Showing papers on "Reference electrode published in 1995"

Biosensor, and a method and a device for quantifying a substrate in a sample liquid using the same

Abstract: The biosensor of this invention can quantify a substrate in a sample liquid by electrochemically measuring the amount of an electron acceptor that has been reduced by electrons generated in a reaction between the substrate and an oxidoreductase. The biosensor has an electrically insulating substrate and an electrode system formed on the substrate including a working electrode, a counter electrode and a third electrode used for detecting a liquid junction. The third electrode can be used merely for detecting a liquid junction, or can be used as both a reference electrode and a liquid junction detecting electrode.

Active Reaction Sites for Oxygen Reduction in La0.9Sr0.1MnO3 / YSZ Electrodes

Abstract: Active reaction sites for 02 reduction in La0.~Sr01MnO3 electrode have been characterized by addressing the origin of the cathodic polarization effects on this electrode material. Cathodic polarization (up to - 1.2 V vs. Pt reference electrode} had several effects on O2 reduction kinetics. First, the O2 reduction rate was favorably increased when the perovskite electrode was cathodically polarized. Second, in situ x-ray photoelectron spectroscopy results indicated that the Mn ions are electrochemically reduced and concomitantly the oxygen stoichiometry decreases. Reduction of Mn ions was further demonstrated in the cyclic voltammogram traced under nitrogen atmosphere. Third, hysteresis in cathodic currents was observed in the cyclic voltammograms of the perovskite/YSZ/Pt system, and the hysteresis phenomena were more prominent at higher O~ pressure. We interpreted these findings to mean that the internal and/or external surface oxide vacancies participate in the O2 reduction reaction. However, it has been explained from the Po2-dependent hysteresis phenomena that, even though those surface sites are active in the O2 reduction~ their activity is less than that of the three-phase boundary sites since additional diffusional processes are required for the former sites. Consequently, the three-phase boundary sites are the major reaction sites at lower O2 pressure, which leads to a small hysteresis. However, at higher 02 pressure, the surface sites also participate in the reaction, resulting in a larger hysteresis.

Diagnostic flow cell device

Abstract: The present invention provides a diagnostic flow cell for determining the presence or amount of an analyte which may be contained in a test sample. The flow cell comprises a spacing layer having a longitudinal void disposed between a pair of opposed substrates. The spacing layer and the opposed substrates define a flow channel wherein reagent means can be immobilized. When the immobilized reagent means is contacted with an analyte, the reagent means can produce an electrically, optically, or electrically and optically detectable response to the analyte. Hence, the reagent means that is immobilized within the flow channel can comprise (i) a counter electrode, a reference electrode and a working electrode, (ii) an optically sensitive dye or (iii) a counter electrode, a reference electrode and a working electrode and an optically sensitive dye. The flow cell can be interfaced with means for introducing a test sample into and out of the flow cell's flow channel and detection means for detecting a signal generated by the immobilized reagent means. The present invention also provides methods for detecting the presence or amount of an analyte which may be contained in a test sample.

Method for glucose sensing

Abstract: A method for measuring the concentration of glucose diffused from a source to a working electrode which assembly includes a scavenging electrode is disclosed. The electrode of the invention is comprised of 1) a working electrode; 2) a scavenging electrode; 3) an electroosmotic electrode; and 4) a electrically insulating gap defined by adjacent edges of 1) and 2) and electrically isolating 1) and 2). The scavenging electrode substantially reduces or eliminates "edge-effects" or error in signal transported to the working electrode via a path which includes a radial vector component, i.e., eliminates chemical signal other than that which moves to the catalytic surface of the working electrode via a path which is substantially perpendicular to catalytic surface of the working electrode.

Surface-modified cobalt-based sensor as a phosphate-sensitive electrode

Abstract: A new phosphate ion-sensitive electrode based on a cobalt matrix has been prepared. The electrode showed a relatively selective potentiometric response toward H 2 PO 4 - which seems to originate from the CoO layer covering the electrode surface. The response mechanism of the electrode is discussed in terms of the host-guest chemistry of a nonstoichiometric compound of CoO

Method for quantifying specific compound

Abstract: A biosensor for quantifying a specific compound has a reaction layer containing at least an enzyme, and an electrode system having a working electrode and a counter electrode formed on an insulating base plate; the biosensor detects the specific compound contained in a sample on the basis of an electrochemical response. In quantifying, the working electrode and the counter electrode are short-circuited before the voltage is applied therebetween. The short-circuiting eliminates measuring errors that may occur due to nonuniform dissolution of the reaction layer in a sample, and achieves highly reliable quantification of a specific compound.

