H. Durliat

Use of polypyrrole film containing Fe(CN)63− as pseudo-reference electrode: application for amperometric biosensors

Abstract A polypyrrole-containing Fe(CN) 6 3− modified electrode was prepared by anodic electropolymerization at 0.8 V versus SCE of an aqueous solution containing only pyrrole and K 4 Fe(CN) 6 . The concentration of electroactive Fe(CN) 6 3− ions in the polymer was found to be 30 times higher than that of the ferrocyanide ions in the electrolytic solution. Furthermore the Fe(CN) 6 3− /Fe(CN) 6 4− redox system exhibited a high degree of reversibility. These properties made it possible to use the modified electrode as a pseudo-reference in a weakly polarized two-electrode device for the design of amperometric biosensors involving NAD-dependent dehydrogenases. The assay of d -lactic acid was taken as an example using d -lactate dehydrogenase and diaphorase. The sensitivity of the biosensor, i.e. 20 μA mM −1 cm −2 , was similar to that in previous studies. The modified electrode exhibited a relatively stable potential for currents lower than 100 nA and had an operating life of more than 2 months.

Simultaneous use of dehydrogenases and hexacyanoferrate(III) ion in electrochemical biosensors for l-lactate, d-lactate and l-glutamate ions

The l-lactate, d-lactate and l-glutamate selective amperometric electrochemical biosensors presented were designed so that the last electron-transfer step is hexacyanoferrate(II) oxidation on a platinum electrode. A single enzyme sensor is described for l-lactate assay, where a lactate dehydrogenase extracted from yeast, immobilized on a membrane, will accept potassium hexacyanoferrate(III) as an electronic relay. It is possible to determine l- and d-lactate using bienzymatic sensors with NAD+-dependent dehydrogenases immobilized or in solution. In such a case, a second enzymatic reaction [a diaphorase-catalysed NADH oxidation by hexacyanoferrate(III)] enabled the detection limit to be lowered. For the l-glutamate-specific sensor, the two preceding enzymes were associated with a third one that catalyses a substrate product transformation, making it possible to exploit the enzyme amplification phenomenon. In each instance, the required presence of hexacyanoferrate(III) in the samples to be assayed makes it possible to suggest a simple apparatus with two slightly polarized electrodes. The advantages of enzyme fixation in increasing sensor stability and lowering the detection limit are also highlighted.

Bienzyme amperometric lactate-specific electrode

Abstract The electrode, based on a lactate dehydrogenase and a diaphorase, permits the assay of l -lactate in the concentration range 0.2–8 mM with a response time of about 40 s. Both the enzymes are commercially available. The amperometric detection of hexacyanoferrate(II) at a platinum electrode is done at 0.3 V (vs. SCE) instead of 0.8 V as in the detection of NADH, improving the selectivity of the sensor.

Amperometric and Potentiometric Determination of Catechin as Model of Polyphenols in Wines

Abstract Cyclic voltammetry, steady state voltammetry, differential pulse voltammetry are used in order to characterize the electrochemical behavior of catechin on glassy carbon electrodes. Despite adsorption phenomena, it is possible to assay catechin in the concentration range comprised between 1 × 10−5 and 6 × 10−4 mol dm−3. The surface modification by iodide ions and the electrochemical generation of iodine enable to obtain catalytic current and to oxidize catechin by the exchange of one or two electrons. Potentiometric titration of catechin by iodine with two electrodes polarized by a small current intensity is possible but depends strongly on the rate of titrant introduction.

Contribution of a zero current potential measurement to wine making

The in situ measurement of the zero current potential of a platinum electrode in a fermentation broth gives information about the presence or the absence of dissolved O2 but does not allow to know its concentration. This potential is submitted to an abrupt variation at every stage of the wine making. This parameter indicates to wine maker the different moments of intervention.

Electrochemical characterization of the {(TPA)Mn(III)O2Mn(IV)(TPA)}2(SO4)3 complex

Abstract Thin-layer electrochemistry and steady-state current-potential curves were used to study the electrochemical behavior of the {(TPA)Mn(III)O2Mn(IV)(TPA)}2(SO4)3 complex in an aqueous medium and forecast its role in a catalytic reaction using the usual oxidants. By studying the concentration and pH effects it is possible to assess the complexs stability domain, on the one hand, and to characterize the oxidation state of the two manganese atoms and construct a potential-pH diagram including the various equilibria between the manganese species on the other.

Analysis of impedance measurements performed on the platinum hexacyanoferrate (II) and (III) system in phosphate media

Abstract Impedance measurements of Fe(CN) 3− 6 and Fe(CN) 4− 6 solutions were taken in a potentiostatic mode in phosphate media at pH 7.2 in contact with a polished platinum electrode. Complementary data required to demonstrate the autocoherence of the results were deduced from thin layer spectroelectrochemistry measurements and from experiments carried out on a rotating disc electrode. The standard heterogeneous transfer rate constant was 0.1 cm s −1 and decreased, in the presence of oxygen, when the contact time between the electrode and the solution increased. In addition, we confirm the accuracy of the impedance method for the characterization of an electrode surface before an experiment.

Differential pulse polarography for monitoring cell cultures

The differential pulse polarography has been used on samples taken from the medium during the culture of chinese hamster ovary cells with a view to producing the active principle of an anti-cancer drug.

Theoretical and Experimental Aspects for Improvement of Electrochemical Biosensors by Various Kinds of Immobilization

The performances of amperometric detection biosensors — response time, sensitivity, linearity range - are predicted by calculation for different kinds of immobilisation or confinement of the catalyst(s). The cases of monoenzyme electrodes with the enzyme in solution confined by a semipermeable membrane near the electrode or grafted covalently to a membrane are considered. The calculations were extended to bienzyme sensors with the enzymes grafted to one side, or to both sides of a membrane. The experimental results obtained with L-lactate, D-lactate and L-glutamate specific electrodes are presented and used to qualify the model.