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 degrees 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 x 10(-6) to 1.5 x 10(-4) M while its detection limit, based on a signal-to-noise ratio of 3, was 1.3 x 10(-6) M. The apparent Michaelis-Menten constant (K-m(app)) for immobilized HRP was calculated to be 1.6 x 10(-4) M. (c) 2007 Elsevier Ltd. All rights reserved.