Improving immobilization of lipase onto magnetic microspheres with moderate hydrophobicity/hydrophilicity

Magnetic microspheres with carboxyl groups were prepared by copolymerization of vinyl acetate (VAC), acrylamide (AM), and acrylic acid (AA) in the presence of oleic acid-coated Fe3O4 nanoparticles. Scanning electron microscope (SEM) photo showed that the average diameter of magnetic microspheres was about 400 nm. Also, FTIR spectra analysis indicated that monomers were successfully enfolded on the microspheres’ surface. They were used as support to immobilize lipase via physical adsorption and covalent binding. To investigate the effect of the microsphere surface properties on lipase immobilization, a series of microspheres with different hydrophobic/hydrophilic surface characteristics were prepared by adjusting molar percentages of different monomers. The results showed that microspheres with different hydrophobicities/hydrophilicities had different immobilized ratios and different activity recovery. Compared with microspheres having hydrophilic characteristics, that with hydrophobic characteristics had a much higher lipase binding efficiency. However, this study further demonstrated that moderate hydrophobicity/hydrophilicity of microsphere surface was very important for elevating activity recovery. When AM (hydrophilic monomer) held 14.3% of total amount of monomers, the activity recovery was the highest (reaching 87%, 418 U/g support). Possible reasons for these observations were discussed and a supposed mechanism was speculated.