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Selective detection of o-diphenols (e.g., catechol, dopamine, and pyrogallol) in the presence of simple phenols, m- and p- derivative diphenols, and ascorbic acid has been demonstrated on copper-plated screen-printed electrodes (CuSPEs) in pH 7.4 phosphate buffer solution. The CuSPE showed an unusual catalytic response at -0.05 V versus Ag/AgCl selectively to o-diphenolic compounds. The o-diphenols can thus be determined amperometrically through direct electrochemical oxidation in low potentials (~0 V), where the CuSPE is much less subject to interfering reactions. Such a catalytic phenomenon cannot be observed on conventional Pt and glassy carbon electrodes. The selective mechanism is explained in terms of the formation of cyclic five-member complex intermediate (Cu(II)-o-quinolate). Most important of all, the common drawbacks of electrode fouling through polymerization were completely overcome in this system.

The present study describes the result of an improved numerical method applied to our two-electrode spark gap discharge. The time evolution of the ionization current is obtained and mechanisms describing ionization growth in discharge are presented. The effect of E/N has been investigated by changing either the applied gap voltage or by varying the nitrogen gas pressure. Some fluctuations in the exponential ionization growth are noticed which are related to the secondary ionization by the cathode photoelectric emission. Simulated snapshots were obtained that clearly show the image of electron avalanches traversing the discharge gap. My results are compared with other computational methods and they are in good agreement providing higher accuracy in the results. The advantage of my results is that I have considered a more accurate finite-element method for the numerical computation in which considers the growth of the discharge in both the axial and radial directions with a good stability. Index Terms--Current, discharge, electrode, spark gap, voltage.

This paper presents a study of streamer inception in mineral transformer oil, in point-plane and rod-plane geometry under impulse voltage. The measurements performed with points and rods over a wide range of tip radii show a marked decrease of initiation fields when the electrode radius is increased. The initiation field is divided by 30 over the investigated range (from 1 [micro]m points up to 2 cm rods). This effect compares fairly well with the 'surface effect' known for breakdown voltages under uniform field with large electrodes. Plotting these results together shows the decrease of streamer initiation fields over a very wide electrode surface range (12 decades), proportional to [S.sup.-0.17] (S: electrode surface area, [cm.sup.2]). These results suggest the influence of electrode surface defects on streamer initiation under impulse voltage.

This paper presents a study of streamer inception in transformer oil, in a 'semi-uniform' geometry under impulse voltage. This geometry consists of parallel plane electrodes, with a thin triggering point of calibrated size emerging at the center of one plane. By reducing the length of the point, it is possible to move progressively from a point-plane geometry, up to a quasi-uniform geometry. Compared to a point-plane gap, the initiation of streamers is impeded due to the presence of a metallic plane behind the triggering point, that reduces the tip field. Field calculations allow to extrapolate the results obtained to the case of microscopic surface protrusions and particles. It is possible to predict the streamer initiation voltage, and hence the breakdown voltage under uniform field, from the shape of the protrusion and from streamer initiation fields measured in point-plane geometry.

A technique of fractionation for microparticles was proposed that utilized a unique combination of a dielectrophoretic (DEP) field generated by a quadrupole electrode and a laminar flow in a capillary of 82.5 [micro]m in radius. The fabricated capillary possessed four platinum wires in its inside wall as a quadrupole electrode. In a nonuniform electric field generated by the quadrupole electrode, microparticles, such as polystyrene and carbon, in water experienced DEP forces in the radial direction. When a sample solution was pumped in, an ideal laminar flow perpendicular to the DEP force was formed inside the capillary. The microparticles dynamically migrated by the DEP force across the laminar flow while they were carried by the flow. A theoretical model taking the DEP force and the laminar flow pattern into account predicted the elution profiles of the single microparticles quantitatively. The elution times of the microparticles depended on the dielectric properties and the sizes of the microparticles, as well as the voltage and frequency of the applied alternating current.

The efficiency of electrodes for positive carrier injection into poly(9,9-dioctylfluorene) and copolymers is examined.

The rapid generation and screening of catalytic materials on electrode surfaces is described.

Theoretical concepts and applications of a rotating disk electrode (RDE) of vitreous carbon can be used to show advanced students of chemistry or electrochemical engineering equations that describe mass transport in an RDE. They see the influence of mass transport and charge transfer in electrochemical reactions and calculate the diffusion coefficient of Fe(CN)(sub.6)(super.3-) and Fe(CN)(sub.6)(super.4-). They get familiar with techniques/tools of basic electrochemistry, such as linear sweep voltammetry. The exercise takes about 4 hours in groups of 2-3 students.

