Enzymatic conversion in ion-exchange mixed matrix hollow fiber membranes

This work reports the adsorption of glucose oxidase (GOx) in particle-loaded hollow fibers using polyethersulfone as the matrix and Lewatit strong cation-exchange resins as the functional support. The activity of adsorbed GOx was evaluated under the same pH conditions as the adsorption. Static enzyme immobilization tests yielded high adsorption values at pHs below the isoelectric point (pI) of GOx, where the enzyme assumes the cationic form and adsorbs via electrostatic interaction. The adsorption by electrostatic interactions could be described by a Langmuir isotherm at pH values below the pI of GOx. Adsorption performed above the pI takes place preferentially via hydrophobic interactions. Dynamic GOx adsorption experiments resulted in the same values as those obtained in static experiments. Below the pI of the enzyme, the adsorption was found to be pH dependent. Above the pI of GOx, the adsorption was lower and independent of the pH. Formation of GOx multilayers was observed for all applied pH values. Dynamic glucose conversion measurements showed that the immobilized GOx retains an appreciable activity after adsorption via both methods. GOx immobilized via hydrophobic interactions yielded the highest activity values. Enzymes immobilized via electrostatic interaction showed multilayer adsorption, resulting in a strongly reduced enzymatic activity. The highest enzymatic activity of the adsorbed GOx was found for pH 5.0.