Zinc Oxide Nanoparticle-modified Glassy Carbon Electrode as a Highly Sensitive Electrochemical Sensor for the Detection of Caffeine

Zinc oxide nanoparticles (ZnO NPs) were prepared by a simple, convenient, and cost-effective wet chemical method using the biopolymer starch. The prepared ZnO NPs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR), and UV-visible spectroscopic techniques. The average crystallite size calculated from XRD data using the Debye-Scherer equation was found to be 15 nm. The electrochemical behavior of caffeine (CAF) was studied using a glassy carbon electrode (GCE) modified with zinc oxide nanoparticles by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Compared to unmodified GCE, ZnO NPs-modified GCE (ZnO NPs MGCE) exhibited excellent electrocatalytic activity towards CAF oxidation, which was evident from the increase in the peak current and decrease in the peak potential. Electrochemical impedance study suggested that the charge-transfer capacity of GCE was significantly enhanced by ZnO NPs. The linear response of the peak current on the concentrations of CAF was in the range 2-100 mu M. The detection limit was found to be 0.038 mu M. The proposed sensor was successfully employed for the determination of CAF in commercial beverage samples.