Electrocatalytic Reduction of Hydrogen Peroxide on Polymethylpyrrole–Peroxidase Composite Film Plated on Gold Electrode

Horse radish peroxidase (POD), which is codeposited with polymethylpyrrole on a gold electrode, catalyzes hydrogen peroxide electroreduction. In the case of thin films deposition (Q < 4 mC cm–2), less than one monolayer of enzyme located on the film's surface is involved in the electrochemical reaction. An increase in the limiting current points to an increase in the number of molecules accessible for the reduction of hydrogen peroxide on the surface of the composite system. The calculated values of layer's thickness suggest, for thin films, the formation of an ensemble of nanosize polymethylpyrrole-peroxidase particles. At a larger thickness of the composite coating (Q > 4 mC cm–2), the cathodic current increases only at low polarizations. In this case, probably, the POD molecules located on the surface and in the bulk film are involved in the reaction. From these results we conclude that, in the composite system studied, polymethylpyrrole provides the electron transfer to enzyme molecules, and the reaction's mechanism is likely to be the same in the cases of both carbon and gold substrates.