Showing papers on "Amperometry published in 2000"
TL;DR: The pH-dependent redox potential of the PQQ catalyst allows tuning of the detection potential to enhance the selectivity for thiols over these potential electroactive interferences.
Abstract: A modified electrode sensor for the detection of thiols is described. The sensor was constructed by incorporation of the coenzyme pyrroloquinoline quinone (PQQ) into a polypyrrole (PPy) film on a glassy carbon electrode substrate by the electropolymerization of pyrrole in the presence of PQQ. The electrochemical properties of entrapped PQQ in the PPy film were influenced by the applied potential during electropolymerization and by film thickness, both of which were optimized to yield a stable and reproducible response for entrapped PQQ. The PQQ/PPy sensor was utilized for the amperometric detection of cysteine, homocysteine, penicillamine, N-acetylcysteine, and glutathione. The response for each thiol in pH 8.42 borate buffer was found to be linear with detection limits (S/N = 3) ranging from 13.2 μM for glutathione to 63.7 nM for cysteine with sensitivities of 0.023 nA/μM and 4.71 nA/μM, respectively. The response and detection limits were found to be sensitive to the nature of the thiol and the solution...
215 citations
TL;DR: In this article, the electrochemical oxidation of N,N-dimethylphenylenediamine at glassy carbon electrodes in aqueous solution in the pH range 3-6 is shown to lead to currents which are considerably amplified in the presence of dissolved hydrogen sulfide.
Abstract: The electrochemical oxidation of N,N-dimethylphenylenediamine at glassy carbon electrodes in aqueous solution in the pH range 3-6 is shown to lead to currents which are considerably amplified in the presence of dissolved hydrogen sulfide. The mechanism of the electrode process is investigated and the reaction is shown to provide an attractive basis for the amperometric sensing of sulfide with an accessible range of ca. 3 to 150 muM (0.1 to 4.8 ppm).
178 citations
TL;DR: The potential of the described biosensor was demonstrated by the simultaneous determination of lactate and glucose in untreated tomato juice samples; results were in good agreement with those of a reference method.
172 citations
TL;DR: An amperometric tyrosinase enzyme electrode for the determination of phenols was developed by a simple and effective immobilization method using sol-gel techniques and maintained 73% of its original activity after intermittent use for three weeks when storing in a dry state at 4 degrees C.
168 citations
TL;DR: The properties of glucose sensors fabricated by immobilization of glucose oxidase in a layer of electrochemically deposited polyaniline were investigated and the influence of ascorbic acid and acetaminophen was completely eliminated due to impermeability of polyAniline to these substances.
161 citations
TL;DR: A hydrogen peroxide biosensor was fabricated by coating a sol-gel-peroxidase layer onto a Nafion-methylene green modified electrode, and the sensor achieved 95% of the steady-state current within 20 s.
150 citations
TL;DR: In this paper, a peroxidase biosensor was fabricated by simply dropping sor-gel-peroxide mixture onto glassy carbon electrode surface, and the response time was about 10 s; the linear range was up to 3.4 mM with a detection limit of 5 x 10(-7) M. The sensor exhibited high sensitivity (15 mu A mM(-1)) and good long-term stability.
125 citations
TL;DR: In this paper, two nitric oxide (NO) microsensors using two combinations of nickel tetrasulfonated phthalocyanine (NiTSPc), o-phenylenediamine (o-PD) and Nafion® based layers to modify the surface of 8 μm diameter carbon fiber electrodes.
120 citations
TL;DR: In order to test the possibility of using the devices in the field, chronoamperometry was also used to determine ethanol in the same beer samples and the precision and recovery data indicated that the biosensor should give reliable results under the conditions described.
110 citations
TL;DR: In this article, conductive boron-doped diamond thin film electrodes were examined for the electroanalysis of three sulfa drugs, sulfadiazine, sulfamerazine and sulfamethazine.
105 citations
TL;DR: The electrostatic assembly of the electrochemical interface and the catalytic layers resulted in integrated biochemical systems in which mass transfer diffusion and heterogeneous catalytic and electron transfer steps are efficiently coupled and can be easily manipulated.
TL;DR: Carbon paste electrodes modified with the oxidation products of NAD+ show excellent electrocatalytic activity toward NADH oxidation, reducing its overpotential by about 400 mV, and can be used as amperometric transducers in the design of biosensors based on coupled dehydrogenase enzymes.
