Affinity membranes as a tool for life science applications

As a matrix for affinity membrane technology we chose a flat-sheet microfiltration membrane based on polypropylene. Using photopolymerization to graft epoxy groups onto the pore surface, we worked with glycidyl-methacrylate as a monomer. We developed optimized, efficient, and mild UV irradiation conditions for the two-step photografting process practically preserving the given pore structure of the base membrane. A grafting degree of up to 1.2 mg/cm(2) per surface area of the membrane was obtained. The polypropylene membrane surface became significantly more hydrophilic. Introduction of epoxy groups allowed a stable covalent immobilization of the protein streptavidin serving as receptor for affinity ligand binding. A relatively high streptavidin immobilization capacity of about 65 mug/cm(2) per surface area of the membrane was obtained. Apparently, only about two of the binding sites of the immobilized streptavidin were available for biotin recognition. We also found that the oriented immobilization of biotinylated alkaline phosphatase onto the surface via a streptavidin bridge increased the specific enzymatic activity about sixfold compared with random immobilization of this enzyme.