Direct electrochemical oxidation of DNA on polycrystalline gold electrodes

Electrochemical CV and SWV studies were performed with double stranded DNA from salmon testes (dsDNA) and single stranded DNAs, containing 25 nucleotides (ssDNA) directly adsorbed at polycrystalline An electrodes. A distinct oxidation peak at + 730 mV (SWV, scan rate 0.248 V s(-1)) or at + 730 - + 780 mV (CV, scan rate from 0.3 to 1 V s(-1)) was obtained with DNA-modified Au electrodes after a time-dependent prepolarization step at a positive potential value, i.e., at + 500 mV (vs. Ag \ AgCl), performed with the DNA-modified Au electrodes dipped in a blank buffer solution. No electrochemical activity was detected when ssDNA, containing no guanines, was used for adsorptive modification of the Au electrodes. Electrochemical impedance measurements registered a possible reorganization of the adsorbed DNA layer in the course of the prepolarization, accompanied by decreasing in-phase impedance. ne results enable us to relate the oxidation process observed at the DNA-modified Au electrodes with the oxidation of guanine residues in DNA.