Facile synthesis of monodispersed silica-coated magnetic nanoparticles

Silica-coated magnetic nanoparticles (MNPs) have great potential for use in field of biotechnology owing to their unique properties, which can be manipulated by an external magnetic field gradient. Herein, we describe a method for facile synthesis of monodispersed silica-coated MNPs (MNP at SiO₂ NPs). Commercially available oleate-MNPs were successfully converted to polyvinylpyrrolidone-MNPs (PVP-MNPs), and then coated with silica by the modified Stöber method. More than 95% of MNPs were individually coated with a silica shell; non-magnetic core silica nanoparticles (NPs) were not detected. Notably, the MNP at SiO₂ NPs are highly monodispersed in size (size distribution<2.5%) and synthesis at the scale of grams was easily obtained by a simple scale up process. Moreover, aggregation was not detected upon storage of over three months.