Maximum Current Response Research Articles

Polyaniline-graphite composite film glucose oxidase electrode

A novel polyaniline-graphite composite film glucose oxidase (PGCF GOD) electrode was developed. The PGCF was synthesized by cyclic voltammetry method in 0.5 mol/L H2SO4 solution containing 1 g/L graphite powder and 0.2 mol/L aniline. The PGCF GOD electrode was prepared by doping GOD into the composite film. The morphology of the PGCF and the response property of the PGCF GOD electrode were investigated by scanning electron microscopy and electrochemical measurement, respectively. The results show that the PGCF has a porous and netty structure and the PGCF GOD electrode has excellent response property such as high sensitivity and short response time. Influences of pH value, temperature, glucose concentration and potential on the response current of the electrode were also discussed. The sensor has a maximum steady-state current density of 357.17 μA/cm2 and an apparent Michaelis-Menten constant of 16.57 mmol/L. The maximum current response of the enzyme electrode occurs under the condition of pH 5.5, 0.8 V and 65 °C.

Development of a glucose-6-phosphate biosensor based on coimmobilized p-hydroxybenzoate hydroxylase and glucose-6-phosphate dehydrogenase

This work reports the development of an amperometric glucose-6-phosphate biosensor by coimmobilizing p-hydroxybenzoate hydroxylase (HBH) and glucose-6-phosphate dehydrogenase (G6PDH) on a screen-printed electrode. The principle of the determination scheme is as follows: G6PDH catalyzes the specific dehydrogenation of glucose-6-phosphate by consuming NADP +. The product, NADPH, initiates the irreversible the hydroxylation of p-hydroxybenzoate by HBH in the presence of oxygen to produce 3,4-dihydroxybenzoate, which results in a detectable signal due to its oxidation at the working electrode. The sensor shows a broad linear detection range between 2 μM and 1000 μM with a low detection limit of 1.2 μM. Also, it has a fast measuring time which can achieve 95% of the maximum current response in 20 s after the addition of a given concentration of glucose-6-phosphate with a short recovery time (2 min).

Electrochemical Investigation of Acetaminophen with a Carbon Nano-tube Composite Film Electrode

Electrochemical behaviors of acetaminophen at a muti-wall carbon nano-tube composite film modified glassy carbon electrode were investigated by cyclic voltammetry, linear sweep voltammetry and chronocoulometry. Compared with that obtained at the unmodified electrode, the peak currents were enhanced significantly, and the oxidation peak shifted towards more negative potential with the reduction peak shifted positively. The peak-to-peak separation turned narrow, and suggested that the reversibility was improved greatly. Experimental parameters, such as scan rate, pH and accumulation conditions were optimized. It was found that a maximum current response can be obtained at pH = 5.0 after accumulation at -0.50 V for 80 s. The oxidation peak current was found to be linearly related to acetaminophen concentration over the range of <TEX>$5.0{\times}10^{-7}\;\sim\;1.0{\times}10^{-4}$</TEX> mol <TEX>$L^{-1}$</TEX> with a detection limit of <TEX>$5.0{\times}10^{-8} $</TEX>mol <TEX>$L^{-1}$</TEX>. A convenient and sensitive electrochemical method was developed for the determination of acetaminophen in a commercial paracetamol oral solution. Its practical application demonstrated that it has good selectivity and high sensitivity.

Incorporation of the β3 Subunit Has a Dominant-Negative Effect on the Function of Recombinant Central-Type Neuronal Nicotinic Receptors

