Surface-induced reversible addition-fragmentation chain-transfer (RAFT) polymerization was carried out to grow diblock polymer brush of poly(ethylene glycol) monomethacrylate and N-isopropylacrylamide on magnetic nanoparticles (MNPs). After the chain transfer agent group for RAFT polymerization was chemically bound on the surfaces of MNPs, poly(N-isopropylacrylamide) was grown from the surfaces of MNPs via RAFT polymerization. The initial homopolymer on MNPs was used as the chain transfer agent for the RAFT polymerization of the second monomer. TEM, TGA FTIR and XPS measurements indicated that MNPs were successfully modified. The diblock copolymer brushes decrease the nonspecific adsorption of proteins on MNPs. (C) 2011 Elsevier B.V. All rights reserved.