Because of its presumed ideal reversible behavior, the oxidation of ferrocene is widely used in cyclic voltammetric studies in highly resistive organic solvents as a means of reference electrode potential calibration. In this study, it is shown that a good estimate of the uncompensated resistance value, needed for reference potential correction and also frequently an input parameter in simulation of the theory, can be obtained simultaneously with the ferrocene reference potential measurement using a simple analysis based on the semiintegral. Application to cyclic voltammetric oxidation of ferrocene in dichloromethane (0.1 M NBu(sub 4)PF(sub 6)), under conditions where uncompensated resistances of approximately 2.5 k(Omega) are encountered, is used to illustrate the fidelity of the semiintegral method of analysis. Inclusion of this estimated resistance value as the input parameter in a commercially available digital simulation package confirms that the oxidation of ferrocene in dichloromethane represents a close-to-ideal diffusion-controlled reversible process. However, use of the semiintegral method of data analysis also enables detection of subtle forms of nonideality encountered with the ferrocene oxidation process in other media where kinetically controlled adsorption of the ferricenium cation may occur.

The construction and performance evaluation of a novel Chemical Oxygen Demand (COD) sensor is described. The sensor measures, using an oxygen electrode, a decrease of dissolved oxygen of a given sample resulting from photocatalytic oxidation of the organic compounds therein. As the photocatalyst, titanium dioxide (TiO(sub 2)) fine particles adsorbed on a translucent poly(tetrafluoroethylene) (PTFE) membrane was used. The oxygen electrode with the membrane attached on its tip was used as the sensor probe. The operation characteristics of the sensor are demonstrated using an artificial wastewater and real water samples from lakes in Japan. This method is considered to be reliable, in that the observed parameter is close to the theoretical definition of chemical oxygen demand (COD), the amount of oxygen consumed for oxidation of organic compounds.

The basic principles of multichannel devices with an array of elecrospray tips for high-throughput infusion electrospray ionization mass spectrometry (ESI-MS) have been developed. The prototype plastic devices were fabricated by casting from a solvent-resistant resin. The sample wells on the device were arranged in the format of the standard 96-microtiter well plate, with each sample well connected to an independent electrospray exit port via a microchannel with imbedded electrode. A second plastic plate with distribution microchannels was employed as a cover plate and pressure distributor. Nitrogen gas was used to pressurize individual wells for transport of sample into the electrospray exit port. The design of independent microchannels and electrospray exit ports allowed very high throughput and duty cycle, as well as elimination of any potential sample carryover. The device was placed on a computer-controlled translation stage for precise positioning of the electrospray exit ports in front of the mass spectrometer sampling orifice. High-throughput ESI-MS was demonstrated by analyzing 96 peptide samples in 480 s, corresponding to a potential throughput of 720 samples/h. As a model application, the device was used for the MS determination of inhibition constants of several inhibitors of HIV-1 protease.

Reciprocal derivative chronopotentiometry is shown to be well suited for performing electrochemistry in highly resistive solutions in connection to conventional-sized electrodes. The fundamentally different operational principles of reciprocal derivative chronopotentiometry (compared to controlled-potential voltammetry) reduces its susceptibility to solution resistance effects. The influences of the electrolyte concentration and constant current upon the reciprocal derivative chronopotentiometric peak area and potential are examined in different solvents. Well-defined, analytically useful peaks are observed in highly resistive media (with low electrolyte/analyte ratios). Narrower peaks, shifted to higher potential values, are observed upon increasing the solution resistance. Yet, the analytical signal (square root of the peak area) is nearly independent of the ohmic drop. The experimental results are compared with the theoretical predictions. Considerable ohmic drop distortions are observed in analogous voltammetric experiments. The defined chronopotentiometric peaks permit convenient quantitation of micromolar analyte concentrations in highly resistive media. Such observations open the door to new electrochemical applications of conventional electrodes that were previously restricted to ultramicroelectrodes.

By using a high concentration of an interfering ion and a low one of the primary ion in the inner reference solution of polymeric membrane ion-selective electrodes (ISEs), the lower detection limit may be improved and unbiased thermodynamic selectivity coefficients may be obtained. To this purpose, a cation-exchange resin is used here to keep the low concentration of the primary cation constant. Different compositions of the internal solution are required for obtaining optimal lower detection limits and unbiased selectivity coefficients. All ISEs studied here, i.e., for K(super +), Ca(super 2+), and NH(sub 4)(sukper +), based on valinomycin, ETH 5234, and nonactin/monactin, respectively, show improved lower detection limits in the range of 10(super -7.6) (NH(sub 4)(super +)) to 10(super -8.8) M (Ca(super 2+)). Nemstian responses and, therefore, unbiased selectivity coefficients are obtained with the K(super +)-ISE for the discriminated ions, Na(super +), Mg(super 2+), and Ca(super 2+).

