Hydroxyl radical assisted enzyme-free electrochemical detection and oxidation of cholesterol by a galvanically deposited layer-by-layer ZnO/WO3 thin film nanocomposite

Abstract

Accurate and rapid determination of cholesterol levels in bio-fluids is important because it is an important index for the bio-medical diagnosis of several lethal diseases. Accordingly, electrochemical non-enzymatic bio-sensors offer accurate and rapid detection and exhibit unique features, such as simple handling, affordability, and a very low detection limit with a wider linear range. In this study, a simple, low-cost galvanic deposition technique was employed to develop a thin layer of nanoflakes WO₃ on hexagonal ZnO nanoplate using Zn foil as an oxidizable anode, and the composite film (ZnO/WO₃) was explored for the electrochemical non-enzymatic detection of cholesterol. The film offers excellent sensitivity (176.6 μA cm⁻² mM⁻¹) with a very low detection limit (5.5 nM) at the electrode interfacial surface. During the electro-oxidation of cholesterol, the electrode utilized operational potential (+0.43 V vs. Ag/AgCl) to convert to oxysterol with higher selectivity using hydroxyl radicals (˙OH) as intermediates. The production of ˙OH radicals was confirmed by the effect of terephthalic acid (TPA) on the analyte using photoluminescence spectroscopy. Selectivity in the presence of other interfering agents, long-term stability, repeatability and reproducibility of the biosensor was also ensured for practical application in clinical diagnosis in a real blood sample.