Amperometric determination of total phenolic content in wine by laccase immobilized onto silver nanoparticles/zinc oxide nanoparticles modified gold electrode

A method is described for construction of a highly sensitive amperometric biosensor for measurement of total phenolic compounds in wine by immobilizing laccase covalently onto nanocomposite of silver nanoparticles (AgNPs)/zinc oxide nanoparticles (ZnONPs) electrochemically deposited onto gold (Au) electrode. Scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy were applied for characterization of the surface morphology of the modified electrode, and cyclic voltammetry was used to investigate the electrochemical properties of the proposed electrode toward the oxidation of guaiacol. The linearity between the oxidation current and the guaiacol concentration was obtained in a range of 0.1 to 500 μM with a detection limit of 0.05 μM (signal-to-noise ratio (S/N) = 3) and sensitivity of 0.71 μA μM–1 cm–2. The electrode showed increased oxidation and reduced reduction current with the deposition of AgNPs/ZnONPs on it. RCT values of ZnONPs/Au, AgNPs/ZnONPs/Au, and laccase/AgNPs/ZnONPs/Au electrode were 220, 175, and 380 Ω, respectively. The biosensor showed an optimal response within 8 s at pH 6.0 (0.1 M acetate buffer) and 35 °C when operated at 0.22 V against Ag/AgCl. Analytical recovery of added guaiacol was 98%. The method showed a good correlation (r = 0.99) with the standard spectrophotometric method, with the regression equation being y = 1.0053x − 3.5541. The biosensor lost 25% of its initial activity after 200 uses over 5 months.