair essentially becomes a part of the electrode due to its charge. This increase in charge is more significant than any reduction in the surface area due to the DNA's binding. This leads to an increase in current to the packed electrode, leading to a concomitant decrease in Rct.

The fluid flow through the porous electrode increases mixing, minimizes diffusion, and generates a significantly enhanced fluidic shear force. This force e can unbind most of the false-positive signals generated by non-specific binding, such as physical adhesive or biofouling. The porous electrode also provides a high surface area to volume ratio to capture the target analyte leading to increased sensitivity. We have an automatic fluidic control system in ESSENCE that minimized any errors in the operation of ESSENCE. Our system has high selectivity and sensitivity for DNA (fM sensitivity, selective against non-target DNA), breast cancer biomarker proteins (p53, pg/L sensitivity, selective against non-target HER2).

Figure 1

Horn structure has been utilized to enhance the sound wave intensity via various hour Glass type structures fro ancient ages such as Viking ages. In this report, Previously we reported the optical enhancement from the nanometer size circular aperture via hour glass type nanostructure. We will discuss the optical horn effect from microfabricated hourglass type nanoslits. In this report, the naoslit nanostructures are fabricated via conventional Si technology, and its optical characterizations are carried out using ND YAG 532 nm laser along with Nikon Ti Halogen lamp equipped with Princeton Spectrophotometer. The huge optical enhancement from the fabricated nanoslit with its ranging from ~ 1 nm to 30 nm will be reported and discussed. In addition, the plasmonic nanoslit array was fabricated on Au thin film with each slit of a ~ 10 nm width and a 300 nm length, and its optical characterization will be reported.

With the COVID-19 pandemic extending over a year now, it has become even more important to detect the SARS-CoV-2 virus as early as possible. Detecting the virus is of utmost importance to ensure safe return to schools, offices, public places, etc. Continuous monitoring of classrooms, workspaces has thus become the need of the hour. For this purpose, there is a pressing need for real-time sensors that can detect and warn the presence of SARS-CoV-2 virus in air. As a remedy to this problem, we have developed an ultra-fast electrochemical sensor device that detects the SARS-CoV-2 virus present in air. The SARS-CoV-2 viral proteins interact with a Ni-based electrode at an alkaline pH to produce a positive current difference compared to a baseline solution devoid of any viral proteins. The mechanism of detection is hypothesized to be analogous to the binding mechanism of SARS-CoV-2 on human body surfaces. As a result of such a mechanism, it is believed that local pH changes occur at the electric double layer and are captured as current signatures by the sensor. Our sensor device has selectively detected SARS-CoV-2 when tested in the presence of H1N1 Influenza A, SARS-CoV, and Human CoV OC43. Moreover, the use of electrochemical technique has rendered a very low detection limit for the sensor. Using continuous monitoring devices such as this ultra-fast COVID-19 diagnostic sensor for monitoring the air surrounding us would be the way forward for ensuring safe return to normalcy post-pandemic.

Acknowledgment:

This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA) under Agreement No. HR00112190063.

Keywords:

SARS-CoV-2 detection; Electrochemical viral sensor; COVID-19 diagnostic test

Over the last two decades, scientists acquired more and more insights on the conversion of patterned polymer precursors into predictable 3D carbon shapes using pyrolysis (also carbonization). Our team, using photo lithography, electrospinning or a combination of both techniques, patterned polymer precursor structures so that after pyrolysis they yielded, for example, suspended carbon nanowires (see Figure 1a), carbon mats (see Figure 1b), carbon interdigitated arrays (C-IDEAS) (see Figure 1c) and even carbon origami (see Figure 1 d).

More recently, gaining better control over the carbon microstructure in some of those carbon shapes also became possible. The key to the latter is a precise control of the polymer precursor chains and the exact atomic composition of the polymer before and during pyrolysis.

Using simultaneous control of the linear speed of the spinneret and the rotational speed of a drum collector in near field electrospinning (NFE) enables one to organize polymer precursor chains, that after pyrolysis, lead to aligned ultra-thin (as low as 5 nm) highly crystalline carbon fibers freely suspended and in good ohmic contact with carbon scaffolds on a silicon substrate (Figure 1a) ¹.

The application of far field electrospinning (FFE) techniques allows one to utilize electrohydrodynamic forces to align polymer molecular chains within the spun fiber mats. This polymer chain alignment was then preserved by mechanical compression of the polymer fabrics during the formative stabilization step. Perhaps the most surprising outcome of this second C-MEMS approach illustrated in Figure 1 b was the demonstration of the conversion of these PAN fiber mats through pyrolysis into a uniformly graphitized carbon. The resulting carbon exhibits an oriented but fragmented lattice structure, as visualized by HRTEM imaging. Further characterization with XPS indicated that this type of stress activated pyrolytic carbon is innately rich in nitrogen heteroatoms. The electrochemical kinetics of these carbon mats reveal a heterogenous electron transfer rate 5 to 14 times higher than that of standard pyrolytic PAN carbons and 2 to 10 times higher than polished commercial glassy carbon in both the surface insensitive and sensitive redox probes ².

Using conventional UV photolithography to pattern SU8, followed by pyrolysis, we fabricated 3D carbon interdigitated electrode arrays (C-IDEAS) with redox amplification factors as high as 37 (Figure 1c)³. In ongoing follow-on work, we are now investigating means to further increase the amplification factor by reducing the electrode gap and increasing the electrode height. In this case the mechanical alignment of polymer chains (see FFE and NFE) is not applicable and we are converting the top carbon electrode material to graphene through the deposition of Ni and annealing instead.

Two years ago (2019), we demonstrated for the first time an origami-based carbon microfabrication method for permanently folded three-dimensional structures by combining lithography, controlled thermal softening and hardening, and elastocapillarity⁴. Selective lithography for cross-linking of photopolymers was used to obtain localized control over the material properties (for folds and faces) to enable selective and programmed folding of the origami. In addition to achieving tailorable inhomogeneous material properties, selective exposure was also used to bond the origami shapes onto a substrate surface. The three-dimensional polymer structures were then converted through pyrolysis into carbon shapes thus enhancing the achievable structural, electrical, and electrochemical properties and to broaden the applications of this elastocapillary-based fabrication method (see Figure 1 d). Finally in 2020, we were able to create the same carbon origami by heat-assisted self-folding, doing away with the need for droplet induced folding ^5. Pyrolysis leads to a glassy carbon microstructure in the carbon origami shapes obtained. As for C-IDEAS, Ni deposition and annealing can be employed to convert the microstructure from glassy carbon to graphene.

References

1. Jufeng Deng, Chong Liu, Marc Madou, "Ultra-thin carbon nanofibers based on graphitization of near-field electrospun polyacrylonitrile," Nanoscale, Royal Society of Chemistry, Issue 19, 2020.

2. Holmberg, Sunshine, et al. "Stress-activated pyrolytic carbon nanofibers for electrochemical platforms." Electrochemical Acta290 (2018): 639-648.

3. Kamath and M. J. Madou, "Three-Dimensional Carbon Interdigitated Electrode Arrays for Redox-Amplification," Anal. Chem., vol. 86, no. 6, pp. 2963-2971, Mar. 2014.

4. Fabrication of polymer and carbon polyhedra through controlled cross-linking and capillary deformations, Derosh George, Edwin A. Peraza Hernandez, a Roger C. Lo and Marc Madou, Soft Matter, Volume 15 Issue 45 (2019): Pages 9171-9177.

5. George, Derosh, Marc Madou, and Edwin A. Peraza Hernandez. "Programmable single-layer polymer films for millimeter and sub-millimeter self-folding origami." Active and Passive Smart Structures and Integrated Systems IX. Vol. 11376. International Society for Optics and Photonics, 2020.

Figure 1

In our laboratory, numeral efforts have been directed to improving sensing properties of various kinds of gas sensors, which are based on the different sensing principles, capable of using for our safety and health. The following four topics will be delivered in my presentation.

• Meso- and Marco-Porous Structural Controlled Metal Oxides for Semiconductor Gas Sensors¹⁾

To improve the sensing performance of semiconductor metal oxide gas sensors, strict design and control of meso- and macro-porous structure of sensor materials are of primary importance, i.e. controlling of diffusivity of target gases in the sensing layer toward the position of sensor electrodes, which is the most sensitive region of the sensors, in addition to controlling of catalytic activities of sensor materials. We have used various kinds of surfactants and polymethylmethacrylate microspheres with different sizes to control meso- and macro-porous structure of metal oxides, respectively (see Fig. 1). Examples for the improvement of H₂ and NO₂ sensing properties by porous structural control will be reported.

• TiO₂-Based Diode-Type H₂ Gas Sensors Operable both in Air and in N₂²⁾

For future popularization of hydrogen-powered vehicles, household fuel-cell cogeneration systems and etc., development of more sensitive and selective H₂ sensors than commercial ones is of primally importance. We have so far demonstrated that diode-type gas sensors using noble-metal (N) sensing electrodes and an anodized titania film show a quite large H₂ response even under oxygen-free atmosphere as well as relatively excellent H₂ selectivity to other inflammable gases, in comparison with other gas sensors. The mechanism for enhancing the H₂-sensing properties by the surface modification of the Pt-sensing electrode with Au (see Fig. 2) will be mainly reported.

• Solid Electrolyte CO Gas Sensors Operable at Temperatures less than Room Temperature³⁾

Detection of CO is of primary importance from the view point of safety in many industrial processes as well as our daily life. We have found that the sintered disk-type NASICON(Na₃Zr₂Si₂PO₁₂)-based solid electrolyte gas sensors equipped with a metal oxide (MO)-added Pt sensing electrode and a pristine Pt or another metal oxide-added Pt reference electrode on the same side of the disk can detect CO at temperatures less than room temperature (see Fig. 3). The outstanding CO sensing characteristics of this type of CO sensors will be reported.

• Adsorption/Combustion-Type Micro VOC Sensors⁴⁾

We have reported that adsorption/combustion-type micro gas sensors, which were fabricated by utilizing the microelectromechanical system (MEMS) technology and an oxide-film fabrication technique by drop coating employing an air-pulse fluid dispenser, are quite promising as gas-sensing devices for detecting a low concentration of various volatile organic compounds (VOCs) in comparison with other types of gas sensors (see Fig. 4). The potential of this type of sensors, in detecting selectively a low concentration of VOCs, which are possible biomakers for diagnosis of specific diseases and health checking, will be reported.

References

• Ueda, I. Boehme, T. Hyodo, Y. Shimizu, U. Weimar, N. Barsan, Enhanced NO₂-sensing properties of Au-loaded porous In₂O₃ gas sensors at low operating temperatures, Chemosensors, 8, 72 (2020).

• Shimizu, T. Hyodo, Sensing properties of diode-type gas sensors, Advances in Science and Technology, 99, 61-65 (2017).

• Ueda, H. Takeda, K. Kamada, T. Hyodo, Y. Shimizu, Enhanced CO response of NASICON-based gas sensors using oxide-added Pt sensing electrode at low temperature operation, Electrochemistry, 85(4), 174-178 (2017).

• Hyodo, Y. Shimizu, Adsorption/combustion-type micro gas sensors: Typical VOC-sensing properties and material-design approach for highly sensitive and selective VOC detection, Analytical Sciences, 36(4), 401-411 (2020).

Figure 1

Carbon dioxide (CO₂) has been shown to contribute to human health consequences indoors, such as shortness of breath, nasal and optic irritation, dizziness, and nausea. Given these precarious conditions for human health, various efforts have emerged toward development of CO₂ monitors for indoor deployment. The chief problem in gas sensing is the design of a sensor that is highly-sensitive and selective to targeted species, energy-efficient, inexpensive to fabricate, stable, and convenient for users. One of the most popular CO₂ sensors in commercial operations is the nondispersive infrared (NDIR) CO₂ sensor. While boasting high accuracy and longevity, the CO₂ NDIR sensor has traditionally been challenged by power consumption, cost, and bulky dimensions. In contrast to the NDIR sensing technology, colorimetric sensing retains several advantages, including easy preparation, user convenience, and obvious responses detectable by the human eye.

In this work, we situate metal–organic frameworks (MOFs) as highly-porous, crystalline sorbents for sensitive colorimetric CO₂ detection. In particular, a zeolitic imidazolate framework (ZIF) is chosen as the sorptive material due to its chemical stability and tunable CO₂ affinity. The colorimetric gas sensor is developed by incorporating a CO₂-affinative basic function and a pH indicator into the ZIF. The developed colorimetric CO₂ sensor exhibits an obvious response to a wide range of CO₂ levels of interest to indoor air detection (with a lower limit of detection below 1,000 ppm CO₂). Powder X-ray diffraction confirms its chemical stability over one month in ambient conditions. Ultraviolet-visible spectroscopy reveals quantitative differences in colorimetric responses across a span of CO₂ concentrations (700 – 7,500 ppm CO₂). The color response is attributed to a two-step reaction mechanism whereby the pH indicator deprotonates the reaction intermediate between the adsorbed CO₂ reacting with the basic function, shifting the pH and inducing a color change. Given its simple fabrication, rapid and obvious response, and stability in ambient environment, the ZIF-based colorimetric sensor provides a promising route for an improved indoor air quality monitoring.

Acknowledgements

We would like to thank the National Science Foundation for support in the form of a Graduate Research Fellowship (GRF) and Grant # 1903188, as well as the Bakar Fellows Program.

Human-robot interaction in soft robots involves physical touch with the user. Soft matter materials such as silicone and urethane are often used in the bodies of soft robots. These materials have advantages excellent softness and waterproofness, however the tackiness of the surface causes solid dust and lipophilic stains to adhere. In order to realize long-term operation of the soft robot for communication, a method of preventing external stains is required. Coating, which is one of the methods, is not recommended because it impairs the texture of soft materials.

Therefore, we focus on hydrogels which have excellent water content and adsorptivity. The stains are classified into three types: water-soluble stains, lipophilic stains, and solid stains. Hydrogel absorbs water-based stains. Moisture inside can be expected to have a oil-repellent function that prevents the invasion of lipophilic stains. Then, it is also possible to impart electrical properties and adsorb solid dust by changing the monomer contained in the gel to anionic or cationic.

On the other hand, although these gel materials have excellent functionality for preventing stains, there are problems that water evaporates and shrinks, and that the caught stains remain on the surface or inside. In order to solve this problem, we introduce a gel fiber system. This system forms the gel fiber-covered surface and adsorbs external dust. In this study, the stain removing performance of the fibrous gel on the surface is quantified using image processing.

This case study demonstrates resistive Pt temperature sensors fabricated by a novel Atomic Layer 3D-printer, a revolutionary rapid prototyping tool utilizing a combination of atomic layer deposition (ALD), microfluidics and high precision 3D printing [1], first time introduced at AVS ALD 2020 [2], and also discussed in detail in the ECS 2021 G01 symposium [3]. The printed sensors are characterized and compared to a thin film sensor made using conventional (physical vapor deposition, lithography) methods and also to a Pt100 standard.

ALD works like a chemical vapor deposition (CVD) but the precursors react with the substrate one at a time, in a sequential, self-limiting manner, offering thickness control on the level of atomic layers. Combining ALD and 3D printing, the Atomic Layer 3D-printer allows for deposition of thin films with controllable thickness in the sub-nm range in a pre-programmed X-Y pattern, with no need for lithography or additional patterning, on a wide variety of substrates.

