Direct electrochemistry of cytochrome c surface-confined on DNA-modified gold electrodes

The direct electron transfer of surface-confined horse heart cytochrome c (Cyt c) was achieved using single- or double-stranded (ss- or ds-) calf-thymus DNA immobilized on gold electrodes. The formal potential (E°′) for Cyt c in a 10 mM PBS (pH7.0) buffer at a scan rate of 20 mV s−1 was −0.027 V with dsDNA and −0.016 V with ssDNA, respectively. The interaction between Cyt c and DNA makes the formal potential shift negatively when compared to that of Cyt c in solution (+0.258 V vs. SHE, i.e. +0.017 vs. SCE). Both UV–visible and reflection-absorption infrared spectroscopy indicate that the surface-confined Cyt c existed in its native form. The fractional coverage of bound Cyt c was 0.51 (with dsDNA) and 0.46 (with ssDNA) a single monolayer. The binding site sizes were determined to be 13 base pairs per Cyt c molecule with dsDNA and 26 nucleotides binding 1 Cyt c molecule with ssDNA. At a dsDNA/Au electrode, reduction and oxidation electron-transfer rate constant values of ks,Red=21 s−1 and ks,Ox=15 s−1 were obtained. At the ssDNA/Au electrode, the values were ks,Red=24 s−1 and ks,Ox=19 s−1, respectively. The incorporated Cyt c was strongly affected by variations in both the ionic strength and pH of the solution. The quantitative determination of Cyt c by differential pulse voltammetry (DPV) using DNA-modified electrodes was also explored.