Direct Electrochemistry of Cytochrome c Adlayer on the ITO Electrode

Abstract

The electrochemical redox reaction of a cytochrome c (Cyt c) adlayer on an indium tin oxide (ITO) electrode was directly monitored and the surface concentrations of Cyt c versus solution concentrations were obtained from cyclic voltammograms. The results indicate that the surface concentration increases from 0.35 × 10 - 12 to 1.53 × 10 - 12 mol·cm - 2 when the solution concentration is increased from 2 to 10 μmol·L - 1 . A quasi-linear relationship between the reciprocals of surface concentration and solution concentration was observed, indicating that Cyt c adsorption on the ITO electrode closely obeys the Langmuir isothermal adsorption model. The cyclic voltammograms of the Cyt c solutions with the ITO electrode reveal that both adsorbed and dissociated Cyt c molecules are involved in the electrode reaction and that the contribution of dissociated molecules is much larger than that of adsorbed ones. The electrode reaction is basically diffusion controlled and quasi-reversible. Based on the Nicholson method, the average standard heterogeneous rate constant was determined to be 1.65×10 - 3 cm·s - 1 . The electrochemical