Methods for forming core-shell magnetic nanoparticles are provided. The method can include: forming an oxide shell around a metal oxide core to form a core-shell magnetic nanoparticle; attaching an anchoring agent to the magnetic nanoparticle; reacting a RAFT agent with the functional group of the anchoring agent such that the RAFT agent is bonded to the magnetic nanoparticle through the anchoring agent; and attaching a polymeric chain to the RAFT agent.