Microelectrode Gap Research Articles

Comparison between TiO2/rGO and TiO2 with Various Microelectrode Gaps for Biosensor Applications

Sensitive, selective, and stable materials are important to act as an electron transport layer to construct signals in biosensors. Graphene-based biosensors get attention in this industry due to their selective and sensitive properties. We fabricated TiO2/rGO and TiO2 using spin coating in this study. Thermal evaporation deposited the silver. The picoammeter examined the influence of microelectrode gap sizes (50, 100, and 250 μm) on electrical performance. It was revealed that a smaller gap generates better electrical performance. At the smallest gap, the 50μm TiO2 (8.04E-12 A) and TiO2/rGO (2.385E-8 A) at 0.04V. The morphological and chemical analysis supported the electrical behavior of TiO2/rGO and TiO2. These results show that the method used was able to form a TiO2/rGO film that is sensitive to the size of the gap between two microelectrodes.

Current–voltage characteristics and breakdown of different structural planar microelectrodes in atmospheric air

With the development of applications for microelectromechanical system (MEMS) components and micromachining technology, planar microelectrodes have attracted considerable interest. To study the discharge characteristics of these structures, planar microelectrodes with a variety of plate-shaped and needle-shaped microelectrode structures fabricated from indium tin oxide (ITO) and copper (Cu) with microelectrode gaps ranging from 5 to 35 µm were manufactured using MEMS technology in this study. Experiments carried out in atmospheric air show that the microelectrode configuration has a crucial impact on the discharge current, breakdown voltage, and current response to varying electrode gaps. The electrode surface area plays a significant role in the discharge characteristics of planar microelectrodes, which is a factor dominating the discharge current and breakdown voltage. The commonly used formulas in macroscale corona discharge cannot be directly applied to planar microelectrodes. Planar microelectrodes fabricated with Cu on Si substrates have larger discharge currents, higher breakdown voltages, and better resistance to breakdown strength than ITO ones on quartz substrates under nA-scale current, while ITO damaged microelectrodes because of breakdown can still discharge when accompanied by different discharge characteristics.

Nanoscale assembly of optoelectronic CdTe microwires using AC dielectrophoresis

This paper describes the effect of varying experimental parameters on the morphology and optoelectronic response of cadmium telluride quantum dot (CdTe QD) microwires formed using alternating current dielectrophoresis (AC-DEP). The thioglyocolic acid (TGA) capped CdTe QDs were assembled at room temperature across interdigitated electrodes (IDEs) under an applied electric field while simultaneously allowing solvent evaporation. The number of iterative rehydration steps required for bridging the microelectrode gaps of sizes 50–150 μm was found to depend on the electric field strength, particle concentration and electrode gap size. The frequency of the AC field applied, particle concentration and capping ligand were further optimized to regulate the fluorescence intensity, current density and chemical sensing behavior of the microassemblies. The overall process was found to be simple, rapid and scalable, and potentially holds promise for energy and sensing applications.

Time-resolved imaging of the electrical breakdown of planar microelectrode gap in atmospheric air

The aim of this study was to obtain time-resolved images of the electrical breakdown of a planar microelectrode gap along the surface of a glass substrate in atmospheric air. The obtained images revealed details of the events leading to the breakdown. First, a point light emission appeared at the cathode, indicating breakdown initiated by the field emission of electrons from the cathode under extremely high electric fields. Then, a flare-like broad light emission was generated at the anode. Finally, breakdown occurred over the entire gap by the expansion and merger of the two emissions.

Surfactant-Assisted Voltage-Driven Silver Nanoparticle Chain Formation across Microelectrode Gaps in Air.

Here we describe the electrodeposition of Ag in the presence of cetyltrimethylammonium bromide (CTAB) onto 5 μm gap Au interdigitated array (IDA) electrodes that are bare, thiol-functionalized, or thiol-functionalized and seeded with 4 nm diameter Au nanoparticles (NPs). After deposition, applying a voltage between 5 and 10 V in air for 0 to 1000 s resulted in one-dimensional (1D) Ag NP chains spanning across the IDA gap. The Ag NP chains form on IDAs functionalized with thiols and Au NP-seeded at about 5 V and at 10 V for the other nonseeded surfaces. Ag NP chains do not form at all up to 10 V when IDAs are treated with ozone or water soaking to remove possible CTA(+) ions from the surface, when Ag deposition takes place in the absence of CTAB, or when the voltage is applied under dry N2 (low humidity). Chain formation occurs by Ag moving from the positive to negative electrode. Coating the devices with a negatively charged surfactant, sodium dodecyl sulfate, also results in Ag NP chains by Ag moving from the positive to the negative electrodes, which confirms that the chains form by electrochemical oxidation at the positive electrode and deposition at the negative electrode. The surfactant ions and thin layer of water present in the humid environment facilitate this electrochemical process.

Graphite oxide multilayers for device fabrication: Enzyme‐based electrical sensing of glucose

In this paper, the use of graphite oxide multilayers as a transducer material for the fabrication of electronic devices is outlined. Graphite oxide flakes were produced in a solution‐based exfoliation method optimized for large area thin layers with narrow size distribution. A dielectrophoretic technique was used for scalable trapping of the graphite oxide onto the microelectrode pairs patterned over glass chips. The graphite oxide trapped in between microelectrode gaps was subjected to a very rapid thermal annealing step in ambient in order to make good electrical contacts with source and drain electrodes. After this, the graphite oxide devices were characterized for their electrical transport using impedance spectroscopy and field‐effect measurements in an electrochemical gate configuration. The conductivities of the graphite oxide devices were tested against the thermal treatment in air in order to determine a nominal burn‐out as well as the optimal parameters for device characteristics. The devices were surface modified with glucose oxidase and deployed for sensor operation. This work suggests for the use of graphite oxide thin‐layers as an easy and suitable alternative for the fabrication of electronic sensor platforms circumventing the dependence over tedious chemical and physical graphene oxide reduction methods.Schematic illustration of the graphite oxide (GrO) multilayer‐based electronic chips fabricated over glass substrates. The chips were deployed as sensors for the electronic detection of glucose. Schematics not fit to scale.

Assembly and Fabrication of Single-Wall Carbon Nanotube Field Effect Transistor Using Dielectrophoresis Method

On account of their sizes and unique properties, single-wall carbon nanotubes are candidates for a number of building blocks in nanoscale electronics. With respect to the assembly of carbon nanotube field effect transistor, the dielectrophoresis technology is adopted, which assembles SWCNTs between the microelectrodes, SWCNTs are affected by the electrophoretic force which is carried out by the related theoretical analysis in a nonuniform electric field. The driving electric field of dielectrophoresis is simulated by the comsol software. According to the simulation results, a number of the experiments are done. The applied alternating current voltage has a frequency of 2 MHz and an amplitude of 10 V. It turns out that the required experimental parameters of the efficient assembly of SWCNT are obtained. AFM scanning and electrical properties of SWCNTs show that the method can achieve the effective assembly of carbon nanotube field effect transistor. SWCNTs are driven in the microelectrode gap, having a good arrangement of uniform orientation and assembly results, and proportional to the arrangement density along the electrode width direction and the duration of DEP. As a result, it also provides an effective method of assembly and fabrication for other one-dimensional nanomaterials assembly of nanoelectronic devices.

A Method Study on Assembly of Single-Wall Carbon Nanotube Field Effect Transistor Using Dielectrophoresis

Single-wall carbon nanotubes are candidates for a number of building blocks in nanoscale electronics. With respect to the assembly of carbon nanotube field effect transistor, the dielectrophoresis technology is adopted, which assembles SWCNTs between the micro-electrodes, SWCNTs are affected by the electrophoretic force which is carried out by the related theoretical analysis in a nonuniform electric field. The driving electric field of dielectrophoresis is simulated by the comsol software. According to the simulation results, a number of the experiments are done. It turns out that the required experimental parameters of the efficient assembly of SWCNT were obtained. AFM scanning and electrical properties of SWCNTs show that the method can achieve the effective assembly of carbon nanotube field effect transistor. SWCNTs are driven in the microelectrode gap, having a good arrangement of uniform orientation and assembly results, and proportional to the arrangement density along the electrode width direction and the duration of DEP. Meanwhile, it also provides an effective method of assembly and manufacture for other one-dimensional nanomaterials assembly of nanoelectronic devices.

Chemical-Modification-Enhanced Dielectrophoretic Assembly of Controllable and Reversible Silica Submicrowires from Nanoparticles

In this article, the dielectrophoretic (DEP) assembly of chemically-modified silica nanoparticles (SiNPs) was introduced. Five types of surface-modified SiNPs, including OH-SiNPs, COOH-SiNPs, CH(3)HPO(2)-SiNPs, PEG-SiNPs, and NH(2)-SiNPs, have been investigated. After applying an ac field with relatively high intensity and frequency, it was shown that only COOH-SiNPs and CH(3)HPO(2)-SiNPs could be self-assembled on the microelectrodes by the DEP forces. The results indicated that the anionic group modification could obviously enhance the DEP self-assembly of SiNPs on the microelectrodes. Then the DEP assembly of CH(3)HPO(2)-SiNPs was selected as a representative to be investigated further. By using Rubpy dye doped in the core of the CH(3)HPO(2)-SiNPs, the assembly process was visualized in real time by inverse fluorescence microscopy. Precise control over the frequency of the applied ac field showed that the DEP forces can assemble CH(3)HPO(2)-SiNPs from aqueous suspensions into submicrowires, and it was found that the number of assembled submicrowires between the microelectrode gaps could be well controlled with reversibility. Furthermore, the DEP assembly process of CH(3)HPO(2)-SiNPs was sensitive to the pH of the dispersed medium. These findings would provide a way to circumvent the difficulty in controlling the dielectrophoretic assembly process of nanoparticles and offer application opportunities for the DEP assembly of chemically modified SiNPs.

Fabrication of Mesostructured Cobalt Oxide Sensor and Its Application for CO Detector

The paper presents a method for mesostructured cobalt oxide sensor fabrication by the template replication method and immobilization using dielectrophoresis process. The method consists of enriching the mesostructured cobalt oxide particles in a microelectrode gap that drove mesostructured cobalt oxide particles to a high electric field region and then exposed to CO gas. The cobalt oxide sensor has improved sensing performance in carbon monoxide (CO) detection at concentration as low as 10 ppm and a very short recovering time, due to the higher surface area.

Effect of a square wave on an assembly of multi-walled carbon nanotubes using AC dielectrophoresis

Here, we report an alignment and attachment of multi-walled carbon nanotubes (MWNTs) between microelectrodes using alternating current (AC) dielectrophoresis, where the AC dielectrophoresis is induced by a square wave rather than the conventional sinusoidal wave. A parametric study showed that square-wave-based AC dielectrophoresis is useful in alignment and attachment of MWNTs on a microelectrode gap, and that the square wave is effective in aligning the MWNTs in a low-frequency range (∼10 kHz) without addition of a direct current (DC) signal. Moreover, we could attach the MWNTs between microelectrodes with minimal amounts of impurities by adjusting the square-wave duty cycle.

