Poly(aniline)–poly(acrylate) composite films as modified electrodes for the oxidation of NADH

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Abstract
Poly(aniline), electrochemically deposited on an electrode surface in the presence of poly(acrylic acid), forms a film which remains protonated, and conducting, at pH 7. The resulting modified electrode is an electrocatalytic surface for NADH oxidation at +0.05 V vs. SCE in 0.1 M citrate–phosphate buffer at pH 7. The amperometric responses of these composite poly(aniline) films for NADH oxidation were studied in detail and fitted to a kinetic model in which the NADH diffuses into the polymer film and then binds to catalytic sites within the film where it undergoes reduction to NAD+. The rate determining process depends on the concentration of NADH present and the polymer film thickness. A comparison of the results presented here for the poly(aniline)–poly(acrylate) films with earlier work on poly(aniline)–poly(vinylsulfonate) films shows that the currents obtained for NADH at these poly(aniline)–poly(acrylate) films are approximately one third of those obtained for the poly(aniline)–poly(vinylsulfonate) films under similar conditions, that the currents saturate at lower NADH concentration and that the response is less stable towards repeated measurements. The poly(aniline)–poly(acrylate) films are, however, less readily inhibited by NAD+ and possess the potential advantage that the carboxylate groups can be used as sites for chemical attachment of enzymes or NADH derivatives by using simple coupling reactions.

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