Electrochemical reduction of NAD+ on graphene oxide and chemically reduced graphene oxide nanosheets

Abstract

In this work, the electrochemical reduction of nicotinamide adenine dinucleotide (NAD+) was studied on graphene oxide (GO) and chemically reduced graphene oxide (CRGO) nanosheets. GO was prepared by modified Hummer’s method and reduced using hydrazine hydrate to obtain CRGO. The material was characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The TEM studies reveal the presence of nanosheets and the XRD exhibited the characteristic pattern of GO and CRGO respectively. The Raman spectrum showed a slight red shift for CRGO compared to GO. The electrochemical reduction of NAD+ was investigated on bare and modified glassy carbon electrode (GCE) using various electrochemical techniques such as linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The reduction of NAD+ to NADH occurs at a relatively lower potential of −1.04 V on GO/GCE compared to CRGO/GCE (−1.08 V) and bare GCE (−1.12 V). GO/GCE showed enhanced catalytic activity due to the presence of defect structures and oxygen functional groups on the carbon framework. The kinetic studies further revealed that reduction is an adsorption controlled process. From LSV obtained at different scan rates the number of electrons transferred was deduced as 1.7 and 1.2 for GO/GCE and CRGO/GCE respectively and the values are correlated with other electrochemical techniques such as hydrodynamic voltammetry and DPV. The heterogeneous rate constant determined from hydrodynamic voltammetry showed that GO/GCE (8.5 × 10−5 cm s−1) exhibited higher rate constant than CRGO/GCE (7.4 × 10−7 cm s−1). EIS was carried out at different cathodic potentials to analyze the kinetics at the electrode-electrolyte interface. The detection of NAD+ was performed on GO/GCE using DPV which showed a linear range of 100–1100 µM with a LOD of 19.36 µM. It was found that GO/GCE showed good catalytic activity compared to CRGO/GCE with better electron transfer kinetics.