Electrocatalytic oxidation of NADH at graphene-modified electrodes based on electropolymerized poly(thionine-methylene blue) films from nature deep eutectic solvents

In this paper, a sensing platform for the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) was proposed. It was prepared by the electropolymerization of poly(thionine-methylene blue) (PTH-MB) in ternary nature deep eutectic solvent (NADES) on a glassy carbon electrode (GCE) that was modified with electrochemically reduced graphene oxide (ERG). The modified electrode was denoted as PTH-MB NADES -ERG/GCE. Cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), Raman spectroscopy, and Ultra Violet-Visible Spectroscopy (UV–Vis) were used to characterize the preparation processes. The electrochemical performances of the electrode in NADH oxidation were studied via CV and current-time methods. The NADH oxidation overpotential was lower on PTH-MB NADES -ERG/GCE compared to that on GCE, ERG/GCE, and PTH-MB NADES /GCE. The PTH-MB NADES -ERG/GCE showed excellent electrocatalytic activity for NADH oxidation with a linear range of 0.51–3333.33 µM (R 2  = 0.9534) and a detection limit of 0.159 nM. The sensor was further tested for NADH determination in artificial urine samples, showing promising biomedical applications.