Interdigitated Microarray Electrode Research Articles

Self-powered hydrogen peroxide sensor and its application as a biosensor

Simple and robust properties are essential aspects of biosensing chips. The combination of Prussian blue (PB)-modified Au and Pt electrodes produces an electric current with H2O2 in the solution. We fabricated a patterned substrate of interdigitated microarray electrodes with this combination (Au/PB–Pt interdigitated electrodes (IDEs)). The substrate shows linear current generation with the H2O2 concentration (0–0.2 mM). The H2O2 sensor performance has a very small detection limit of 0.02 μM. The device structure based on glucose oxidase (GOx)-immobilized Au/PB–Pt IDEs was also prepared and it acts as a glucose sensor (0–4 mM). Here, H2O2 produced by the GOx enzymatic reaction is detected by the IDEs. This phenomenon shows that the device structure based on the oxidative enzyme-immobilized Au/PB–Pt IDEs provides a simple amperometric biosensor without any external potential source.

Development of High-Sensitive Detection System for Redox Analytes Having a Standard Potential Higher Than O2 Evolution by Using Micropatterned Conductive Boron-Doped DLC Electrodes

1. Introduction Recently, cobalt, manganese and cerium are widely used in mass-produced products such as a lithium ion battery. It has been reported that the excessive consumption of these metal ions causes various diseases like neurotoxicity. In industrial wastewater discharge standards, Co2+, Mn2+ and Ce3+contents of wastewater has been regulated below several micro-molar. These redox species are generally analyzed using photochemical method. Some time, however, is required for analysis using the method and initial measures cannot be taken promptly when problems such as the content of metal ions exceeding the discharge standard occur. Therefore, electrochemical monitoring system which can shorten time of analysis should be developed. The standard potential of Co2+, Mn2+ and Ce3+ are higher than that of O2evolution potential. Redox reactions of these analytes cannot be observed at conventional metal electrodes. In this study, boron-doped diamond-like carbon (B-DLC) [1] with higher overpotential for O2evolution was selected as the electrode that redox reaction of the analytes can be observed. The detection limit of Ce3+ (model analyte) at a flat-disk electrode of B-DLC was 39 mM. Our research group tried to fabricate interdigitated microarray electrodes (IDA) because it shows one or two orders of magnitude higher sensitivity than that of the flat-disk electrode. IDA are composed of two sets of microband array neighbored (called generator and collector). The potential of one microband pairs (collector) is set at reduction potential of redox analyte, and that of the other is swept toward oxidation potential (dual mode). Redox cycling occurs between two sets of the microband pairs. The generator exhibits higher amplification of oxidation current by redox cycling compared to the current without applying the potential on the collector (single mode). We have reported that B-DLC-IDA with 2 mm/2 mm of bandwidth/gap exhibited ca.10 times amplification factor corresponding to the theoretical value [2]. The amplification factor of Ce3+, however, was half of the theoretical value. As a result, the detection limit was 8.8 mM. The reduction of Ce4+ is not promoted at the collector because the sample solution is a reductant. Moreover, Ce3+generated at the collector is hardly supplied to generator by diffusion, which causes inefficient redox cycling. When the collector is set at an oxidation potential, Ce3+ are constantly supplied to the collector by nonplanar diffusion. Ce4+generated at the collector is considered to be supplied to the generator at a higher diffusion rate. In this report, amplification factor of Ce3+was tried to be improved by changing the potential set at the collector. 2. Experimental B-DLC was synthesized on quartz substrates with RF plasma CVD method using a mixed solution of n-hexane and trimethyl borate as a source material. RF power was 175 W and the deposition time was 40 minutes. The alminium pattern of IDA was fabricated by the lift-off technique using photoresist and alminium deposition. Alminium on B-DLC-IDA was removed in a sodium hydroxide solution after O2plasma etching of B-DLC. The structure of B-DLC-IDA was designed to be 65 pairs of microbands with a length of 200 μm and bandwidth/gap of 2.0 mm. Single-dual mode measurements were carried out using the B-DLC-IDA in 1 mM Ce(NO3)3 + 0.1 M HNO3solution. 3. Results and discussion Figure1 shows the optical micrographs of the B-DLC-IDA. The bandwidths and gaps were observed to be 1.96 and 2.04 mm, respectively. The deviation between the actual gap and the designed value was less than 2%. Raman spectra of B-DLC were identical before and after the processing of IDA. It was confirmed that amorphous structure and composition ratio of sp2/sp2+sp3 (= 75%) in B-DLC did not change during IDA processing. The working potential range in 0.1 M sulfuric acid was constant after IDA processing. These results suggest that the redox reaction of Ce3+can be served at the B-DLC-IDA. In the dual mode of Ce3+, the potential of the collector was set at 1.37 V, and the potential of generator was swept from 0.8 to 1.7 V. Amplification factor closed to the theoretical value could be obtained. The detection limit of Ce3+was decreased from 8.8 to 4.4 mM by changing the applied potential of the collector from 1.25 to 1.37 V. 4. Summary Fabrication of the B-DLC-IDA and optimizing method of electrochemical measurement can establish highly sensitive electrochemical system that can analyze redox species with a standard potential higher than O2evolution. 5.

