Poly(aniline) composites as bioelectrochemical sensors

Previous work completed within the Electrochemistry Department at Southampton University has shown that poly(aniline) is an electrocatalytic surface for the oxidation of NADH at pH 5. The work presented in this thesis shows that by incorporating poly(anions) into poly(aniline) during polymer growth we can obtain stable reproducible amperometric responses to NADH at 0.1 V vs. SCE in pH 7 citrate/phosphate buffer. Incorporation of two poly(anions) has been studied; poly(vinylsulfonate) and poly(styrenesulfonate). A kinetic model describing the reaction between the polymer and NADH is proposed for both composites. The quality of the theoretical fit to the experimental data is excellent and implies that the reaction occurs throughout the whole of the film via a Michaelis-Menten type reaction and that the product of the reaction NAD+ inhibits the observed response. The observed current responses to NADH oxidation are an order of magnitude lower for the poly(styrenesulfonate) as compared to the poly(vinylsulfonate) composite films. From comparison of the parameters obtained from kinetic modeling and from SEM data it is proposed that this is due to slower diffusion into the poly(styrene) composite films as a result of their dense structure compared with the poly(vinylsulfonate) analogues.The response of these poly(aniline) composite electrodes at +0.1 V vs. SCE to three common interferents has been assessed. No response was observed for either uric acid or acetoaminophenol even at concentrations well in excess of their physiological levels. However at this potential both composites are shown to be excellent catalytic surfaces for ascorbic acid oxidation.The amperometric responses to ascorbic acid are shown to be both stable and reproducible. Kinetic analysis of the experimental data shows that the reaction occurs only at the polymer/solution interface. Preliminary results also indicate that NAD+ inhibits the responses of these electrodes to ascorbic acid.