Spectroelectrochemical studies on surface immobilized cytochrome c on ITO electrode by slab optical waveguide spectroscopy

Direct electron transfer between surface-immobilized cytochrome c and an indium-tin-oxide (ITO) electrode was investigated using ITO slab optical waveguide (SOWG) spectroscopy. The peak position of the absorption band of cytochrome c immobilized on the ITO electrode changed repeatedly between 409 and 414 nm with the electrode potential sweep, which corresponded to the oxidized and reduced forms of cytochrome c, respectively. It took a few seconds to complete the electron transfer reaction for surface-immobilized cytochrome c of less than monolayer coverage. The redox potential of surface-immobilized cytochrome c was estimated to be approximately -0.2 V vs. Ag/AgCl from the absorbance intensity change with respect to potential applied to the ITO electrode. These results suggest that, after adsorption on the ITO electrode, cytochrome c was still electrochemically active. (C) 2003 Elsevier Science B.V. All rights reserved.