A highly sensitive uric acid biosensor based on vertically arranged ZnO nanorods on a ZnO nanoparticle-seeded electrode

Abstract

Uric acid (UA) level quantification is crucial for the diagnosis and treatment of cardiovascular, arthritis, renal disorder, and preeclampsia diseases. We report the solvent-assisted synthesis of zinc oxide (ZnO) nanoparticles (NPs) which we used to make a seed layer on a conductive fluorine-doped tin oxide (FTO) electrode. Vertically-arranged ZnO nanorods (NRs) were grown using a hydrothermal method. The ZnO NPs and NRs were characterized in detail, which revealed the smaller sizes (10–15 nm) of the NPs and the vertically-arranged nature of the NRs. Furthermore, a highly sensitive UA biosensor was constructed with vertically-arranged ZnO NRs. The electrochemical characterization of the UA biosensor (Nafion/uricase/ZnO NRs–ZnO NPs/FTO) using differential pulse voltammetry (DPV) demonstrated linearity over a wide UA concentration range (0.01–1.5 mM) with a high sensitivity (345.44 μA mM⁻¹ cm⁻²) and limit of detection (LOD; 2.5 μM). The biosensor also showed good selectivity, high reproducibility, and enhanced shelf-life. Additionally, practical feasibility was tested in a real (i.e., human blood serum) sample. The boosted UA biosensor performance is attributed to the vertically-arranged ZnO NRs, which immobilize a large amount of enzyme owing to their high surface-to-volume ratio, compared to flat surface-based biosensors. The present strategy, using vertically-arranged ZnO NRs on NP-seeded electrodes, can be extended to fabricate different ZnO NR-based chemical/biosensing devices.