Abstract: The electrochemical oxidation of the adenine moiety in NAD+ and other adenine nucleotides at carbon paste electrodes gives rise to redox-active products which strongly adsorb on the electrode surface. Carbon paste electrodes modified with the oxidation products of NAD+ show excellent electrocatalytic activity toward NADH oxidation, reducing its overpotential by about 400 mV. The rate constant for the catalytic oxidation of NADH, determined by rotating disk electrode measurements and extrapolation to zero concentration of NADH, was found to be 2.5 x 10(5) M-1 s-1. The catalytic oxidation current allows the amperometric detection of NADH at an applied potential of +50 mV (Ag/AgCl) with a detection limit of 4.0 x 10(-7) M and linear response up to 1.0 x 10(-5) M NADH. These modified electrodes can be used as amperometric transducers in the design of biosensors based on coupled dehydrogenase enzymes and, in fact, we have designed an amperometric biosensor for glycerol based on the glycerol dehydrogenase (GlDH) system. The enzyme GlDH and its cofactor NAD+ were co-immobilized in a carbon paste electrode using an electropolymerized layer of nonconducting poly(o-phenylenediamine) (PPD). After partial oxidation of the immobilized NAD+, the modified electrode allows the amperometric detection of the NADH enzymatically obtained at applied potential above 0 V (Ag/AgCl). The resulting biosensor shows a fast and linear response to glycerol within the concentration range of 1.0 x 10(-6)-1.0 x 10(-4) M with a detection limit of 4.3 x 10(-7) M. The amperometric response remains stable for at least 3 days. The biosensor was applied to the determination of glycerol in a plant-extract syrup, with results in good agreement with those for the standard spectrophotometric method.
TL;DR: A disposable, amperometric micro flow injection electrochemical biosensor that can be applied to the identification and quantification of highly toxic organophosphorus (OP) compounds in the environment, on the spot and in a short time is described.
TL;DR: The proposed NC/PbO2 strip sensor is shown to be virtually insusceptible to interfering species such as acetaminophen and ascorbic and uric acids and to exhibit good performance, in terms of the sensor-to-sensor reproducibility, the sensitivity, and the linearity.
Abstract: A new type of disposable amperometric sensor is devised by screen printing thick-film electrodes directly on a porous nitrocellulose (NC) strip. The chromatographic NC strip is then utilized to introduce various sample pretreatment layers. As a preliminary application, a glucose biosensor based on hydrogen peroxide detection is constructed by immobilizing glucose oxidase (GOx) on the NC electrode strip and by formulating a strong oxidation layer (i.e., PbO2) at the sample loading area, placed below the GOx reaction band. The screen-printed PbO2 paste serves as a sample pretreatment layer that removes interference by its strong oxidizing ability. Samples applied are carried chromatographically, via the PbO2 paste, to the GOx layer, and glucose is catalyzed to liberate hydrogen peroxide, which is then detected at the electrode surface. The proposed NC/PbO2 strip sensor is shown to be virtually insusceptible to interfering species such as acetaminophen and ascorbic and uric acids and to exhibit good performance, in terms of the sensor-to-sensor reproducibility (standard deviation, +/-0.026 - +/-0.086 microA), the sensitivity (slope, -0.183 microA/mM), and the linearity (correlation coefficient, 0.994 in the range of 0-10 mM).
TL;DR: In this article, an improvement of the operational stability of amperometric sensors based on Prussian Blue (PB) modified glassy carbon electrodes is presented, and the long term performance of the sensors was evaluated by injection of hydrogen peroxide (5 µM in potassium buffer) solutions in a flow-injection system during a period of 5 ‐10 h.
Abstract: Improvement of the operational stability of amperometric sensors based on Prussian Blue (PB) modified glassy carbon electrodes is presented. The long term performance of the sensors was evaluated by injection of hydrogen peroxide (5 µM in potassium buffer) solutions in a flow-injection system during a period of 5 ‐10 h. The following parameters were investigated and correlated with the performance of the sensor: the times for electrodeposition and electrochemical activation, temperature, storage time, pH, composition of the buffer solution and of volume sample injected. These analytical characteristics of the modified electrode can be emphasized: initial sensitivity of 0.3 A cm ‐2 M ‐1 , detection limit of ca. 0.5 µM, precise results (r.s.d.< 1.5%) and possibility to carry out around 50 samples (50 µL) per hour.
