Table of contents

Mismatched base pairs, such as different conformations of the G·A mispair, cause only minor structural changes in the host DNA molecule, thereby making mispair recognition an arduous task. Electron transport in DNA that depends strongly on the hopping transfer integrals between the nearest base pairs, which in turn are affected by the presence of a mispair, might be an attractive approach in this regard. We report here on our investigations, via the I–V characteristics, of the effect of a mispair on the electrical properties of homogeneous and generic DNA molecules. The I–V characteristics of DNA were studied numerically within the double-stranded tight-binding model. The parameters of the tight-binding model, such as the transfer integrals and on-site energies, are determined from first-principles calculations. The changes in electrical current through the DNA chain due to the presence of a mispair depend on the conformation of the G·A mispair and are appreciable for DNA consisting of up to 90 base pairs. For homogeneous DNA sequences the current through DNA is suppressed and the strongest suppression is realized for the G(anti)·A(syn) conformation of the G·A mispair. For inhomogeneous (generic) DNA molecules, the mispair result can be either a suppression or an enhancement of the current, depending on the type of mispairs and actual DNA sequence.

A modified optical tweezers set-up has been used to generate microbubbles in flowing, biologically relevant fluids and human whole blood that contains carbon nanotubes (CNTs) using low power (≤5 mW), infrared (1064 nm wavelength), continuous wave laser light. Temperature driven effects at the tweezers' focal point help to optically trap these microbubbles. It is observed that proximate CNTs are driven towards the focal spot where, on encountering the microbubble, they adhere to it. Such CNT-loaded microbubbles can be transported both along and against the flow of surrounding fluid, and can also be exploded to cause fragmentation of the bundles. Thus, microbubbles may be used for scavenging, transporting and dispersal of potentially toxic CNTs in biologically relevant environments.

Metallic and superparamagnetic DNA-templated nanoparticle (NP) chains are examined as potential imaging agents. Proton relaxation times (T₁ and T₂) are measured for DNA nanostructures using nuclear magnetic resonance (NMR) spectroscopy. The layer-by-layer (LBL) method was used to encapsulate the DNA-templated NP chains and demonstrated a change in proton relaxation times. Results from this study suggest that LBL-coated, DNA-templated nanostructures can serve as effective imaging agents for magnetic resonance imaging (MRI) applications.

Gold nanoparticles (Au NPs) are a potential x-ray computed tomography (CT) contrast agent. A biocompatible and bioinactive surface is necessary for application of gold nanoparticle to CT imaging. Polyethylene glycol (PEG)-attached dendrimers have been used as a drug carrier with long blood circulation. In this study, the Au NPs were grown in the PEGylated dendrimer to produce a CT contrast agent. The Au NPs were grown by adding gold ions and ascorbic acid at various equivalents to the Au NP-encapsulated dendrimer solution. Both size and surface plasmon absorption of the grown Au NPs increased with adding a large number of gold ions. The x-ray attenuation of the Au NPs also increased after the seeded growth. The Au NPs grown in the PEG-attached dendrimer at the maximum under our conditions exhibited a similar CT value to a commercial iodine agent, iopamidol, in vitro. The Au NP-loaded PEGylated dendrimer and iopamidol were injected into mice and CT images were obtained at different times. The Au NP-loaded PEGylated dendrimer achieved a blood pool imaging, which was greater than a commercial iodine agent. Even though iopamidol was excreted rapidly, the PEGylated dendrimer loading the grown Au NP was accumulated in the liver.

Silicon nanowire (Si NW)-based field effect transistors (FETs) have shown great potential as biosensors (bioFETs) for ultra-sensitive and label-free detection of biomolecular interactions. Their sensitivity depends not only on the device properties, but also on the function of the biological recognition motif attached to the Si NWs. In this study, we show that SiNWs can be chemically functionalized with Ni:NTA motifs, suitable for the specific immobilization of proteins via a short polyhistidine tag (His-tag) at close proximity to the SiNW surface. We demonstrate that the proteins preserve their function upon immobilization onto SiNWs. Importantly, the protein immobilization on the Si NWs is shown to be reversible after addition of EDTA or imidazole, thus allowing the regeneration of the bioFET when needed, such as in the case of proteins having a limited lifetime. We anticipate that our methodology may find a generic use for the development of bioFETs exploiting functional protein assays because of its high compatibility to various types of NWs and proteins.