Method of making and amperometric electrodes

Abstract: A method of making and an amperometric electrode are provided An electrode carbon ink is applied to a polymer substrate to form a working electrode The substrate carrying the working electrode is placed in a gas plasma cleaner, such as an oxygen or nitrogen plasma, to clean the working electrode A high radio frequency signal excites the gas plasma for a short exposure time in a range between 10 seconds and 30 seconds Then a reagent layer is deposited to the plasma treated working electrode

Amperometric cholesterol biosensor

Abstract: A sensor for the amperometric assay of cholesterol is provided which comprises a sensing electrode containing a first redox mediator and a reference electrode in simultaneous contact with a reagent strip containing a second redox mediator. The presence of the second redox mediator greatly amplifies the current flow produced by the presence of cholesterol and produces linear correlation of current flow with concentration over an extended range. The sensing electrode comprises a non-conductive support member having an electrically conductive layer containing the first redox mediator. The reference electrode is typically a Ag/AgCl electrode formed by coating an ink containing Ag/AgCl dispersed in a resin on a non-conductive base. The reagent strip is a porous or fibrous carrier, typically a paper, impregnated with a mixture containing the second redox mediator, cholesterol esterase, cholesterol oxidase, horseradish peroxidase, at least one surfactant and at least one stabilizer comprising an aqueous thickening agent. In one version of the sensor, the sensing electrode comprises a support member of polyester film coated with an electrically conductive graphite composition containing dimethylferrocene as the first redox mediator and the second redox mediator comprises 3,3',5,5'-tetramethylbenzidine. The sensor may be constructed in several physical forms. In one form, the sensing and reference electrodes are in the form of strips and the reagent strip is sandwiched between the electrically conductive layers of the electrodes with the reference electrode having a hole, through which the reagent strip is exposed, for the introduction of sample.

Electrochemical Detection of Trace Hydrogen Sulfide in Gaseous Samples by Porous Silver Electrodes Supported on Ion-Exchange Membranes (Solid Polymer Electrolytes)

Abstract: A highly sensitive and fast-responding electroanalytical sensor for the determination of hydrogen sulfide in gaseous atmospheres is described which eliminates oxygen interferences. It consists of a porous silver working electrode (facing the sample) supported on one face of an ion-exchange membrane, which serves as a solid polymer electrolyte. The other side of the membrane faces an internal electrolyte solution containing the counter and reference electrodes. The performance of this sensor has been tested for the electroanalysis of H 2 S by amperometric monitoring, cathodic stripping measurements, and flow injection analysis. In all cases, the device displays a high current sensitivity and a low background noise, so that quite low detection limits (45 ppb v/v, 0.07 ppb v/v, and 3.7×10 -13 mol in amperometric, cathodic stripping, and flow injection measurements, respectively) are estimated for a signal-to-noise ratio of 3. The responses are found to be characterized by both a good reproducibility and a linear dependence on the concentration of H 2 S over fairly wide ranges, as well as by a short response time (ca. 0.5 s to attain a 95% response). This fast response time arises from the lack of a gas-permeable membrane and direct gas contact to the triple interphase among the gaseous analyte, the porous working electrode, and the solid polymer electrolyte. The absence of any effect due to the most important potential interfering species and the possibility of adopting such a device for the direct detection of H 2 S in ambient air and for industrial hygiene measurements are discussed

Electrocatalytic glucose sensor

Abstract: An electrocatalytic sensor in catheter type of construction for determining glucose in body fluids, especially in the blood, having the following features: a tubular body made of bio-compatible material that is subdivided into three sections, a sleeve-shaped reference electrode arranged between the first and the second, or between the second and the third section of the tubular body, a sleeve-shaped working electrode arranged--correspondingly--between the second and the third, or between the first and the second section of the tubular body, said working electrode having a slit extending in longitudinal direction over the full length, a hydrophilic membrane stretched over the working electrode whose ends are guided through the slit into the interior of the electrode and which is held in the slit by a wedge made of bio-compatible material, a counter-electrode which seals the one end of the tubular body, and lead wires to the electrodes arranged within the tubular body which are brought to the outside through the other end of the tubular body.

Method of making sensor electrodes

Abstract: A method for fabricating high-resolution, biocompatible electrodes (11) is disclosed, allowing production of an electrochemical sensor which is capable of precise analyte concentration determination on a very small sample size. Electrically conducting material (3) is affixed to a first insulating substrate (4). A second insulating substrate (5) is then affixed to the electrically conducting material (3) and patterned using photolithography to define an electrode area (8). Alternatively, the electrically conducting material (3) may be screen printed directly onto a standard printed circuit board substrate (4) in the case of a counter or reference electrode. In either case, the substrate may be rigid or flexible. When the electrodes produced in accordance with the present invention are then used in an electrochemical sensor which includes a reagent, the small and highly-defined electrode areas (8, 9) permit highly-accurate electrochemical analyte measurements to be performed on very small sample sizes.

