Table of contents

Antifungal agents are essential drugs used to treat fungal infections caused by various types of fungi. Due to their mechanism of action, these drugs bear serious adverse reactions, interact with a wide range of other drugs, and negatively impact the environment. Therefore, there is a need for accurate, sensitive, and reliable detection methods to minimize and possibly avoid their potentially negative effects. Even though so far classical methods have proven to be effective in detecting these drugs, some of their disadvantages have led the scientific community to focus its efforts on electrochemical methods, as they are simpler to use, more sensitive, and require a smaller quantity of sample and minimal sample pretreatment. This mini-review focuses on electrochemical sensors developed between 2017 and 2022 to detect and quantify antifungal azoles, highlighting their response characteristics, sensitivity, and applicability in real samples analysis.

Plant pathogens massively affect crop productivity and are one of the significant challenges in attaining sustainable development goals related to agriculture, food production, and addressing hunger issues. Conventional techniques of generic seasonal chemical spraying severely damage the environment and human health. On the contrary, nanomaterials-based biosensors have emerged as economical, efficient, selective, prompt, and precise strategies for plant pathogen and disease diagnosis. The integration of nano-biosensors with artificial intelligence, internet-of-things, cloud computing, drones, and 5G communication has recently raised the paradigm of internet-of-nano-things-inspired intelligent plant-diagnostic biosensors. This prospect highlights these modern-age plant-pathogen biosensors for shaping smart and 5th generation agricultural practices.

Highlights

• Traditional approaches to combat plant diseases and pathogens requires large human resources

• Integration of internet-of-nano-things in plant biosensors enabled economical, efficient, selective, prompt and precise diagnosing strategies

• Utilization of drones, IoTs, AI, 5G communication enabled on-site rapid detection of plant pathogens

• Internet-on-nano-things inspired plant diagnostic biosensors are future of food production and security to meet SDGs

Diabetes leads to chronic microvascular complications for the heart, kidney, and eyes due to uncontrolled glycemic fluctuations. Self-monitoring blood glucose meters can only provide a snapshot of glucose level and are incapable of capturing the granular glucose fluctuations over the 24 h in day. The clinical research has indicated that random blood glucose fluctuations can lead to organ damage. In pursuit of better glucose management, Continuous Glucose Monitoring (CGM) is emerging as a popular alternative owing to its ability to detect instantaneous changes in glucose levels and to alert the users of impending hypo- or hyper-glycemic events. In the last decade, several CGM devices have been launched in the market based on different glucose sensing chemistries and techniques. More research is still needed to come up with novel bio sensing concepts to make CGM low cost and highly accurate. Here, we elaborate the CGM techniques such as electrochemical, optical, reverse iontophoresis, microdialysis, and impedance spectroscopy. We emphasize on the widely used electrochemical CGMs with a focus on sensor design and bio-compatibility. We also provide an outlook for the future technologies, highlighting the need for innovative materials, possibility of integrating with the Internet of Things (IoT) for real-time e-health monitoring.

Interleukin-31 has been reported to be involved with chronic skin conditions like atopic dermatitis (AD). This work focuses on the development of a portable IL-31 detection system that works with passive sweat over the physiologically relevant range-150–620 pg ml⁻¹. Four simulated flaring profiles were used to benchmark the IL-31 rise and fall detection capabilities of the sensor. These temporal profiles were generated according to the SCORAD range for severity of AD and were spanned across different dosing regimens. The sensing platform displays good sensitivity with a limit of detection of 50 pg ml⁻¹ and dynamic range of 50–750 pg ml⁻¹ for the flaring profiles in synthetic and human sweat, and with coupled portable electronics. Furthermore, in order to create a robust and predictive system, a machine learning algorithm was incorporated to create a flare prediction system. This algorithm shows high accuracy for the test data sets and provides the proof-of-concept for the use of ml coupled electrochemical systems for chronic diseases like AD.

In this study, a PoL/RGO material was successfully synthesized and employed to modify the working electrode for determining MPB in medication products through voltammetric techniques. The structure of the nanocomposite was characterized by UV–vis and FT-IR spectrum and its application to the MPB electrochemical detection was tested by the CV and DPV techniques. In the result, the modified PoL-RGO/GCE electrode exhibited a superior response toward MPB by applying the DPV method, compares to using the bare GCE, with a limit of detection (LOD), a limit of quantification (LOQ) is 0.20 μM and 0.70 μM, respectively and the concentration ranging from 1 to 200 μM. In addition, the repeatability (RSD of 2.2, 1.6, 1.4 for 5, 50 and 100 μM MPB, respectively), and the reproducibility (RSD of 4.7%) of the technique were examined as well. This illustrates the performance of the electrochemical sensor was statistically investigated by the CV and DPV methods demonstrating accuracy comparable to other analytical methods as well as indicating that MPB can be determined in cosmetics with high recovery ranging from 97% to 104.3%.