Titanium–tungsten nanocrystals (NCs) were fabricated by a self-assembly rapid thermal annealing (RTA) process. Well isolated Ti_0.46W_0.54 NCs were embedded in the gate dielectric stack of SiO₂/Al₂O₃. A metal–oxide–semiconductor (MOS) capacitor was fabricated to investigate its application in a non-volatile memory (NVM) device. It demonstrated a large memory window of 6.2 V in terms of flat-band voltage (V_FB) shift under a dual-directional sweeping gate voltage of − 10 to 10 V. A 1.1 V V_FB shift under a low dual-directional sweeping gate voltage of − 4 to 4 V was also observed. The retention characteristic of this MOS capacitor was demonstrated by a 0.5 V memory window after 10⁴ s of elapsed time at room temperature. The endurance characteristic was demonstrated by a program/erase cycling test.

We report a top-down process for the fabrication of single-crystalline silicon nanowire circuits and devices. Local oxidation nanolithography is applied to define very narrow oxide masks on top of a silicon-on-insulator substrate. In a plasma etching, the nano-oxide mask generates a nanowire with a rectangular section. The nanowire width coincides with the lateral size of the mask. In this way, uniform and well-defined transistors with channel widths in the 10–20 nm range have been fabricated. The nanowires can be positioned with sub-100 nm lateral accuracy. The transistors exhibit an on/off current ratio of 10⁵. The atomic force microscope nanolithography offers full control of the nanowire's shape from straight to circular or a combination of them. It also enables the integration of several nanowires within the same circuit. The nanowire transistors have been applied to detect immunological processes.

Room-temperature (RT) coalescence of double-walled carbon nanotubes has been observed for the first time. A combined pre-treatment of localized electron irradiation, Joule heating, and electromigration leads to the formation of large vacancy clusters, which can survive for tens of seconds during surface reconstruction. The dangling bonds of the edge atoms are highly reactive and thus promote the coalescence even at RT.

By using a dry etch chemistry which relies on the highly preferential etching of silicon, over that of gallium (Ga), we show resist-free fabrication of precision, high aspect ratio nanostructures and microstructures in silicon using a focused ion beam (FIB) and an inductively coupled plasma reactive ion etcher (ICP-RIE). Silicon etch masks are patterned via Ga ⁺ ion implantation in a FIB and then anisotropically etched in an ICP-RIE using fluorinated etch chemistries. We determine the critical areal density of the implanted Ga layer in silicon required to achieve a desired etch depth for both a Pseudo Bosch (SF₆/C₄F₈) and cryogenic fluorine (SF₆/O₂) silicon etching. High fidelity nanoscale structures down to 30 nm and high aspect ratio structures of 17:1 are demonstrated. Since etch masks may be patterned on uneven surfaces, we utilize this lithography to create multilayer structures in silicon. The linear selectivity versus implanted Ga density enables grayscale lithography. Limits on the ultimate resolution and selectivity of Ga lithography are also discussed.

We demonstrate the fabrication of highly ordered silicon oxide dotted arrays prepared from polydimethylsiloxane (PDMS) filled nanoporous block copolymer (BCP) films and the preparation of nanoporous, flexible Teflon or polyimide films. Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) films were annealed in toluene vapor to enhance the lateral order of micellar arrays and were subsequently immersed in alcohol to produce nano-sized pores, which can be used as templates for filling a thin layer of PDMS. When a thin layer of PDMS was spin-coated onto nanoporous BCP films and thermally annealed at a certain temperature, the PDMS was drawn into the pores by capillary action. PDMS filled BCP templates were exposed to oxygen plasma environments in order to fabricate silicon oxide dotted arrays. By addition of PS homopolymer to PS-b-P2VP copolymer, the separation distances of micellar arrays were tuned. As-prepared silicon oxide dotted arrays were used as a hard master for fabricating nanoporous Teflon or polyimide films by spin-coating polymer precursor solutions onto silicon patterns and peeling off. This simple process enables us to fabricate highly ordered nanoporous BCP templates, silicon oxide dots, and flexible nanoporous polymer patterns with feature size of sub-20 nm over 5 cm × 5 cm.

Herein we describe the realization of nanowalled polymeric microtubes through a novel and versatile approach combining the layer-by-layer (LbL) deposition technique, the self-rolling of hybrid polymer/semiconductor microtubes and the subsequent removal of the semiconductor template. The realized channels were characterized in detail using scanning electron and atomic force microscopes. Additionally, we report on the incorporation of a dye molecule within the nanowalls of such microtubes, demonstrating a distribution of the fluorescence signal throughout the whole channel volume. This approach offers the possibility to tailor the properties of micro/nanotubes in terms of size, wall thickness and composition, thus enabling their employment for several applications.

