A new tyrosinase biosensor based on tailoring the porosity of A1(2)O(3) sol-gel to co-immobilize tyrosinase and the mediator

A new tyrosinase biosensor has been developed, based on the co-immobilizati on of tyrosinase and the mediator, Fe(CN)(6)(4-), in positively charged Al2 O3 sol-gel membranes. Different sizes of molecules were entrapped into the sol-gel membranes with different size pores, which were obtained by changin g the ratio of Al : H2O during the sol-gel process. Tyrosinase was immobili zed on a matrix with relatively large pores, Fe(CN)(6)(4-) was immobilized on a matrix with smaller pores. The stability of the encapsulation molecule s was further enhanced by the electrostatic interaction between the molecul es and matrix. The enzyme immobilized in the porous and hydrophilic sol-gel matrices is much stable and retains its functional activity to a large ext ent. The accumulation of the o-quinones in the alumina film greatly improve d 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. A ll rights reserved.