Electrocatalytical oxidation of NADH with dopamine covalently bound to self-assembled cysteamine monolayers on a gold electrode

The preparation of a gold electrode modified by dopamine covalently bound to self-assembled cysteamine monolayer (dopamine-SAM) is described. The modified electrode exhibits a quasi reversible surface wave in phosphate buffer (pH 7.0). The charge transfer coefficient acid the apparent surface electron transfer rate constant for the redox couple of Q/QH(2) at the dopamine-SAM modified electrode are found to be 0.442 and 1.06 s(-1), respectively. The electrode shows a drastic enhancement in the oxidation of NADH and a stable electrochemical behavior for high NADH concentration. The anodic overpotential is reduced by ca. 400 mV compared with those obtained at bare gold electrodes. The current response of DPV increases linearly with the NADH concentration from 0.1 mM to 1.0 mM. In addition, it is found that for 2.0 mM NADH, the diffusion coefficient equals to (2.4 +/- 0.2) x 10(-6) cm(2) s(-1) in 0.05 M phosphate buffer (pH 7.0) containing 0.1 M KCl, and it is in good agreement with previous results. (C) 1997 Elsevier Science S.A.