Abstract: - A novel active biocatalytic reaction system is proposed by covalently immobilizing porcine pancreas trypsin within the thermore-sponsive polymer shell of superparamagnetic Fe3O4 nanoparticles. Active ester-functional nanocarriers suitable for the immobilization of amino functional targets are obtained in a single polymeriza-tion step by grafting-from copolymerization of an active ester monomer from superparamagnetic cores. The comonomer, oligo(ethylene glycol) methyl ether methacrylate, has excellent water solubility at room temperature, biocompatibility, and a tunable lower critical solution temperature (LCST) in water. The phase separation can alternatively be initiated by magnetic heating caused by magnetic losses in ac magnetic fields.