In Situ Synthesis of Iron Oxide within Polyvinylamine Nanoparticle Reactors

Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility with a size less than 200 nm are of great interest for medical applications. Traditionally, synthetic and natural polymers have been employed as surface modifiers to stabilize magnetite nanoparticle suspensions and improve their function in vivo. Unfortunately, current surface modification strategies often are not successful in maintaining colloidal stability during synthesis or during transfer of magnetite nanoparticle to an aqueous phase. Here, a unique methodology for synthesizing magnetite within stable polymer nanoparticle dispersions has been developed. Polyvinylamine (PVAm) nanoparticles absorbed iron ions from solution via binding of iron with primary amine groups. Iron-loaded nanoparticles were then used as a reactor to synthesize iron oxide. The resulting PVAm nanoparticles exhibited more than 10% magnetite loading, offered excellent colloidal stability, and contained reactive primary amines for possible drug conjugation or surface modification. Transmission electron microscopy (TEM) images showed that the dispersions contained ∼100 nm diameter PVAm nanoparticles incorporating iron oxide particles with a size less than ∼10 nm. The aqueous synthesis of iron oxide inside PVAm nanoparticles is an effective approach to maintain colloidal stability and offers particles with a high density of reactive site for ligand grafting. This scheme provides a unique synthetic methodology for medical applications such as contrast-enhanced magnetic resonance imaging or drug delivery.