Construction and application of an amperometric uric acid biosensor based on covalent immobilization of uricase on iron oxide nanoparticles/chitosan-g-polyaniline composite film electrodeposited on Pt electrode

Commercial uricase was immobilized covalently onto iron oxide nanoparticles/chitosangraft-polyaniline (Fe3O4-NPs/CHIT-g-PANI) composite film electrodeposited on surface of Pt electrode. Transmission electron microscopy (TEM) was used for characterization of Fe3O4-NPs. A uric acid biosensor was fabricated using/Fe3O4-NPs/CHIT-g-PANI/Pt electrode as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode. The enzyme electrode was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The biosensor exhibited an optimum response within 1s at pH 7.5 and 30 °C, when polarized at 0.4 V vs Ag/AgCl. The electrocatalytic response showed a linear dependence on uric acid concentration ranging from 0.1 to 800 μM. The sensitivity of the biosensor was 0.44 mA mM−1 cm−2, with a detection limit of 0.1 μM (S/N = 3). Apparent Michaelis–Menton (Km) value for uric acid was 12.5 μM, and Imax 0.008A. The biosensor showed only 10% loss in its initial response after 120 uses over 100 days, when stored at 4 °C. The biosensor measured uric acid in the serum of apparently healthy persons, which correlated well with a standard enzymic colorimetric method (r = 0.98).