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 sot-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 muA/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 x 10(-7) to 2.6 x 10(-4) M with a detection limit of 1.0 X 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. (C) 2003 Elsevier B.V. All rights reserved.