Which of Three Voltammetric Methods, When Applied to a The presence of uncompensated resistance and double-layer capacitance confounds the accurate measurements of the bulk concentration of electroreactant and the reversible half-wave potential from an experimental voltammogram. It is pertinent to ask which simple voltammetric technique - chronopotentiometry, linear-scan voltammetry, or potential-step voltammetry - is best able to confront these difficulties. We have carried out a modeling study in an attempt to answer this question. First, we devised an exact method of simulating each variety of reversible voltammogram, incorporating the effects of resistance and capacitance. Next, we developed an unprejudiced method of analyzing these voltammograms to recover both electrochemical parameters. Then we performed a sensitivity analysis on a very large number of simulated voltammograms by measuring the apparent haft-wave potential and concentration when slightly erroneous values of resistance and capacitance were employed in the recovery step. Thereby we hoped to ascertain how uncertainty in the magnitudes of the two interfering electrical elements affects the measured values of the two electrochemical parameters. Basing conclusions on the sizes of the four sensitivity indices, we conclude, surprisingly, that linear-scan voltammetry, not chronopotentiometry, is most often the method of choice.

The development of a poly(dimethylsiloxane)-based (PDMS-based) microchip electrophoresis system employing dual-electrode electrochemical detection is described. This is the first report of dual-electrode electrochemical detection in a microchip format and of electrochemical detection on chips fabricated from PDMS. The device described in this paper consists of a top layer of PDMS containing the separation and injection channels and a bottom glass layer onto which gold detection electrodes have been deposited. The two layers form a tight reversible seal, eliminating the need for high-temperature bonding, which can be detrimental to electrode stability. The channels can also be temporarily removed for cleaning, significantly extending the lifetime of the chip. The performance of the chip was evaluated using catechol as a test compound. The response was linear from 10 to 500 (mu)M with an LOD (S/N = 3) of 4 (mu)M and a sensitivity of 45.9 pA/(mu)M. Collection efficiencies for catechol ranged from 28.7 to 25.9% at field strengths between 200 and 400 V/cm. Dual-electrode detection in the series configuration was shown to be useful for the selective monitoring of species undergoing chemically reversible redox reactions and for peak identification in the electropherogram of an unresolved mixture.

A three-enzyme layered assembly on Au electrodes or Au-quartz crystals, consisting of horseradish peroxidase, HRP, choline oxidase, ChO, and acetylcholine esterase, AChE, is used to sense acetylcholine by the HRP-mediated oxidation of 3,3',5,5'-tetramethylbenzidine, TMB (1), by H(sub 2)O(sub 2), and the formation of the insoluble product (2) on the respective transducers. The analyte-substrate, acetylcholine, is hydrolyzed by AChE to choline that is oxidized by ChO and O(sub 2) to yield the respective betaine and H(sub 2)O(sub 2). The amounts of generated H(sub 2)O(sub 2) and the resulting insoluble product on the transducers correlate with the concentration of acetylcholine in the samples. The formation of the insoluble product (2) on electrode supports is followed by faradaic impedance spectroscopy that probes the increased interfacial electron-transfer resistance upon the formation of 2, and by cyclic voltammetry that reflects electron-transfer barriers upon the formation of the precipitate. The frequency of the Au-quartz crystal decreases as a result of the accumulation of the insoluble precipitate. The amount of insoluble product formed on the transducers is controlled by the concentration of acetylcholine and by the time interval of biocatalyzed precipitation. The generation of the insoluble product provides a means to amplify the sensing processes. Acetylcholine concentrations corresponding to 1 x 10(super -5) M are easily sensed by the different transducers.