The printer nozzle moves relative to the substrate in a highly controlled manner (in this case ~2 mm/s). The nozzle is a miniature spatial ALD system where the precursor (MeCpPtMe₃ in this case) flows out of the center of the nozzle, surrounded by a concentric rings of vacuum and a reactant gas, in this case ozone (O₃). The result is an area-selective ALD, where each nozzle pass over the substrate equals to one ALD cycle, with a typical deposition rate of ~0.9 nm/cycle.

In this study, resistive Pt temperature sensors were fabricated on the SiO₂/Si substrates by printing >2 mm long Pt-wires of different thicknesses (approx. range 10-40 nm thick) using 100-500 ALD cycles at 200, 225 and 250 °C, where the width of the wires (~400 µm) was defined by the used nozzle geometry (Fig. 1 shows the fabrication flow).

Morphology studies of the Pt surface by scanning electron microscopy (Fig. 2) revealed that the film growth in the initial stages follows island-like nucleation, eventually becoming progressively denser with increasing number of ALD cycles. The Pt wire deposited using 200 cycles (nozzle passes) consist of interconnected network of Pt grains, while the one made using 400 cycles (~ 30 nm thick) consists of a continuous polycrystalline Pt film. This growth mechanism is typical for this thermal ALD (Pt+O₃) process [4].

Sensors were annealed at 600 °C in N₂ to ensure temperature stability, and equipped with Au contact pads 2 mm apart (made by e-beam PVD through a shadow mask) for electrical characterization. The resistance was measured in the 25-400 °C range (selected characteristics shown in Fig. 3a), as well as in cryogenic temperatures down to 3 K (not shown here).

Interestingly, higher temperature sensitivity S (Fig. 3b) was found for samples made by 200 ALD cycles, with a morphology of a network of interconnected Pt grains.

The comparison of temperature coefficients of resistivity α (normalized sensitivity, Fig. 3c) clearly shown that the printed ALD Pt demonstrate better temperature sensing characteristics than the conventional 30 nm e-beam PVD Pt thin film, and is comparable also to the Pt100 standard.

We will also discuss sensors printed on corrugated surfaces, i.e. black Si and Si gratings.

The resistive Pt temperature sensors demonstrated in this study fabricated by a novel Atomic Layer 3D-printer are suitable for rapid printing in small-footprint areas where temperature sensing is required. Targeted, low temperature deposition with no need for lithographic masks or additional patterning paves the way for myriads of applications, e.g. on a chip, or in a battery. The characteristics of these sensors are shown to be comparable to a thin film sensor fabricated using conventional processing, as well as a Pt100 standard, thanks to high film quality delivered by the ALD process.

We acknowledge the support of the H2020-EU ATOPLOT project (grant ID: 950785).

References

[1] Atomic layer process printer (2020, June 03). Patent WO/2020/245230. [Online]. Available: https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2020245230

[2] Kundrata I, et al., An Atomic-Layer 3D Printer. Talk at [AVS ALD/ALE 2020]

[3] Barr M., et al., Atomic Layer 3D Printing: Influence of Reactor Design and Pattern Geometry [ECS 2021, Symposium G01 - ALD applications]

[4] Lee HBR, Pickrahn K, Bent SF, Effect of O₃ on Growth of Pt by Atomic Layer Deposition, J. Phys. Chem. C 2014, 118, 12325

Figure 1

The development of robust, low-cost and reproducible sensors for point-of-care (POC) applications is of the utmost importance and electrochemical techniques have been thoroughly implemented into POC devices. Electrochemistry is a powerful candidate for advancements in POC diagnostics due largely to its ease of use and its compatibility with electronic readers that can be controlled by smartphones. Of the various electrochemical techniques used in fabricating POC devices, potentiometry (i.e., the use of ion-selective electrodes (ISEs)) is extremely useful for the following reasons: (i) it is highly selective (through the incorporation of molecular recognition elements), (ii) requires simple equipment for the signal readout, (iii) it is multiplexable, and (iv) provides a fast response time. This talk will focus on the development of a new approach, utilizing 3-D printing, to fabricate the sensing element of ISEs, the ion-selective membrane (ISM). 3-D printing has already made a significant impact on the field of chemistry and is rapidly being utilized in various electrochemical endeavors, ranging from printing HPLC columns to conductive electrodes. Here, we highlight the advantages of utilizing 3-D printing for ion-selective membrane (ISM) fabrication and discuss examples of using 3-D printed ISMs towards the detection of various analytes related to human health (i.e., electrolytes and biomarkers). The precise control over the dimensions and shapes of ISMs, afforded by the precision of modern 3-D printers, allows for the fabrication of ISMs of various sizes and topographies for seamless integration into POC diagnostics. Beyond the ISE, 3D-printing is also a convenient tool for developing stable and reliable reference electrodes. These advancements, coupled with new 3-D printing capabilities will lead to unique opportunities in the fabrication of complete, low-cost diagnostic "packages" with extreme utility for broad applications at the POC.

The development of methods for measuring the deformation of soft material is an important task in soft robotics. A contact sensor such as a piezoelectric device can be embedded in a soft material to sense the deformation of the material [1,2]. However, this method is subject to the delamination between the flexible material and the sensor because of material mismatch. Sensors made of flexible materials such as gels and elastomers can alleviate the problem of material mismatch [3, 4].

We present a method for fabrication of flexible gel sensors with 3D printed microchannels. This method is based on the Soft Lithography technique, an easy and cheap fabrication method for intricate polydimethylsiloxane (PDMS) microfluidic devices [5,6]. The microchannels are filled with ion gels and stretched inside PDMS.

Experiments: Figure below shows the fabrication steps for the ion gel sensor. The scaffold for microchannels is 3D-printed with acrylonitrile butadiene styrene (ABS). Then PDMS is poured into a mold and the scaffold is suspended in the PDMS. PDMS is cured in 65 degrees Celsius for 40 to 60 minutes. After the curing process, ABS is dissolved in acetone for 12h. Then DMAAm gel with sodium chloride solution is injected into the microchannels and cured for 3 min in UV Box. The impedance of the gel in the microchannels is measured by applying AC voltage (±1 V, 1 kHz) with Digilent Analog Discovery 2.

Results: When a load was applied to the ion gel sensor and then removed, the impedance immediately decreased and then gradually increased to a larger value than the original value. Therefore, the ion gel sensor is considered to have hysteresis due to the viscoelasticity of the ion gel.

References:

1. Yuki Takishima et al 2021 ECS J. Solid State Sci. Technol.10 https://doi.org/10.1149/2162-8777/abea5f

2. Yuta Hara et al2020 ECS J. Solid State Sci. Technol.9 https://doi.org/10.1149/2162-8777/aba913

3. Ajit Khosla, and Bonnie Lynne Gray. "Electrically conductive, thermosetting elastomeric material and uses therefor." U.S. Patent No. 8,357,858. 22 Jan. 2013.

4. Kumkum Ahmed et al2019. Polym J51, 511–521. https://doi.org/10.1038/s41428-018-0166-z

5. Kazunari Yoshida et al 2020Microsyst Technol. https://doi.org/10.1007/s00542-020-04904-8

6. Khosla, A. (2011). Micropatternable multifunctional nanocomposite polymers for flexible soft MEMS applications(Doctoral dissertation, Applied Science: School of Engineering Science).

Figure 1

Introduction:

In recent years, soft robots made of soft, highly elastic materials have been attracting attention as an alternative to conventional robots made of hard rigid bodies such as metal. Soft robots are expected to play an active role in fields where there are many opportunities to interact with humans, such as collaborative work, nursing care, and welfare. Soft robots are often made of polymers such as rubber, gel, and plastic. By controlling the properties of flexible materials, such as large elastic deformation, elastic modulus, and viscoelasticity, it is possible to design and develop functionalities that take advantage of the softness, which has not been possible with conventional robot technology. In this study, we investigated how to control the physical properties of soft matter by compositing the 3D printed lattice structure of soft matter with silicone rubber.

Experiments: 3D model data of the lattice, called "igeta structure" (beam and girder structure) was designed using OpenSCAD, script-based 3D CAD software. Five 3D models of lattice structures with different crossing angles were created and they were 3D printed with an FDM 3D printer using Thermoplastic polyurethane (TPU) material. The printed lattice models were placed in a 20mm cubic mold, and silicone rubber (Ecoflex00-30) was poured into the mold and cured. Compression tests in three orthogonal axes (X, Y, and Z) were performed on these five models using an ORIENTEC STA-1150 universal testing machine.

Results and discussion: Figure 1 shows the Young's modulus of igeta structure and silicone composite models calculated from compression tests. Anisotropy of Young's modulus varied depending on the crossing angles of the lattice structure. In particular, the Young's modulus in the x-axis is remarkably changed. These results confirm that it is possible to change the anisotropy of the elastic material depending on the shape of the lattice structure. Its will be useful for designing soft robots and confirming their functions.

Figure 1

Foodborne illnesses have a pronounced impact on the global community, with cases numbering into the hundreds of millions annually and associated treatments costing tens of billions of dollars. Our inability to commercially detect food contamination in real-time is at the center of this crisis, as it places emphasis on static expiry dates that lack accuracy. These predicted dates not only fail to convey contamination, but also result in the disposal of mass amounts of edible food products. When contaminants are retroactively detected, measures such as food recalls are logistically complex and have massive economic ramifications. Existing methods for real-time detection of contaminants are expensive, require sophisticated equipment or offer poor detection capabilities, thus preventing commercialization. Additionally, detection requires packaging to be opened, making it unfeasible to monitor food products on an individual basis. Here, we propose a detection system centered upon the covalent immobilization of pathogen-specific RNA-cleaving fluorescent deoxyribozymes (RFDs) onto food wraps for real-time pathogen detection. These biomolecules exhibit a significant increase in fluorescence when exposed to their respective target. By functionalizing food wrap materials through plasma treatment, suitable crosslinkers can be used to bind amine modified RFDs onto the bulk wrap material. In particular, carbon dioxide plasma paired with carbodiimide chemistry presents itself as a well-studied immobilization approach that is applicable within the proposed sensing platform. Additionally, the use of microcontact printing to pattern RFD-crosslinker solutions onto food wraps presents a strategy suitable for industry scale-up. Given the transparency of food wrap materials and the printed sensor, this platform also overcomes the current need to open packaging for pathogen detection. Ultimately, we envision a patterned RFD barcode that provides multiplex detection of common foodborne pathogens. Use of a handheld fluorescence reader would allow for inexpensive, portable detection of food contamination along the entirety of the food production pipeline.

Classic chemical sensors integrated in phones, vehicles, and industrial plants monitor the levels of humidity or carbonaceous/oxygen species to track environmental changes. According to current projections, the gas sensor market is estimated to grow at an annual rate of 7% between 2021-2026 (valued at USD 1.5 billion by 2026).^[1] The projections indicate the strong need to increase the ability of sensors to sense a wider range of chemicals for future electronics not only to continue monitoring environmental changes but also to ensure the health and safety of humans. To achieve this goal, more chemical sensing principles and hardware must be developed. The critical factors that determine the sensing performance for rather corrosive toxins such as SO₂ are to develop a suitable electrochemistry and sensor material selection stable in this environment, and operating at low temperature (ideally below 300 °C) to assure a low energy footprint per sensing device volume. One of the best investigated SO₂ electrochemical (type III) sensors are those based on the solid-state Na⁺ conductor NASICON a known conductor vastly applied also as a battery solid state electrolyte. Despite the promise, the limited Na⁺ conductivity at ambient around 10⁻⁷ S cm⁻¹ challenges intrinsically to establish fast sensor response time and lower operation temperatures (energy footprint); which is also typically accompanied by degradation of the sensor performance and poor reproducibility. We propose in this work as a promising alternative cubic Li-garnet Li₇La₃Zr₂O₁₂ (LLZO) as a solid-state electrolyte for new SO₂ sensors due to their three orders of magnitude increased ionic conductivity (~mS cm⁻¹) and higher electrochemical stability window, which allows a wider definition and choice for sensing material electrodes. The material class of Li-garnets is known for about a decade^[2,3] and has proven success for solid state batteries, however, it had only recently been introduced to serve as electrolyte for type III sensors tracking less corrosive gases such as CO₂ with fast sensing and recovery times.^[4,5]

Here, we provide a proof-of-principle for the specific electrochemistry, material selection, and design of a Li-garnet LLZO-based electrochemical sensor, targeting the highly corrosive environmental pollutant sulfur dioxide (SO₂).^[6][7] For that, we explore the following sensor electrochemistry and investigated the major aspects that affect the electromotive force response according to the Nernstian behavior and the response/recovery time of the sensor, explicitly the auxiliary sensing electrode composition and microstructure. Novel composite sensing electrode designs using LLZO based on porous scaffold, employed to define a high number of reaction sites, allowed to successfully track SO₂ at the dangerous levels of 0–10 ppm with close-to-theoretical SO₂ sensitivity. The introduction of the composite sensing electrode Li₂SO₄–CaSO₄–LLZO with the LLZO electrolyte conductor achieved close-to-theoretical sensitivity of 47.7 mV/dec at remarkably low operating temperature of the sensor of 240 °C. We wish to highlight that this outperforms previously reported SO₂ type III electrochemical sensors operating on Zr⁴⁺ (400 °C) or Na⁺ (600 °C) ion-conducting solid electrolytes in terms of their operation temperature and has as a consequence impact on the sensor power consumption. The insights on the sensing electrochemistry, reactions involved and control over the interface sensing electrode/Li⁺ electrolyte structures and phase stability provide first guidelines for future Li-garnet sensors to monitor with fast response a wider range of environmental pollutants and toxins.

References

[1] MarketsandMarkets^TM, "Gas Sensors Market by Analysis, Type, Technology, Technology, Output Type, Product Type, Application | COVID-19 Impact Analysis," can be found under https://www.marketsandmarkets.com/Market-Reports/gas-sensor-market-245141093.html, last accessed 03-15-2021.

[2] M. Balaish, J. C. Gonzalez-Rosillo, K. J. Kim, Y. Zhu, J. D. Hood, J. L. M. Rupp, Nat. Energy2021, DOI 10.1038/s41560-020-00759-5.

[3] J. L. M. Zhu, Y; Gonzalez-Rosillo, J C; Balaish, M; Hood, Z D; Kim, K J; Rupp, Nat. Rev. Mater.2020, DOI https://doi.org/10.1038/s41578-020-00261-0.

[4] Y. Zhu, V. Thangadurai, W. Weppner, Sensors Actuators, B Chem.2013, 176, 284.

[5] M. Struzik, I. Garbayo, R. Pfenninger, J. L. M. Rupp, Adv. Mater.2018, 30, 1.

[6] M. Balaish, J. L. M. Rupp, Adv. Mater.2021, DOI 10.1002/(ISSN)1521-4095.

[7] M. Balaish, Z. D. H. Hood, J. Rupp, Gas Sensor Device Containing Lithium Garnet, 2021, US 63/154,336.

