Development of functional temperature-responsive poly(styrene-co-N-isopropylacrylamide) latex for enzyme immobilization

Latex particles composed of styrene, N-isopropylacrylamide (NIPAAm), and MA A or GMA were synthesized by emulsifier-free emulsion polymerization. These sub-micron core-shell type non-porous latices are temperature-responsive d ue to the presence of temperature-sensitive monomer (NIPAAm), and shows rev ersible flocculation/dispersion properties in response to change in tempera ture and/or salinity. The comonomer MAA or GMA could provide functional gro ups for immobilization of enzyme through covalent bindings. Immobilized alp ha -chymotrypsin could be reused for 10 times after thermal flocculation an d sedimentation of the enzyme-containing latices in 1 M saline at 30 degree sC, followed by re-dispersion in cold buffer. The optimum conditions for en zyme immobilization were studied and discussed, including polymer compositi ons, concentration of activation reagent, immobilization pH, and enzyme loa ding. Immobilized enzyme showed enhanced thermal stability compared with fr ee enzyme. The specific activity of enzyme after immobilization is close to that of the free enzyme for GMA-containing latex, and around 40% of the fr ee enzyme for MAA-containing latex, even for macromolecular substrates such as casein.