TL;DR: An amperometric enzyme biosensor for the direct measurement of parathion was developed and it was found that the current signal was linearly related to the parathions concentration, and the detection limit was less than 1 ng/mL.
Abstract: An amperometric enzyme biosensor for the direct measurement of parathion was developed. The biosensor is based on parathion hydrolase from Pseudomonas sp. isolated from contaminated soil. The enzyme, which was immobilized on a carbon electrode, catalyzes the hydrolysis of parathion to form p-nitrophenol, which was detected by its anodic oxidation. The enzymatic and electrochemical reactions were examined and optimized. Screen-printed electrodes and a microflow injection system provide the means to significantly reduce the volume of the detected samples. Pulsed techniques further increased the sensitivity of the measurement. The current signal was linearly related to the parathion concentration, and the detection limit was less than 1 ng/mL. The biosensor is rapid as well and can be used outdoors and indoors by a nonqualified person.
TL;DR: The optimized redox hydrogel-based biosensors were evaluated in terms of stability and selectivity, and were used for the determination of total amine content in fish samples kept for 10 days in different conditions.
Abstract: This work presents the design and optimization of amperometric biosensors for the determination of biogenic amines (e.g., histamine, putrescine, cadaverine, tyramine, cystamine, agmatine, spermidine), commonly present in food products, and their application for monitoring of freshness in fish samples. The biosensors were used as the working electrodes of a three-electrode electrochemical cell of wall-jet type, operated at −50 mV vs Ag/AgCl, in a flow injection system. Two different bienzyme electrode designs were considered, one based on the two enzymes [a newly isolated and purified amine oxidase (AO) and horseradish peroxidase (HRP)] simply adsorbed onto graphite electrodes, and one when they were cross-linked to an Os-based redox polymer. The redox hydrogel-based biosensors showed better biosensors characteristics, i.e., sensitivity of 0.194 A M-1 cm-2 for putrescine and 0.073 A M-1 cm-2 for histamine, and detection limits (calculated as three times the signal-to-noise ratio) of 0.17 μM for putrescine ...
TL;DR: Preliminary experiments with water samples collected in areas where pollution with anilines may be expected showed that the capillary electrophoresis method is highly specific, with few interferences showing up in the electropherograms.
TL;DR: In this article, a polypyrrole (PPY) or poly( o -phenylenediamine) (POPD)-modified electrode was used to detect hydrogen peroxide formed during the enzymatic reaction.
Abstract: Glucose oxidase (GOD) was immobilized in either a layer of polypyrrole (PPY) or poly( o -phenylenediamine) (POPD) by electropolymerization of the corresponding monomer on platinum electrode modified by Prussian Blue (PB). The resulting biosensors showed amperometric responses to glucose due to the detection of hydrogen peroxide formed during the enzymatic reaction and could be operated by both in an anodic manner at a potential of 0.6 V vs. Ag/AgCl, or a cathodic manner at 0.0 or 0.2 V. In the case of POPD-modified electrode, the influence of interferents like ascorbate or acetaminophen could be reduced drastically.
TL;DR: The immobilized MADH on the electrode exhibited Michaelis-Menten behavior similar to that of the free enzyme in solution with a Km value of 1.3 mM, which could be used to reliably detect histamine over a concentration range from approximately 25 microM to 4 mM.
Abstract: Methylamine dehydrogenase (MADH) has been immobilized in a polypyrrole (PPy) film on an electrode surface and used as an amine sensor for the determination of primary amines. Its response to histamine has been characterized in detail. The PPy film containing MADH was formed electrochemically on a gold minielectrode (1-mm diameter) in the presence of ferricyanide. The film was then coated with Nafion. This enzyme electrode did not require any additional cofactors and was not sensitive to oxygen. It exhibited a maximum response current to histamine at applied potentials of 0.24−0.33 V and at pH 7.5−8.5. This MADH−PPy sensor exhibited a response time of less than 3 s. The immobilized MADH on the electrode exhibited Michaelis−Menten behavior similar to that of the free enzyme in solution with a Km value of 1.3 mM. This sensor could be used to reliably detect histamine over a concentration range from approximately 25 μM to 4 mM. This is the first example of a biosensor that uses an immobilized enzyme that poss...
TL;DR: A miniaturized glucose biosensor in which glucose oxidase (GOD) and poly(p-phenylenediamine) (poly-PPD) were coimmobilized at the surface of a platinum microdisk electrode was developed and used successfully for amperometric determination of glucose.
