Electrocatalytic oxidation of NADH using a pencil graphite electrode modified with quercetin

In the present study, the electrocatalytic oxidation of reduced β nicotinamide adenine dinucleotide (NADH) was investigated using a pencil graphite electrode modified with quercetin (PGE/QH2). The PGE/QH2 was prepared through two steps: (i) the pre-treatment of PGE at 1.40 V vs. Ag|AgCl|KCl(sat.) in pH 7.0 phosphate buffer containing 0.1 M KCl for 60 s and (ii) adsorption of QH2 on the PGE via immersion of PGE into a 1.0 mM QH2 solution (in ethanol) for 60 s. Cyclic voltammetric studies show that the peak potential of NADH oxidation shifts from +500 mV at bare PGE to +300 mV at PGE/QH2. The electrocatalytic currents obtained from amperometric measurements at +300 mV vs. Ag|AgCl|KCl(sat.) and in phosphate buffer solution at pH 7.0 containing 0.1 M KCl were linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 0.5 μM to 100 μM. The limit of detection was found to be 0.15 μM.