A gold nanoparticle-attached indium tin oxide (Au/ITO) electrode was applied for myoglobin (Mb) immobilization. The direct electron transfer of Mb was shown by the stable and well-behaved voltammetric responses for Mb immobilized on the Au/ITO electrode in buffer solutions. The effects of scan rate, pH value and oxygen on the direct electrochemistry of Mb were observed. Based on the catalytic activity of Mb immobilized on a gold nanoparticle-modified ITO (Mb/Au/ITO) electrode toward the reduction of H2O2, a mediator-free H2O2 sensor was developed, which showed good reproducibility and stability in pH 7.0 buffer. A linear relationship existed between the catalytic current and the H2O2 concentration in the range of 2.5 x 10(-6)-5 x 10(-4) M with a detection limit (S/N = 3) of 4.8 x 10(-7) M. (c) 2004 Elsevier B.V. All rights reserved.