TL;DR: In this article, a CuPtCl 6 /glassy carbon chemically modified electrode was used as an amperometric sensor for xanthine and hypoxanthine with a detection limit of 1×10 −7 ǫM.
TL;DR: In this paper, layer-by-layer assembled multilayer films were obtained on the surface of quartz slides and gold electrode by alternating deposition of negatively charged horseradish peroxidase (HRP) and quaternized poly(4-vinylpyridine) complexed of (Os(bpy) 2 Cl) +/2+ (PVP-Os).
TL;DR: The amperometric detection employing a carbon disk electrode as a working electrode to determine the thiol compounds, including cysteine, glutathione, 6-thiopurine, and methimazole following their separation by capillary zone electrophoresis (CZE) is described in this paper.
TL;DR: In this article, a miniaturized analytical system for separating and detecting toxic hydrazine compounds, based on the coupling of micromachined capillary electrophoresis (CE) chips with removable thick-film amperometric detectors is described.
Abstract: A miniaturized analytical system for separating and detecting toxic hydrazine compounds, based on the coupling of micromachined capillary electrophoresis (CE) chips with removable thick-film amperometric detectors is described. The study also represents the first example of using a chemically modified electrode for microchip CE applications. The microsystem with the electrocatalytic palladium-deposited detector offers a rapid (2 min) low-potential (+0.5 V vs. Ag/AgCl) simultaneous detection of hydrazine, methylhydrazine, dimethylhydrazine, and phenylhydrazine. Such compounds could be detected down to the 1.5×10–6 M level, with linearity over the 2×10–5 M–2×10–4 M range examined. While the concept of miniaturized separation/detection systems is presented within the framework of hydrazine compounds, such devices should be attractive for field monitoring of other classes of toxic contaminants. The design of the microsystem permits rapid replacement of the detector strip and a convenient surface modification (in a separate, optimal cell). The development of fast-responding miniaturized systems, with negligible waste production, holds particular promise for meeting the requirements of field ‘Green Analytical Chemistry’.
TL;DR: In this article, an amperometric biosensor for sulfite has been developed, which was tested on samples of unspiked and spiked estuarine, river and tap waters, and it was found that the initial response was retained for at least 45 days.
Abstract: An amperometric biosensor for sulfite has been developed. The enzyme sulfite oxidase (SOD) and electron acceptor cytochrome c are mixed into the carbon ink that is deposited onto the working electrode of a screen-printed strip. A silver–silver chloride electrode is printed alongside the working electrode and serves as reference/counter electrode. The electrochemical behaviour of the biosensor surface in plain buffer has been investigated by cyclic voltammetry. In the voltage range −0.5 to +0.5 V, a well-defined anodic peak appeared at −0.15 V and a less well-defined anodic peak at about +0.2 V. In the presence of SO32−, the cyclic voltammogram obtained with the biosensor exhibited an increase in magnitude of the more positive peak; this was considered to result from the electrocatalytic oxidation of SO32− involving SOD and the heme (Fe2+/Fe3+) centre of cytochrome c. Amperometry in stirred solution was used to construct a hydrodynamic voltammogram for SO32− using the biosensor; this exhibited a single wave with a plateau beginning at +0.3 V. This wave corresponds to the electrocatalytic response observed by cyclic voltammetry. The pH and concentration of buffer components have been optimised for the determination of SO32− by amperometry in stirred solution. Using these conditions, a detection limit of 4 ppm was obtained. The stability of the biosensors was examined after storage in 0.05 M phosphate buffer pH 7.4 at 4°C; it was found that the initial response was retained for at least 45 days. The proposed biosensors were evaluated on samples of unspiked and spiked estuarine, river and tap waters. The recovery and precision data indicated that the devices could be expected to give reliable data in these waters.
TL;DR: Improved protocols were applied for a dynamic analysis of intracellular metabolites in Saccharomyces cerevisiae in response to a glucose pulse.
TL;DR: In continuous-flow amperometric experiments, the Os-gel-HRP/XOD/GCEs were quick to stabilize background current and show linear and sensitive response towards hypoxanthine in a concentration range from 0.5 to 80 μM with a detection limit of 0.2 μM (S/N=3).
TL;DR: In this paper, a modified carbon paste electrode was prepared with an aqueous insoluble redox mediator, ruthenium(III) diphenyldithiocarbamate.