Electrochemical and catalytic investigation of carbon paste modified with Toluidine Blue O covalently immobilised on silica gel

Toluidine Blue O (TBO) was covalently bound on silica gel and mixed with graphite powder and paraffin oil to produce modified carbon paste electrodes. The formal potential (E°′) of the covalently bound TBO was found to be −100 mV versus Ag|AgCl (KCl sat.) at pH 7.0 and the E°′ varied less than anticipated for a 2-electron–proton type mediator with pH. The bound TBO was found to act as an efficient electron acceptor for NADH as well as electron donor for oxidised horseradish peroxidase (HRP). The kinetics and the mechanism of the reaction between NADH and TBO were investigated with cyclic voltammetry and using a rotating disc electrode. Further experiments were done in the flow injection mode injecting different concentrations of NADH. Similar studies were done in the presence of hydrogen peroxide when HRP was adsorbed onto the TBO modified silica gel carbon paste electrodes.