In this research 3D printing has been utilized in the fabrication of ion selective membranes (ISMs) for point-of-care (POC) diagnostics. 3D printing has been integrated into chemistry in many different areas to reduce cost, time of fabrication, and remove complexity in methodology. 3D printing ISMs has decreased the time of fabrication as well as the cost with the enhanced ability to mass produce customized membranes for a variety of applications. To demonstrate the broad utility of employing 3D printed ISMs, important analytes such as bilirubin (i.e., an important biomarker in the detection of hyperbilirubinemia) and benzalkonium (i.e., a common antimicrobial used in eye, ear, and nasal drops) have been detected with linear detection from 10 mM to 5 µM and 1 mM to 19 µM, respectively. 3D printed ISMs have also shown highly reproducible results with both conventional solid and liquid-contact ion selective electrodes as well as POC devices. Integrating 3D printing into ISM fabrication has led to the ability to fabricate a diagnostic panel rapidly and reproducibly for several analytes for POC applications.

Cerium oxide nanoparticles (CeO₂NPs) have shown par-excellent performance for applications like sensing, electrochemical catalysis, solar cells, chemical mechanical polishing/planarization, and catalytic converts. The nanoscale size combined with the available surface area that exposes highly active surface atoms/vacancies bring unique and highly desirable properties that opens up new possibilities in such application. However, large-scale processing of nanomaterials is challenging and necessitate scaling them up to macrostructure assemblies that can be easily handled without losing their original nanoscale size. In addition, assembling NPs into solid macrostructures would greatly impact applications that require handing gram-scale amounts of nanoparticles in solid-state processable form. Here, we describe a facile approach for synthesizing centimeter-sized porous monolithic CeO₂ nanoparticles. This monolith is prepared though the hydrothermal treatment of the parent nanoparticles in solution to form a gel-like material, which turns into a crack-free solid monolith upon drying with a high surface area of 190 m²·g^-1. As a proof of concept, we used CeNPs monolith/conductive polymer for detecting and quantifying solar radiation enabling this material useful for wearable electronics applications.

The sustainable future of our world depends fundamentally on soil fertility and the fine balance between soil nutrients and the physical soil environment. In order to feed 7 billion people, humans have more than doubled global land-based cycling of nitrogen (N) and greatly influenced cycles of other major nutrients (e.g. carbon (C), phosphorus (P), potassium (K) and Sulphur (S)). As a consequence, they are now out of balance, causing major environmental, health and economic problems. Insufficient access to nutrients limits food production and contributes to land degradation, while finite P reserves represent a potential risk for future global food security, requiring prudent use.

These issues warrant effective soil management strategies across different spatial and temporal scales. Ultimately, this depends on how accurately we can measure nutrient levels in soils over a large area in real-time with a high spatial and temporal resolution that is economically feasible.

In the last several years, we are focusing our efforts on modification and adaptation of Ion Selective Electrodes (ISEs) that hold great promise for in situ analysis of plant nutrients. Unfortunately, relatively poor precision and robustness as well as requirements for pre- and post measurement handling prohibit their reliable use in the field by non-trained personnel (e.g. farmers) which is our ultimate goal.

We will herein describe and discuss our efforts on the development of significantly simplified sensor substrates, measuring protocols, and integration with statistical methods aimed at improvement of precision. Moreover, we will demonstrate recent data obtained using our newly developed portable device that allows in situ determination of up to 16 analytes enhanced with the wireless data transmission capability.

In this work, it will be presented the chromium electrodeposition mechanisms with the use of a Scanning ElectroChemical Microscopy (SECM) micro-electrode. Among several factors, the pH is key to achieve even a metallic deposit. pH buffers and complexing agents are often used for this purpose [1] but in the vicinity of the electrode, at the electrode/electrolyte interface, strong variations are highly likely to occur. To this respect, since pH is a key parameter, a pH micro-electrode is intended to be developed to scan the pH gradient upon the electrodeposition of chromium. The first part of this work is so devoted to the pH micro-electrode realization from microelectrode on which iridium oxide is deposited. Iridium oxide has been reported to be suitable for local pH sensing [2-4]. Different parameters have been studied such as IrO_x thickness and thermal treatment. The addition of Nafion has been assessed as well to achieve a tradeoff between fast response time, good selectivity and good stability [5]. An optimized IrO_x micro-electrode has been obtained and used as SECM micro-electrode to get the evolution of the pH at the electrode/electrolyte interface upon electrodeposition. Different micro-electrode diameters have been used to improve the resolution. These results are promising and will allow going further to the development of chromium electrodeposition electrolyte helping to select the different complexing agents.

[1] D. Del Pianta et al. Determination of the chromium(III) reduction mechanism during chromium electroplating. Electrochimica Acta (2018) 234-241.

[2] H. A. Elsen et al. Effects of electrodeposition conditions and protocol on the properties of iridium oxide pH sensors electrodes. J. Electrochem Soc. 156 (2009).

[3] C. S. Santos et al. Fabrication and use od dual-function iridium oxide coated gold SECM tips. An application to pH monitoring above copper electrode surface during nitrate reduction. Electroanalysis 28 (2016) 1441-1447.

[4] Z. Zhu et al. A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316 stainless steel corrosion at open circuit potential. Sensors and Actuators B 25 (2018) 1974-1982.

[5] I. G. Borislav et al. Thin-film IrO_x pH microelectrode for microfluidic-based microsystems. Biosensors and Bioelectronics 21 (2005) 248-256.

The advancement of smart apparels capable of tracking human physiological signals and body locomotion have a great potential to revolutionize human performance sensing and personalized health monitoring through transforming daily life clothing into sensors. Quantitative evaluation of kinetic parameters of individual gait along with physiological signals can be employed in games and sports, as well as in diagnosis of many diseases such as Parkinson's, Multiple Sclerosis, and sleep disorders. Among different methodologies in developing wearable sensors such as inertial measurement units, textile-based electromechanical sensors encompass the majority of widely adopted applications. Electromechanical sensors fall into three major categories based on their active mechanisms: piezoelectric sensors, triboelectric sensors, and piezoresistive sensors. Recently, different combination of materials and designs have been reported to develop wearable sensors, each of which provides a unique window into a slightly different range of motion sensitivity. For example, some human signals and motions lie in the small-scale range of pressures such as those of a subtle touch, arterial pulses, and sound vibrations, while the other body movements lie in medium to large range of pressures, such as joint movements, and locomotion during sleep and intense activities. The ability to design an unobtrusive wearable sensor being highly responsive in the required range of signals calls for getting an insight into the difference between the three mechanisms of electromechanical sensing and their corresponding responses under certain conditions.

Here, we introduced a set of materials selection principles which gives researchers an in-depth insight into how to design a wearable electromechanical sensor when it comes to acquire data from a specific source of motion. In order to achieve this goal, we performed a set of purposefully designed experiments on three types of wash-stable fabric-based electromechanical sensors that had already been introduced by our lab, i.e., triboelectric sensor, piezoelectric sensor, and piezoionic sensor as a subset of piezoresistive ones. These experiments explored the effect of impact pressure, bending angle and speed, frequency, presence of a base pressure, response time, breathability, and having a multi-layer structure on the performance and sensitivity of each type of sensors. For an instance, it turned out that the triboelectric and piezoelectric sensors are a more reliable sensing element for dynamic pressures, such as joint movements, with the former being failed in the presence of a base pressure. Piezoresistive sensors are the one with the ability to sense both static and dynamic pressures, as well as being responsive under a base pressure. However, piezoresistive one would not be a choice when it comes to bending applications. Upon this comprehensive comparison, we demonstrated a conclusive map which can provide the researchers with distinguishing features of these three types of sensors to be used in corresponding niche applications.

For example, some human signals and motions lie in the small-scale range of pressures such as those of a subtle touch, arterial pulses, and sound vibrations, while the other body movements lie in medium to large range of pressures, such as joint movements, and locomotion during sleep and intense activities. The ability to design an unobtrusive wearable sensor being highly responsive in the required range of signals calls for getting an insight into the difference between the three mechanisms of electromechanical sensing and their corresponding responses under certain conditions.

Figure 1

With the dramatic progress of Internet-of-Things technology and Artificial Intelligence (AI) algorithms, portable healthcare monitoring has been highlighted as a facile pre-diagnosing strategy for tracking individual health status without hospitalization. In this regard, a wide range of wearable sensors, which extract bio-information such as body temperature, blood pressure, or respiratory patterns, have been developed so far. Although numerous factors are considered during sensor development depending on the types of analytes or target locations in the human body, acquiring sufficient flexibility must be a priority to endure uncontrollable stress caused by the surrounding conditions.

Diverse flexible materials have been exploited as suitable substrates for wearable sensors that fulfill the desired mechanical stability. Among them, textiles have tremendous advantages in terms of remarkable stability, skin compatibility, lightweight, and breathability. However, owing to their inherently rough surface, high porosity, and surface hydrophobicity, the formation of a uniform sensing film on fabric has been regarded as a much daunting task compared to a flat and rigid substrate. Liquid-phase coating methods such as spin-coating, dip-casting, or doctor-blading have failed to create a uniform and reproducible film on a fabric. Additives like binders are sometimes effective for improving conformability, but creating thin layers, which is significant for high-performance sensors, still remains challenging. Vapor phase coating methods are, arguably, the most efficient tactics for coating sensing films on fabrics. Inorganic or metallic materials, deposited by a comprehensive deposition tool based on physical vapor deposition, chemical vapor deposition, or atomic layer deposition techniques, have been typically considered as active materials for strain sensors, thermometers, or pressure sensors. However, the inorganic materials with poor flexibility or stretchability are vulnerable to be cracked readily even under mild mechanical stress. Thus, exploring materials and contriving their proper coating methods should be further progressed for realizing desired fabric-based wearable sensors.

Herein, we utilize the oxidative chemical vapor deposition (oCVD) technique for creating a conformal Poly(3,4-ethylene dioxythiophene) (PEDOT) layer on multiple fabrics (nylon, polyester, and cotton) without any binder or additives. The oCVD is capable of creating a highly conductive PEDOT (nominally, 1-10 S cm^-1 on cotton fabric; 500-1500 S cm^-1 on glasses) of which thickness is readily controllable from 50 nm to 1 μm by varying the deposition time. Moreover, the mechanical stability, breathability, and lightness of fabrics are consistent even after PEDOT coating, implying the oCVD could form a promising sensing material while maintaining all advantages of fabrics. Based on the unique properties of excellent conformality, high conductivity, and good mechanical flexibility^1-5, we fabricate simple resistive-typed sensors by directly printing the PEDOT on a commercial glove and disposable mask, consisting of polymers such as polypropylene or polyester. The glove and mask sensors are capable of extracting blood pressure information and respiratory rates in real-time with remarkable precision. This is the first report proving the usability of the oCVD method on fabric-based sensors, thus, paving the way for developing versatile healthcare devices.

This work was partly supported by the NSF Award No. ECCS-1931088.

References

1. Lee, S.; Song, H. W.; Cho, J. Y.; Radevski, N.; Truc, L. N. T.; Sung, T. H.; Jiang, Z. T.; No, K., Mobility of Air-Stable p-type Polythiophene Field-Effect Transistors Fabricated Using Oxidative Chemical Vapor Deposition. Journal of Electronic Materials 2020,49 (6), 3465-3471.

2. Drewelow, G.; Wook Song, H.; Jiang, Z.-T.; Lee, S., Factors controlling conductivity of PEDOT deposited using oxidative chemical vapor deposition. Applied Surface Science 2020,501, 144105.

3. Lee, S.; Borrelli, D. C.; Jo, W. J.; Reed, A. S.; Gleason, K. K., Nanostructured Unsubstituted Polythiophene Films Deposited Using Oxidative Chemical Vapor Deposition: Hopping Conduction and Thermal Stability. Advanced Materials Interfaces 2018,5 (9).

4. Lee, S.; Gleason, K. K., Enhanced Optical Property with Tunable Band Gap of Cross-linked PEDOT Copolymers via Oxidative Chemical Vapor Deposition. Adv. Funct. Mater. 2015,25 (1), 85-93.

5. Lee, S.; Paine, D. C.; Gleason, K. K., Heavily Doped poly(3,4-ethylenedioxythiophene) Thin Films with High Carrier Mobility Deposited Using Oxidative CVD: Conductivity Stability and Carrier Transport. Adv. Funct. Mater. 2014,24 (45), 7187-7196.

Figure 1

The ability to detect small signals in plants is highly important since it can provide early stage detection of plant stress by micro metabolites sensing. This work presents a first demonstration of redox cycling amplification in plant sensors improving signal level. The concept and the setup is discussed demonstrating a five-fold redox cycling amplification by using on-chip interdigitated microelectrodes arrays (IDA).

The concept of plant sensors refers to any sensor which is used to monitor the plant's status or correlated parameters in the plant's environment. In this work, the plant sensor monitors signals which are expressed by the plant itself, i.e. whether it is well hydrated, is it experiencing a heat shock, etc. In this work, modified plants were tailored to generate β-glucuronidase (GUS), a bio-signaling molecule, due to an induced stress effect. The expressed enzyme then reacts with PNPG (4-Nitrophenyl β-D-glucopyranoside) to produce p-nitrophenol which acts as the electroactive species.

P-nitrophenol electrochemical characterization show that the molecule is reduced at -0.75 V, associated with a four-electron reaction of the nitro group reduction into hydroxylamine species. Subsequent reduction and oxidation peaks at +0.15 V and +0.18 V occurs due to 4-hydroxyl-amino-phenol to 4-nitrosophenol oxidation and the subsequent reversible reduction.

When using redox cycling amplification, two closely packed working electrodes are individually biased at different potentials. In the first working electrode, referred to as the generator, the initial oxidation (or reduction) occurs. The second working electrode, the collector, subsequently reduces (or oxidizes) the oxidized (or reduced) form back to its initial state. The target molecule transfers charges during every successive reaction, effectively amplifying the detected current per molecule. The collection efficiency of the redox cycling process depends on the reversibility of the reaction, therefore only the reversible oxidation of the hydroxylamine species and the reduction of the NO group.

In our work, we have demonstrated five-fold redox amplification in cyclic voltammetry related to the reduction of p-nitrophenol, the biologic reaction's product.

Suspension-cultured Msk8 tomato cells with constitutive expression of GUS enzyme were derived from plant tissue and suspended in 0.1 M phosphate buffer (PB) of pH 5.8. The cells were stirred in a glass with 0.13M p-nitrophenyl beta-D glucuronide (PNPG) for 30 minutes. The measurement was conducted in a batch cell (Micrux, Spain) using a gold IDA chip with 5mm electrodes and 5mm spacings, and an Ag/AgCl thin film electrodeposited electrode. The collector electrode (WE2) was biased at -0.8 V and the generator electrode (WE1) was scanned from -1 V to +1 V in a cyclic voltammetry measurement.

Cycling voltammetry of redox cycling

As shown in the attached figure, in the negative values of the voltammetric measurement, the generator electrode exhibits a reduction slope, which relates to the electroactive product's reduction. From zero potential and in the positive range, the generator's current rises to a plateu, due to 4-hydroxyl-amino-phenol oxidation. The collector electrode shows a reduction behavior which is a mirror image of the generator's oxidation. From this behavior we conclude that at small overpotentials, the generator reaction is limited by its kinetics. At larger overpotentials, the process is mass transport limited, though, unlike generic three electrodes systems, does not characterize in a peak. The mass transport is almost constant since the majority of the oxidized molecules are reduced at the collector and return to the generator at a constant rate, dependent on the diffusion characteristics of the IDA electrodes. The redox amplification factor is 5, calculated as the current at the generator divided by the current at standard three electrodes measurements.

