Enhancement of stability of glucose oxidase by immobilization onto metal ion-chelated poly(N-vinyl imidazole) hydrogels.

Poly(N-vinylimidazole), PVIm, gels were prepared by gamma-irradiation polymerization of N-vinylimidazole in aqueous solutions as an affinity gel for glucose oxidase (GOx). These affinity gels with a water swelling ratio of 1800% for plain polymeric gel and between 30-80% for Cu(II) and Co(II)-chelated gels at pH 6.0 in phosphate buffer were used in the GOx adsorption studies. Maximum metal ion adsorption capacity of these hydrogels was found to be 3.64 mmol/g dry gel for Cu(II) and 1.72 mmol/g dry gel for Co(II) leading to GOx adsorption capacities of 343 and 528 mg enzyme/g dry gel, respectively, as compared to 228 mg for the plain dry PVIm gel. Activity studies were carried out using plain and the metal ion-chelated form of this hydrogel to investigate the stability and retained activity of the GOx in different buffer solutions and at different temperatures. Activity of the enzyme, either in free or immobilized form on the gel, decreased dramatically in acetate buffer solutions. In phosphate buffer solution, however, stability of enzyme has been found to be significantly high reaching 90% retained activity at the end of a 40-day period at 4 degrees C for Co(II) chelated systems. After immobilization of the enzyme onto metal-chelated hydrogel, the thermal stability of enzyme was enhanced significantly showing 23% activity, even at 75 degrees C.