Throwaway type chemical sensor

Abstract: An enzyme electrode for a chemical sensor includes an electrode including a pair of working electrodes, a reference electrode and a counter-electrode. A first film is formed on one of the working electrodes, which includes a polyvinyl alcohol and a surface-active agent. A second film is formed on the other working electrode including polyvinyl alcohol, surface-active agent and enzyme. An overcoat film of high polymer electrolyer including a pH buffer is formed on the first and second films. The polymerization degree of the polyvinyl alcohol is from 300 to 3000 and the high polymer electrolyer may be alginic acid, polystyrene sulfonic acid or polyacrylic acid, and the pH buffer is a positive ion having a valence of 1.

The electrochemical behavior of methylene blue at a microcylinder carbon fiber electrode

Abstract: The electrochemical behavior of methylene blue (MB) at a carbon fiber microcylinder electrode, was studied by cyclic voltammetry. The charge transfer coefficient α of the electrode reaction with two-electron transfer is 0.5, and the number of H+ participating in the electrode process is 3 at pH 2.2–5.4, 2 at pH 5.4–6.0 and 1 at pH 6.0–10.7, respectively. The standard electron transfer rate constant ko′, and standard formal potential Eo′ of MB at various pH were determined by using the carbon fiber microcylinder electrode. The electrode reaction mechanism of methylene blue at various pH is proposed. The adsorbability of MB at the electrode is discussed and explored by cyclic voltammetry and chronocoulometric technique.

Application of potential-modulated UV-visible reflectance spectroscopy to electron transfer rate measurements for adsorbed species on electrode surfaces

Abstract: The electrode reaction rate constant of an electrochemically active species adsorbed on an electrode surface was determined by potential-modulated UV-visible reflectance spectroscopy. In-phase and 90° out-of-phase components of the electroreflectance signal at an electrode/adsorbed layer interface in response to a sinusoidal modulation of the electrode potential were formalized as a function of the modulation frequency. The heterogeneous rate constant k s (the overall rate constant) of the electrode reaction of a dye adsorbed on a glassy carbon electrode surface was determined by analyzing the frequency dependence of the electroreflectance signal. The electrode reaction rate constant k s were 4.9 x 10 3 s -1 for hemin and 5.4 x 10 2 s -1 for Nile Blue A.

Amperometric Detection of Peroxides with Poly(anilinomethylferrocene)-Modified Enzyme Electrodes

Abstract: An amperometric enzyme electrode employing covalently attached horseradish peroxidase to glassy carbon electrode and a ferrocene-modified polyaniline film deposited by the electrochemical polymerization of N-(ferrocenylmethyl)aniline monomer is reported. The electrode responded rapidly to micromolar concentrations of peroxides, in accordance with the following trend: hydrogen peroxide>cumene hydroperoxide>tert-butyl hydroperoxide. The effect of operational parameters, such as methods of enzyme immobilization, operating potential of the working electrode, pH, and effect of molecular oxygen, were explored for optimum analytical performance

A Continuous, Implantable Lactate Sensor

Abstract: An implantable sensor for continuous monitoring of lactate in the bloodstream or tissues has been made. The sensor includes a lactate electrode based on immobilized L-lactate oxidase coupled to a potentiostatic oxygen electrode and an often reference electrode to account for local oxygen. This design renders the response essentially independent of oxygen concentration. In vitro characterization demonstrated that the sensor can respond specifically to lactate over a broad concentration range. This response is stable for more than 1 week during continuous in vitro operation at body temperature. As an acute implant in the canine right atrium, the sensor produced a continuous recording of lactate that was in good agreement with conventional, discrete blood lactate assays

Electrochemical Pretreatment of Carbon Electrodes as a Function of Potential, pH, and Time

Abstract: The electrochemical pretreatment of carbon electrodes through the oxidation and reduction of the electrode surface is a widely used procedure to improve electrode response; however, there still remain many unanswered questions about the nature of the pretreatment process. The main variables of the pretreatment process are the oxidation and reduction potentials, the composition and pH of the electrolyte solution, and the length of time of oxidation and reduction. This study focuses on the effects of these variables on the primary redox reactions that are responsible for activation of the electrodes. In the first part of this study, an anodic process starting at +1.6 V (SCE) and a cathodic process with a peak potential of approximately -1.0 V were observed with a glassy carbon electrode in solutions of pH 12 or greater. These processes are similar to those reported for pretreatment in acidic and neutral solutions and are distinct from the previously reported anodic process in 1 M NaOH which occurs between +0.9 and +1.5 V and gives a cathodic process with a peak potential at +0.2 V. In the second part of this study, the pH dependence of the anodic and cathodic processes in the pH range from 2 to 12 was examined by changing the pH of the solution during the course of oxidizing and reducing a glassy carbon electrode surface tile keeping the electrode under potential control at all times. The results support the idea of the formation of different species on the electrode surface when anodization is done at different pH's. During the course of the study, the length of time of anodization also was found to have an effect on the observed reduction potentials

