Electrocatalytic studies of Cytochrome c functionalized single walled carbon nanotubes on self-assembled monolayer of 4-ATP on gold

Abstract

Direct electron transfer of redox proteins on electrode surfaces using surface immobilized protein films is gaining importance as it provides significant insight into the functioning of biological systems and in the development of biosensors. We have studied functionalized cytochrome c (cyt c) surfaces by covalently using glutaraldehyde as a cross linker and also non-covalently by a simple immersion process of physical adsorption. The third method described in this paper involves combining the affinity of the redox proteins for single walled carbon nanotube (SWNT) surface and its non-covalent binding to the 4-aminothiophenol (4-ATP) self-assembled monolayer on Au. The immobilized composite films facilitate the interfacial electron transfer and electrocatalytic activity of cyt c. The cyt c immobilized surfaces were characterized by scanning probe techniques, cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The AFM images of the protein immobilized surface show dense distribution of SWNT- cyt c on the surface forming several clusters. A closer examination using STM shows dense distribution of proteins on 4-ATP surface. We have correlated the voltammetric results with the information obtained from AFM and STM images to explain the electrocatalytic activity of the protein layer on the electrode surface.