Dependency on switching potential

We have shown that by enabling the initial reduction of p-nitrophenol and scanning the potentials down to a switching potential more negative than its reduction potential, the reversible redox cycling reaction was carried out. When performing a similar measurement with a switching potential less negative than -0.75 V, the redox cycling signal was not observed.

pH dependency

The solution's pH was adjusted from 4 to 6. It was shown that with increasing the pH, the potential in which the plateau was reached has become less positive, and the plateau current has decreased. These two results indicate that the process is proton dependent in this pH range.

Summary and conclusions

Following the successful feasibility study and encouraging initial results, the redox cycling phenomena in direct contact to the plant's leaves and stems will be tested in order to develop an early detection, fully integrated redox cycling chip-on-plant soft and flexible sensor based on our supersonic cluster beam deposition and femtosecond laser micro-processing previously reported novel process.

Figure 1

The Industrial setting is considered as a harsh environment for sensors. These sensors form the part of the Industrial internet of things (IIoT). For the IIoT to materialize, the simultaneous power supply and electronic control of electrochemical sensors is one of the major challenges. This can be solved using the concept of simultaneous wireless power and data transmission (WPDT). The authors present a brief overview of the coupling based wireless power transmissions and wave-based systems. The authors lay special emphasis on the Zenneck wave (ZW) and single wire (SW) transmission systems. Both ZW and SW systems have specific advantages over existing methods when supplying power and data to electrochemical sensors under industrial settings where metal forms the bulk of the environment. Traditional wireless systems undergo power and signal loss due to Faraday-shielding, whereas ZW and SW system operate effectively under these conditions. The authors demonstrate that a power of 40 watts can be successfully transmitted across metal shielded environments. This kind of power supply is desirable for wireless potentiostats.

References

[1] Daniel M. Jenkins et al 2019 J. Electrochem. Soc.166 B3056 https://doi.org/10.1149/2.0061909jes

[2] Oruganti, S.K., Liu, F., Paul, D. et al. 2020 Sci Rep 10, 925. https://doi.org/10.1038/s41598-020-57554-1

[3] S. K. Oruganti, A. Khosla and T. G. Thundat 2020 IEEE Access, 8, 187965 https://doi.org/10.1109/ACCESS.2020.3030658

Figure 1

We have reported the CO sensing properties of sintered disk-type NASICON(Na₃Zr₂Si₂PO₁₂)-based solid electrolyte gas sensors equipped with a metal oxide (MO)-added Pt sensing electrode (SE, Pt(nMO) (n: MO additive amount in wt%)) and a pristine Pt or another metal oxide (M'O)-added Pt counter electrode (CE, Pt or Pt(nM'O)) on the same side of the disk [1, 2]. The outstanding CO sensing characteristics of these NASICON-based sensors are 1) no reference atmosphere necessary (both SE and CE can be exposed to the same atmosphere, leading to a simple sensor structure), 2) capable of operation at room temperature and also at temperatures below the freezing point, 3) improvement of CO selectivity against H₂ in humid environment at room temperature operation, whereas CO response decreased slightly, 4) CO response based on the mixed potential theory, etc.

To realize a further simple manufacturing process of sensor elements and also excellent CO sensing properties, the present study was directed to establishing the optimum fabrication conditions of porous thick film NASICON-based solid electrolyte CO gas sensors.

Pt paste (Tanaka Corp., TR-7907) mixed with 15 wt% of a metal oxide (Pt(15MO)) and pristine Pt paste were applied in a rectangular shape (1 × 4 mm) with a distance of 4 mm on the same surface of a quadrate alumina substrate (10 × 10 mm), then the same past was used to attach a Pt lead wire to each electrode, followed by drying at 100°C for 10 min in air. Thereafter, NASICON paste was applied on the alumina substrate equipped with a pair of the electrodes and dried at 100°C for 1 h, followed by calcination in the temperature range of 700 to 900°C for 0.5 h in air. The thickness of porous NASICON thick films fabricated was ca. 1 mm. The sensor thus fabricated is denoted as Pt(15MO)/Pt-T, where T represents the calcination temperature. Response properties to 300 ppm CO balanced with dry air of as-fabricated sensors and those subjected to the following aging treatment, heating at 400°C for 1 h in dry air and then exposure to 3,000 ppm CO balanced with air at 400°C for 0.5 h, were measured at 30°C and −10°C. The sensor subjected to the aging treatment is referred to as Pt(15MO)/Pt-Ta. The metal oxides tested were Bi₂O₃, Cr₂O₃ and CeO₂. The electromotive force (E, mV) of the sensors was measured with a digital electrometer as a sensing signal. The magnitude of CO gas response was defined as a difference in E measured between in 300 ppm CO balanced with air and in base air.

Figures 1 and 2 show CO response transients of Pt(15Bi₂O₃)/Pt-T and Pt(15Bi₂O₃)/Pt-Ta at 30°C. Even for porous thick film sensors, we could obtain CO response abilities as those observed for sintered disk-type sensors [1, 2]. When Bi₂O₃ was used as an additive to SE, the aging treatment improved sensing stability, enhanced CO response and shortened the response and recovery time, especially for the sensor calcined at 700°C. CO response properties were also much improved by the aging treatment in the case of the Cr₂O₃ addition, but were deteriorated in the case of the CeO₂ addition. Similar aging effects were also observed at the operation of −10°C, whereas the excellent CO response properties were observed at different calcination temperature values. Another notable feature is the shift in E to a positive direction upon exposure to CO for both the Bi₂O₃ and Cr₂O₃ additions, irrespective of the calcination and operating temperatures, but to a negative direction for the Pt(15CeO₃)/Pt-T sensors. The detailed CO sensing performance of these sensors will be delivered in my presentation.

Reference

[1] H. Takeda, T. Ueda, K. Kamada, K. Matsuo, T. Hyodo, Y. Shimizu, CO-sensing properties of a NASICON-based gas sensor attached with Pt mixed with Bi₂O₃ as a sensing electrode, Electrochimica Acta, 155, 8−15 (2015).

[2] T. Ueda, H. Takeda, K. Kamada, T. Hyodo, Y. Shimizu, Enhanced CO response of NASICON-based gas sensors using oxide-added Pt sensing electrode at low temperature operation, Electrochemistry, 85(4), 174−178 (2017).

Figure 1

Metal-organic frameworks (MOFs) are porous defective crystalline compounds that can form clathrates. In principle, the defects in these materials behave like the defects in other metal oxides such as ZnO, which are used as metal-oxide semiconductor gas sensors. Traditional chemical resistivity based MOS gas sensors require electrical contact to the sensing materials. These contacts are imperfect and will subsequently introduce errors into the measurements. In this paper, we will demonstrate the feasibility of using contactless broadband dielectric spectroscopy (BDS)-based metrology in gas monitoring that avoids distortions in the reported resistivity values due to probe use, and parasitic errors (i.e., tool-measurand interactions). Specifically, we will show how radio frequency (RF) propagation characteristics can be applied to study discrete processes involved in HKUST-1 SURMOF (Surface Anchored Metal-Organic Framework) sensing and detection of gases and volatile organic compounds (VOCs). HKUST-1 MOF films, also known as Cu₃(BTC)₂ (BTC: benzenetricarboxylicacid), consist of metal ions connected by organic ligands, forming highly ordered porous structures and are commonly grown by a layer-by-layer (LBL) liquid phase epitaxy (LPE) technique. We intend to use BDS to investigate the initial oxidization of MOF gas sensing material in air and nitrogen at temperatures below 200 °C, and to show that the technique yields new mechanistic insights that are unobtainable with the conventional resistance-based measurements.

As the population ages, the number of elderly people walking outside is expected to increase. The weakening of muscle strength by aging leads to a decrease in walking speed and increases the risk of falling. [1,2] In addition, Soft materials have been used in a wide scope of fields such as soft robotics, medicine, and welfare, because they are safer and closer to biological characteristics than conventional metallic materials [3,4]. The purpose of this study is to develop a soft material with a nonlinear mechanical response by Hybrid structural design using multiple materials, which can be applied as a shoe bottom material that supports keeping walk speed while reducing the risk of falling, and robot hands that resemble human fingers. In this research, we focus on giving an extra-viscosity to silicone rubber by embedding a flow channel of viscous fluid [5,6].

Experiments: A water-soluble flow channel model (15mm cubic, Parallel crosses structure) was 3D printed with an FDM 3D printer (QIDITECH X-pro) using polyvinyl alcohol (PVA) filament. The channel model was fixed in the center of a mold (20 mm cubic inside dimension), then silicone resin (Ecoflex00-30, Smooth-on) was poured and cured. After the curing, the silicone part is removed from the mold and dipped in water to dissolve the PVA flow channel model. The dissolved hollow part in the silicone was filled with highly viscous fluid (hydroxyl propyl cellulose (HPC, Wako) in water). The fluid was colored with black pigment so that the fluid can be visually recognized through the translucent silicone part. As a Material evaluation, we measured the viscosity frequency dependence of the HPC aqueous solution was measured using a rheometer (Anton Paar, MCR302), And then we measured the dynamic viscoelasticity of the fabricated samples using a DMA tester (RSA-G2 (TA Instruments) or homemade tester).

Results: Fig.1 shows the fabricated silicone sample. To dissolve the embedded PVA part in the silicone part, the silicone part had to be sliced into two pieces to make the edge of the PVA part exposed to water for smooth dissolution and diffusion. To infuse the viscous fluid into the hollow of the silicone part, we used a manual centrifuge machine to apply high gravity for smooth entering of the viscous fluid and degassing. Fig.2 shows the Measurement results of DMA test. In this results, we verified the change in tangent loss tan δ due to thixotropy of the HPC aqueous solution. Figure 2 shows that the sample filled with the viscous fluid has a lower tan δ than the simple silicone. From this result, we considered that the deformation (about 1.8 mm) was small for the sample size (20 mm cubic) injected with viscous fluid. Therefore, we attempted to utilize a 3D printer to create a DMA testing machine capable of large deformation at low frequencies. In this conference, we will report the fabrication method and evaluation results of the fabricated samples.

Figure 1

There continues to be major interest in detection and discrimination of volatile organic compounds (VOCs) because these compounds are pervasive in common environments, such as buildings, factories, and in households, among others. These VOCs can be detrimental to both human health and organisms in the environment. The quartz crystal microbalance (QCM) has become a popular analytical instrument to detect various VOCs [1]. However, most QCM studies are performed in a laboratory setting with cumbersome benchtop instruments. To utilize the QCM technique in a manner that permits researchers to be outside of a laboratory environment, such as VOCs detection on-site and point-of-care testing (POCT), it is important to develop a suitably portable QCM measurement system that maintains acceptable system performance, such as frequency resolution and measurement time, which requires low-power input [2, 3]. To fulfill this demand, we propose a QCM measurement electronic system that uses a phase-locked loop (PLL) circuit as a frequency-to-voltage converter and measures an output voltage level to calculate frequency shifts of the resonator. Our proposed system does not rely on the quality of a clock frequency, which is important in typical frequency counters to improve measurement performance. Instead, a common microcontroller is used to calculate frequency shift. In this work, a portable QCM system based on this strategy was developed, and its performance successfully characterized by measuring changes in system output voltage corresponding to input frequency changes. Temperature dependence of frequency changes was also investigated from 15 to 55 °C. With a resonance frequency of 5 MHz, the system showed a frequency resolution of 0.22 Hz, which is significantly less than a common frequency counter. For validation, we employed Ionic Liquids and a Group of Uniform Materials based on Organic Salts (GUMBOS) as chemosensitive coating materials for VOCs detection [4]. Measurement results of the frequency shift caused by VOCs from the developed system were comparable to those obtained from experiments with a commercial system (QSense Analyzer, Biolin Scientific), which demonstrates the feasibility of applying this electronic strategy for development of a portable QCM measurement system.

References

[1] C. Speller, N. Siraj, S. Vaughan, L. N. Speller, and I. M. Warner, "QCM virtual multisensor array for fuel discrimination and detection of gasoline adulteration," Fuel, vol. 199, pp. 38-46, 2017.

[2] Bearzotti, A. Macagnano, P. Papa, I. Venditti, and E. Zampetti, "A study of a QCM sensor based on pentacene for the detection of BTX vapors in air," Sensors and Actuators B: Chemical, vol. 240, pp. 1160–1164, 2017.

[3] D. Wilson, "Recent progress in the design and clinical development of electronic-nose technologies," Nanobiosensors in Disease Diagnosis, vol. 5, pp. 15-27, 2016.

[4] S. R. Vaughan, N. C. Speller, P. Chhotaray, K. S. Mccarter, N. Siraj, R. L. Pérez, Y. Li, and I. M. Warner, "Class specific discrimination of volatile organic compounds using a quartz crystal microbalance based multisensor array," Talanta, vol. 188, pp. 423-428, 2018.

In this paper, we report Raspberry Pi-based, portable sensors for rapid and in situ determination of analytes relevant for bio-environmental analysis (PiSENS). We exploit the principle of digital colorimetry and the use of Red-Green-Blue (RGB) color system for quantitative assessment of color. The PiSENS was largely built using materials that can be found in a DIY shop while utilizing a Raspberry Pi and its imaging camera for data acquisition and processing. To automate the analysis and simplify the usage, we have written a python script which utilizes the principles outlined above. We will herein demonstrate two modes of PiSENS.

PiSENS-A is developed for continuous monitoring of NO_x in air and is based on color development as a consequence of the interaction of the gas with an absorbing solution. We utilize the traditional Saltzman reaction for capturing NO₂ from the air that results in color development upon contact with a suitable absorbing solution. The PiSENS-A allowed data acquisition with a high temporal resolution, while low construction and operation costs open the possibility for the production and installation of a number of devices in order to increase spatial resolution.

PiSENS-O is developed for the detection of analytes in water. The analysis is based on the utilization of polymer membrane-based optodes. We demonstrate the utility of PiSENS-O by the determination of Na⁺ and NO₃^- in water. The results show that the precision expressed as relative standard deviation (%RSD) is in the range of 2.0-12.5% and 5-27% for Na⁺ and NO₃^- respectively, while the accuracy expressed as the relative error (RE%) was 2.9% for both ions.

The low construction and operational cost, and portability are very exciting as it shows potential to significantly improve the spatio-temporal frequency of analysis especially in rural and/or remote communities where access to expensive and complex instrumentation is limited. Furthermore, WiFi and/or Bluetooth capability of Raspberry Pi can be exploited for instantaneous data transmission, mapping, and the development of large-scale networks assisting in the development of high precision models.

Abstract:

3D food printing is a method of making a novel three-dimensional processed food based on digital data by applying additive manufacturing technology to food materials [1]. Food 3D printers are expected to serve foods with controlling nutrients and textures suitable for an individual's health. There are many different types of food 3D printers such as screw type, syringe type, inkjet type, etc. But there are few 3D printers capable of printing hard textured foods. We aim to develop a food 3D printer capable of printing hard textured food with starch suspension [2]. In the printing process, the starch suspension is irradiated with a blue laser, and irradiated spot is gelatinized by heat generated by photothermal conversion.