Screen printing as cost-efficient fabrication method for DNA-chips with electrical readout for detection of viral DNA

The fast development in the field of DNA analytics is driven by the need for cost-effective and high-throughput methods for the detection of biomolecules. The detection of DNA using metal nanoparticles as labels is an interesting alternative to the standard fluorescence technique. Fluorescence is highly sensitive and broadly established, but shows limitations, for example instability of the signal and the requirement for sophisticated and high-cost equipment. A recently developed approach realizes a method for the electrical detection of DNA, based on the induction of silver nanoparticles growth in microelectrode gaps on the surface of a DNA-chip. This breakthrough towards robust and cost-effective detection was still hampered by the need for microstructured (and therefore expensive) substrates. We demonstrate that it is possible to utilize screen printed electrode structures for a chip-based electrical DNA detection. The electrode structures were produced on a glass substrate which made an additional optical readout possible. The screen printed structures show the required precision and are compatible with the applied biochemical protocols. A comparison with chip substrates produced by standard photolithography showed the same sensitivity and specificity for the screen printed chips. Screen printing of electrode structures for DNA-chip with electrical detection offers an interesting and cost-efficient possibility to produce DNA-chips with microstructured electrodes.

Fabrication of bio/nano interfaces between biological cells and carbon nanotubes using dielectrophoresis

The authors have previously demonstrated the manipulation of bacteria and carbon nanotubes (CNTs) using dielectrophoresis (DEP) and its application for various types of biological and chemical sensors. This paper demonstrates simultaneous DEP handling of bacteria and CNTs, which are mixed and suspended in water. The CNTs were solubilized in water using microplasma-based treatment. When a microelectrode was energized with an ac voltage in the suspension of Escherichia coli (E. coli) cells and multi-walled CNTs (MWCNTs), both of them were simultaneously trapped in the microelectrode gap. Scanning electron microscopy (SEM) images revealed that E. coli cells were trapped on the surface or the tip of MWCNTs, where the electric field strength was intensified due to high aspect ratio of MWCNTs. As a result, bio/nano interfaces between bacteria and MWCNTs were automatically formed in a self-assembly manner. A potential application of the DEP-fabricated bio/nano interfaces is a drug delivery system (DDS), which is realized by transporting drug molecules from CNTs to cells across the cell membrane, which can be electroporated by the local high electric field formed on the CNT surface.

Characterization and DNA Sensing Properties of Nanogapped Array Electrodes

We report here on the fabrication and characterization of nanogapped electrodes for DNA sensing. The gap created with 1,10-decanedithiol is estimated to be ca. 1.3 nm when dithiol-linked nanoparticles were deposited over the gap of the microelectrode as a film. Taking this approach, we can fabricate a molecular electronic device with an electrode spacing accuracy of a few nanometers. Use of the nanogapped electrode has led us to detect very small electrical signals, and therefore it was attempted for DNA sensor applications. The sensing property was intimately involved in measuring the amount of nanoparticle building blocks of the nanogapped array on the microelectrode gap. From the viewpoint of sensitivity, we have conducted a study on the most relevant conditions of film preparation.

Dielectrophoretic manipulation of DNA in microelectrode gaps for single-molecule constructs

The construction with biomolecules and their manipulation represent a key step for developing new miniaturized structures. Such micro or nanometer systems promise a variety of novel features. Dielectrophoresis (DEP) is a powerful tool for trapping and orienting individual molecules in microelectrode arrangements, and was demonstrated to be applicable to DNA. This relatively rigid biomolecule could (after defined immobilization) act as template for further modifications and functionalizations, e.g. metallization. Parameters of the DEP process were adapted to the given electrode layout and for trapping a few or even a single DNA strand. Characterization with atomic force microscopy (AFM) extends the standard method of fluorescence imaging by resolving the resulting structures with single molecule resolution.

Dielectrophoretic Manipulation and Real‐Time Electrical Detection of Single‐Nanowire Bridges in Aqueous Saline Solutions

Dielectrophoretic manipulation of nanoscale materials is typically performed in nonionic, highly insulating solvents. However, biomolecular recognition processes, such as DNA hybridization and protein binding, typically operate in highly conducting, aqueous saline solutions. Here, we report investigations of the manipulation and real-time detection of individual nanowires bridging microelectrode gaps in saline solutions. Measurements of the electrode impedance versus frequency show a crossover in behavior at a critical frequency that is dependent on the ionic strength. We demonstrate that by operating above this critical frequency, it is possible to use dielectrophoresis to manipulate nanowires across electrode gaps in saline solutions. By using electrical ground planes and nulling schemes to reduce the background currents, we further demonstrate the ability to electrically detect bridging and unbridging events of individual nanowires in saline solutions. The ability to both manipulate and detect bridging events with electrical signals provides a pathway toward automated assembly of nanoscale devices that incorporate biomolecular recognition elements.