The beta3 neuronal nicotinic subunit is localized in dopaminergic areas of the central nervous system, in which many other neuronal nicotinic subunits are expressed. So far, beta3 has only been shown to form functional receptors when expressed together with the alpha3 and beta4 subunits. We have systematically tested in Xenopus laevis oocytes the effects of coexpressing human beta3 with every pairwise functional combination of neuronal nicotinic subunits likely to be relevant to the central nervous system. Expression of alpha7 homomers or alpha/beta pairs (alpha2, alpha3, alpha4, or alpha6 together with beta2 or beta4) produced robust nicotinic currents for all combinations, save alpha6beta2 and alpha6beta4. Coexpression of wild-type beta3 led to a nearly complete loss of function (measured as maximum current response to acetylcholine) for alpha7 and for all functional alpha/beta pairs except for alpha3beta4. This effect was also seen in hippocampal neurons in culture, which lost their robust alpha7-like responses when transfected with beta3. The level of surface expression of nicotinic binding sites (alpha3beta4, alpha4beta2, and alpha7) in tsA201 cells was only marginally affected by beta3 expression. Furthermore, the dominant-negative effect of beta3 was abolished by a valine-serine mutation in the 9' position of the second transmembrane domain of beta3, a mutation believed to facilitate channel gating. Our results show that incorporation of beta3 into neuronal nicotinic receptors other than alpha3beta4 has a powerful dominant-negative effect, probably due to impairment in gating. This raises the possibility of a novel regulatory role for the beta3 subunit on neuronal nicotinic signaling in the central nervous system.

Glucose oxidase electrodes of a terpolymer poly(aniline-co- o-anisidine-co- o-toluidine) as biosensors

A simple technique is described for constructing a glucose sensor by the entrapment of glucose oxidase (GOD) in a poly (aniline-co- o-anisidine-co- o-toluidine) [P(A-co- o-A-co- o-T)] thin films, which were electrochemically deposited on a platinum plate in phosphate and acetate buffer. The maximum current response was observed for the said electrodes at pH 5.5 and potential 0.60 V (versus Ag/AgCl). The phosphate buffer gives high stability and fast response as compared to acetate buffer in amperometric measurements.

Utilisation of polypyrrole modified electrode for the determination of pesticides

Cyclic voltammetric studies of isoproturon and carbendazim using polypyrrole modified glassy carbon electrode were carried out. The electrode and reaction conditions, which yielded maximum current signal, were selected for the development of stripping voltammetric procedure for the determination of the pesticides. The oxidation peak around 1.3 V obtained for isoproturon and carbendazim while employing polypyrrole modified electrode showed maximum current response. This peak was chosen for stripping analysis using square wave mode. The experimental parameters were optimized and the calibration plot was obtained. The LOD was 0.5 ng mL−1 for isoproturon and 5 ng mL−1 for carbendazim. The relative standard deviation for 5 identical measurements was 2.81% and 3.33% for isoproturon and carbendazim respectively. The applicability of the method was verified by determining the pesticides in spiked soil and water samples.

Glucose oxidase electrodes of polyaniline, poly(o‐toluidine) and their copolymer as a biosensor: a comparative study

AbstractA simple technique is described for constructing a glucose sensor by the entrapment of glucose oxidase (GOD) in a polyaniline (PA), poly(o‐toluidine) (POT) and their copolymer poly(aniline‐co‐o‐toluidine) (PA‐co‐POT) thin films, which were electrochemically deposited on a platinum plate in phosphate and acetate buffer. The maximum current response was observed for PA, POT, and PA‐co‐POT GOD electrodes at pH 5.5 and potential 0.60 V (v. Ag/AgCl). The phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements. PA GOD electrode shows the fastest response followed by PA‐co‐POT and POT GOD electrodes. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Glucose oxidase electrodes of poly(o-anisidine), poly(o-toluidine), and their copolymer as biosensors: A comparative study

Thin films of poly(o-anisidine) (POA), poly(o-toluidine) (POT), and their copolymer poly(o-anisidine-co-o-toluidine) (POA-co-POT) were electropolymerized in solutions containing 0.1M monomer(s) and 1M H2SO4 as an electrolyte through the application of a sequential linear potential scanning rate of 50 mV/s between −0.2 and 1.0 V versus an Ag/AgCl electrode on a platinum electrode. A simple technique was used to construct glucose sensors through the entrapment of glucose oxidase (GOD) in thin films of POA, POT, and their copolymer POA-co-POT, which were electrochemically deposited on a platinum plate in phosphate and acetate buffers. The maximum current response was observed for POA, POT, and POA-co-POT GOD electrodes at pH 5.5 and at a potential of 0.60 V (vs Ag/AgCl). The phosphate buffer yielded a fast response in comparison with the acetate buffer in amperometric measurements. The POT GOD electrode showed a fast response and was followed by POA-co-POT and POA GOD electrodes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1877–1884, 2004