Experiments: The Food 3D printer is based on a commercially available 3D printer Geetech i3 pro B. The extruder unit of Geetech i3 pro B is replaced by a blue laser (wavelength 450 nm) module (alfawise 5500mm ). The maximum laser output is 5.5W. We select a visible blue laser that is common and safe. As the first experiment, We print a pyramid shape (shown in Fig.1) using starch suspension as a printing material. The pyramid has composed of five layers and the thickness of each layer is 0.5 mm. The bottom layer is a 10mm square and the higher layer has shorter edges. Fig.2 shows a schematic diagram of the modeling method. The starch suspension (50 % wt in water) is poured (added) into the container and leveled to make 0.5mm thickness. The liquid surface of the Suspension is irradiated with laser and gelatinized. 3D printing is performed by repeating those processes. Tartrazine (0.03% wt) is added for enhancing the absorption of the blue laser. The laser scan speed is set at 5.0 mm/s.

Results: Fig.3 shows a Photo of the 3D printed pyramid structure. We successfully 3D printed pyramid structure with starch suspension. The 3D printed pyramid structure is larger than the original pyramid 3D data. We assume that the gelatinized starch absorbed water and swelled during and after the 3d printing process.

References:

1. Jonathan David Blutinger, 2018, Characterization of dough baked via blue laser. Journal of Food Engineering. 232, 56-64

2. Rahman, J.M.H., Shiblee, M.N.I., Ahmed, K., Khosla, A., Kawakami, M. and Furukawa, H., 2020. Rheological and mechanical properties of edible gel materials for 3D food printing technology. Heliyon, 6(12), p.e05859. https://doi.org/10.1016/j.heliyon.2020.e05859.

Figure 1

⁹⁹Tc, a pure β-emitter with E_max =294 keV, is one of the most significant (t_1/2 =2.1×10⁵ y) nuclear waste isotopes, produced by the fission of U with a yield of 6%. Under normal environmental conditions, it is mostly encountered as the pertechnetate ion, TcO₄^-, which is highly soluble and consequently mobile in water. For this reason, and because it often is the first contaminant to be present in detectable levels, its monitoring into groundwater is a statutory requirement for every nuclear license site. Because of its relatively low concentration in environmental samples, current determination methods of ⁹⁹Tc involve several steps, such as chemical separation from the matrix, purification and source preparation, prior to radiometric (e.g. liquid scintillation counting) or mass spectroscopic (e.g. inductively coupled plasma mass spectroscopy) determination. The detection of ⁹⁹Tc may take up to several days, thus making these techniques inappropriate for an emergency situation. Hence, We report on the development of a sensor for the real time monitoring of ⁹⁹Tc in groundwater based on the Quartz Crystal Microbalance (QCM). The QCM is a piezoelectric resonator, which oscillates in a resonant frequency f_s when an electric potential is applied across its body. It is capable of measuring very small changes in mass at its surface, through the change of the resonant frequency. We modify it to respond exclusively to the presence of TcO₄^-, by application of a novel Ag-4,4bipyridine metal-organic framework thin film built layer-by-layer on a self-assembled monolayer of 4-mercaptopyridine on the gold surface. The film's structure is characterised by several techniques such as XPS, AFM and XRD and we evaluate its response and selectivity by monitoring the changes in the resonant frequency as a function of the concentration of ReO₄^-, which is a non-radioactive chemical surrogate for TcO₄^-. Finally, we model the adsorption of ReO₄^- and other interferences with adsorption isotherms such as Langmuir, Freundlich and Sips.

Pathogenic E. coli are a significant threat both as a foodborne pathogen and a leading cause of urinary tract infections. Conventional methods to detect these microbes require centralized laboratory facilities and specialized equipment, as well as hours to days to complete. We have developed a sensitive electrochemical sensor to covalently capture, detect, and quantify viable pathogenic E. coli from complex matrices with a detection limit of 12 CFU/mL and a linear range of detection up to 10⁷ CFU/mL. The technology enables quantification within two hours on disposable electrodes, even from milk and artificial urine. Endogenous E. coli were successfully detected from commonly-contaminated samples, including eggs, raw chicken, spinach, and romaine lettuce, in addition to an infected urine sample. The E. coli quantification tracked well with the current gold-standard of colony counting. This platform represents a major step in the development of field-deployable sensors to detect these dangerous microbes.

Microcystins are a group of toxic cyclic heptapeptides produced by common cyanobacteria. The accumulation of microcystins in water reservoirs is an emerging worldwide problem. Exposure to microcystins is mainly associated with hepatotoxicity and carcinogenesis and leads to both acute and chronic damages. Microcystin-LR (MC-LR), the most common microcystin, accounts for most reported poisonings and is considered an imminent threat to human and animal health. Consequently, stringent regulation has recently been imposed by the World Health Organization (WHO), limiting the allowed MC-LR concentration in drinking water to <1 μg/L and a maximal daily intake of 0.04 μg/kg body weight. Current methods for MC-LR detection generally rely on chromatography coupled with mass spectrometry requiring bulky and expensive equipment, highly trained personnel, and labor-intensive preparation steps. Therefore, there is an urgent need for an affordable, on-site diagnostic tool providing a rapid quantitative determination of MC-LR in surface waters.

We have developed an electrochemical biosensor for MC-LR detection based on the transduction of bimolecular binding into an electrochemical signal. Specific antibodies were integrated with a biochip and measurement platform, applied in the detection of MC-LR by electrochemical impedance spectroscopy. Using the miniaturized platform, quantitative detection of MC-LR was feasible, exhibiting a dynamic range of five logarithmic concentrations and a limit of detection of 3 ng/L (3 part-per-trillion). This LOD is superior to currently employed solid-phase immunoassays. Furthermore, specific detection of MC-LR from models of cyanobacteria-contaminated water was demonstrated by the developed biosensor. Based on our findings, we anticipate that in the near future electrochemical biosensors would be an essential tool in water monitoring and environmental diagnostics.

Figure 1

MXenes are an emerging class of 2D layered nanomaterials that provide large surface area, hydrophilicity, high ion transport properties, low diffusion barrier, biocompatibility, and ease of surface functionalization. Due to their unique features, MXenes have gained substantial attention in fields such as batteries and supercapacitors and their application in chemical and biological sensors is growing. Their composition and layered structure make MXenes particularly attractive for biosensing applications. This presentation is focused on the synthesis and characterization of MXene-CeO₂ nanocomposite for glucose sensing. The developed MXene-nanoparticles hybrid was then used as a transducer surface and supporting material for the immobilization of enzymes in an electrochemical biosensor setup. The incorporation of MXene into the sensor design enhanced the efficiency of the developed biosensor in terms of facilitating charge transfer and maximizing cerium oxide and biomolecule loading. Opportunities for developing wearable sensors and systems with integrated biomolecule recognition will be highlighted.

One of the challenges in analytical chemistry is to develop a method that is not only sensitive but also selective for detection and quantification of a target analyte. Herein, we report a strategy that combines a molecularly imprinted polymer (MIP) as the selective element with electrogenerated chemiluminescence (ECL) as the sensitive analytical signal generator for detection of a hallucinogenic drug N,N-dimethyltryptamine (DMT). MIPs hold specific binding capability toward probed targets, and their molecular recognition behavior is similar to that of specific antibodies to antigens or probe single-strand DNAs to complemental target DNA sequencies. Additionally, MIPs are chemically stable, easily synthesized, and cost-effective. On the other hand, ECL has been regarded as one of the most sensitive analytical techniques for ultra-trace analyte determination. This is because ECL is a kind of spectroscopy initiated by electrochemistry without using any light source. For the present work, DMT specific MIPs were prepared by anodic electrodeposition of aminobenzoic acid as monomer mixed with DMT as template molecule on a glassy carbon electrode that had coated with a Ru(bpy)₃²⁺ trapped nafion film. ECL signals at the electrodes with DMT immobilized MIPs were acquired in a phosphate buffered solution upon the anodic potential scanning. A non-imprinted polymer (NIP) was also prepared in absence of template under similar conditions. The MIP-ECL sensor showed a wide dynamic range of 0.05 to 100 µM to DMT with an estimated detection limit of 0.05 µM. The reproducibility, stability, and selectivity of the sensor were also examined.

Figure 1

Amine and amine derivatives are known to have carcinogenic effects and recognized as priority pollutants on the United States Environmental Protection Agency (EPA) [1]. It is very important to detect amines, which are known to have carcinogenic effects, in natural water sources (drinking water, lakes, seas) where they can interact with humans quickly, transportably and with high sensitivity. Industrial establishments such as petroleum refineries, synthetic polymers, paints, tires, pharmaceuticals and explosives are the main sources of amine release into the nature. Hair dyes, exhaust gases, burning or degradation of protein-rich plants, and meat consumption, which are thought to cause cancer development and have been investigated intensely, can be considered as non-industrial sources of amine release [1, 2]. Although methods such as gas chromatography (GC), high performance liquid chromatography (HPLC), photometry, ion mobility chromatography, capillary electrophoresis are used to detect amine and amine derivative compounds (aromatic amines, aliphatic amines) in liquid [1, 3, 4]. These methods are very complex, require expert users and alternative techniques are being investigated due to their cumbersome structure.

The development of sensor systems in analytical chemistry for the identification and detection of organic compounds still poses a major problem. While the interest in QCM-based sensors is increasing day by day, it has become a proven transducer platform for sensing applications in liquid [5]. Sensor systems with different structures are produced to selectively detect each compound. These sensor systems need to be redesigned as they often exhibit low sensor characteristics directly in liquid. In response, Suslick et al. showed that pH indicators, solvatochromic molecules and colored metal complexes were used to decompose organic compounds in water [6]. In addition, QCM-based studies on the determination of chemical pollutants in liquid directly continue increasingly today.

The preliminary results were patented [7]. V₂O₅ thin film was deposited on one side of transducers via thermal evaporation method as active material with 20 nm thicknesses. AT-cut QCMs of 5 MHz fundamental frequency with gold electrodes were used as transducers. Structural and optical analyses of the V₂O₅ thin films were performed. SEM image of V₂O₅ thin film is given in fig. a and clearly seen that smooth surface morphology.

V₂O₅ thin film coated QCM sensor were tested to amine and amine derivatives and other chemical pollutants can be seen in nature due to some industrial process residue in water media. The tested analytes were chloramine T, butylamine, hexylamine, thrietylamine, dichloromethane, chloroform, chlorbenzene, trichlorethylene, tetrachlorethylene, p-xylene, bisphenol A, methiocarb, propoxur, triadimenol, tebuconazole, iprodine and triadimefon. Sensor tests were performed with QCM-Z500 (KSV Instruments, Finland) device which has thermostated measurement system for a single QCM sensor. The KSV QCM-Z500 device determines the resonance frequency of the quartz crystal in the liquid in the frequency range of 5-55 MHz and the quality factor (Q) of the resonance by impedance analysis.

Typical real-time sensor response of the QCM sensor coated with V₂O₅ to chloramine in water can be seen in fig b. The frequency variation changes rapidly in the negative direction when the analyte is sent to the test cell and reaches its maximum value. The average response time (t₉₀) of the developed sensor all concentrations tested is around 3s. In addition, it is seen that the test cell quickly returns to the baseline with the sending of pure water and it is seen in fig b that there is no drift at the baseline level during the whole test. The sensitivity of the developed sensor against chloramine T in water is calculated as 12 Hz/ppm and the limit of detection (LOD) value is 80 ppb. The LOD value is 50 times below the limit value specified in the EPA standards. The developed sensor was selectively respond to amine derivatives.

References

1. United States Environmental Protection November 2002

2. M. Pinheiro, E. Touraud, and O. Thomas, Dye. Pigment., 61, 121–139 (2004) http://www.sciencedirect.com/science/article/pii/S0143720803002092.

3. G. Snyderwine, R. Sinha, J. S. Felton, and L. R. Ferguson, Mutat. Res. Mol. Mech. Mutagen., 506–507, 1–8 (2002) http://www.sciencedirect.com/science/article/pii/S002751070200146X.

4. Önal, Food Chem., 103, 1475–1486 (2007) http://www.sciencedirect.com/science/article/pii/S0308814606006972.

5. E. Speight and M. A. Cooper, J. Mol. Recognit., 25, 451–473 (2012) https://doi.org/10.1002/jmr.2209.

6. Zhang and K. S. Suslick, J. Am. Chem. Soc., 127, 11548–11549 (2005) https://doi.org/10.1021/ja052606z.

7. Erbahar, et. al, Use of piezoelectric transducers modified with metal oxide-based thin films for direct detection of amine derivatives in liquid media, (2018) US20180080902A1.

Figure 1

Peroxynitrite is a very reactive and cytotoxic species that plays important pathophysiological roles, particularly in the brain. It is also suspected to be a factor involved in tissue damage that results from long term deep brain neural stimulation. Accurate determination of peroxynitrite concentration is inherently difficult due to its high reactivity and concentration range. Various methods for peroxynitrite determination have been reported including indirect spectroscopic assays and, recently, direct electrochemical methods. Currently, this field is still actively growing in the pursuit of viable electrochemical probes or catalytic materials as interfaces for efficient peroxynitrite detection. A durable and reliable electrochemical sensor would be valuable in order to monitor peroxynitrite generation near sites of electrical neurostimulation.

In this work, we prepared and characterized a functional thin film material based on an organic selenide on graphite electrodes and used the interface in sensitive electrochemical determination of peroxynitrite. First, we describe the preparation and grafting of the catalytic material based on the electrodeposition of organic selenides on graphite electrodes. Next, we report on the characterization of the resulting grafted film material on graphite interface using various physicochemical methods including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS). We then tested the performance of resulting aniline selenide catalytic material on modified electrodes as peroxynitrite sensing interfaces using voltammetry and dose-response amperometry. The grafted thin film material showed a significant enhancement in peroxynitrite oxidative current compared to electrodes with aniline only (i.e. materials devoid of selenium) under the same conditions. In the presentation we will show that the enhancement in peroxynitrite signal is the result of an electrocatalytic mechanism where the grafted selenide-based organic material at the oxidized state mediates the electrocatalytic oxidation of peroxynitrite. In terms of selectivity, the electrocatalytic detection of PON on electrodes modified with the selenide compound responds better and selectively toward PON as a target analyte over other potentially interfering analytes such as nitric oxide, nitrite, and nitrate. To the best of our knowledge, this is the first time a selenium-based organic material electrochemically grafted at an electrode surface is used for catalytic detection and quantification of peroxynitrite.