A new approach to construct a multilayered enzyme film on the Au surface for use as a biosensing interface is described. The film was prepared by alternate layer-bylayer depositions of G4 poly(amidoamine) dendrimers and periodate-oxidized glucose oxidase (GOx). The cyclic voltammograms obtained from the Au electrodes modified with the GOx/dendrimer multilayers revealed that bioelectrocatalyfic response is directly correlated to the number of deposited bilayers, that is, to the amount of active enzyme immobilized on the Au electrode surface. From the analysis of voltammetric signals, the coverage of active enzyme per GOx/dendrimer bilayer during the multilayer-forming steps was estimated, which demonstrates that the multilayer is constructed in a spatially ordered manner. Also, with the ellipsometric measurements, a linear increment of the film thickness was registered, supporting the formation of the proposed multilayered structure. The E5D5 electrode showed the sensitivity of 14.7 (mu)A*mM(super -1) glucose.cm-(super -2) and remained stable over 20 days under day-by-day calibrations. The proposed method is simple and would be applicable to the constructions of thickness- and sensitivity-controllable biosensing interfaces composed of multienzymes as well as a single enzyme.

A sensitive electrochemical detection method (ECD) for capillary electrophoresis has been developed that is applicable to a much wider range of analytes than more conventional ECD methods. Using a modified Osteryoung square-wave voltammetry method, the adsorption of what are normally considered nonelectrochemically active analyres onto a platinum electrode was found to produce a concentration-proportional response. Although the mechanisms that cause this response may be complex, it appears that it is due to changes in the electrode/solution interface that accompany adsorption of the analyte onto the electrode rather than a simple redox process. Analytes that possess (pi)-electron density appeared to chemisorb rather than only physically adsorb onto the electrode and gave the best response with detection limits of < 10(super -8) M while maintaining good linearity. Because this detection method requires only that the analyte adsorb onto the electrode, it has the advantage of much wider applicability than previously reported electrochemical detection methods. The applicability of this detection method was investigated for a variety of analytes and background electrolyte conditions (varied pH, ionic strength, buffer additives). Comparisons of the sensitivity of this method to UV detection showed that, even for analytes that have good UV chromophores, sensitivities greater than 1 order of magnitude were obtained using adsorption-based electrochemical detection.

The coupling of screen-printing and laser micromachining technology has been used to create a nanovial with 'built-in' working and reference electrodes. The volume of the nanovial was calculated to be 7.2 nL using dimensions determined by SEM. The electrochemical nanovial was characterized using the ferri/ferrocyanide redox couple. Cyclic voltammetry and chronoamperometry experiments were performed with electrochemical nanovials utilizing 5% (v/v) glycerin in the solutions and a humidified headspace to control evaporation of the small-volume samples. Chronoamperometry experiments gave results consistent with a diffusion-limited process and revealed a working electrode surface area of 2.6 x 10(super 4) (mu)m(super 2). The ultrasmall-volume cells represent a simple, reliable, low-cost approach for the fabrication of complete electrochemical nanovials.

Results demonstrate that the deviations in infinite-cell-gap capacitance analysis occurs at an aperture ratio of unity between the gap thickness of the liquid crystal and the electrode width. Data further reveal that the conformational mapping derived capacitance-voltage curve is very similar to the one derived from two-dimensional simultions

A radial multichannel pseudospark switch was incorporated into a plasma focus system.

Two combinatorial approaches for rapid automated screening of electrochemical activity of modified electrode surfaces are described. One approach enables simultaneous comparison of electrochemical current by fluorescence associated with pH changes that accompany consumption or production of protons at the electrode surface during a redox process. However, this method cannot distinguish small differences in current at differently modified electrodes. A second approach relies on computer-automated, serial measurement of electrochemical current at each electrode of a 64-electrode array immersed in a single electrochemical cell. Unlike the fluorescent screen, the second method is capable of distinguishing small differences in current at differently modified electrodes, as demonstrated here for gold electrode surfaces covered with organosulfur monolayers of different chain lengths. The improved precision of the computer-automated direct electrochemical method enables examination of active zones that have been first identified by less precise parallel fluorescent screening methods. The direct electrochemical measurement method can easily be extended to a variety of electrode materials, including fuel cell electrocatalysts and redox storage materials. A complete description of the methodology, hardware and computer program for automated measurement is provided.

A high-voltage stimulator has been designed to allow transcutaneous stimulation of tactile fibers of the fingertip. The stimulator's output stage was based upon an improved Howland current pump topology, modified to allow high load impedances and small currents. The compliance voltage of approximately 800 V is achieved using commercially available high-voltage operational amplifiers. The output current accuracy is better than [+ or -]5% over the range of 1 to 25 mA for 30 [[micro]second] or longer pulses. The rise time for square pulses is less than 1 [[micro]second]. High-voltage, common-mode, latch-up power supply problems and solutions are discussed. The stimulator's input stage is optically coupled to the controlling computer and complies with applicable safety standards for use in a hospital environment. The design presented here is for monophasic stimulation only, but could be modified for biphasic stimulation. Index Terms - Common mode latch-up, current source, electrocutaneous stimulation, electrode/skin interface, electrotactile stimulation, high voltage, pain.