Development of High-Sensitive Detection System for Redox Analytes Having a Standard Potential Higher Than O2 Evolution by Using Micropatterned Conductive Boron-Doped DLC Electrodes

High sensitive electroanalytical system for redox analytes with standard potential higher than O2 evolution was developed by realizing interdigitated microarray electrodes based on boron-doped DLC (B-DLC-IDA). For Ce3+/4+ with the standard potential of 1.6 V, the amplification of response current derived from redox cycling was observed at B-DLC-IDA in the dual mode measurement. The amperometric current was amplified 180-fold by applying the potential of 1.7 V and 0.8 V to the collector and the generator electrodes in chronoamperometriy (CA) at the dual mode measurement. Theoretical detection limit (S/N = 3) toward Ce3+ was 0.13 μM. This detection limit was able to be improved to the value 2 orders of magnitude lower than that at B-DLC flat electrode by developing the electroanalytical system using B-DLC-IDA electrodes.

Sensitive and Spatially Multiplexed Detection System Based on Dielectrophoretic Manipulation of DNA-Encoded Particles Used as Immunoreactions Platform

In this work, we designed a new immunodevice that combines competitive immunoreactions on the microparticles, accumulation of these particles by negative dielectrophoresis (n-DEP), and their subsequent capture through hybridization among single-stranded DNAs (ssDNAs). Two widely used pesticides, atrazine and bromopropylate, were used as target molecules to test the resulting simultaneous detection system. For sensing, we prepared two different sets of microparticles: one modified with atrazine-conjugated bovine serum albumin (BSA-2d) and ssDNA-J1(up) and the other with bromopropylate-conjugated aminodextran (AD-155) and ssDNA-J2(up). The microparticles were incubated in a mixture of analyte-specific antibody and analyte at different concentrations to trap the unreacted antibodies prior to being labeled with antibodies conjugated with a fluorescence molecule. A suspension containing both types of microparticles was introduced into an n-DEP device consisting of an interdigitated microarray (IDA) electrode and channel modified with ssDNA-J1(down) and ssDNA-J2(down), which are complementary to ssDNA-J1(up) and ssDNA-J2(up), respectively. The n-DEP force generated by applying AC voltage to the IDA electrode displaced the microparticles toward the encoded areas, causing them to rapidly accumulate on the upper surfaces. Hybridization allowed us to distinguish the microparticles and sense multiple analytes by spatial recognition in the DNA-encoded areas. The fluorescence intensity of the captured particles, which depends on analyte concentrations, was measured selectively by focusing on specific areas. The strategy is advantageous for sensitivity due to the equivalent trapping efficiency by DNA hybridization and large surface area of the microparticle for immunoreactions. The rapidity and simplicity were still supported by particle manipulation. Using this concept, we detect atrazine and bromopropylate simultaneously with limits of detection (LODs) of 0.2 μg·L(-1), which covered the maximum residue level (MRL) in food samples established the European Union (EU) and Japan Ministry of Health, Labor and Welfare (MHLW).