Overexpression of interleukin 6 (IL-6) in human blood could indicate the severity of many medical conditions such as inflammatory diseases, infections, and different types of cancer including lung, colorectal, prostate, and breast cancers. More importantly, in patients with COVID-19, the risk of respiratory failure could be examined via measuring the level of IL-6 expression. Early diagnosis of the aforementioned diseases requires precise detection of IL-6 at very low concentrations (≤5 pg mL^-1). While different biosensing approaches such as electrochemical methods, chemiluminescence immunoassays, and immunofluorescence assays (IFA) have shown satisfactory limit of detections (LODs) for IL-6, they could only perform well in buffer or processed serum, and their sensitivities are significantly reduced in more complex biofluids such as human whole plasma or blood. Here, we introduce a novel IFA platform capable of detecting IL-6 in human whole plasma with an LOD of 0.5 pg mL^-1 which is significantly lower than the reported LODs in buffer and plasma via IFA methods. The new IFA system comprises IL-6 capture antibodies covalently micropatterned on a lubricant infused matrix. The lubricant infused surface coating that is utilized in our system can effectively supress non-specific adsorption of all biomolecules, thereby diminishing the background noise and enhancing the sensitivity of the biosensor in complex biofluids. The micro-sized islands of the IL-6 capture antibodies throughout the lubricated surface provide a large number of sample analytes to be measured for high throughput purposes. Moreover, we have developed a new type of bioink in which the capture antibodies are conjugated with an epoxy-based silane coupling agent allowing for covalently attachment of the capture antibodies to the fluorosilanized surface via microcontact printing technique. In addition, the assay is performed on low-cost poly(methyl methacrylate) (PMMA) substrate using simple sandwich-based ELISA.

Recently, attention to the amounts of amino acids in critical care patients' blood have risen, emphasizing the loss of amino acids during renal replacement therapy. Recent clinical studies demonstrate that the majority of continuous renal replacement therapy patients experience a significant loss in total amino acid levels reaching up to 14–22 g per session. These alterations result in negative nitrogen balance, which is independently associated with longer stay in intensive care unit, prolonged overall hospital stay and increased rates of morbidity and mortality. Furthermore, critical care patients are known to have deficits in some of specific amino acids (glutamate, glutamine, lysine). These imbalances are further exacerbated by the renal replacement therapy, adding up to the promotion of the systemic inflammatory response syndrome, engaged in various pathologies and resulting in a worse clinical outcome of the patients. Therefore, it is highly important to develop a biosensing technology with capabilities to measure total and, in some cases, specific amino acids.

In this work we present a biosensing platform capable of fast quantification of total amino acids' concentration in real media, in a physiological concentration range (5–500 µmol/l). There are many reports in literature concerning amino acid biosensors, however, no electrochemical biosensor is commercially available, and amino acids today are measured by using slow and expensive colorimetric detections kits or chromatographic analyzers. Thus, the key novelty point of this work is the development of the electrochemical amino acids biosensing platform, which is expected to operate in clinical conditions. In addition, we have developed a new solution for the developed system such as new enzymatic membranes, electroconductive surfaces as well as specific measurements algorithms (Figure 1). All the solutions combined together provide a sensitive biosensor for the detection of amino acids, and could be applied for patients undergoing renal replacement therapy (Figure 1 A).

Figure 1

Mucosal surface in the gastrointestinal track and oral cavity are colonized by more than 700 types of microorganism. The bacteria interaction is depended on the location of its formation and dynamics. Streptococcus mutans, is known pathogenic bacteria present in oral microbiome, which metabolizes sucrose and other carbohydrates to produce lactic acid and lowers the pH 5.5 or less, which causes caries and periodontal diseases. Therefore, study of growth and dynamics of Sm bacteria is critical to understand oral cavity formation. Fluorescent in-situ hybridization probe (FISH) with confocal laser scanning microscopy (CLSM) is widely used for monitoring of biofilm with spatial resolution. However, these sophisticated instruments are not economically viable for multiple replication or high throughput applications. Here, we have used single frequency impedance spectroscopy as fast and non-invasive technique to monitor real time growth of Sm biofilm and kinetics of its formation.

Real time monitoring of Sm biofilm was performed by the continuous recording of impedance while Sm bacteria was grown on glass substrate in BMM with 30 mM sucrose feeding. The cell-sensors impedance has been reported in the arbitrary unit as normalized impedance called cell-index (CI). Sensors were first tested in phosphate buffer solution (PBS) and then changed to BMM as background signal. After stabilization of sensors, streptococcus mutane was injected. There is increase of CI after Sm injection from zero to 0.3 at 10kHz frequency then decreased ~ 0.2. The decrease of CI at 10 kHz is lactic acid release by the Sm bacteria which causes decrease in solution resistance. The CI value at 1 Hz is increased from zero to ~ 1 after bacteria inoculation. The increase in CI at lower frequency is due to growth of Sm bacteria on the electrodes surface which causes increase of capacitance. After 56 hrs of growth of Sm, surfactant sodium dodecyl sulphate (SDS, CMC) was injected for investigation of sensitivity of impedancemetry sensors on destruction of bacteria biofilm. There is decrease in CI value at 1 Hz suggests that Sm biofilm matrix was partially collapsed. So, this study suggests that, high frequency impedance-based sensor can be used as solution resistance sensors and low frequency impedance based sensor can be used as capacitive based sensor for monitoring of biofilm growth.

Fast scan cyclic voltammetry (FSCV) and carbon-fiber microelectrodes (CFMEs) have been utilized to detect several important neurochemicals in vivo. However, this method is limited due to the ability to discriminate dopamine from several of its metabolites. Polymers such as PEDOT, Nafion, and Polyethyleneimine (PEI) will be utilized to modify microelectrodes to measure neurochemicals by altering the size, charge, and morphology of the electrode surface. Moreover, novel waveform development will also be utilized to measure many neurochemicals and metabolites such as dopamine, norepinephrine, normetanephrine, 3-methoxytyramine (3-MT), homovanillic acid (HVA), 3,4 dihydroxyphenylacetic acid (DOPAC), and other metabolites. Dopamine will be differentiated from its metabolites based on the shape and position of the cyclic voltammogram, which is a chemical fingerprint of neurotransmitter detection. We have measured the stimulated release of dopamine in zebrafish retina, which illustrates this technique in biological tissue. The multiplexing of dopamine metabolites and dopamine will have many implications in better understanding complex disease, behavioral, and pharmacological states.

This work will also discuss the development of multielectrode arrays (MEAs) for neurotransmitter detection with fast scan cyclic voltammetry in multiple brain regions simultaneously. These arrays will be coupled to multichannel potentiostats from Pine Research. Parylene and silicon insulated carbon fiber microelectrode arrays were shown to be able to measure neurochemicals in multiple brain regions simultaneously when coupled with multichannel potentiostats. Moreover, we have utilized techniques such as plasma enhanced chemical vapor deposition (PECVD) to deposit conductive carbon nanospikes onto the surface of existing metal multielectrode arrays to give them dual functionality as neurotransmitter sensors with FSCV in addition to being used primarily for electrical stimulation and recording. Other assays have shown the utility of electrodepositing carbon nanotubes and polymers such as PEDOT to coat metal arrays with carbon to give them dual sensing capabilities. Applications of measurements with these carbon electrodes will be illustrated with measurements in mouse brain slices, zebrafish brain and retina, DNA, amino acids, and neuropeptides.

Figure 1

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder characterized by cognitive and memory deterioration, which requires an early diagnosis for effectiveness of treatment. Immunosensors based on AD biomarkers stand out as a fast, inexpensive and practical alternative for an early detection before it's first symptoms. The development of Screen-Printed Electrodes (SPEs) meets a growing demand in the market for applications such as signal transducers in biosensor devices. The screen-printing technology stands out due to its simplicity of elaboration, the possibility of mass production of disposable electrodes and ease in miniaturization for use in portable devices. The objective of this work is to develop a simple and low cost method to manufacture a Screen Printed Carbon Electrode (SPCE) system to detect AD.

The microelectrodes were obtained from carbon paste on two substrates: one from High Density Polyethylene (HDPE), and another one from Polyvinyl Chloride (PVC), shown Figure 1. The electrochemical response to adsorption of self-assembled polymer and lipid films was studied by cyclic voltammetry. The HDPE designed in Figure 3, offered a less capacitive and sensitive response to the assembly of the films compared to PVC. The immunosensor for AD diagnosis based on the detection of the IgG anti-Aβ1-40 autoantibody was built on SPCEs using layer by layer technique (LBL), as shown in Figure 4. The first bilayer consists of pure or functionalized Polyethyleneimine (PEI), and the second of liposomes of Dipalmitoyl Phosphatidyl Glycerol (DPPG) immobilizing the Aβ1-40 peptide, repeating this process in the second bilayer. In order to improve their sensory response, PEI functionalized with graphene produced via electrochemical exfoliation of graphite (EEG) was used, in the proportions of 0.6%, 1.2%, 2.4% and 10% (w / w).

Cyclic voltammetry was used to evaluate the electrochemical behavior of the SPCE in three cycles, at potentials from -0.6 V to 0.6 V with a support electrolyte containing PBS pH 7.4, Figure 5. Electrochemical Impedance Spectroscopy (EIS) measurements, Figure 6, were evaluated, with frequencies ranging from 0.1 MHz to 0.1 Hz, amplitude 10mV, for pure and modified SPCEs with PEI and their EEG composites. For detection, autoantibody solutions, diluted in PBS, were prepared in concentrations ranging from 1ng / ml to 10 µg / ml.

There was an evident decrease in capacitance in the samples of PEI with EEG, as seen in the voltammograms. After the functionalization of PEI, the capacitive currents of the electrodes clearly decreased, possibly due to an increase in the conductivity of the electrodes. On the other hand, the EIS curves for the electrodes with PEI functionalized, despite appearing to have larger modules than those in which it is not functionalized, the inclination of impedance spectra at low frequency presents minor slopes. This is possibly due to the higher permeation of charges in the interstices of the PEI, as observed in the microscopies in Figure 7, associating the capacitive process of these functionalized PEI electrodes capable of carrying more charge than the purely capacitive electrodes with bilayers composed only of PEI. This gave them a significantly higher degree of conductivity. After functionalization with EEG, the graphene particles appear to be dispersed in a disordered way on the polymer, being a possible cause of charge dispersion in pores, increasing their contact area, and justifying greater impedance values. PEI bands, as described in Figure 8, refer to asymmetric stretches of the C-N group at 1045, 1119, 1310 cm^-1, 1598 and 1651 cm^-1. Last band may be associated both to symmetrical angular deformation in plane for the -NH₂ to amides (possibly provided by reaction between EEG carbonyl and PEI amines) and PEI existing amines It was noticed a change in the band at 1651 cm^-1 in PEI composites with 0.6%, 2.4% and 10% assigned to amide formation, conferring a suitable dispersion. However, for others EEG contents, amide bands may be masked by amine groups of PEI.

Sensorial measurements were better performed at HDPE subtract modified with PEI functionalized with EEG until 1.2% of content. There was an exponential growth trend in the normalized area of the voltammograms, Figure 9, as the Aβ1-40 autoantibody concentrations increased, distinguishing its variation. However, after 1μg / ml the curve stabilized showing the limit of detection (LOD).

Figure 1

The utilization and commercialization of electronic based point of care (PoC) diagnostic devices has been hindered by the lack of repeatability and stability associated with such devices. Consequently, the enzyme-linked immunosorbent assay (ELISA) remains the dominant immunoassay used for the detection of serological diseases despite the numerous drawbacks associated with this platform.^{1, 2} Most notably, the ELISA relies on trained laboratory personnel to perform the assay in a centralized laboratory, which increases both the cost and time to actionable treatment. An electrochemical impedance biosensor is an example of a label-free biosensing platform that has high sensitivity and can be easily miniaturized and mass produced at a low cost, thus improving the time to actionable treatment.^3-7

It has been shown that the repeatability and stability of electronic based biosensors is not associated with the transducing element but rather is dependent on the sensor-molecule interface.⁸ This interface typically consists of an alkanethiolate-based self-assembled monolayer (SAM) chemisorbed onto a gold (Au) substrate. In the case of Electrochemical Impedance Spectroscopy (EIS) sensing, the SAM forms a barrier to the ionic transport of the selected redox coupling agent. The molecular structure of the alkanethiolate determine the uniformity and density of the SAM, which directly affects its ability to impede the ionic transport of the redox coupling agent. Molecular dynamics studies have shown that shorter, less-ordered alkanethiolates rotate more easily than longer alkylthiolates.⁹ Their ability to rotate facilitates the gradual coverage of pinholes and defects present on the sensor-molecule interface.⁹ A separate study has shown that short chain (6C) alkanethiolates leads to significant drift in EIS measurements.¹⁰ The drift in charge transfer resistance of the 6C SAM was hypothesized to be associated with the surface reorganization of these thiols. The observed drift in the SAM measurements has been reported to be greater in magnitude than the measured change in charge transfer resistance upon binding of a receptor, thus compromising the reliability of biosensing measurements.¹⁰ This work uses a 16C alkanethiolate SAM to show that the stability and reproducibility of EIS measurements is directly dependent on the coverage of pinholes and defects present on the Au substrate as well as the crystallinity of the SAM. Cyclic Voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) were used to measure the density and uniformity of the SAM, respectively. We show that stability in EIS measurements of the sensor-molecule interface directly corresponds to stable and reproducible measurements associated with the attachment of the selected receptor and lastly of the target analyte. Thus, through the rational design of a stable sensor-molecule interface we can minimize the drift associated with the SAM, and consequently the receptor interface. Thus, improving both the sensitivity and limit of detection of EIS based sensors.

References

1. Yalow, R. S.; Berson, S. A., Immunoassay of endogenous plasma insulin in man. The Journal of clinical investigation, 1960, 39 (7), 1157-1175.

2. Prevention, C. f. D. C. a. Understanding the EIA Test. https://www.cdc.gov/lyme/diagnosistesting/labtest/twostep/eia/index.html

3. Cui, Y., Wei, Q. Q., Park, H. K., and Lieber, C. M., Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species, Science, 2001, 293, 1289-1292.

4. Park, I., Li, Z., Pisano, A. P., and Williams, R. S., Top-down fabricated silicon nanowire sensors for real-time chemical detection, Nanotechnology, 2001, 21, 015501.

5. Patolsky, F., Zheng, G. F., Hayden, O., Lakadamyali, M., Zhuang, X. W., and Lieber, C. M., Electrical detection of single viruses, Proceedings of the National Academy of Sciences of the United States of America, 2004, 101, 14017-14022.

6. Pui, T. S., Agarwal, A., Ye, F., Ton, Z. Q., Huang, Y. X., and Chen, P. Ultra-sensitive detection of adipocytokines with CMOS-compatible silicon nanowire arrays, Nanoscale, 2009, 1, 159-163.

7. Stern, E., Vacic, A., Rajan, N. K., Criscione, J. M., Park, J., Ilic, B. R., Mooney, D. J., Reed, M. A., and Fahmy, T. M. Label-free biomarker detection from whole blood, Nature Nanotechnology, 2010, 5, 138-142.

8. Tarasov, A.; Tsai, M.-Y.; Flynn, E. M.; Joiner, C. A.; Taylor, R. C.; Vogel, E. M., Gold-coated graphene field-effect transistors for quantitative analysis of protein–antibody interactions. 2D Mater. 2015, 2, 044008.

9. Jiang, L., Sangeeth, C. S., Yuan, L., Thompson, D., & Nijhuis, C. A. (2015). One-Nanometer thin Monolayers remove the deleterious effect of substrate defects in Molecular Tunnel Junctions. Nano Letters, 2015 15(10), 6643-6649.

