Fast cyclic voltammetry of redox system NAD+/NADH on the copper nanodoped mercury monolayer carbon fiber electrode

The study of the redox pair NAD(+)/NADH by means of fast cyclic voltammetry (v = 0.1-2000 V s(-1)) on a nanostructured copper doped mercury monolayer carbon fiber electrode (Cu-MMCFE) was carried out. It was found that the process of NAD(+)/NADH interconversion occurs rapidly through the catalytic reduction of NAD(+) by generated atomary hydrogen H-0, with its subsequent catalytic regeneration by a chemical reaction between the reduced form of the coenzyme and cupric ions which are in turn regenerated by the hydrogen molecular ion H-2(+). The electrocatalytic NAD(+) reduction and NADH oxidation in protein (BSA) containing solutions intensifies the signal by more than three orders, assuring registration of a voltammetric signal for both coenzyme forms at picomolar level. The NAD(+)/NADH picomolar voltammetric sensitivity may be explained by examination of three electrocatalytic cycles established on the electrode between the redox pairs H+/0 (H-2(+)/H-2), Cu2+/0 and NAD(+)/NADH. The electrocatalytic voltammetric signals of NAD(+) and NADH agree reasonably well, providing evidence that the electrocatalytic process of NAD(+)/NADH interconversion on the modified electrode occurs with maintenance of its (co)enzymatic activity. The electrochemical peculiarities of the nanostructured electrode are proposed and the mechanism of NAD(+)/NADH electrocatalytic redox transformation discussed. (C) 2011 Elsevier B.V. All rights reserved.