Immobilization of Invertase in DAD Type Polymers: Combination of Benzothiadiazole Acceptor Unit and 3,4-Ethylenedioxythiophene and Thiophene Donor Units

Abstract

Conductive polymers with donor-acceptor-donor (DAD) type units; benzothiadiazole acceptor unit and 3,4-ethylenedioxythiophene (EDOT) and thiophene (Th) donor units, were investigated for immobilization of invertase. The polymers were prepared potentio-dynamically from their monomers, M-1 (Th-benzothiadiazole-Th), M-2 (EDOT-benzothiadiazole-EDOT), M-3 (Th-benzothiadiazoleEDOT) and a copolymer, which is a homolog to homopolymer of M-3, was prepared from M-1 and M-2. Invertase was trapped between a two layer-composite; DAD polymer and polypyrrole. The characterization of immobilized invertase was performed using a spectrophotometric method at 540 nm. Kinetic parameters, V-max, maximum reaction rate and K-m, Michaelis-Menten constant values of immobilized invertase in DAD type homopolymer (P-3), 0.95 mu mol min(-1) and 22.7 mM, respectively, are found between those of homopolymers P-1 and P-2 and are better than the copolymer. Polymers and copolymers exhibited a broad optimal temperature profile between 30 and 50 degrees C compared to the free enzyme. Optimum pH (5.0) is the same as for free invertase. The electrodes were found to be stable with 100% activity during one day for 40 consecutive measurements. As to the self-life, 25% of the initial activity was lost in the first ten days, then the electrodes were stable with 75% activity for a 40 day storage at 4 degrees C.