Immobilization and electrochemical redox behavior of cytochrome c on fullerene film-modified electrodes

Two different fullerene film-modified electrodes were prepared and used for surface immobilization and electrochemical property investigation of horse heart cytochrome c (cyt c). Both a pristine fullerene film and fullerene-palladium (C60-Pd) polymer film-modified platinum, glassy carbon and indium–tin–oxide (ITO) electrodes were used. The immobilized cyt c was characterized by piezoelectric microgravimetry at a quartz crystal microbalance (QCM), UV–visible absorption, and X-ray photoelectron spectroscopy (XPS), as well as cyclic voltammetry (CV) techniques. The UV–visible spectral studies revealed a small blue shift of both the Soret and Q band of the heme moiety of cyt c, immobilized on the C60-Pd polymer film-modified ITO electrode, as compared to the bands of cyt c in solution suggesting that molecules of cyt c are densely packed onto the surface of the modified electrode. The CV studies revealed a quasi-reversible electrode behavior of the heme moiety indicating the occurrence of kinetically hindered electron transfer. A good agreement was found between the values of cyt c electrode surface coverage determined by piezoelectric microgravimetry and cyclic voltammetry. For piezoelectric microgravimetry, these values ranged from 0.5×10−10 to 2.5×10−10 mol cm−2, depending upon the amount of cyt c present in solution and the time allowed for immobilization, which compared with a value of 3.6±0.4×10−10 mol cm−2 determined by CV. The possible mechanisms of cyt c immobilization on the C60 film and C60-Pd film-modified electrodes are also discussed.