Preparation And Chracterization Of Hydrophilic Magnetic Submicron Partilces

PEG-1540-bis-（maleic monoester）、 PEG-400-bis-（maleic monoester）and PEG-1540-maleic monoester-succinic monoester were prepared asmonomers by reactions of PEG （PEG-1540, PEG-400） with correspondinganhydrides. Magnetic-submicron-particles （MSPs） functionalized withcarboxyl groups were prepared by one-step radical polymerization of suchmonoester（s） in W/O microemulsion systems to coat magnetofluids. SuchMSPs generally had abundant carboxyl groups suitable for immobilizingbiomolecules, negligible nonspecific bindings, excellent suspension stabilityand desirable structural stability at pH over7.0, but appeared as cluster-likeparticles with micrometer sizes. Their saturation magnetization and sterichindrance around carboxyl groups on their surfaces were mainly affected bythe chain length, ratio in mixtures, and quantities in microemulsion systemsof the two types of monomers used. Under optimized conditions,MSP-PEG-D4with diameters of0.32μm, saturation magnetization over46emu·g-1and titrated carboxyl groups of about0.43mmole·g^-1were obtained.After conversion of carboxyl groups on such MSPs into activated esters,glutathione-S-transferase was immobilized at about10mg·g^-1MSPs, andstreptavidin weas immobilized at6mg·g^-1MSPs, via N-acylation.Immobilized streptavidin retained （61±18）%of its specific activity （n=8）, but immobilized glutathione-S-transferase retained only about5%of itsspecific activity, possibly due to the modification of its essential aminogroups. This facile one-step approach was promising to prepare MSPs formost biomedical applications.