A Mediator-Free Tyrosinase Biosensor Based on ZnO Sol-Gel Matrix

Abstract

A tyrosinase biosensor was developed based on the immobilization of tyrosinase in a positively charged ZnO sol-gel matrix on a glass carbon electrode. It has been found that the ZnO sol-gel matrix provided an advantageous microenvironment in terms of its favorable isoelectric point for tyrosinase loading and the immobilized tyrosinase retained its activity to a large extent. Phenolic compounds were determined by the direct reduction of biocatalytically generated quinone species at −200 mV (vs. SCE) without any mediator. The parameters of the fabrication process and the various experimental variables for the enzyme electrode were optimized. The resulting biosensor can reach 95% of steady-state current within15 s and sensitivity as high as 168 μA mmol L−1. The linear range for phenol determination was from 1.5×10−7 to 4.0×10−5 mol L−1 with a detection limit of 8.0×10−8 mol L−1. The biosensor response retained 75% of the initial response after two weeks. The performance of the developed biosensor was compared with that of biosensors based on other sol-gel matrices.