Over the past few decades, electrochemiluminescence (ECL) has been used as a powerful analytical tool for in vitro diagnosis due to its promising potential in light-emitting and, which has greatly promoted recent for biosensor studies. Plenty of research articles on the ECL technique have been published by various researchers around the globe. On the other hand, studies on the coupling of ECL sensing strategies with other techniques are recently getting widespread attention. ECL strategies have been effectively coupled with scanning electrochemical microscope (SECM), flow injection analysis (FIA), and capillary electrophoresis. These coupled techniques have been effectively employed for various health care applications. Among these techniques, FIA coupled ECL sensing strategies have been designated as the most emerging technique, especially sensing of clinical samples. This critical review discusses the vibrant developments in FIA-ECL, the mechanism of ECL, the design of FIA-ECL, and highlights the application of FIA-ECL for the detection of immunoassays, catecholamines, antioxidant compounds, choline, tetracyclines, and pharmaceutical drugs. The current review will pave the way for the design and development of FIA-ECL for efficient point-of-care applications.

Biosensors based on Electrochemical Impedance Spectroscopy (EIS) detect the binding of an analyte to a receptor functionalized electrode by measuring the subsequent change in the extracted charge-transfer resistance (R_CT). In this work, the stability of a long chain alkanethiol, 16-mercaptohexadecanoic acid was compared to that of a polymer-based surface linker, ortho-aminobenzoic acid (o-ABA). These two classes of surface linkers were selected due to the marked differences in their structural properties. The drift in R_CT observed for the native SAM functionalized gold electrodes was observed to correlate to the drift in the subsequent receptor functionalized SAM. This indicates the importance of the gold-molecule interface for reliable biosensing. Additionally, the magnitude of the baseline drift correlated to the percentage of thiol molecules improperly bound to the gold electrode as evaluated using X-ray Photoelectron Spectroscopy (XPS). Alternatively, the o-ABA functionalized gold electrodes demonstrated negligible drift in the R_CT. Furthermore, these polymer functionalized gold electrodes do not require a stabilization period in the buffer solution prior to receptor functionalization. This work emphasizes the importance of understanding and leveraging the structural properties of various classes of surface linkers to ensure the stability of impedimetric measurements.

Two stochastic sensors based on modification of nitrogen and boron dopped exfoliated graphene with a complex of protoporphyrin and cobalt, were used for molecular recognition and quantification of MLH1, MSH2, MSH6, PMS2 and KRAS biomarkers in biological samples (whole blood, urine, saliva, tumoral tissue). Limits of determination of fg ml⁻¹ magnitude order and broad linear concentration ranges favorized their determination from very low to higher concentrations in biological samples. The student t-test showed that there is no significant difference between the results obtained by utilizing the two microsensors for screening tests, at 99% confidence level, the results obtained being lowr than the tabulated value.

A simple and selective enzyme-free electrochemical sensor for H₂O₂ has been designed and fabricated using ionic liquid (IL) tagged anthraquinone (AQ) modified electrode (AQ-PF₆-IL). This newly synthesized AQ-PF₆-IL has been systematically characterized, after which it has been immobilized over a screen-printed electrode to produce AQ-PF₆-IL/SPE. The electrochemical investigation of AQ-PF₆-IL/SPE displayed a set of distinct redox peaks attributable to the anthraquinone/anthrahydroquinone redox pair. Interestingly, AQ-PF₆-IL/SPE has shown enhanced peak current at reduced formal potential for AQ, when compared to AQ/SPE. Further, the electrocatalytic activity of AQ-PF₆-IL/SPE towards the reduction of H₂O₂ was investigated with the sequential addition of H₂O₂. A rapid and appreciable enhancement in cathodic peak currents was observed and thus demonstrating the excellent electrochemical reduction of H₂O₂ at the newly developed sensor. Besides, AQ-PF₆-IL/SPE established a good linear behaviour over a concentration range of 10–1228 μM with a high sensitivity of 0.281 μA μM⁻¹ cm⁻² and low detection limit of 2.87 μM. The fabricated sensor displayed excellent stability, good anti-interference ability, along with acceptable reproducibility. The superior properties of the developed sensor could be attributed to the newly designed AQ-PF₆-IL, wherein the redox characteristics of AQ mediator are integrated with the high stability and conductivity of IL.

