A novel strategy to immobilize enzymes on microporous membranes via dicarboxylic acid halides

Abstract

A major challenge in enhancing the acceptability of enzymes in enzymatic membrane bioreactors (EMBRs) for industrial processes lies in effectively immobilizing enzymes on supports while maintaining their conformation and activity. This work describes a novel methodology using dicarboxylic acid halides as a spacer for the surface-initiated, covalent immobilization of enzymes onto microporous membranes. One of the reactive carboxyl groups from the dicarboxylic acid halides was immobilized onto the membrane surface and the other was conjugated with an amino group of enzymes via an active ester method. Sebacoyl chloride (SC) and trypsin were used as models of the dicarboxylic acid halide and enzyme, respectively. The effects of the reaction conditions such as reaction temperature, trypsin concentration, reaction time, and SC concentration were investigated on the immobilization efficiency with respect to the surface density, specific activity, and activity retention of the immobilized trypsin. The optimum surface density was 36 μg cm⁻², and the corresponding membrane showed an excellent specific activity of 22 U cm⁻² with a high activity retention of 26% in a soaking mode. Furthermore, in a filtration mode, these values largely improved to 118 U cm⁻² and 145% respectively due to the enhanced diffusion force, meaning that the immobilized trypsin on/in the membrane has higher activity than non-immobilized, native trypsin. In addition, the immobilized trypsin exhibited a remarkable improvement in thermal resistance, continuous operation capability, and reusability. Furthermore, the presented method was also applicable to lipase. This technique provides a practical and simple method to immobilize enzymes and offers a tool to design the membranes used in EMBRs.