A method and a device for quantifying a substrate in a sample liquid using a biosensor

Abstract: A method and a device for quantifying a substrate in a sample liquid by use of a biosensor are provided. The biosensor can quantify the substrate by electrochemically measuring an amount of an electron acceptor that has been reduced by electrons generated in a reaction between the substrate in the sample liquid and an oxidoreductase. The biosensor includes: an electrically insulating substrate; an electrode system formed on the substrate including a working electrode, a counter electrode, and a third electrode used for detecting a liquid junction; and a reaction layer that is formed over at least the working electrode and the counter electrode of the electrode system and includes the oxidoreductase. The method includes the steps of: applying a voltage between the counter electrode and the third electrode; supplying the sample liquid to the reaction layer; detecting an electrical change between the counter electrode and the third electrode generated by the supply of the sample liquid to the reaction layer; applying a voltage to the working electrode after the detection using at least the third electrode as a reference; and measuring a current generated between the working electrode and the counter electrode.

Voltammetric method and apparatus

Abstract: During voltammetric analysis of liquids, the indicator electrode must be frequently changed in order to prevent memory effects and resultant changes to basic conditions during measurement. In order to be able to change the indicator electrodes simply, a plurality of indicator electrodes are arranged on a common carrier. For accommodation of the liquid (2) to be analysed, a vessel (1) is provided and the carrier (5) is mounted to move in relation to this vessel (1) in such a way that one of the indicator electrodes (6) can be selectively brought into the area intended for the liquid. The reference electrode (8) necessary for the measurement is arranged in the vessel (1) and likewise connected with the measuring device (20). With that, changing of the selected electrode (6) ensues by moving the carrier (5) relative to said vessel (1).

Active matrix type liquid crystal display device and its manufacture

Abstract: PROBLEM TO BE SOLVED: To remarkably expand the tolerance for aligning upper and lower substrates by enhancing the opening ratio in a liquid crystal display device driven by an electric field almost parallel with the surface of the substrate. SOLUTION: In this active matrix type liquid crystal display device, a display electrode 104, a reference electrode 105, a scanning signal line 102, a video signal line 103 and an active element are provided in each pixel area of surfaces of liquid crystal layer sides of transparent substrates disposed to face oppositely each other via a liquid crystal layer and light beams transmitting the liquid crystal layer are modulated by generating the electric field parallel with the transparent substrates in the liquid crystal layer by a voltage to be impressed between the display electrode 104 and the reference electrode 105. Then, the device has the reference electrode 105 adjacently arranged to the video signal line 103, has an insulated layer between the video signal line 103 and the adjacently arranged reference electrode 105 and also has a structure in which the video signal line 103 and the reference electrode 105 have a superposed part and a light shielding layer 202 is arranged only in the direction parallel with the scanning signal line 102 in the pixel display area.

Electrode modification with a poly(NiII-tetramethyldibenzotetraaza[14]annulene) film. Electrochemical behavior and redox catalysis in alkaline solutions. I

Abstract: The voltammetric behavior in alkaline solution of a nickel-based chemically modified electrode (Ni-CME) prepared by oxidative electropolymerization of a nickel–tetraazaannulene complex (NiIIL) was investigated. After electrochemical deposition of the (NiIIL)n film in dichloromethane on a conducting substrate, the modified electrode was continuously cycled in alkaline solution until a steady voltammetric profile was obtained. Although upon electrochemical treatment in basic solutions the nickel–nitrogen tetracoordination of the (NiIIL)n film is probably lost, the nickel species remain entrapped inside the polymeric skeleton and exhibit stable redox behavior resembling that of the nickel hydroxide electrode. This makes it possible to prepare very thin films of nickel-based modified electrodes. In cyclic voltammetry experiments the Ni-CME exhibits a pH dependence of the peak potentials typical of the α-Ni(OH)2/γ-NiOOH redox process, and a separation between anodic and cathodic peak potentials of 64mV at pH 13.2 and 10 mVs−1. The redox catalysis at Ni-CMEs of representative compounds that are not easily electrooxidized, such as choline, cadaverine, γ-amino butyric acid (GABA), benzyl alcohol, and glycine, is demonstrated. The good stability of these nickel-based modified electrodes makes them attractive in analytical applications.