Electrochemical evaluation of coumestan modified carbon paste electrode: Study on its application as a NADH biosensor in presence of uric acid

The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) has been studied on a coumestan derivative modified carbon paste electrode (CMCPE), using cyclic voltammetry, chronoamperometry and differential pulse voltammetry as diagnostic techniques. The surface charge transfer rate constant, ks, and the charge transfer coefficient, α, for electron transfer between the CPE and the spiked derivative coumestan were estimated in different pHs, according to the procedure of Laviron. The cyclic voltammograms of the modified electrode indicate that the reactivity of spiked derivative coumestan is strongly dependent on the solution pH. Two linear segments were found with slope values of −55.6 and −28.8 mV/pH in the ranges of pH 2.0–9.7 and 9.7–12.0, respectively. The CMCPE shows excellent electrocatalytic activity toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 240 mV compared to the process at an unmodified electrode. The heterogeneous rate constant for oxidation of NADH at the CMCPE was also determined by cyclic voltammetry and chronoamperometry measurements. Differential pulse voltammetry (DPV) exhibits two linear dynamic ranges and a lower detection limit of 0.10 μM for NADH. Finally, the CMCPE could separate the oxidation peak potentials of NADH and uric acid present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable.