Amperometric Tyrosinase Biosensor Based on Carbon Nanotube–Titania–Nafion Composite Film

A highly sensitive and stable amperometric tyrosinase biosensor has been developed based on multiwalled carbon nanotube (MWCNT) dispersed in mesoporous composite films of sol–gel‐derived titania and perfluorosulfonated ionomer (Nafion). Tyrosinase was immobilized within a thin film of MWCNT–titania–Nafion composite film coated on a glassy carbon electrode. Phenolic compounds were determined by the direct reduction of biocatalytically‐liberated quinone species at −100 mV versus Ag/AgCl (3 M NaCl) without a mediator. The present tyrosinase biosensor showed good analytical performances in terms of response time, sensitivity, and stability compared to those obtained with other biosensors based on different sol–gel matrices. Due to the large pore size of the MWCNT–titania–Nafion composite, the present biosensor showed remarkably fast response time with less than 3 s. The present biosensor responds linearly to phenol from 1.0×10 −7 M to 5.0×10 −5 M with an excellent sensitivity of 417 mA/M and a detection limit of 9.5×10 −8 M ( S / N =3). The enzyme electrode retained 89% of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.