Cooperative assembly of magnetic nanoparticles and block copolypeptides in aqueous media

We demonstrate that highly crystalline, monodisperse maghemite (gamma-Fe2O3) nanoparticles, synthesized in organic solvents, can be effectively transferred into an aqueous medium using an ammonium salt and stabilized at neutral pH. The nanoparticles remain monodisperse, as characterized by TEM and XRD, as well as superparamagnetic, as determined by SQUID magnetometry. When the aqueous maghemite is combined with the block copolypeptide poly(EG(2)-lys)(100)-b-poly(asp)(30), the nanoparticles assemble into uniform clusters comprised of approximately 20 nanoparticles, resulting in a water soluble block copolypeptide-nanoparticle composite structure.