Rapid and separation-free sandwich immunosensing based on accumulation of microbeads by negative-dielectrophoresis

We report here a rapid and separation-free immunoassay using a dielectrophoresis (DEP) device consisting of an interdigitated microarray (IDA) electrode and a polydimethylsiloxane (PDMS) substrate. On applying an AC voltage to the IDA in a negative-DEP (n-DEP) frequency region, goat anti-mouse immunoglobulin (anti-mouse IgG)-immobilized microbeads moved to the surface of the PDMS substrate placed above the IDA. The microbeads accumulated at designated areas of the PDMS surface that had been precoated with anti-mouse IgG. When the fluorescence microbeads bearing anti-mouse IgG were suspended in an analyte (mouse IgG) solution, the microbeads trapped the analyte to form immunocomplexes on microbeads. The microbeads reacted with mouse IgG accumulated and were captured at the designated areas of the PDMS surface via an antibody–antigen–antibody (sandwich) reaction. The captured microbeads were detected selectively by fluorescence measurements at the focused designated areas, regardless of the presence of uncaptured microbeads suspended in solution. Thus, the separation and washing-out steps usually required for conventional immunoassay are eliminated in the presented procedure. Since the formation of the sandwich structures was accelerated significantly by n-DEP, a period as short as 30 s was sufficient to detect the immunoreaction at the surface. The fluorescence intensity of the captured microbeads at the designated areas increased with analyte concentration in the range 0.01–10 ng/mL. The present procedure therefore yields a rapid, sensitive, and separation-free immunoassay in a simple device.

Micropattern of Colloidal Crystal by Using Electrophoretic Deposition Process with Three-Electrode System

A novel micropatterning process for a particle assembly has been performed by using an electrophoretic deposition (EPD) method with a local electric field in a colloidal suspension generated by a three-electrode system. Monodisperse silica colloidal spheres with a diameter of 300 nm were used to fabricate micropattern of colloidal crystal. An interdigitated gold-microarray electrode with a 10 μm of width and a gold plate electrode were used as the working and the counter electrodes, respectively. After optimization of the EPD processing parameters, a micropattern was constructed from silica colloidal spheres. It had a relatively close-packed structure formed onto the interdigitated microarray electrode. This micropattern showed a characteristic optical reflectance peak due to Bragg’s law.

Potentiometric miniaturized pH sensors based on polypyrrole films

Potentiometric pH miniaturized sensors based on electrosynthesized polypyrrole films were developped. These pH sensors consist in two interdigitated microarray electrodes which were fabricated using photolithography process. One electrode of the sensor is coated by a polypyrrole film while the other one is coated by a silver film used as reference electrode. The potentiometric responses of these sensors were generally linear to pH changes in the range from 2 to 11. More, some sensors appeared to be stable in time during 30 days. The effect of the thickness of polymer film to potentiometric responses was also studied. It appeared that thinner polypyrrole films gave better potentiometric responses than thicker ones.

Methanol vapor‐induced morphology and current–voltage characteristic changes in a cast‐coated nafion film/interdigitated microarray electrode

AbstractMethanol vapor‐induced membranous changes in a cast‐coated Nafion thin film were studied through current–voltage (I–V) characteristics with an interdigitated microarray (IDA) electrode and atomic force microscopy (AFM). The obtained I–V curves showed that the as‐prepared Nafion film was stable under humidified nitrogen gas; however, the I–V profile dramatically changed with exposure to methanol vapor. Next, the morphology of the film was compared before and after methanol exposure with AFM images. On the basis of our observations, we found that the as‐prepared film had an irregularly complicated microstructure, whereas the structure became homogeneous in appearance after 30 min of exposure to methanol gas. The alternating‐current conductivity data, showing almost the same magnitude before and after exposure, strongly suggested that the I–V profile shift was based on a change in an electrode reaction mechanism induced by a change in the junction at the Nafion/IDA electrode interface. Furthermore, the methanol vapor‐pre‐exposed Nafion was stable for further exposure to methanol vapor, water vapor, or both. With the stabilized film used in combination with the IDA electrode, a reversible change in the magnitude of the current was observed when the methanol/water vapor ratio was varied. This indicated that the electrode reaction had good reproducibility after the treatment. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1103–1109, 2002

Amorphous tin oxide films: preparation and characterization as an anode active material for lithium ion batteries

