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 H0, 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 H2+. 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 (H2+/H2), 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.

► Cu doped mercury monolayer carbon fiber electrode as catalyst for NAD+/H conversion. ► Hydrogen intermediates H0 and H2+ as electrocatalytic recycling agents. ► The presence of BSA and the use of fast voltammetry assures NAD+/H picomolar sensitivity.