Fabrication of colloidal stable, thermosensitive, and biocompatible magnetite nanoparticles and study of their reversible agglomeration in aqueous milieu

A number of catechol-terminated copolymers of di(ethylene glycol) methyl ether methacrylate (MEO(2)MA) and poly(ethylene glycol) methyl ether methacrylate (OEGMA) with varied MEO(2)MA-to-OEGMA molar ratios were synthesized via atom transfer radical polymerization triggered by dopamine-derived initiators. They were grafted on magnetite nanoparticles (NPs) via ligand exchange, thus imparting the NPs with robust colloidal stability against salt and excellent biocompatibility. Of importance is that similar to the copolymers of MEO(2)MA and OEGMA, their coated magnetic NPs showed a lower critical solution temperature. This leads to a reversible agglomeration of the resulting composite NPs in buffer and physiological solution in response to the environment temperature. This reversible and thermosensitive agglomeration were also observed within red blood cells after loading the resulting composite NPs into the cells. The agglomeration of magnetite NPs in red blood cells endowed the NP-loaded composite cells with a better magnetic response, for example, contrast enhancement for magnetic resonance imaging.