Novel uric acid sensor based on enzyme electrode modified by ZnO nanoparticles and multiwall carbon nanotubes

In this work, we report the development of a highly sensitive and stable uric acid sensor based on the synergic action of multiwalled carbon nanotubes (MWNTs) and ZnO nanoparticles. MWNTs were first cast on pyrolytic graphite (PG) wafers. ZnO nanoparticles were then decorated onto the negatively charged MWNTs via the Vapor Liquid Solid (VLS) growth. Uricase was immobilized on the ZnO nanoparticles surface because of their large differences in the isoelectric point (IEP). Last, a cationic polydiallyldimethylammonium chloride (PDDA) layer was coated onto the uricase-contained ZnO nanoparticle layer and resulted in the PDDA/uricase/ZnO/MWNTs multilayer structure. The unique multilayer structure provides a favorable microenvironment to keep the bioactivity of uricase, which led to rapid amperometric response toward uric acid. Amperometric detection of uric acid was carried out at 320 mV (vs. SCE) in 0.05 mol/L (M) phosphate buffer solution (pH 6.8). For the sensor, a wide linear response range of 5.0 μM to 1 mM with a linear sensitivity of 393 mA cm^-2M^-1, a detection limit of 2.0 μM (3σ), and a long-term stability of 160 days can be obtained by using differential pulse voltammetry (DPV). Testing results in human urine obtained from the sensors were also compared with the data obtained by spectrometry. For five samples with different concentrations of urine, the relative deviations between them were smaller than 3.8%. The recovery was between 96.5 and 104.0%.