A disposable immunomagnetic electrochemical sensor involving a magnetic particle-based solid phase and a Nation film-coated screen-printed electrode (Nafion-SPE) stuck at the bottom of a polystyrene cylinder (microwell of 300 [[micro]liter]) was developed and evaluated in a competitive immunoassay of the widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The competitive binding of 2,4-D and 2,4-D labeled with alkaline phosphatase (AP) for a limited amount of polyclonal anti-2,4-D antibodycoated magnetic beads was monitored electrochemically by measuring the AP label activity bound to the beads. The phosphoric acid ester of [[(4-hydroxyphenyl)amino]carbonyl]cobaltocenium hexafluorophosphate was used as the AP substrate. This anionic substrate ([S.sup.-]) is enzymatically transformed at pH 9.0 into a cationic phenol derivative ([P.sup.+]) which can be easily accumulated in the polyanionic Nation coating and determined by cyclic voltammetry. During the enzyme reaction, the AP-associated beads were localized on the surface of the Nafion-SPE with the aid of a magnet, thus effectively increasing the concentration of [P.sup.+] in the Nation-modified electrode vicinity. The enzyme generation of [P.sup.-] close to the electrode surface, and thereby to the Nation film, resulted in a high amplification of the response. A detection limit of 0.01 [[micro]gram] [L.sup.-1] 2,4-D was thus achieved. The performance of the sensor was successfully evaluated on river water samples spiked with 2,4-D, indicating that this convenient and sensitive technique offers great promise for decentralized environmental applications.

The construction, performance characteristics, and application of a polymeric membrane coated on a graphite electrode with unique selectivity toward histidine are reported. The electrode was prepared by incorporating chloro(5,10,15,20-tetraphenylporphyrinato) manganese(III) [Mn(TPP)Cl] into a plasticized poly(vinyl chloride) membrane. The influences of membrane composition, pH, and foreign ions were investigated. Calibration plots with near Nernstian slopes for histidine were observed, -55.4 mV/decade, over a linear range of four decades of concentration (1 x [10.sup.-5] to 1 x [10.sup.-1] M). The electrode has a detection limit of 5 x [10.sup.-6] M histidine and shows a fast response time of about 1 min. The electrode shows high selectivities toward histidine over several amino acids and common inorganic anions.

Corona from high-voltage electrodes is employed in various electrostatic installations, such as ozonizers, air filters, powder sprayers, and separators. Multiple-needle electrode designs are preferred whenever low corona onset voltage and good resistance to mechanical shocks are required. This paper aims at identifying a simple solution to overcome the main drawback of this type of electrodes, the nonuniformity of the generated space charge. The experiments were carried out with various models of electrodes, having one or several rows of stainless steel needles. A current probe, consisting of an enameled copper wire (0.4 mm diameter), was embedded in the center of a plane collecting electrode. For a given interelectrode distance (5-50 mm) and a fixed position of the multiple-needle electrode, the collecting plate was translated along two orthogonal directions, so that the current probe could scan a 75 mm x 75 mm square. The results depended on the interelectrode distance and on the high-voltage level. An explanation is given to some observations made on a roll-type electrostatic separator provided with two models of multiple-needle corona electrodes. An improved electrode design was proposed for the industrial installations. Index Terms - Corona discharge, electrostatic processes, electrostatic separation, high-voltage applications.

SOD activity was quantified by the use of a cytochrome c-modified gold electrode. The electrode responded rapidly to superoxide radicals in solution. Steady-state superoxide concentrations were established by control of the calibration conditions. On this basis very low SOD activities were detected (10-200 munits/mL). This method showed good correlation with the standard photometric test and was applied for the determination of SOD activity entrapped into liposomes. Interference by hydrogen peroxide and uric acid was characterized and minimized using long-chain thiols for the first electrode modification step. The complete modification proved to be stable for several days.