Application of dielectrophoresis to fabrication of carbon nanohorn gas sensor

This paper describes an electrokinetic fabrication method for a gas sensor composed of single-wall carbon nanohorns (SWCNHs) using dielectrophoresis (DEP). The authors have previously demonstrated that DEP manipulation of carbon nanotubes (CNTs) can be applied to the fabrication of a CNT gas sensor. In the present study, we further explored the possibility of electrokinetic manipulation of SWCNHs. The latter have different structures and properties compared to CNTs. The SWCNHs were synthesized using the ‘arc in water with gas injection’ method. The SWCNH aggregates were dispersed in ethanol and trapped in an interdigitated microelectrode gap under the action of positive DEP. After the DEP process, the ethanol was evaporated and the microelectrode retaining the SWCNHs was exposed to nitrogen dioxide (NO 2) or ammonia (NH 3) gas while the electrode impedance was monitored. It was found that conductance of the DEP-fabricated SWCNH sensor increased or decreased upon exposure to ppm-levels of NO 2 or NH 3, respectively. These results were similar to those previously obtained for CNT gas sensors and suggest that the SWCNH aggregate behaves as a p-type semiconductor. The comparison reveals that intrinsic NO 2 sensitivity of the SWCNHs is lower than that of single-wall CNTs (SWCNTs) but comparable with the intrinsic sensitivity of multiple-wall CNTs (MWCNTs).

Parallel Fabrication of DNA‐Aligned Metal Nanostructures in Microelectrode Gaps by a Self‐Organization Process

Individual DNA structures were positioned in microelectrode arrays and utilized as templates for nanoparticle binding in order to realize nanowire arrangements (see image). An electrical characterization demonstrated the successful integration of these metal nanostructures into the microelectrode setup.

Pearl Chain Formation of Nanoparticles in Microelectrode Gaps by Dielectrophoresis

The integration of molecular structures into microscopic electrode arrays is achieved by dielectrophoresis of gold nanoparticles in electrode gaps. Using microelectrodes realized by photolithography, we demonstrate here the generation of pearl chain arrangements of nanoparticles in structures accessible for standard technologies. To preserve the individual particle structures in the final nanowire arrangement, various strategies were employed. An electrical characterization of the pearl chains yielded an Ohmic behavior. The effect of increased current on these structures is studied at the ultramicroscopic level.

A paralleled readout system for an electrical DNA-hybridization assay based on a microstructured electrode array

DNA analytics is a growing field based on the increasing knowledge about the genome with special implications for the understanding of molecular bases for diseases. Driven by the need for cost-effective and high-throughput methods for molecular detection, DNA chips are an interesting alternative to more traditional analytical methods in this field. The standard readout principle for DNA chips is fluorescence based. Fluorescence is highly sensitive and broadly established, but shows limitations regarding quantification (due to signal and/or dye instability) and the need for sophisticated (and therefore high-cost) equipment. This article introduces a readout system for an alternative detection scheme based on electrical detection of nanoparticle-labeled DNA. If labeled DNA is present in the analyte solution, it will bind on complementary capture DNA immobilized in a microelectrode gap. A subsequent metal enhancement step leads to a deposition of conductive material on the nanoparticles, and finally an electrical contact between the electrodes. This detection scheme offers the potential for a simple (low-cost as well as robust) and highly miniaturizable method, which could be well-suited for point-of-care applications in the context of lab-on-a-chip technologies. The demonstrated apparatus allows a parallel readout of an entire array of microstructured measurement sites. The readout is combined with data-processing by an embedded personal computer, resulting in an autonomous instrument that measures and presents the results. The design and realization of such a system is described, and first measurements are presented.