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Microelectrode Array (microelectrode + array)
Selected AbstractsAn In Situ Copper Plated Boron-Doped Diamond Microelectrode Array for the Sensitive Electrochemical Detection of NitrateELECTROANALYSIS, Issue 20 2005Sarah Ward-Jones Abstract The first example of using a copper microelectrode array for use in electroanalysis is explored and exemplified with the electroanalytical quantification of nitrate. The analytical approach is based upon the in situ deposition of copper at a boron-doped diamond (BDD) microelectrode array. The immobilized copper layer is electrocatalytic for nitrate reduction and exhibits an analytically useful range from 1.2 to 124,,M with a marked selectivity for nitrate ion over nitrate, with a limit of detection of 0.76,,M. The analytical applicability was examined through standard addition determinations of nitrate in drinking and river water samples. [source] Fabrication and Characterization of DNA/QPVP-Os Redox-Active Multilayer FilmELECTROANALYSIS, Issue 23 2004Jianyun Liu Abstract Calf thymus DNA was immobilized on functionalized glassy carbon, gold and quartz substrates, respectively, by the layer-by-layer (LBL) assembly method with a polycation QPVP-Os, a quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2,-bipyridine) as counterions. UV-visible absorption and surface plasmon resonance spectroscopy (SPR) showed that the resulting film was uniform with the average thickness 3.4,nm for one bilayer. Cyclic voltammetry (CV) showed that the total surface coverage of the polycations increases as each QPVP-Os/DNA bilayer added to the electrode surface, but the surface formal potential of Os-centered redox reaction shifts negatively, which is mainly attributed to the intercalation of redox-active complex to DNA chain. The electron transfer kinetics of electroactive QPVP-Os in the multilayer film was investigated by electrochemical impedance experiment for the first time. The permeability of Fe(CN) in the solution into the multilayer film depends on the number of bilayers in the film. It is worth noting that when the multilayer film is up to 4 bilayers, the CV curves of the multilayer films display the typical characteristic of a microelectrode array. The nanoporous structure of the multilayer film was further confirmed by the surface morphology analysis using atomic force microscopy (AFM). [source] Integrated Microanalytical System Coupling Permeation Liquid Membrane and Voltammetry for Trace Metal Speciation.ELECTROANALYSIS, Issue 10 2004Optimization, Technical Description Abstract A new minicell coupling the liquid-liquid extraction technique called permeation liquid membrane (PLM) with an integrated Ir-based Hg-plated microelectrode array for voltammetric detection has been developed for the speciation of heavy metals in natural waters. Lead and cadmium have been used as model compounds. The PLM consists of a carrier (0.1,M 22DD+0.1,M lauric acid) dissolved in 1,:,1 mixture of toluene/phenylhexane held in the small pores (30,nm) of a hydrophobic polypropylene membrane (Celgard 2500). One side of this membrane is in contact with a flowing source solution, containing the metal ions of interest. An acceptor or strip solution (pyrophosphate) is placed on the other side of the PLM with the microelectrode array placed at 480,,m of the PLM. The analyte is transported by the carrier from the source solution to the strip solution. The originality of the new minicell is that accumulation in the strip solution is voltammetrically followed by the integrated microelectrode array in real time, and at low concentration level, using square-wave anodic stripping voltammetry (SWASV). In order to protect the Hg microelectrodes from the adsorption of the hydrophobic carrier, the microelectrodes are embedded in a thin gel layer (280,,m) of 1.5% LGL agarose gel containing 10% of hydrophobic silica particles C18. The choice of optimum conditions is discussed in details in this article. Due to the very small effective strip volume of the new cell (less than 1,,L), high enrichment factor can be obtained (e.g., 330 for Pb) after 2,hours of accumulation. No deaeration of the solutions is required for SWASV measurements. Detection limits under these conditions are 2,pM and 75,pM for Pb and Cd, respectively, using a voltammetric deposition time of 5,min. In addition, no fouling effects were observed with natural water samples. [source] Accumulation and filtering of nanoparticles in microchannels using electrohydrodynamically induced vortical flowsELECTROPHORESIS, Issue 14 2008Maika Felten Abstract We present an approach for the accumulation and filtering of nano- and microparticles in microfluidic devices that is based on the generation of electric traveling waves in the radio-frequency range. Upon application of the electric field via a microelectrode array, complex particle trajectories and particle accumulation are observed in well-defined regions in a microchannel. Through the quantitative mapping of the 3-D flow pattern using two-focus fluorescence cross-correlation spectroscopy, two vortices could be identified as one of the sources of the force field that induces the formation of particle clouds. Dielectrophoretic forces that