Electrochemical determination of methyl parathion using a modified electrode

Electrochemical studies of pesticides using various electrode systems attain prominence in recent years because of their application in trace determinations. Cyclic voltammetric studies of methyl parathion on a glassy carbon electrode at various pH in 50% aqueous ethanol medium were carried out. Influence of pH led to the selection of pH 1.0 as the best pH for the electroanalysis of methyl parathion. The number of electrons transferred was determined using controlled potential coulometry. On the basis of the results a probable reduction mechanism was proposed. Cyclic voltammetric studies of methyl parathion using polypyrrole deposited and sodium montmorillonite clay modified electrodes in the presence of cetyl trimethyl ammonium bromide were carried out. The clay-modified electrode and the reduction peak around −0.2 V were selected for stripping analysis owing to their maximum current response. The experimental parameters were optimized using the differential pulse stripping mode. A calibration plot was made. The determination limit and standard deviations were arrived. The applicability of the method was also verified in a sample soil analysis.

Uricase-catalyzed oxidation of uric acid using an artificial electron acceptor and fabrication of amperometric uric acid sensors with use of a redox ladder polymer.

Electrochemical oxidation of uric acid catalyzed by uricase (uric acid oxidase, UOx; EC 1.7.3.3) was studied using several redox compounds including 5-methylphenazinium (MP) and 1-methoxy-5-methylphenazinium (MMP) as electron acceptors for UOx, which does not contain any redox cofactor. It was found that MP and MMP were useful to mediate electrons from UOx to an electrode in the enzymatic oxidation of uric acid. A novel redox polymer, poly(N-methyl-o-phenylenediamine)(poly-MPD), containing the MP units was also found to possess the mediation ability for UOx, and poly-MPD was immobilized together with UOx onto an electrode substrate covered with a self-assembled monolayer of 2-aminoethanethiolate with use of glutaraldehyde as a binding agent. The resulting electrode (poly-MPD/UOx/Au) exhibited amperometric responses to uric acid with very fast response of approximately 30 s, allowing reagentless amperometric determination in a concentration range covering that in the blood of a healthy human being. Kinetic parameters of the apparent Michaelis constant and the maximum current response obtained at the poly-MPD/UOx/Au suggested that electrochemical oxidation of uric acid was controlled by diffusion of uric acid into the enzyme film and that the redox polymer worked well in mediating between active sites of UOx molecules and the electrode substrate.

Electrical and pyroelectric properties of lithium tantalate thin films

Thin films of lithium tantalate have been deposited by RF sputtering on SiO2-coated silicon substrates. Either a planar structure with RuO2 interdigitated top electrodes or sandwich structure including a sputter-deposited RuO2 buried layer have been used. The dielectric properties and the ac resistivity of the tantalate films have been investigated as a function of frequency and of temperature. At room temperature and 1 kHz the dielectric constant is 40 and the resistivity is 2X108 Ωcm for a RuO2/tantalate/RuO2 sandwich structure. The resistivity is typically 100 times larger when measured on a planar structure. The ferroelectric and pyroelectric properties of either unpoled or poled lithium tantalate thin films have also been investigated. At room temperature, the maximum pyroelectric current and voitage response are 11μA/W and 19 V/W, respectively. In comparison with the planar structures, the sandwich structures exhibit a degraded response. This is attributed to a reaction of the tantalate layer with the RuO2 buried layer during the crystallization processing step.

Electrochemical quartz crystal microbalance study of the electrochemical behavior of riboflavin at gold electrodes

AbstractThe electrochemical and adsorption behaviors of riboflavin (RF) at gold electrodes has been studied by using an electrochemical quartz crystal microbalance (EQCM). Useful information is obtained not only about electrochemical behavior but also about mass changes on the electrode surface. The electrochemical properties and frequency shifts were investigated in RF solutions at different pH values, concentrations and scan rates. Reversible voltammograms were observed for pH ⩽ 9.71. There was no electrochemical reaction for pH &gt; 9.71. The maximum current response was obtained at about pH 8. The current response was proportional to the square root of scan rates when the concentration of RF was lower than 1.0 × 10−4 molL−1 (pH 6.92). On the contrary, at concentrations higher than 1.0 × 10−4 mol L−1 (pH 6.92), it was proportional to the scan rates.