Hydrogen peroxide (H₂O₂) is extensively used for sterilization purposes in the food industries and pharmaceuticals as an antimicrobial agent. According to the Food and Agriculture Organization (FAO), the permissible level of H₂O₂ in milk is in the range of 0.04 to 0.05% w/v, so it has been prohibited to use as a preservative agent. Herein, we reported the electrochemical sensing of H₂O₂ in milk samples using an activated glassy carbon electrode (AGCE). For this purpose, activation of GCE was carried out in 0.1 M H₂SO₄ by continuous potential sweeping between −0.7 to 1.8 V for 25 cycles. The AGCE showed a redox peak at -0.18 V in the neutral medium corresponding to the quinone functional groups present on the electrode surface. AGCE was studied in (pH 7.4) 0.1 M PBS for the electro-catalysis of H₂O₂. The surface of the activated electrode was analysed by Raman spectroscopy and contact angle measurements. In addition, for the activated surface, the contact angle was found to be 85° which indicated the hydrophilic nature of the surface. The different optimization parameters such as (1) effect of electrolyte ions, (2) electrooxidation cycles, and (3) oxidation potential windows were studied to improve the activation process. Finally, AGCE was used to detect H₂O₂ from 0.1 to 10 mM and the limit of detection (LOD) was found to be 0.053 mM with a linear correlation coefficient (R²) of 0.9633. The selectivity of the sensor towards H₂O₂ was carried out in the presence of other interferents. The sensitivity of the AGCE sensor was calculated as 17.16 μA mol cm⁻². Finally, the commercial application of the sensor was verified by testing it in milk samples with H₂O₂ in the recovery range of 95%–98%.

To the best of our knowledge, very few works have been done for the continuous real-time monitoring of Proton Exchange Membrane Fuel Cells (PEMFCs) membrane degradation based on fluoride-specific electrochemical microsensors. PEMFCs are eco-smart energy sources for efficient transportation but experience variable degradation rates that wear the Membrane Electrode Assembly (MEA), a critical component of the fuel cell's functionality. Current market options lack specific diagnostics and a legitimate indication of when exactly the membrane needs to be replaced. As such, this work focused on manufacturing a sensor for measuring MEA degradation in real-time by selectively monitoring fluoride concentration in effluent water, a signature PEMFCs degradation status, through functionalized LaF₃:(Au nanoparticle) thin films (∼60 nm). The sensor's exceptional specificity/sensitivity has been achieved in real-time at a sub 10 ppb level, optimized through spin-coating deposition and post-annealing process. Its multimodal readout has been achieved and studied through the characterizations of open circuit potential, cyclic voltammetry, chronoamperometry, and differential pulse voltammetry revealing a consistent linear decrease of 15.7 mA cm⁻² at 0 ppb to 10.2 mA cm⁻², while also maintaining its low-cost, small size, and robustness.

In the present work, twelve inorganic thermoluminescence dosimeteric (TLD) materials doped with some rare earth elements (LiF:Sm, LiBaP₂O₇:Eu, CaCO₃:Eu, CaSO₄:Dy, SrSO₄:Sm, CdSO₄:Dy, BaSO₄:Eu, Li₂B₄O₇:Dy, MgB₄O₇:Gd, Al₂O₃:Gd, MgAl₂O₄:Ce and LiCaAlF₆:Eu) and three organic TLD materials (C₃H₇NO₂, C₇H₈O₂ and C₄H₆BaO₄) were selected for comparative analysis on the basis of different photon sensing parameters. About nine photon sensing parameters viz. mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), mean free path (mfp), half value layer (HVL), tenth value layer (TVL), effective atomic number (EAN), effective electron number (EEN), exposure buildup factor (EBF) and energy absorption buildup factor (EABF) were obtained for the selected fifteen TLDs. The simultaneous variation of these photon sensing parameters for the selected TLDs with photon energy and composition has been analyzed. The results of present comparative analysis help radiation physicists to easily select a particular dosimeter for their research laboratory from different existing compositions. All photon sensing parameters viz. MAC, LAC, mfp, HVL, TVL, EAN, EEN, EBF and EABF for selected TLDs strongly depend upon incident energy and chemical composition in lower and higher energy regions. Among the selected TLDs; BaSO₄: Eu³⁺ offers best results (maximum values for MAC, EAN, EEN; and minimum values for mfp, HVL, TVL, EBF, EABF); whereas MgB₄O₇:Gd³⁺ offers EAN value close to tissue and less variation in most of the sensing parameters with respect to photon energy.

Highlights

• Comparative analysis of fifteen TLDs with respect to different photon sensing parameters.

• Dopants plays a significant role in the sensing property.

• Selected TLDs are able to measure the doses from different nuclear radiations over wide ranges from ?Gy to KGy with few exceptions.

• BaSO₄:Eu³⁺ offers best results (maximum values for MAC, EAN, EEN; and minimum values for mfp, HVL, TVL, EBF, EABF);

• MgB₄O₇:Gd³⁺ offers EAN value close to tissue and less variation in most of the sensing parameters with respect to photon energy.