An improved way to prepare superparamagnetic magnetite-silica core-shell nanoparticles for possible biological application

This paper describes an improved approach for the coating of superparamagnetic magnetite nanoparticles with shells of amorphous silica. Magnetite (Fe3O4) nanoparticles are prepared by partial reduction coprecipitation method and modified by adding citric acid. The silica coating is conveniently controlled by a dilute silicate solution pretreatment and subsequent Stöber process directly in ethanol. Transmission electron microscopy, photon correlation spectroscopy and zeta-potential analysis results show that the attractions between the superparamagnetic nanoparticles are screened by the silica coating. With enough tetraethylorthosilicate added, the stable core-shell colloid was obtained. Vibrating sample magnetometer characterization shows that the magnetic core-shell structure is superparamagntic.