Covalent immobilization of glucose oxidase on microporous membranes prepared from poly(vinylidene fluoride) with grafted poly(acrylic acid) side chains

Microfiltration (MF) membranes were prepared from the acrylic acid graft-copolymerized poly(vinylidene fluoride) (the AAc-g-PVDF copolymer) by the phase inversion method. The membranes were used as substrate carriers for the immobilization of glucose oxidase (GOD). The immobilization proceeded via amide linkage formation between the amino groups of GOD and the activated carboxyl groups of the AAc polymer side chains on the surfaces, including the pore surfaces, of the AAc-g-PVDF MF membrane. The surface composition of the membranes before and after enzyme immobilization was studied by X-ray photoelectron spectroscopy (XPS). The amount of the immobilized GOD, as determined by the dye interaction method, increased linearly with the concentration of AAc polymer side chains on the membrane surface. The reduction in activity of the immobilized GOD was considered to be due to, among other factors, diffusion limitation and steric hindrance. In comparison with the free enzyme, the immobilized enzyme was less sensitive to temperature and pH deactivation. The kinetic parameters of the enzyme reaction, the Michaelis constant (Km) and the maximum reaction velocity (V-max), were also determined. The immobilized GOD exhibited a significantly enhanced stability during storage in buffer solution over that of the free enzyme. The results obtained showed that the AAc-g-PVDF MF membranes are suitable substrate carriers for the immobilization of glucose oxidase. (C) 2002 Elsevier Science B.V. All rights reserved.