Tin oxide thin films were prepared by the electrostatic spray deposition at 400°C, followed by annealing at 500°C in air. X-ray diffraction and X-ray photoelectron spectroscopy revealed that the resulting films were amorphous SnO 2. The electrochemical properties of the SnO 2 films with lithium were studied by in situ conductivity measurements using an interdigitated microarray electrode as well as by cyclic voltammetry, galvanostatic cycling measurements and ac-impedance spectroscopy in 1 M LiClO 4/(PC+EC). The SnO 2 film electrodes exhibited reversible capacities greater than 1300 mA h g −1 when cycled between 0.05 and 2.5 V at 0.2 mA cm −2. However, this capacity faded rapidly after repeated cycling. If the electrode was cycled between 0 and 1.0 V, a reversible capacity of 600 mA h g −1 was maintained for more than 100 cycles. In addition, a stable reversible capacity of about 500 mA h g −1 was obtained even at current density as high as 2 mA cm −2. Thus it is suggested that a higher potential than 1.5 V would cause reformation of tin oxide, which may destroy the stable nanocomposite structure of metallic tin and lithium. These arguments were supported by in situ conductivity measurements with microarray electrodes.

High Magnetic Field Effects on Interdigitated Microarray Electrodes

Abstract High magnetic field effects were determined for a typical electrochemical reaction, the oxidation of hexacyanoferrate(II) to hexacyanoferrate(III) on interdigitated microarray electrodes. A characteristic dependence on the magnetic field direction was observed. Using a unique feature of the microarray electrode, an attempt was made to obtain a new method to analyze the components of the flux, and a hopeful way was shown to apply these microarray electrodes in a magnetic field.

Electrochemical In-Situ Conductivity Measurements for Thin Film of Li1-xMn2O4 Spinel

Electrical conductivity of LiMn{sub 2}O{sub 4}, which is a promising cathode active material for lithium ion batteries, was monitored in situ during electrochemical lithium extraction and reinsertion reactions in 1 M LiClO{sub 4} propylene carbonate solution. The in-situ conductivity measurement was achieved by means of an interdigitated microarray electrode coated with a uniform and dense film of LiMn{sub 2}O{sub 4}. The conductivity of Li{sub 1{minus}x}Mn{sub 2}O{sub 4} was found to exhibit a peak-shaped profile as a function of lithium content. The conductivity of Cr{sup 3+}-doped spinel, LiMn{sub 1.95}Cr{sub 0.05}O{sub 4}, decreased monotonically with decreasing lithium content. These results are discussed by considering the effects of phase transformation on the conductivity of these materials.

Electrochemical Detection Based on Redox Cycling Using Interdigitated Microarray Electrodes at µL/min Flow Rates

The influence of convection on the degree of redox cycling at interdigitated microarray electrodes in a flow system was investigated in the end column detection mode for flow rates below 20 µL/min. It was found that the degree of redox cycling increased with decreasing flow rates and values of 2.9 and 2.2 were obtained for a flow rate of 2 and 20 µL/min, respectively, using photolithographically fabricated interdigitated arrays consisting of 140 microbands separated by 6 µm. The obtained degrees of redox cycling were lower than the value of 4.4 obtained in a stationary solution in the batch mode as a result of a decreased collection efficiency between adjacent microbands and a relatively low conversion efficiency at each microband in the presence of the flow. It is shown that a collection efficiency of more than 90 % is needed to produce an order of magnitude increase in the current due to redox cycling in a stationary solution. When using a microarray electrode consisting of 280 microbands in a thin layer flow cell, a conversion efficiency of close to 100 % could be obtained at flow rates below 1 µL/min. In the latter case, a significantly larger flow rate dependence of the current was found compared to that for a single microband electrode.

Electrochemical Detection Based on Redox Cycling Using Interdigitated Microarray Electrodes at µL/min Flow Rates

The influence of convection on the degree of redox cycling at interdigitated microarray electrodes in a flow system was investigated in the end column detection mode for flow rates below 20 mu L/min. It was found that the degree of redox cycling increased

Subnanoliter volume wall-jet cells combined with interdigitated microarray electrode and enzyme modified planar microelectrode