In this paper we report on the 'direct-write' fabrication and electrical characteristics of a nanoscale logic inverter, integrating enhancement-mode (E-mode) and depletion-mode (D-mode) field-effect transistors (FETs) on a single zinc oxide (ZnO) nanowire. 'Direct-writing' of platinum metal electrodes and a dielectric layer is executed on individual single-crystalline ZnO nanowires using either a focused electron beam (FEB) or a focused ion beam (FIB). We fabricate a top-gate FET structure, in which the gate electrode wraps around the ZnO nanowire, resulting in a more efficient gate response than the conventional back-gate nanowire transistors. For E-mode device operation, the gate electrode (platinum) is deposited directly onto the ZnO nanowire by a FEB, which creates a Schottky barrier and in turn a fully depleted channel. Conversely, sandwiching an insulating layer between the FIB-deposited gate electrode and the nanowire channel makes D-mode operation possible. Integrated E- and D-mode FETs on a single nanowire exhibit the characteristics of a direct-coupled FET logic (DCFL) inverter with a high gain and noise margin.

Soft nanoimprint lithography (soft NIL) relies on a mechanical deformation of a resist by a patterned polymer used as a mold. Here, we report on the investigation of the nanopattern fidelity of the high pressure imprint process based on a perfluorinated polyether (PFPE) soft mold material. The perfluorinated polyether material was found to be well suited to transfer the mold pattern into the resist by a direct imprinting process at low cost. Moderate deformations of the polymer mold structures occurring during the high pressure imprint are systematically studied. Features of decreased size are found to be more sensitive to pattern distortions. An optimized pattern design with increased structure density and constant pattern ratio is developed to minimize deformation effects. Imprints performed on the basis of these design rules result in reduced deformations and repeal their size dependence. The improved pattern transfer, especially for small structural elements, turns the direct and cost-effective soft UV-NIL into an interesting technique also for patterning tasks in the lower nanometer range.

Many amines are proven or suspected to be carcinogenic and have been implicated in inducing cancer of the bladder. Therefore, the monitoring of their levels in environmental samples is important for the protection of health and the environment. Herein, a novel method for effective immobilization of Ru(bpy)₃^{2 +} on the electrode surface of TiO₂ nanotube arrays (TNs) is developed for the first time. The method involves Ru(bpy)₃^{2 +} spontaneously adsorbed on the surface of negatively charged TiO₂ nanotubes due to electrostatic interaction to produce a Ru(bpy)₃^{2 +} /TNs/Ti (Ru–TNs–Ti) solid-state electrochemiluminescence (ECL) sensor. The prepared solid-state sensor was used to detect the changes of concentrations of pollutant tripropylamine (TPA) in water. The sensor exhibits excellent ECL behavior, very good stability and high sensitivity. This study may provide new insight into the design and preparation of an advanced solid-state ECL sensor for monitoring of amines in water.

A stable and sensitive biosensor for phenol detection based on a screen printed electrode modified with tyrosinase, multiwall carbon nanotubes and glutaraldehyde is designed and applied in a flow injection analytical system.

The proposed carbon nanotube matrix is easy to prepare and ensures a very good entrapment environment for the enzyme, being simpler and cheaper than other reported strategies. In addition, the proposed matrix allows for a very fast operation of the enzyme, that leads to a response time of 15 s.

Several parameters such as the working potential, pH of the measuring solution, biosensor response time, detection limit, linear range of response and sensitivity are studied. The obtained detection limit for phenol was 0.14 × 10 ^{− 6} M. The biosensor keeps its activity during continuous FIA measurements at room temperature, showing a stable response (RSD 5%) within a two week working period at room temperature.

The developed biosensor is being applied for phenol detection in seawater samples and seems to be a promising alternative for automatic control of seawater contamination. The developed detection system can be extended to other enzyme biosensors with interest for several other applications.