Background/Objectives: Bioelectrical impedance vector analysis (BIVA) is increasingly used in clinical research to assess soft tissue hydration. It is known that physical characteristics of electrodes, such as low intrinsic impedance, low electrode/skin contact impedance and type of gel, affect the reliability of noninvasive bioimpedance assessments. The aim of this study was to determine the effect of intrinsic impedance of electrode on the bioimpedance vector displacement in RXc graph. Subjects/Methods: The intrinsic impedance is measured in nine pregelled disposable Ag/AgCl electrodes usually used for bioimpedance measures. The BIVA method is performed on 35 healthy volunteers using a 50 kHz phase-sensitive bioimpedance analyzer (BIA 101 Anniversary) with the lowest intrinsic impedance electrode and highest. The individual bioimpedance vector is plotted on the bivariate normal interval of reference population. The differences in the mean bioimpedance vectors obtained with each electrode are plotted, with their 95% confidence ellipses, on the dRXc graph. The paired one-sample Hotelling's T[sup.2]-test is used to compare the differences of the mean bioimpedance vectors. Results: We found large variability in intrinsic resistance (11-665 [OMEGA]) and reactance (0.25-2.5 [OMEGA]) values of the electrodes analyzed and significant displacement (P [less than] 0.05) of bioimpedance vector positions in healthy adults according to the paired one-sample Hotelling's T[sup.2]-test. Conclusions: A robust study of all physical characteristics of commercial Ag/AgCl electrodes is necessary to reach consensus on pregelled Ag/AgCl electrodes valid for bioimpedance measurement. This information will enable BIVA users to avoid systemic errors when performing BIVA assessments, specifically when these measurements are used for clinical interpretations. European Journal of Clinical Nutrition (2016) 70, 1401-1407; doi: 10.1038/ejcn.2016.121; published online 6 July 2016, Author(s): L Nescolarde [1]; H Lukaski [2]; A De Lorenzo [3]; B de-Mateo-Silleras [4]; M P Redondo-del-Río [4]; M A Camina-Martín [4] Introduction The use of bioelectrical impedance methods to [...]

Nafion or sodium poly(styrenesulfonate) (NaPSS) entrapped in either sol-gel-derived silica or cross-linked poly(vinyl alcohol) (PVA) composite coatings on spectroscopic graphite electrodes were investigated electrochemically with [[[Re.sup.I][(DMPE).sub.3]].sup.+], where DMPE = 1,2-bis(dimethylphosphino)ethane. Among these composite coatings, Nafion-entrapped sol-gel-derived silica (Nafion-silica) exhibited a sensitivity for [[[Re.sup.I][(DMPE).sub.3]].sup.+] [approximately]4 times higher than that of NaPSS-entrapped sol-gel-derived silica or NaPSS-entrapped PVA. When Nation was entrapped in cross-linked PVA matrix, however, the voltammetric response was found to be only [approximately]14% of that of Nation and Nation-silica composite coatings. Dispersing Nation in sol-gel-derived silica matrix improves the slow diffusion of [[[Re.sup.I][(DMPE).sub.3]].sup.+] in Nation, thus leading to a higher sensitivity than Nation in a shorter preconcentration time. Such a Nafion-silica composite is promising for both electrochemical and spectroelectrochemical sensing of [[[Re.sup.I][(DMPE).sub.3]].sup.+]. It was also found that increasing the high potential of a cyclic voltammetric scan greatly reduces the amount of [[[Re.sup.II][(DMPE).sub.3]].sup.2+] available for reduction in the reverse potential scan, suggesting that the electrochemically generated [[[Re.sup.II][(DMPE).sub.3]].sup.2+] was consumed in the more positive potential region.

Nafion or sodium poly(styrenesulfonate) (NaPSS) entrapped in either sol-gel-derived silica or cross-linked poly(vinyl alcohol) (PVA) composite coatings on spectroscopic graphite electrodes were investigated electrochemically with [[[Re.sup.I][(DMPE).sub.3]].sup.+], where DMPE = 1,2-bis(dimethylphosphino)ethane. Among these composite coatings, Nafion-entrapped sol-gel-derived silica (Nafion-silica) exhibited a sensitivity for [[[Re.sup.I][(DMPE).sub.3]].sup.+] [approximately]4 times higher than that of NaPSS-entrapped sol-gel-derived silica or NaPSS-entrapped PVA. When Nation was entrapped in cross-linked PVA matrix, however, the voltammetric response was found to be only [approximately]14% of that of Nation and Nation-silica composite coatings. Dispersing Nation in sol-gel-derived silica matrix improves the slow diffusion of [[[Re.sup.I][(DMPE).sub.3]].sup.+] in Nation, thus leading to a higher sensitivity than Nation in a shorter preconcentration time. Such a Nafion-silica composite is promising for both electrochemical and spectroelectrochemical sensing of [[[Re.sup.I][(DMPE).sub.3]].sup.+]. It was also found that increasing the high potential of a cyclic voltammetric scan greatly reduces the amount of [[[Re.sup.II][(DMPE).sub.3]].sup.2+] available for reduction in the reverse potential scan, suggesting that the electrochemically generated [[[Re.sup.II][(DMPE).sub.3]].sup.2+] was consumed in the more positive potential region.

