Poly(carboxybetaine methacrylate)-grafted silica nanoparticle: A novel carrier for enzyme immobilization

Polymer-coated nanoparticles are favorable carriers for enzyme immobilization for their advantages of high specific surface area, small mass transfer resistance and a large number of active groups for covalent bonding of enzymes. Of the various polymers, zwitterionic polymers have been found to work as protein stabilizers. Inspired by the literature outcomes, we have herein developed a novel nanoparticle-based carrier modified by grafting a highly hydrophilic zwitterionic polymer, poly(carboxybetaine methacrylate) (pCBMA), on silica nanoparticles (SNPs), which was denoted as SNPs-pCBMA. For comparison, an uncharged polymer, poly(glycidyl methacrylate) (pGMA), was also grafted onto SNPs to prepare SNPs-pGMA. The two types of polymer-grafted SNPs were extensively characterized and used for the covalent bonding of two enzymes, catalase and lipase (pGMA-CAT, pCBMA-CRL, pGMA-CRL and pCBMA-CRL). The results revealed that both the immobilized enzymes on SNPs-pCBMA exhibited higher thermal and storage stabilities than those on SNPs-pGMA, due to protective effects of the zwitterionic polymer. For example, by incubation at 50 °C for 20 min, the residual activities of pCBMA-CAT and pCBMA-CRL kept 60.5% and 60.3% of their initial activities, respectively, higher than those of pGMA-CAT and pGMA-CRL (55.6% and 48.3%, respectively). The immobilized enzymes on SNPs-pCBMA also exhibited higher stability under neutral and alkaline conditions and good reusability. Taken together, the research proved that pCBMA-grafted materials were promising support for enzyme immobilizations.