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

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.