An enzyme switch, or microelectrochemical enzyme transistor, responsive to hydrogen peroxide was made by connecting two carbon band electrodes ([approximately]10 [[micro]meter] wide, 4.5 mm long separated by a 20-[[micro]meter] gap) with an anodically grown film of poly(aniline). Horseradish peroxidase (EC 1.11.1.7) was either adsorbed onto the poly(aniline) film or immobilized in an insulating poly(1,2-diaminobenzene) polymer grown electrochemically on top of the poly(aniline) film to complete the device. In the completed device, the conductivity of the poly(aniline) film changes from conducting (between - 0.05 and + 0.3 V vs SCE at pH 5) to insulating (> +0.3 V vs SCE at pH 5) on addition of hydrogen peroxide. The change in conductivity is brought about by oxidation of the poly(aniline) film by direct electrochemical communication between the enzyme and the conducting polymer. This was confirmed by measuring the potential of the poly(aniline) film during switching of the conductivity in the presence of hydrogen peroxide. The devices can be reused by rereducing the poly(aniline) electrochemically to a potential below +0.3 V vs SCE. A blind test showed that the device can be used to determine unknown concentrations of [H.sub.2][O.sub.2] in solution and that, when used with hydrogen peroxide concentrations below 0.5 mmol [dm.sup.-3], the same device maybe reused several times. The possible development of devices of this type for use in applications requiring the measurement of low levels of hydrogen peroxide or horseradish peroxidase is discussed.

A capacitive approach has been employed to develop a novel method to determine phospholipase activity. The sensing electrodes have a structure like Au/S[(C[H.sub.2]).sub.17]C[H.sub.3]/substrate/electrolyte. Hydrolysis of the substrate, mediated by phospholipase A2, leads to the formation of water-soluble products from the insoluble substrate. This results in desorption of these products into aqueous phase and corresponding increase of the electrode capacitance. The requirement of high water solubility of the reaction products can be achieved in two ways. In the first, short-chain phospholipids are used as the substrate, in which case, water-soluble products are formed and no additional reagents are required to promote desorption of these products. The sensors prepared by this strategy provide sensitive qualitative detection of phospholipases. The second way is based on the use of a water-soluble acceptor (for example, [Beta]-cyclodextrin) to solubilize the products of hydrolysis. It allows semiquantitative detection of phospholipase activity toward long-chain natural substrates. The reaction kinetics for this case was found to be monoexponential and linearly dependent on the phospholipase concentration. The detection limit of this method, as tested with phospholipase [A.sub.2] from bee venom and soy bean lecithin as the substrate, is [approximately]0.5 ng/mL (500 [micro]units/mL).

Singly charged amines and sulfonic acids as cationic and anionic aliphatic model substances, respectively, were detected in capillary electrophoresis with all-solid-state ion-selective electrodes. The sensitivity for these compounds is a function of their lipophilicity. The signal detected is generally greater for molecules with a larger organic part. The utility of the method is further demonstrated by the detection of a group of aromatic compounds in the form of the anionic analgesics (S)-(+)-2-(4-isobutylphenyl)propionic acid, 2-[(2,6-dichlorophenyl)amino]benzeneacetic acid, and o-acetylsalicylic acid. Further determined were the artificial sweeteners cyclamate, acesulfame-K, and saccharin. Detection limits for the different substances were between 2.5 x [10.sup.-6] and 1 x [10.sup.-5] M.