Miniaturized wall-jet type flow cells with an active volume of 0.042-15 nL were fabricated for use as highly sensitive electrochemical detectors for capillary electrophoresis/electrochemical detection and small on-line enzyme sensors. The cells consisted of three glass plates and a fused-silica capillary. Two of the plates had microfabricated flow channels and guide trenches for the capillary and working, reference, and counter electrodes. The other plate had a film electrode. When an interdigitated microarray electrode (total area, 66 microm x 64 microm; bandwidth and gap, 2 microm) was installed in the flow cell, the redox cycling enhanced the current at flow rates of less than 100 nL/min even though there were only eight pairs of microbands. A sharp dopamine peak enhanced by the redox cycling was observed when the cell was used for capillary electrophoresis. A square film electrode modified with glutamate oxidase and Os-poly(vinylpyridine) containing HRP was also installed in the flow cell and used to measure neurotransmitter release from cultured nerve cells. When the flow rate was relatively high, the response time of the modified electrode was comparable to that of a cylindrical carbon fiber electrode (33 microm o.d.) modified with the same enzyme and mediator. We observed a transient cathodic current response assigned to the glutamate release with the electrode in the flow cell in a suction mode measurement when we stimulated cultured nerve cells electrically with a dual microelectrode.

In situ conductance measurement to investigate roles of conductive additives in lithium ion battery electrodes

Electrical dc conductance of a composite electrode for a lithium-ion battery was monitored in situ during successive charge/discharge cycles, in order to investigate functions of conductive additives. Such measurement was achieved by means of an interdigitated microarray electrode with a bipotentiostat. The composite films of mesocarbon microbeads (MCMBs) heat-treated at 1000°C were studied with conductive additives of acetylene black or a synthetic graphite in a 1 M LiClO 4 non-aqueous carbonate solution. The role of the conductive additives is discussed in connection with their type and content within the composites. In addition, we propose a modified preparation procedure for the composites having a high retention of conductance.

In situ conductivity measurements of LiMn 2 O 4 thin films during lithium insertion/extraction by using interdigitated microarray electrodes

Thin films of LiMn2O4 have been prepared by RF magnetron sputtering on interdigitated microarray electrodes. In situ conductivity–potential profiles and cyclic voltammograms during extraction/insertion processes of Li ions were obtained simultaneously in nonaqueous and aqueous electrolyte solutions (1 M LiClO4/propylene carbonate and 1 M LiCl/water). The electronic conductivity of Li1– x Mn2O4 was found not to show metallic transition and maintain its semiconducting state during the extraction/insertion of Li ion. A slight decrease in conductivity was observed with increasing the anodic potential, i.e., with increasing x (lithium extraction) and recovered reversibly when the potential returned to the cathodic side (re-insertion of Li ions). Similar results were obtained in both aqueous and nonaqueous electrolyte solutions.

ChemInform Abstract: In situ Conductivity Measurements of LiCoO2 Film During Lithium Insertion/Extraction by Using Interdigitated Microarray Electrodes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

In Situ Conductivity Measurements of LiCoO2 Film during Lithium Insertion/Extraction by Using Interdigitated Microarray Electrodes

In situ conductivity‐potential profiles and cyclic voltammograms of an thin film were obtained simultaneously by using an interdigitated microarray electrode with a constant potential difference. The electronic conductivity of increased exponentially with potential during lithium extraction from 2.7 to 4.0 V. The conductivity changes drastically when very small amounts of Li () are extracted.

Electrochemical behaviour of V-groove microelectrodes fabricated by micromachining

Abstract The electrochemical behaviour of V-groove microelectrodes (10–100 μm wide) was investigated and compared with that of planar band microelectrodes with the same sizes. The V-groove electrodes were fabricated by anisotropic etching on a 〈100〉 silicon wafer in KOH solutions. The cyclic voltammetric investigation at the V-groove electrodes revealed a different scan rate dependence of the peak current from that at the planar band microelectrodes. When the V-groove electrode was covered with a platinum plate lid electrode, the redox cycling between the two electrodes proceeds efficiently, exhibiting higher collection efficiencies than at the ordinary interdigitated microarray electrode with the same size. The high collection efficiency originated from the small effective diffusion length.

In Situ Conductivity Measurements during Lithium Intercalation/Deintercalation on V2O5 Thin Film by Using Interdigitated Microarray Electrodes

Abstract The conductivity change of a vacuum deposited V2O5 thin film during lithium intercalation/deintercalation was investigated using an interdigitated microarray electrode. The conductivity-potential profile showed two peaks (ca. 1.7 × 10−3 S cm−1) at 3.23 V and 3.41 V vs. Li/Li+, corresponding to the peaks in the cyclic voltammogram for Li intercalation/deintercalation. The conductivity decreased below 10−5 S cm−1 when the potential was scanned to the region more negative than 3.0 V vs. Li/Li+ and an irreversible conductivity change was observed when the potential was scanned back.