Mediatorless catalytic oxidation of NADH at a disposable electrochemical sensor

We report here a simple, selective and sensitive method for the determination of NADH in neutral aqueous solution by using an electrochemically preanodized screen printed carbon electrode (SPCE*) without the addition of any redox mediator. The preanodization procedure makes the SPCE more electroactive towards NADH oxidation with a decrease of ∼300 mV in the overpotential without electrode fouling. It is proposed that surface reorientation to generate more edge plane sites during the preanodization procedure, as confirmed by a distinctive Raman band at ∼1360 cm−1, is the main cause for the facilitated electron transfer for the oxidation of NADH. Presence of large excess of ascorbic acid does not interfere the detection of NADH and the SPCE* shows individual voltammetric peaks for ascorbic acid and NADH. Under optimized conditions, the obtained calibration plot shows a linear range up to 100 μM with a detection limit (S/N = 3) of 157 nM by flow injection analysis.