10. Xu, X.; Makaraviciute, A.; Kumar, S.; Wen, C.; Sjödin, M.; Abdurakhmanov, E.U.; Danielson, H.; Nyholm, L.; Zhang Z.; Structural Changes of Mercaptohexanol SelfAssembled Monolayers on Gold and Their Influence on Impedimetric Aptamer Sensors, Analytical Chemistry., 2019 91 (22), 14697-14704

Introduction:

We present an electrochemical sensor to monitor Cl^- concentration using a chloride specific silver electrode connected to electrodes of different surface areas and materials in a bipolar arrangement (figure 1). Using a bipolar arrangement may pose benefits for an ion selective electrode compared to traditional methods. Two key benefits are 1) the partition of the measurement versus reference compartments, and 2) the ability to apply various overpotentials across the system. These two attributes help eliminate the effect of some interference and may allow us to tune the linear range of the sensor.

The sensor function relies on balancing the association of Cl^- and Ag⁺ with the conversion of Prussian blue to Prussian white. The entire system is held at a defined potential using a potentiostat across working electrode 1 and reference electrode 1 (below). As Cl^-are added to the sample compartment, Cl^-will associate with Ag⁺ to form Ag/AgCl altering the potential across the bipolar electrode. To ensure the conservation of charge the ratio of Prussian blue to Prussian white will also shift. This change in ratio is measured using open circuit potential against a second working electrode. The open circuit potential response for each of these electrodes is then modeled using the Nernst equation, and mixed potential theory^1–3.

Methods:

Deposition of Prussian blue was carried out using 1mL volume of 2.5mM FeCl₃, and 2.5mM ferricyanide, in a supporting electrolyte of 0.1M hydrochloric acid and 0.1M KCl solution. An overpotential of 0.4V versus Ag/AgCl was applied to the working electrode for 3 cycles of 4 minutes while monitoring the current. After deposition, the electrode was vigorously rinsed in MQ water and activated using cyclic voltammetry. This procedure was carried out on both the gold and platinum electrodes.

For proof of concept, the chloride sensitive electrode was fabricated by taking a single junction Ag/AgCl electrode and removing the silver wire. This wire was then anodized using a positive potential of 0.4V versus Ag/AgCl was held against a platinum counter electrode in 1M KCl solution. The electrode was stored in 1M KCl until further use.

The various potentials applied across the entire cell were chosen by running cyclic voltammetry in 10mM potassium phosphate buffer with pH 7. The oxidation and reduction peaks were then selected, as well as the formal potential, which we calculated by taking the average of the 2 peaks.

Results and Discussion:

The bipolar reference electrode was tested against various interfering substances such as glucose, Na⁺, K⁺, and pH based on the in vivo environment (interstitial fluid ranges). The linear range, and limit of detection for Cl^- was found across each electrode type and size. We also investigated the effect of applying different potentials across the cell and compare the limit of detection, and linear range. Based on this we found the reduction potential resulted in best limit of detection. Finally, the impact of the measurement compartment ion concentration was tested by changing the concentration of Cl^- in the measurement compartment.

References:

• Park, J. H.; Zhou, H.; Percival, S. J.; Zhang, B.; Fan, F.-R. F.; Bard, A. J. Open Circuit (Mixed) Potential Changes Upon Contact Between Different Inert Electrodes–Size and Kinetic Effects. Anal. Chem. 2013, 85 (2), 964–970.

• Smith, L. A.; Glasscott, M. W.; Vannoy, K. J.; Dick, J. E. Enzyme Kinetics via Open Circuit Potentiometry. Anal. Chem. 2020, 92 (2), 2266–2273.

• Jansod, S.; Cherubini, T.; Soda, Y.; Bakker, E. Optical Sensing with a Potentiometric Sensing Array by Prussian Blue Film Integrated Closed Bipolar Electrodes. Anal. Chem. 2020, 92 (13), 9138–9145.

Figure 1

Recent changes in the legal status of cannabis augmented by a rapidly evolving social acceptance towards its consumption, highlight the immediate need for a reliable, non-invasive, point-of-use detection method for cannabis intoxication. Marijuana intoxication reduces motor coordination, slows reaction time, and impairs peripheral vision, concentration, and decision making. The rise in access and consumption of marijuana is anticipated to lead to an increase in drivers and workers impaired from its effects. Current tests for marijuana consumption are invasive (rely on blood/urine), logistically challenging (require weeks to analyze), and can only conclusively confirm use within the past month (not real-time detection). In the absence of a portable, non-invasive analytical tool to quantify marijuana intoxication, real-time THC sobriety tests rely heavily on subjective techniques that are prone to human error and/or bias. Consequently, these methods are inadequate for law enforcement, who need who need to quickly and accurately determine an individual's state of impairment, and employers, who forbid "working under the influence", but would allow responsible "off-duty" cannabis consumption to go unpenalized, so long as it does not affect job performance.

Although there is no federal legislative consensus on the definition of marijuana intoxication, it is known that Δ9-Tetrahydrocannabinol (THC), the principle psychotropic in marijuana, has an approximate 3-hour detection window in the body that roughly correlates with symptoms of peak cannabis impairment. A small, but detectable, concentration of THC remains in equilibrium in the lungs during this 3-hour window, allowing the use of breath to be leveraged as a non-invasive method to determine recent cannabis consumption. After 3 hours, cannabinoid metabolites are rapidly diminished from the blood and lungs and absorbed into fatty tissue and the brain, reducing the efficacy of breath for use in non-invasive detection methods. While the low concentration of cannabinoids in breath (µg/L – pg/L) complicates detection, and there is ongoing debate as to how chronic marijuana use, gender, and body type affect baseline THC levels, there is a growing consensus that a breathalyzer will ultimately provide the best solution for a non-invasive, point-of-use detector for cannabis intoxication.

Seacoast Science, Inc. is co-developing a hand-held marijuana breathalyzer in collaboration with Professors Nathaniel Lynd and Feng Zhang of UT Austin. This device will allow for the real-time, point-of-use detection and quantification of cannabinoids measured in the gas-phase. The underlying detection technology is based on the use of smart, biomimetic polymers with enhanced cannabinoid affinity measured by Micro-Electro-Mechanical Systems (MEMS) transducers (ie. chemicapacitors and chemiresistors). We will present results confirming reliable detection of a panel of gas-phase cannabinoids measured using this system in a controlled environmental chamber. The use of chemometric analysis to identify selected cannabinoids vs. common interferents will also be discussed. This technology allows a roadmap for the non-invasive analytical detection of cannabinoids in breath, which serve as biomarkers for marijuana intoxication.

There is a great challenge to detect and remove heavy metals which have posed a severe threat to our ecological systems. The extreme toxicity of heavy metals such as Arsenic (III) is a top priority to the Environmental Protection Agency due to carcinogenic aspects and Asⁿ⁺ exists in the earth's crust and groundwater. It has been found that serious health problems and various skin cancers can occur due to long term exposure to contaminated water with arsenic. The high demand to develop effective and low cost electrochemical sensors that are reliable to detect low concentration of arsenic with such techniques as square wave anodic stripping voltammetry are highly needed. The design and fabrication electrode surface can facilitate the oxidation of the analyte from the surface under optimized synthesized Ag nanoparticle carbon electrode surface. The synthesis of silver nanoparticles by utilizing beet juice was a nontoxic synthesis protocol "green technology". The synthesized silver nanoparticles were deposited onto the working carbon electrode to detect Arsenic (III). The confirmation of successful synthesis of silver nanoparticles from beet juice was confirmed by UV-Vis peak around 450 nm and further confirmation from an FTIR . The modified silver nanoparticle carbon electrode enhanced the catalytic activity of the surface to detect the As(III) better than the bare C electrode surface. Plot of Arseinc (III) versus Current in mA gave a linear calibration plot of 0.99 over 4 magnitudes of concentration. The stability, good shelf life and reusability of the modified silver nanoparticle carbon electrode as an electrochemical sensor for the detection of As(III) were analyzed and will be presented accordingly.

Gout is a disease associated with defective metabolism of uric acid that also results in arthritis with chalkstone deposits on bones of the feet, causing acute painful episodes. Both gout and hyperuricemia are diseases linked with certain levels of uric acid in suffers and even some patients with renal diseases. With the relationship between serum uric acid and urea as biometabolites, it was necessary to examine their uremic contents as contributive factors to chronic gout. This study was necessary since early detection of urea and uric acid, even at very minute levels, in human blood may foster a better understanding of renal health, facilitate prompt gout diagnosis, and eventually promote healthy living. In the present study, CuO/ZnO/reduced graphene oxide (rGO) nanocomposite modified pencil graphite electrodes are fabricated and appropriately characterized using surface morphological techniques (e.g., atomic force microscopy and scanning electron microscopy) and electrochemical techniques (e.g., cyclic voltammetry and electrochemical impedance spectroscopy). These nanocomposites sensors acted as substrates for adsorbing and detecting of urea and uric acid. Results from this study revealed a fabrication process for making modified electrode-based sensors for effective and simultaneous detection of both biomarkers at exceptionally low limit of detection (LOD) in uremic samples. No matrix interferences were recorded in both plasma and serum test samples. The optimum concentrations of these nanocomposites on the biosensor surfaces significantly recorded detection limits at 1.80 × 10^-9 M for urea and 2.69× 10^-9 M for uric acid in plasma while levels of urea and uric acid stood at 2.06 × 10^-9 and 3.10× 10^-9 M, respectively, in serum samples. The efficacy of this biomarker detection protocol was also examined from pharmacokinetic studies for both substances in their standard solutions and spiked uremic samples. Prompt sensing of these kinds of metabolites as disease biomarkers at low LOD is important in the assessment of degrading health conditions of gout patients as well as in monitoring inherent concentration changes for potential treatments. Furthermore, this detection protocol may have a future in bioassay involving gout diagnosis in renal patients, assessment of gross renal health or even in-vitro and in-vivo applications for monitoring drug dosages.

Keywords: Gout, Biosensing; Uric acid; Simultaneous detection; Disease biomarker; Limit of detection

Disinfectants are essential to keep water safe as they kill pathogens by oxidizing the cell membrane. Free chlorine, potassium permanganate, monochloramine, hydrogen peroxide, chlorine dioxide, ozone, and hypobromous acid are the most commonly used disinfectants for the disinfection of water.¹ Monitoring the concentration of the disinfectant is crucial as the effectiveness mainly depends on the amount of disinfectants present in water.² Insufficient levels of disinfectant in drinking water could impose health risks as pathogens could regrow in the distribution system. Standard methods for measuring the disinfectant levels are colorimetric and titrimetric.³ For free chlorine, DPD colorimetric method is well established.^1,4 For potassium permanganate (KMnO₄), colorimetric methods (persulfate and periodate) and spectroscopic methods are available.^1,5 Currently, the monitoring of disinfectants is done on samples collected at the treatment plant and in different locations throughout the distribution system. This reagent-based measurement of discrete samples requires reagents and spectroscopic readout devices and can suffer from interference. Therefore, these methods are not suitable for the continuous monitoring of the disinfectant.⁶ Furthermore, there is no known method that can differentiate between multiple disinfectants in real samples without any previous knowledge.

Two of the most important water quality parameters are pH and oxidation-reduction potential (ORP). Disinfectants undergo different reactions at different pH, resulting in different active species for different pH. ORP measurement can be used to monitor whether the disinfection was successful as oxidants' reactivity in water depends on redox conditions.⁷ ORP of a solution is associated with the pH and the concentration of the disinfectant. At a fixed pH, the ORP of a disinfectant will depend on the concentration. Therefore, just by knowing the ORP, we cannot distinguish disinfectant unless the pH or concentration of the oxidant is known.^8,9

To sort out these parameters, we propose to introduce a chemiresistive sensing array capable of distinguishing and quantifying disinfectants. Due to simpler fabrication techniques, lower cost and the ability to sense various analytes through appropriate ligand, chemiresistors have great promise in water quality sensing.^6,10 Previously reported chemiresistive sensor for continuous measurement of free chlorine used carbon nanotube (CNT) substrate functionalized with a redox-active aniline oligomer named phenyl capped aniline tetramer (PCAT).¹¹ Oxidation of PCAT attached to the surface of CNT by free chlorine leads to a change in the oxidation state of the oligoaniline; this change in oxidation state in the molecule changes the doping characteristics of CNT leading to a change in resistance of the CNT film. This resistance change was used to quantify the concentration of free chlorine.¹¹

In this work, we have constructed an array of single-walled carbon nanotubes (SWCNT) sensors functionalized with five redox-active molecules. Structurally different from each other, these molecules will create different active sites. Upon interaction with analytes, each molecule will give different magnitudes of responses. Sensor responses are collected for free chlorine and KMnO₄ over a range of concentrations for pH 6.5 and 7.5. In general, sensors give increasing responses to the increasing concentration and decreasing pH of the solution. Though the responses from the sensors have a similar trend to the change of the parameters their varied magnitudes make them suitable for an array. Sensor responses are then analyzed with principal component analysis (PCA). PCA analysis shows clear separation between the analytes and as well as to different pH and concentrations of the solutions (figure). We have therefore demonstrated an array of chemiresistive sensors that can distinguish and quantify disinfectants.

References:

1. US Environmental Protection Agency - Office of Water, Alternative disinfectants and oxidants Guidance manual, 1st Ed., p. 1–328, (Washington, DC) US Environmental Agency, (1999).

2. I. M. Sayre, J. Am. Water Work. Assoc., 80, 53–60 (1988).

3. World Health Organization, Guidelines for drinking water-quality: Fourth edition incorporating first addendum, 4th ed + 1st add, p. 541, World Health Organization, (2017).

4. A. T. Palin, J. Am. Water Work. Assoc., 49, 873–880 (1957).

5. S. T. McBeath, D. P. Wilkinson, and N. J. D. Graham, Chemosphere, 251, 126626 (2020).

6. P. Kruse, J. Phys. D. Appl. Phys., 51, 203002 (2018).

7. Y. H. Kim and R. Hensley, Water Environ. Res., 69, 1008–1014 (1997).

8. A. Copeland and D. A. Lytle, J. Am. Water Work. Assoc., 106, E10–E20 (2014).

9. T. V Suslow, Uni. Cali. Agri. Nat. Res., 8149 (2004).

10. A. Mohtasebi and P. Kruse, Phys. Sci. Rev., 3, 20170133 (2018).

11. L. H. H. Hsu, E. Hoque, P. Kruse, and P. Ravi Selvaganapathy, Appl. Phys. Lett., 106, 063102 (2015).

Figure 1

Introduction

Ionic Liquids (ILs) are molten salts at room temperature and have both solvent and electrolyte properties. ILs have been actively studied for use in electrochemical gas sensors, thanks to their gas absorption property, electrochemical stability, and low evaporation loss. For example, gas sensors based on the changes in electrical double layer capacitance or in bulk impedance induced by gas dissolution in ionic liquids have been reported [1, 2]. However, there are few reports on the selective recognition of volatile organic compounds such as metabolites in human exhaled air against interfering gases. In this study, we demonstrated selective recognitions of acetone, which is a typical low-molecular-weight metabolic gas in human exhaled air, against hydrogen, which is a metabolite of enterobacteria, by electrochemical impedance measurement using ionic liquids.

Method

The interdigitated electrodes made of Cr/Pt shown in Fig. 1 were fabricated on a glass substrate. The 3-nm-thick chromium film acting as the adhesion layer was deposited by electron beam evaporation technique, which was followed by the pattern definition and evaporation of 100-nm-thick platinum electrode acting as the main electrical conduction layer. The droplet of 3-μL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, a kind of ionic liquids, was casted onto the electrodes, which completed the fabrication of a two-terminal electrochemical sensor.

The impedance measurements were performed under various atmospheres. The following shows the sequence of atmospheres under which the impedance responses of the fabricated sensors were measured.

ⅰ) Dry air (3 min)

ⅱ) (case Ⅰ) 25-ppm H₂ in dry air (3 min)

ⅱ) (case Ⅱ) 25-ppm CH₃COCH₃ in dry air (3 min)

ⅲ) dry air (3 min)

In the second process ii), case I or case II was chosen from two target gases; hydrogen and acetone. The gas flow rate was kept constant at 200 sccm. Impedance measurements were performed using an LCR meter (Keysight E4980A) with DC bias of 0.0 V and AC amplitude of 10 mV. The measurement frequency was varied from 300 kHz to 20 Hz.

Results

Fig. 2 shows the measured sensor response at (a) 200 kHz, (b) 30 Hz, and (c) 350 Hz. The sensor response is defined as impedance change ΔZ_re due to target molecules normalized by the impedance in dry air Z_re(Air), where Z_re represents the real part of the impedance. The equation used to extract the sensor response is shown in Fig. 2. We noticed that the sensor response was strongly dependent on the measured frequency. Z_re decreases at 200 kHz in both the CH₃COCH₃ and H₂ atmospheres (Fig. 2(a)), whereas it is increased by the target molecules at 30 Hz (Fig. 2(b)). The directions of the impedance changes were the same for both the target molecules. On the other hand, at 350 Hz (Fig. 2(c)), Z_re decreases in the CH₃COCH₃ atmosphere, although it stays constant in the H₂ atmosphere. This clearly demonstrates that CH₃COCH₃ can be selectively detected against H₂ by impedance measurement with an appropriate measurement frequency.

Discussion and Conclusion

We consider that the equivalent circuit of the present system includes an element related with the bulk IL resistance and one related with the electrical double layer at the electrode/IL interfaces. The measurement of the impedance phase angle reveals that the phase angle is close to 0 degrees at 200 kHz and close to -90 degrees at 30 Hz. Therefore, we consider that high-frequency (200 kHz) Z_re is affected by the bulk IL resistance change induced by dissolved gaseous molecules and that low-frequency (30 Hz) Z_re is influenced by the change in electrical double layer characteristics. On the other hand, at medium frequencies; namely 350 Hz in this study, the gas-induced effects both on bulk IL resistance and on the electric double layer characteristics causing Z_re modulation may be compensated with each other, and no sensor response was observed under the H₂ atmosphere as shown in Fig. 2(c).

We will extract the equivalent circuit model for the system used in this experiment and examine how the parameters of circuit elements change in the H₂ and CH₃COCH₃ atmospheres in comparison with the standard dry air atmosphere. By investigating the frequency dependence of the impact of each parameter change on Z_re, we will clarify the mechanism of Z_re constancy in the H₂ atmosphere at medium frequencies.

References

[1] Zhe Wang, et al., Analytical chemistry, 88, 1959 (2016).

[2] M. Honda, et al., In Proceedings of IEEE SENSORS, 1 (2012).

Figure 1

Computing Technologies today come in myriad forms and types,but what is more important is that Computing Technologies Feed and Munge on Data.

Without data to Munge,computing devices may as well go hungry(literally) and become extinct or irrelevant.

But the contrary is the case as new data(structured and unstructured) is being generated exponentially daily beyond measure.

This is more so with the continuous advent of newer data collection and generating device technologies such as IoT sensors,mobile computing technologies and emerging Human-Computer Interaction Technology Devices.

The integral Role and significance of Sensors to the emerging IoT Computing Technology, in providing signals in either digital or analog form that the computer interprets as data and uses for processing and other computation related tasks is what we undertake to discuss and outline in this paper.

Gold nanoparticles of various morphologies have been synthesized using different synthetic approaches. Sonochemical synthesis results in the formation of 25 nm sized gold nano discs and 30 nm sized polyhedral structures with surface area of 179.5 m²/g and 150.5 m²/g respectively[1]. The UV-Visible spectrum shows the SPR peaks due to in plane and out of plane excitation modes. Microemulsion synthesis using Tergitol NP-9 surfactant resulted in the production of hexagonal gold nanoparticles (avg. size: 20 nm) at 0.05 M HAuCl₄ (aq) and spherical morphologies with an average size of 25 nm and 15 nm at molar concentrations of 0.04 M and 0.03 M HAuCl₄ (aq) respectively[2]. Gold nanoparticles show the surface plasmon resonance peaks at 540 nm and 580 nm along with peaks corresponding to higher order plasmon resonance modes at shorter wavelengths. The surface area was found to increase with decrease in particle size. An ecofriendly synthetic route was also employed to synthesize gold nanoparticles using candida albicans fungal cell free extract[3]. Gold nanocrystals of 5 nm have been obtained with specific surface area of 18.9 m²/g. The encapsulation of gold nanoparticle by biomolecules of the cell free extract was confirmed by FTIR and TGA studies. Gold nanoparticle show surface plasmon resonance (SPR) peak at 540 nm. Gold nanoparticles have been tested for antimicrobial activity against fungal and bacterial species. Gold nano discs displayed higher antimicrobial action against fungus candida albicans as compared to gold polyhedral structures by inhibiting H+-ATPase activity. Biosynthesized gold nanoparticles showed good antimicrobial activity against Staphylococcus aureus and Escherichia coli. However, Escherichia coli, a gram-negative bacterium was found to be more susceptible to gold nanoparticles as compared to Staphylococcus aureus, a gram-positive bacterium. The microemulsion synthesized gold nanoparticles were tested against Candida albicans both alone and in combination with fluconazole. The gold nanoparticles in combination with fluconazole showed maximum inhibition and the antifungal activity increased with decrease in particle size.

References:

[1] Wani I A and Ahmad T 2013 Size and shape dependent antifungal activity of gold nanoparticles: a case study of Candida Colloids Surf. B Biointerfaces101 162–70

[2] Ahmad T, Wani I A, Manzoor N, Ahmed J, Kalam A and Al-Shihri A S 2014 Structural characterization, antifungal activity and optical properties of gold nanoparticles prepared by reverse micelles Adv. Sci. Lett.20 1631–6

[3] Ahmad T, Wani I A, Manzoor N, Ahmed J and Asiri A M 2013 Biosynthesis, structural characterization and antimicrobial activity of gold and silver nanoparticles Colloids Surf. B Biointerfaces107 227–34

ISEs possess several advantages, such as high speed, ease of preparation, simple instrumentation, fast response time, wide concentration range, good selectivity and economically affordable. ISE based electrochemical sensors are useful in analysis of food products, drinking water, beverages, fertilizers, soil industrial effluents etc. Generally sensors are based on electroactive materials and provide a rapid and convenient means for quantitative estimation of anions and cations in biological and industrial samples. The aim of present work is to synthesize modified clay with heteropoly acids. These modified clays may have significant electrochemical activity in Ion selective electrodes. These clays can be employed as ionophore to develop chemical sensors for their application as sensors and in potentiometric titrations as indicator electrode.

Designing an electrochemical sensor which is cost-effective along with high stability and activity is challenging. It requires a proper architecture of supporting electrode materials. Herein, we have successfully synthesized and explored the electrochemical activity of 3D – hierarchical flower like cerium vanadate (CeVO₄) anchored on g-C₃N₄ towards the detection of Nitrofurantoin. A series of spectroscopic and morphological techniques like XRD, FT-IR, and FESEM clearly confirms the formation of CeVO₄ and CeVO₄@g-C₃N₄ nanocomposite. The electrocatalytic activity of the CeVO₄@g-C₃N₄ modified screen printed carbon paste electrode (SPCE); for detecting nitrofurantoin was evaluated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). A significant improvement in the rate of charge transfer and conductivity was observed, owing to the 3D flower like structure of the CeVO₄ nanoparticles. This resulted in a significant improvement in the electrochemical performance with a wide dynamic linear range and a very low detection limit of 0.0010 µM, showed a high sensitivity in the presence of potential interfering compounds. The proposed CeVO₄@g-C₃N₄ modified sensor showed interesting results when evaluated for its real-time applications for detecting nitrofurantoin in human blood serum samples, and also commercially available pharmaceutical tablets. It showed an excellent recovery range for real sample analysis and can be applied to make commercial electrochemical device with potential sensing abilities.

Figure 1

The knee is a complex joint, with intrinsic and extrinsic stability mechanisms, as well as a complex muscular interaction that allows controlled mobility during gait, and since it is a weight-bearing joint, its function is directly subject to the development of the knee. gait as a physiological action, therefore the assessment of the knee as part of gait is essential for the understanding of mobility in the 3 planes of movement dynamically, as well as the alterations that can occur due to structural injuries of the knee, as well as gait due to muscular or neuromuscular alteration.

One of the most frequent traumatic injuries in the general population and therefore with great impact on normal gait is the anterior cruciate ligament injury in the knee, and since these injuries can have sequelae during the rest of life they are of great Importance, the incidence of these injuries is estimated at 200,000 cases per year in the United States, and since few countries keep systemic incidence records, these data are not local, but in these countries the incidence is Germany 32 per 100,000 and 29 per 100.00 in USA (Singh, 2018). In addition, ruptures may occur in the same individuals, which are attributed mainly to incomplete diagnoses with poor characterization of the injury, or the instability that it produced, and therefore incomplete treatment of the injury, errors in surgical technique, or an insufficient rehabilitation with lack of strength (Csintalan, 2008).

The evaluation of gait alterations is carried out in 2 diametrically opposed environments, the first one is research, where assessment is carried out with tools such as gait analysis or dynamic goniometry, and the second one is the clinical environment, where it is done a subjective and poorly standardized assessment that does not allow adequate integration of diagnosis and treatment.

Joint stability assessment and diagnosis strategies are found in a wide range of options, from the assessment of subjective parameters, referred by the patient, static and passive measurements of joint laxity, or postural balance tests (Hatfield, Hammond, & Hunt, 2015), but none of these strategies allows a quantification of stability during activities such as walking (Knoop et al., 2012). Gait analysis allows assessment of knee function and estimating joint stability (Protopapadaki, Drechsler, Cramp, Coutts, & Scott, 2007).

The interpretation of joint mobility implies a challenge since analyzing joint dynamics in vivo requires invasive methods, also in joints such as the knee that have intrinsic and extrinsic stability mechanisms, as well as involuntary compensatory mechanisms, which depend on the supported nervous system (Van Tunen et al., 2018).

Assessing the joint stability of the knee in clinical practice, and research scenarios, is widely supported by the subjective instability reported by patients, this symptom, although subjective, is one that is related to gait disturbances, due to pain, and instability (Schrijvers et al., 2019), however, the lack of generally accepted parameters for assessing stability makes it difficult to compare results between studies (Farrokhi et al., 2014).

The implementation of biosensors, to improve and simplify the Knee movement and clinical assessment has a potential huge impact in the clinical environment due to its high incidence, and on the cost to the Health system not only because the proposed system is inexpensive, but also because of the high incidence of underdiagnosis as a frequent cause of surgery failure.

Contrasting all these perspectives (Ahldén et al., 2012) indicates that one of the biggest problems is the lack of a gold standard, since clinical manual evaluation is the basis for diagnosis and treatment, but is subjective in interpretation and performance, and the integration of different dynamic analysis models have not provided a standardized, validated and reproducible pattern.

The objective of this study was to assess an electro goniometer used combining different biosensors including a multidirectional electro goniometry and surface electromyography to allow an evaluation not only of the movement and displacement of the knee, in a wholesome manner, but also have information about compensation mechanisms, and reflex and involuntary activation of the quadriceps, and How efficient it is, which will help evaluate not only the instability itself but also when it is successfully compensated and when it should be necessary a surgical intervention.

The interaction between multiple biosensors allows us to get a reading that is not only dynamic but also more accurate and has an assessment of different activities, and a better comprehension of the individual evaluation of each knee, and different instability patterns due to the multiple possible combination of simultaneous ligamentary, chondral, meniscal, and capsular injuries.

Early detection of cancer can noticeably increase the survival chance of many cancer patients. Quantifying cancer biomarkers detectable from blood is an efficient way for the early detection of cancer diseases. Among various discovered cancer biomarkers, platelet-derived growth factor-BB (PDGF-BB) is an essential biomarker for early detection of cancer and monitoring cancer patients. This biomarker plays a vital role in developing and lymphatic metastasis of solid malignant tumors such as brain, lung, breast, and liver, which enlightens the importance of developing point-of-care (POC) biosensors for the detection of PDGF-BB. In recent years, the application of synthetic DNA or RNA-based bio-recognizers (i.e., aptamers) in cancer biomarker sensor development has been vastly investigated. Electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for POC. The well-established C-MEMS (carbon microelectromechanical systems) platforms have distinguishing features which are highly suitable for biosensing applications such as low background noise, high capacitance, high stability when exposed to different physical/chemical treatments, biocompatibility, and good electrical conductivity. Furthermore, the surface of C-MEMS can be modified effectively via depositing nanomaterials which can enhance the electrochemical and sensing performances of the C-MEMS based biosensors. In this study, the integration of bipolar exfoliated (BPE) reduced graphene oxide (rGO) with 3D C-MEMS microelectrodes for developing PDGF-BB label-free aptasensors is investigated. A single setup has been used for exfoliation, reduction, and deposition of rGO on the 3D C-MEMS microelectrodes based on the principle of bipolar electrochemistry of graphite in deionized water. The electrochemical bipolar exfoliation of rGO resolves the drawbacks of commonly applied methods for synthesis and deposition of rGO such as requiring complicated and costly processes, excessive use of harsh chemicals, and complex subsequent deposition procedures. The PDGF-BB affinity aptamers were covalently immobilized by binding amino-tag terminated aptamers and rGO surfaces. The scanning electron microscopy (SEM) analysis confirms that the rGO deposited on 3D C-MEMS microelectrodes has a porous vertically aligned structure with pore sizes of around 100 nm. Cyclic voltammetry (CV) was used for characterizing the aptasensors in different stages of development and their sensing performances. The CV analysis confirms that deposition of BPE-rGO noticeably increases the capacitance of 3D C-MEMS electrodes. The turn-off sensing strategy was implemented by measuring the areal capacitance from CV plots. The aptasensor showed a wide linear range of 1 pM-10 nM, high sensitivity of 3.09 mF cm^-2 Logc^-1 (unit of c, pM), and a low detection limit of 0.75 pM. This study demonstrated the successful deposition of BPE-rGO on 3D CMEMS microelectrodes. Considering the high potential of C-MEMS technology and BPE technique's simplicity and efficiency, this novel technique is highly promising for developing feasible and mass-producible lab-on-chip and point-of-care cancer diagnosis technologies.