A new tyrosinase biosensor based on tailoring the porosity of A12O3 sol-gel to co-immobilize tyrosinase and the mediator

A new tyrosinase biosensor has been developed, based on the co-immobilization of tyrosinase and the mediator, Fe(CN)(6)(4-), in positively charged Al2O3 sol-gel membranes. Different sizes of molecules were entrapped into the sol-gel membranes with different size pores, which were obtained by changing the ratio of Al : H2O during the sol-gel process. Tyrosinase was immobilized on a matrix with relatively large pores, Fe(CN)(6)(4-) was immobilized on a matrix with smaller pores. The stability of the encapsulation molecules was further enhanced by the electrostatic interaction between the molecules and matrix. The enzyme immobilized in the porous and hydrophilic sol-gel matrices is much stable and retains its functional activity to a large extent. The accumulation of the o-quinones in the alumina film greatly improved the sensitivity of the sensor. The process parameters for the fabrication of the enzyme biosensor were optimized. The detection limit is 5.0 x 10(-8) mol/l, the Lifetime is more than 1 month. (C)2000 Elsevier Science B.V. All rights reserved.