A novel microscale and surface-based method for the study of the interactions of DNA with other redox-active molecules using DNA-modified electrodes is described. The method is simple, convenient, reliable, reagent-saving, and applicable for DNA studies, especially those involving microsamples. Information such as binding site size (s, in base pairs), binding constant (K), ratio ([[K.sub.Ox]/[K.sub.Red]) of the binding constants for the oxidized and reduced forms of a bound species, binding free energy ([Delta][G.sub.b]), and interaction mode, including changes in the mode of interaction, and 'limiting' ratio [[K.sub.Ox].sup.[convolution]/[[K.sub.Red].sup.[convolution] at zero ionic strength can be obtained using only 3-15 [[micro]gram] of DNA samples. The method was developed using [[Co[(Phen).sub.3]].sup.3+/2+] (Phen = 1,10-phenanthroline)/double-stranded DNA (dsDNA)-modified gold electrodes and [[Co[(bpy).sub.3]].sup.3+/2+] (2,2[prime]-bipyridyl)/dsDNA-modified gold electrodes as model systems. For the [[Co[(Phen).sub.3].sup.3+/2+/] dsDNA-modified gold electrode system, a [K.sub.2-] of (2.5 [+ or -] 0.3) x [10.sup.5] [M.sup.-1] and an s of 5 bp were obtained in 5 mM pH 7.1 Tris-HCl buffer solution containing 50 mM NaCl. For [[Co[(bpy).sub.3]].sup.3+2+]/dsDNA-modified gold electrodes, [K.sub.3+] and s values of (1.3 [+ or -] 0.3) x [10.sup.5] [M.sup.-1] and 3 bp, respectively, were obtained. While the s values are consistent with those reported in the literature obtained by solution methods, the K values are almost an order of magnitude larger. A transition in the nature of the interaction between dsDNA and [[Co[(Phen).sub.3]].sup.3+/2+], from electrostatic to intercalative with increasing ionic strength, was found in our studies. Negative values of [Delta][E.sup.[convolution][prime] for [[Co[(bpy).sub.3]].sup.3+/2+] bound to dsDNA suggest that its interaction with dsDNA is predominantly electrostatic over the ionic strength range of 5-105 mM. The 'limiting' ratio [[K.sub.-3].sup.convolution]/[[K.sub.2+].sup.[convolution] of 22 obtained for [[Co.[(Phen].sub.3]].sup.3+/2+] bound to dsDNA at zero ionic strength suggests that electrostatic interactions are predominant over intercalative ones under these limiting conditions. The ratio for [[Co[(bpy).sub.3]].sup.3+/2+] +/2+ of 16 also indicates that the 3+ form binds to dsDNA more strongly than the 2+ form at zero ionic strength. For [[Co[(Phen).sub.3]].sup.3/2+]single-stranded DNA (ssDNA)-modified gold electrodes, the nonuniformity of the surface structure of ssDNA-modified gold electrodes greatly complicates the analysis. A system consisting of a dsDNA-modified gold electrode and [[Co[(tppz).sub.2]].sup.3-/2+] (tppz = tetra-2-pyridyl- 1,4-pyrazine) was studied by this method, with a [K.sub.2+] value of (5 [+ or -] 1) x [10.sup.5] [M.sup.-1] and an s value of 7 bp being obtained.

The electronic mechanisms of fatigue for Pb(Zr0.53Ti0.47)O3 ferroelectric thin films were examined by regulating the type of carriers introduced in the films. The approach was assisted by n-type and p-type semiconductor electrodes and by developing an interface with insulating properties. Two mechanisms were identified. One involves internal fields induced by the space charge segregation at both electrode interfaces, while the other involves oxygen vacancies.

This paper develops a theoretical framework and sets of differential and integral equations for analyzing the operating characteristics of semiconductor nuclear radiation detectors with arbitrary electrode geometries. Results provide a basis for conceptualization and numerical calculations and are relevant to recent substantial improvements in detector performance achieved through various single-carrier charge collection schemes based on special electrode configurations. During the course of the work, the approach known as static charge analysis is extended to three dimensions and placed on a firmer theoretical basis. Index Terms - Nuclear radiation detector, single-carrier charge collection.

To understand the physical phenomena occurring in a plasma display panel (PDP), 1D and 2D numerical models of discharges have been undertaken. An experimental device has been developed to measure the effective secondary emission coefficient (gamma), and the experimental results relating to the Paschen curves, the curves of gamma vs E/p and the current-voltage characteristics are reported. The values of gamma vs E/p, obtained with circular copper electrodes, are presented.

The flow of charge onto an insulator surface through injection from an electrode touching the surface has been calculated, using conformal mapping together with the boundary element method. Driving fields are assumed to be due to the electrodes and to surface change. Three experimental geometries were used, and surface charge was found to be confined to the area close to the injecting electrode. Absorption and resorption currents do not show mirror symmetry.

Five preparations of photosystem II (PSII), including Ex-Mn-depleted PS II membranes Mn-depleted PSII membranes, Ex-depleted PSII membranes, Ca2+-depleted PSII membranes and untreated PSII membranes, were studied using a calcium-selective electrode to elucidate calcium binding in PSII. The results suggested that untreated PS II has Ca2+ bound to very high-affinity regions. The results further revealed that there was no very high-affinity Ca2+ binding in equilibrium with free Ca2+ in untreated PSII membranes.