Tyrosinase biosensor based on modified screen printed electrodes: measurements of total phenol content

Abstract

A disposable tyrosinase biosensor has been developed for the analysis of phenols and polyphenols, by modifying screen printed electrodes (SPEs) with addition of suitable mediators of redox processes directly into the conductive pastes. The percent ratio of mediator in the pastes was chosen depending on the electrochemical sensitivity either in batch or standard flow conditions. Ferrocene modified carbon electrodes have been used on whose surface the enzyme tyrosinase was immobilized in a glutaraldehyde cross-linked matrix of bovine serum albumin. Mixing the mediator to the electrode pastes should overcome transport limitations, due to its dissolution, which occur in commonly used immobilization procedures. Different immobilization techniques of tyrosinase on SPEs in the detection of phenolic compounds were tested and compared. Modified SPEs showed relatively good reproducibility and detection limits in the micromolar range for all phenolic compounds used. Major sensor parameters have been optimized in flow systems putting special attention on operating potential, pH and buffer composition, which strongly affect the detection of polyphenols and operational stability in wine. The resulting biosensors were stored and dried for a minimum of 8 h at 4°C, and showed a shelf stability of about 30 days. The procedure has been applied both on a synthetic wine matrix and on real samples, to determine the ‘pool’ of phenolic composition in terms of phenol concentration.