Amino oxidase amperometric biosensor for polyamines

An improved amino oxidase enzyme electrode has been constructed and applied to the determination of the amount of polyamines present in real samples. The electrode is based on the amperometric detection of H 2O 2 produced in the enzymatic oxidation of polyamines by amino oxidase. Amino oxidase from soybean seedlings, characterized by an extremely high activity for cadaverine and putrescine, was used. The enzyme was immobilized in an agarose matrix in the presence of glutaraldehyde and bovine serum albumin on the surface of a Pt electrode. Cadaverine, in concentrations between 0.5 and 500 μM, can be quantitatively determined by use of the amino oxidase electrode, the linear calibration range being 0.5–10 μM. The lower detection limit was 0.2 μM and the response time was 15 to 60 s. Putrescine showed similar behaviour. The maximum current response for cadaverine was 5.1 μA/cm 2, with an apparent Michaelis—Menten constant ( K m′) of 0.175 mM. The sensor response was stable for more than 32 hours of continuous operation at room temperature and, in the presence of fish or meat homogenates, no change in the signal-to-noise ratio was observed. The long-term stability, pH and temperature response of the biosensor has also been studied.

Bioelectrochemical responses of the polyaniline glucose oxidase electrode

A simple technique is described for constructing a glucose sensor by the entrapment of glucose oxidase in a polyaniline film which was electrochemically deposited on a platinum foil (4 mm × 4 mm). The new glucose sensor has a fast response time (20–40 s) with high storage and operational stability ( > 60 days). The kinetic behavior of enzymes immobilized in polyaniline film is quite similar to that of solublized enzyme. The maximum current response for the enzyme electrode is at pH 5.6, 0.60 V (vs. SCE) and 40° C.

Amino oxidase amperometric biosensor for polyamines

An improved amino oxidase enzyme electrode has been constructed and applied to the determination of the amount of polyamines present in real samples. The electrode is based on the amperometric detection of H 2O 2 produced in the enzymatic oxidation of polyamines by amino oxidase. Amino oxidase from soybean seedlings, characterized by an extremely high activity for cadaverine and putrescine, was used. The enzyme was immobilized in an agarose matrix in the presence of glutaraldehyde and bovine serum albumin on the surface of a Pt electrode. Cadaverine, in concentrations between 0.5 and 500 μM, can be quantitatively determined by use of the amino oxidase electrode, the linear calibration range being 0.5–10 μM. The lower detection limit was 0.2 μM and the response time was 15 to 60 s. Putrescine showed similar behaviour. The maximum current response for cadaverine was 5.1 μA/cm 2, with an apparent Michaelis-Menten constant ( K m′) of 0.175 mM. The sensor response was stable for more than 32 hours of continuous operation at room temperature and, in the presence of fish or meat homogenates, no change in the signal-to-noise ratio was observed. The long-term stability, pH and temperature response of the biosensor has also been studied.

Effects of low temperature on the positive dynamic current of cardiac Purkinje fibres.

1. The effects of low temperature on the positive dynamic current (mainly Cl(-) current) of sheep cardiac Purkinje fibres were studied using the ;voltage clamp' technique.2. Cooling of Purkinje fibres from 37 degrees C to room temperature (25 degrees C) slowed the time course of the current and decreased its peak amplitude. The Q(10) of the decay of the current was 2.67 over 25-37 degrees C. Removal of inactivation was also delayed and the Q(10) of the rate constant was 2.62 over 30-37 degrees C.3. The decreased peak amplitude of the current on cooling could not be restored by pre-step hyperpolarization. Thus the curve for the steady-state inactivation was simply depressed downward. The Q(10) of the maximum current response was 3.05 over 25-37 degrees C.4. During deep hypothermia (less than 10 degrees C), no Cl(-) current was demonstrated by depolarization up to + 60 mV.5. The high sensitivity to temperature suggests that the current contributes significantly to the prolongation of action potentials during low temperature, but its quantitative role cannot be evaluated without simultaneous evaluation of other plateau currents.