directly act on the particles are the second source of the force field. A thorough 2-D finite element analysis identifies the electric traveling wave mechanism as the cause for the unexpected flow behavior observed. Based on these findings, strategies are discussed, first, for avoiding the vortices to optimize electrohydrodynamic micropumps and, secondly, for utilizing the vortices in the development of microdevices for efficient particle accumulation, separation, and filtering. Such devices may find numerous biomedical applications when highly diluted nano- and microsuspensions have to be processed. [source] Rapid assessment of in vivo cholinergic transmission by amperometric detection of changes in extracellular choline levelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Vinay Parikh Abstract Conventional microdialysis methods for measuring acetylcholine (ACh) efflux do not provide sufficient temporal resolution to relate cholinergic transmission to individual stimuli or behavioral responses, or sufficient spatial resolution to investigate heterogeneities in such regulation within a brain region. In an effort to overcome these constraints, we investigated a ceramic-based microelectrode array designed to measure amperometrically rapid changes in extracellular choline as a marker for cholinergic transmission in the frontoparietal cortex of anesthetized rats. These microelectrodes exhibited detection limits of 300 nm for choline and selectivity (> 100 : 1) of choline over interferents such as ascorbic acid. Intracortical pressure ejections of choline (20 mm, 66,400 nL) and ACh (10 and 100 mm, 200 nL) dose-dependently increased choline-related signals that were cleared to background levels within 10 s. ACh, but not choline-induced signals, were significantly attenuated by co-ejection of the acetylcholinesterase inhibitor neostigmine (Neo; 100 mm). Pressure ejections of drugs known to increase cortical ACh efflux, potassium (KCl; 70 mm, 66, 200 nL) and scopolamine (Scop; 10 mm, 200 nL), also markedly increased extracellular choline signals, which again were inhibited by Neo. Scop-induced choline signals were also found to be tetrodotoxin-sensitive. Collectively, these findings suggest that drug-induced increases in current measured with these microelectrode arrays reflect the oxidation of choline that is neuronally derived from the release and subsequent hydrolysis of ACh. Choline signals assessed using enzyme-selective microelectrode arrays may represent a rapid, sensitive and spatially discrete measure of cholinergic transmission. [source] Cover Picture: J. Biophoton.JOURNAL OF BIOPHOTONICS, Issue 4 20094/200 AC Dielectrophoretic separation of 10 ,m non-fluorescent microspheres from 40 nm red fluorescent nanoparticles on a microelectrode array. The leftmost 3 × 3 microelectrodes are activated. The rightmost column of microelectrodes are used as control. (Top Left) Red Fluorescence image before experiment showing a red haze. (Top Right) Red Fluorescence image of the 40 nm nanoparticles concentrating on the electrodes at the conclusion of the experiment. (Bottom Left) Bright Field image of 10 ,m microspheres distributed in a random pattern before the experiment. (Bottom Right) Bright Field image of 10 ,m microspheres concentrating in between the microelectrodes at the conclusion of the experiment (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comparison of Different Strategies on DNA Chip Fabrication and DNA-Sensing: Optical and Electrochemical ApproachesELECTROANALYSIS, Issue 22 2005Sabine Szunerits Abstract New strategies for the construction of DNA chips and the detection of DNA hybridization will be discussed in this review. The focus will be on the use of polypyrrole as a linker between a substrate and oligonucleotide probes. The modification step is based on the electrochemical copolymerization of pyrrole and oligonucleotides bearing a pyrrole group on its 5, end. This strategy was employed for the immobilization of oligonucleotides on millimeter-sized electrodes, microelectrode arrays, as well as for the local structuring of homogeneous gold surfaces. Our approaches for the localized patterning of gold surfaces will be also discussed. Localized immobilization was achieved by using an electrospotting technique, where a micropipette served as an electrochemical cell where spot sizes with 800,,m diameters were fabricated. The use of a microcell using a Teflon covered metal needle with a cavity of 100,,m resulted in immobilized probe spots of 300,,m. Scanning electrochemical microscopy (SECM) was also used, and surface modifications of 100,,m were obtained depending on the experimental conditions. Different detection methods were employed for the reading of the hybridization event: fluorescence imaging, surface plasmon resonance imaging (SPRI), photocurrent measurements, and voltamperometric measurements using intercalators. Their advantages concerning the various immobilization strategies will also be discussed. [source] Rapid assessment of in vivo cholinergic transmission by amperometric detection of changes in extracellular choline levelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Vinay Parikh Abstract Conventional microdialysis methods for measuring acetylcholine (ACh) efflux do not provide sufficient temporal resolution to relate cholinergic transmission to individual stimuli or behavioral responses, or sufficient spatial resolution to investigate heterogeneities in such regulation within a brain region. In an effort to overcome these constraints, we investigated a ceramic-based microelectrode array designed to measure amperometrically rapid changes in extracellular choline as a marker for cholinergic transmission in the frontoparietal cortex of anesthetized rats. These microelectrodes exhibited detection limits of 300 nm for choline and selectivity (> 100 : 1) of choline over interferents such as ascorbic acid. Intracortical pressure ejections of choline (20 mm, 66,400 nL) and ACh (10 and 100 mm, 200 nL) dose-dependently increased choline-related signals that were cleared to background levels within 10 s. ACh, but not choline-induced signals, were significantly attenuated by co-ejection of the acetylcholinesterase inhibitor neostigmine (Neo; 100 mm). Pressure ejections of drugs known to increase cortical ACh efflux, potassium (KCl; 70 mm, 66, 200 nL) and scopolamine (Scop; 10 mm, 200 nL), also markedly increased extracellular choline signals, which again were inhibited by Neo. Scop-induced choline signals were also found to be tetrodotoxin-sensitive. Collectively, these findings suggest that drug-induced increases in current measured with these microelectrode arrays reflect the oxidation of choline that is neuronally derived from the release and subsequent hydrolysis of ACh. Choline signals assessed using enzyme-selective microelectrode arrays may represent a rapid, sensitive and spatially discrete measure of cholinergic transmission. [source] Advanced silicon microstructures, sensors, and systemsIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2007Oliver Paul Non-Member Abstract This paper presents the progress in silicon-based biomedical microstructures, material characterization techniques, and mechanical microsystems by the authors' research team. Microneedle and microelectrode arrays with fluidic through-wafer vias and electrical contacts were developed. The structures are designed for dermatological and biological applications such as allergy testing, surface electromyography, and spatially resolved impedance spectroscopy. The characterization of thin films has relied on the bulge test. By the formulation of more powerful models, the application range of the bulge test was extended to elastically supported thin-film multilayers. This enables the mechanical properties of thin films to be determined reliably. Finally, progress in the operation and application of novel stress sensors based on CMOS diffusions and field effect transistors and exploiting the pseudo-Hall effect is reported. Their integration into powerful single-chip microsystems is described. Applications include stress mapping, force and torque measurements, and tactile surface probing of microcomponents. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Dielectric cell separation of fine needle aspirates from tumor xenograftsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 21 2008Massimo Cristofanilli Abstract As an approach to isolating tumor cells from fine needle biopsy specimens, we investigated a dielectric cell preparation method using an in vivo xenographic tumor model. Cultured human MDA-MB-435 tumor cells were grown as solid tumors in nude mice and fine needle aspiration biopsies were conducted. Biopsied cells were suspended in sucrose medium and collected on slides patterned with microelectrode arrays (electrosmears) energized by electrical signals in the range 10 to 960 kHz. The unlabeled cells adhered to characteristic regions of the slides in accordance with their morphology as a result of dielectric forces. Tumor cells were trapped between 40 and 60 kHz and were separated according to whether they were mitotic, large and complex, or small. Damaged tumor cells were captured at between 60 and 120 kHz; granulocytes between 70 and 90 kHz; lymphocytes between 85 and 105 kHz; healthy erythrocytes between 140 and 180 kHz, and damaged erythrocytes above 180 kHz. Using intrinsic cell characteristics, the electrosmear presented cell subpopulations from fine needle aspiration biopsy specimens in a manner that is compatible with automated slide-based analysis systems. The approach has the potential to facilitate the analysis of the role of cell subpopulations in disease. [source] Transparent diamond-on-glass micro-electrode arrays for ex-vivo neuronal studyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2008M. Bonnauron Abstract We report on the fabrication of high aspect ratio diamond Micro Electrode Arrays (MEAs) grown on silicon as well as on glass substrates using an optimised nanoseeding technique and Bias Enhanced Nucleation (BEN). Such MEA systems combine high electrode reactivity and high electrical current injection limits with resiliency, biocompatibility and optical transparency of diamond surfaces. We present the technological steps for the fabrication of 2D as well as 3D diamond microelectrode arrays. The patterning issues involve the use of detonation nanodiamond particles (DND). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||