Direct electrochemistry and electrocatalytic activity of cytochrome c covalently immobilized on a boron-doped nanocrystalline diamond electrode.

Cytochrome c (Cyt c) was covalently immobilized on a boron-doped nanocrystalline diamond (BDND) electrode via surface functionalization with undecylenic acid methyl ester and subsequent removal of the protecting ester groups to produce a carboxyl-terminated surface. Cyt c-modified BDND electrode exhibited a pair of quasi-reversible and well-defined redox peaks with a formal potential (E(0)) of 0.061 V (vs Ag/AgCl) in 0.1 M phosphate buffer solution (pH 7.0) and a surface-controlled process with a high electron transfer constant (ks) of 5.2 +/- 0.6 s(-1). The electrochemical properties of as-deposited and Cyt c-modified boron-doped microcrystalline diamond (BDMD) electrodes were also studied for comparison. Investigation of the electrocatalytic activity of the Cyt c-modified BDND electrode toward hydrogen peroxide (H2O2) revealed a rapid amperometric response (5 s). The linear range of response to H2O2 concentration was from 1 to 450 microM, and the detection limit was 0.7 microM at a signal-to-noise ratio of 3. The stability of the Cyt c-modified BDND electrode, in comparison with that of the BDMD and glassy carbon counterpart electrodes, was also evaluated.