A Mechanism of Adsorption of β-Nicotinamide Adenine Dinucleotide on Graphene Sheets: Experiment and Theory

beta-Nicotinamide adenine dinucleotide (NAD(+)) and its reduced form (NADH) play major roles in the development of electrochemical enzyme biosensors; and biofuel cells. Unfortunately, the oxidation of NADH at carbon electrodes suffers from passivation of the electrodes and a decrease in passing currents. Here, we investigate experimentally and theoretically the reasons for such passivation. High-resolution X-ray photoelectron spectroscopy (HR-XPS), voltammetry, and amperometry show that adsorption occurs on the edges and "edge-like" defects of graphene sheets. HR-XPS and ab initio molecular dynamics show that the adsorption of NAD(+) molecules on the edges of graphene happens due to interaction with oxygen-containing groups such as carboxylic groups, while graphene edges substituted only with hydrogen are prone to passivation.