Hexagonal wurtzite InN nanowires are grown via a vapor–liquid–solid (VLS) mechanism with an Au catalyst. Microstructure characterizations of a large number of nanowires demonstrate that the growth direction of InN nanowires is governed by variable NH₃ flux. InN nanowires at a NH₃ flux of 10 standard cubic centimeters per minute (sccm) grow preferentially in a hexagonal close-packed (hcp) direction, while those at 100 sccm NH₃ flux favor the hcp ⟨0001⟩ direction. A free energy minimization model is proposed to interpret this phenomenon. The first-principles calculations reveal that the oriented nucleus has the lowest energy at the lower NH₃ flux. In contrast, when NH₃ flux is high, the ⟨0001⟩ oriented nucleus has the lowest energy.

Ag@SiO₂@Ag sandwich nanostructures were prepared by a facile one-pot synthesis method. The Ag core, SiO₂ shell and Ag nanoparticle shell were all synthesized with polyvinylpyrrolidone, catalysed by ammonia, in the one-pot reaction. The polyvinylpyrrolidone, acting as a smart reducing agent, reduced the Ag ⁺ to Ag cores and Ag shells separately. Furthermore, the polyvinylpyrrolidone served as a protective agent to prevent the silver cores from aggregating. The SiO₂ shell and outer layer Ag nanoparticles were obtained when tetraethyl orthosilicate and ammonia were added to the silver core solution. Ammonia, acting as the catalyst, accelerated the hydrolysis of the tetraethyl orthosilicate to SiO₂, which coated the silver cores. Furthermore, Ag(NH₃)₂ ⁺ ions were formed when aqueous ammonia was added to the solution, which increased the reduction capability. Then the polyvinylpyrrolidone reduced the Ag(NH₃)₂ ⁺ ions to small Ag nanoparticles on the surface of the Ag@SiO₂ and formed Ag@SiO₂@Ag sandwich structures with a standard deviation of less than 4%. This structure effectively prevented the Ag nanoparticles on the silica surface from aggregating. Furthermore, the Ag@SiO₂@Ag sandwich structures showed good catalysis properties due to the large surface area/volume value and activity of surface atoms of Ag particles.

Well-aligned coaxial nanocables, composed of a crystalline α-Si₃N₄ inner core and amorphous SiO₂ outer shell, were prepared on silicon substrates by pyrolysis of a preceramic polymer (perhydropolysilazane) with iron as catalyst. The nanocables have high density, and the longest nanocable can be up to millimeters. Photoluminescence measurement reveals a strong ultraviolet emission band centered at 360 nm and a weaker visible-light emission at 625 nm. The growth mechanism of the nanocables is discussed in detail.

A technique is proposed to grow horizontal carbon nanotubes (CNTs) bridging metal electrodes and to assess their electrical properties. A test structure was utilized that allows for selective electrochemical sidewall catalyst placement. The selectivity of the technique is based on the connection of the desired metal electrodes to the silicon substrate where the potential for electrochemical deposition was applied. Control over the Ni catalyst size (15–30 nm) and density (up to 3 × 10¹¹ particles cm ^{− 2}) is demonstrated. Horizontal CNTs with controlled diameter and density were obtained by CVD growth perpendicular to the sidewalls of patterned TiN electrode structures. Electrode gaps with spacings from 200 nm up to 5 µm could be bridged by both direct CNT–electrode contact and CNT–CNT entanglement. The TiN–CNT–TiN and TiN–CNT–CNT–TiN bridges were electrically characterized without any further post-growth contacting. Resistance values as low as 40 Ω were measured for the smallest gap spacing and depended mainly on the number and configuration of the CNT bridges. The proposed method could be implemented for CNT-based horizontal interconnections and be a route to make different nanoelectronic devices such as chemical and electromechanical sensors.

A novel method is developed to fabricate a SnO₂ nanotube network by utilizing electrospinning and atomic layer deposition (ALD), and the network sensor is proven to exhibit excellent sensitivity to ethanol owing to its hollow, nanostructured character. The electrospun polyacrylonitrile (PAN) nanofibers of 100–200 nm diameter are used as a template after stabilization at 250 °C. An uniform and conformal SnO₂ coating on the nanofiber template is achieved by ALD using dibutyltindiacetate (DBTDA) as the Sn source at 100 °C and the wall thickness is precisely controlled by adjusting the number of ALD cycles. The calcination at 700 °C transforms the amorphous nanofibers into SnO₂ nanotubes composed of several nanometer-sized crystallites. The SnO₂ nanotube network sensor responds to ethanol, H₂, CO, NH₃ and NO₂ gases, but it exhibited an extremely high gas response to ethanol with a short response time (<5 s). The results demonstrate that the combination of electrospinning and ALD is a very effective and promising technique to fabricate long and uniform metal oxide nanotubes with the precise control of wall thickness, which can be applied to various applications such as gas sensors and lithium ion batteries.

The thermal transport properties of hexagonal boron nitride nanoribbons (BNNRs) are investigated. By calculating the phonon spectrum and thermal conductance, it is found that the BNNRs possess excellent thermal transport properties. The thermal conductance of BNNRs can be comparable to that of graphene nanoribbons (GNRs) and even exceed the latter below room temperature. A fitting formula is obtained to describe the features of thermal conductance in BNNRs, which reveals a critical role of the T^1.5 dependence in determining the thermal transport. In addition, an obviously anisotropic thermal transport phenomenon is observed in the nanoribbons. The thermal conductivity of zigzag-edged BNNRs is shown to be about 20% larger than that of armchair-edged nanoribbons at room temperature. The findings indicate that the BNNRs can be applied as important components of excellent thermal devices.

Spherical shaped nanoparticles of series Y_{2 − x}Eu_xO₃ (x = 0.06, 0.10, 0.20, and 2) and Gd_{2 − x}Eu_xO₃ (x = 0.06, 0.10) were prepared by thermolysis of 2,4-pentanedione complexes of Y, Gd, and Eu. The bixbyite phase of Gd_{2 − x}Eu_xO₃ samples was formed at 500 °C, whereas the thermal decomposition of Y and Eu complexes' mixtures occurred at higher temperatures. Linearity in the concentration dependence on lattice parameter confirmed the formation of solid solutions. The distribution of Eu^{3 +} in Gd_{2 − x}Eu_xO₃ was changed with thermal annealing: in the as-prepared sample (x = 0.10) the distribution was preferential at C_3i sites while in the annealed samples, Eu^{3 +} were distributed at both C₂ and C_3i sites. Rietveld refinement of site occupancies as well as emission spectra showed a random distribution of cations in Y_{2 − x}Eu_xO₃. The photoluminescence (PL) measurements of the sample showed red emission with the main peak at 614 nm (⁵D₀–⁷F₂). The PL intensity increased with increasing concentration of Eu^{3 +} in both series. Infrared excitation was required to obtain good Raman spectra. The linear dependence of the main Raman peak wavenumber offers a non-destructive method for monitoring the substitution level and its homogeneity at the micron scale.

N-doped ZnO nanowires are synthesized at a relatively low growth temperature of 500 °C by directly heating zinc powder using NH₃ as the dopant. The incorporation of N into the ZnO nanowires is experimentally confirmed by x-ray photoelectron spectroscopy, Raman spectra and photoluminescence measurements. By combining post annealing experiments after growth with first-principles calculations, the detailed migration mechanism of N and compensation mechanism in N-doped ZnO nanowires are systematically studied. The larger aspect ratio of nanowires favors the formation of oxygen vacancy and out-diffusion of substitutional N (N_O), making N_O in ZnO nanowires always compensated by hydrogen interstitials (H_I). Our results can help to explain the challenge in getting p-type ZnO and shed new light on the possible realization of p-type doping of ZnO in the future.

We studied atomic contact potential variations of Si(111)-7 × 7 by Kelvin probe force microscopy with the amplitude modulation technique at the second resonance of a silicon cantilever. Enhanced sensitivity due to the high mechanical quality factor in ultra-high vacuum enabled local contact potential difference (LCPD) measurements of individual adatoms. The contrast of the measured LCPD map became stronger by reducing the tip–sample distance, and the averaged LCPD value shifted to more negative. The short-range interaction, arising from the covalent bonding interactions, strongly affects the LCPD measurement. Theoretical calculations indicate that the amplitude modulation method has a higher sensitivity than the frequency modulation method in practical cases. The tip–sample distance dependence of LCPD was investigated by numerical calculations.

Strain relaxation mechanisms occurring during self-induced growth of nitride nanowires are investigated by in situ reflection high-energy electron diffraction and ex situ high-resolution transmission electron microscopy. Epitaxial GaN nanowires nucleate on an AlN buffer layer under highly nitrogen-rich conditions via the initial formation of coherently strained three-dimensional islands according to the Volmer–Weber growth mechanism. The epitaxial strain relief in these islands occurs by two different processes. Initially, strain is elastically relieved via several shape transitions. Subsequently, plastic relaxation takes place through the formation of a misfit dislocation at the GaN/AlN interface. At the same time, a final shape transition to fully relaxed nanowires occurs.