Immobilization of glucose oxidase on magnetite particles modified by grafting acrylic acid-acrylamide copolymer - Effect of pH on activity of immobilized glucose oxidase

Copolymerization of acrylic acid and acrylamide was carried out in a redox system consisting of mercapto groups introduced onto the surface of magnetite particles and ceric ions, and acrylic acid-acrylamide copolymer was grafted onto the particles. Glucose oxidase (GOx) was immobilized on the magnetite particles by condensation with carboxyl groups of the grafted copolymer. An optimum value of pH for the GOx immobilized on the copolymer-grafted magnetite was observed between that for native GOx (pH 4-5) and that for the GOx immobilized on poly (acrylic acid)-grafted magnetite (pH 7). It was found that the value of optimum pH showed a tendency to increase with increasing amount of acrylic acid units in the grafted copolymer. These results were attributed to the effect of remaining carboxyl groups of the grafted polymer to acidify the surface of magnetite particles. This effect was confirmed by a clear correlation observed between the zeta potential of magnetite particles and content of carboxyl groups on the particles.