COVALENT IMMOBILIZATION OF GLUCOSE-OXIDASE ON THE SURFACE OF POLYANILINE FILMS GRAFT COPOLYMERIZED WITH ACRYLIC-ACID

Glucose oxidase (GOD) was covalently immobilized on the electroactive polyaniline (PAN) film with surface-grafted acrylic acid (AAc) polymer through the amide linkage formation between amino groups of GOD and t he carboxyl groups of the grafted AAc polymer chains in the presence o f a water-soluble carbodiimide. The surface structure and composition of the graft-modified and enzyme-functionalized PAN films were charact erized by angle-resolved X-ray photoelectron spectroscopy (XPS). The a mounts of immobilized GOD and its activity were also investigated. It was shown that the amount of immobilized GOD increased linearly with t he concentration of surface-grafted AAc polymer chains. The decrease i n activity of the immobilized GOD was considered to be due to, among o ther factors, the reduced accessibility of glucose molecules to the ac tive sites of the enzyme and the conformational change of the GOD mole cules as a result of the covalent immobilization. However, the immobil ized enzyme was less sensitive to thermal inactivation as compared to that of the free form. The optimum pH value of GOD was not affected by the immobilization reaction and the pH stability range was considerab ly widened. The immobilized GOD also exhibits a significantly improved stability during storage in buffer solution over that of the free enz yme. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.