A mediator-free tyrosinase biosensor based on ZnO sol-gel matrix

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 mu A mmol L-1. The linear range for phenol determination was from 1.5 x 10(-7) to 4.0 x 10(-5) mol L-1 with a detection limit of 8.0 x 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.