Abstract Fe 3 O 4 magnetic nanoparticles (MNPs) were modified with (3-aminopropyl) triethoxysilane through silanization. An atom transfer radical polymerization-initiating site immobilized onto amine-functionalized Fe 3 O 4 MNPs. The surface-initiated atom transfer radical polymerization of 4-vinylpyridine was then performed in the presence of Fe 3 O 4– SiO 2–Br nanoparticles, which led to the formation of Fe 3 O 4–SiO 2–P4VP [P4VP= poly ( ...