Mediator-free phenol sensor based on titania sol–gel encapsulation matrix for immobilization of tyrosinase by a vapor deposition method

A novel amperometric phenol sensor was constructed by immobilizing tyrosinase in a titania sol–gel matrix. The tyrosinase entrapped sol–gel film was obtained with a vapor deposition method, which simplified the traditional sol–gel process and avoided the shrinkage and cracking of conventional sol–gel-derived glasses. This matrix provided a microenvironment for retaining the native structure and activity of the entrapped enzyme and a very low mass transport barrier to the enzyme substrates. Phenol could be oxidized by dissolving oxygen in presence of immobilized tyrosinase to form a detectable product, which was determined at −150 mV without any mediator. The phenol sensor exhibited a fast response (less than 5 s) and sensitivity as high as 103 μA/mM, which resulted from the porous structure and high enzyme loading of the sol–gel matrix. The linear range for phenol determination was from 1.2×10 −7 to 2.6×10 −4 M with a detection limit of 1.0×10 −7 M. The apparent Michaelis–Menten constant of the encapsulated tyrosinase was calculated to be (0.29±0.02) mM. The stability of the biosensor was also evaluated.