Direct electron transfer of horseradish peroxidase on Nafion-cysteine modified gold electrode

Direct electron transfer of horseradish peroxidase, immobilized on a functional membrane-modified gold electrode, was studied. The electrode showed a quasi-reversible electrochemical redox behavior with a formal potential of 60 mV (versus Ag/AgCl) in 20 mM potassium phosphate buffer solution at pH 7.0 and temperature 25 °C. The cathodic transfer coefficient was 0.42 and electron transfer rate constant was evaluated to be 1.6 s−1. Furthermore, the modified electrode was used as a biosensor and exhibited a satisfactory stability and sensitivity to H2O2. The linear range of this biosensor for H2O2 determination was from 5.0 × 10−6 to 1.5 × 10−4 M while its detection limit, based on a signal-to-noise ratio of 3, was 1.3 × 10−6 M. The apparent Michaelis–Menten constant (Kmapp) for immobilized HRP was calculated to be 1.6 × 10−4 M.