Electrochemical glucose biosensor based on ZnO nanorods modified with gold nanoparticles

Gold nanoparticles (AuNPs) were synthesized by seeded-growth method. Spherical AuNPs with different sizes were formed by varying the volumes of the gold seed, hydroxylamine hydrochloride, and gold chloride. Zinc oxide nanorods (ZnONRs) were also produced through hydrothermal growth on seeded indium tin oxide (ITO) substrates. Zinc acetate sol seed was dropped onto the substrates, which were then oven dried at 150 °C. After heating the substrates at 500 °C for 2 h in a preheated tube furnace to obtain the ZnO seed, the substrates were immersed in a hydrothermal solution and heated at 80 °C for 4 h to obtain ZnONRs grown on ITO substrates. The synthesized AuNPs were then drop casted onto the ZnONR/ITO substrates, which were air dried to obtain AuNP/ZnONR/ITO electrodes. Glucose oxidase (GOx) enzyme and Nafion were subsequently dropped onto these modified electrodes. The electrochemical activity of the resulting Nafion/GOx/AuNP/ZnONR/ITO electrodes in glucose detection was evaluated through cyclic voltammetry. The size and volume of the AuNPs and the volume of GOx enzyme were found to influence the electrochemical activity. The optimized electrode consisting of Nafion, 60 µL of GOx, 80 µL of 30 nm AuNPs, ZnONRs, and ITO exhibited a low limit of detection of 0.18 mM and high sensitivities of 14.53 and 2.54 µA mM⁻¹ cm⁻² within a wide working range of 0.05–1.0 and 1.0–20 mM, respectively.