Synthesis of monodisperse superparamagnetic Fe/silica nanospherical composites.

A new method for the synthesis of monodisperse superparamagnetic nanospherical composites with a core containing metallic alpha-Fe nanocrystals dispersed in a silica matrix, and a shell only containing silica, is reported. Essential to the formation of this microstructure is to work with lamellar-like structures in conditions close to the upper-phase boundary limit for formation of microemulsions, and to control the solubility and pH of the metallic precursors. An advantage of the method is its versatility, which allows us to change the particle size (both for the nanomagnets and for the composite) and the spatial arrangement of the nanomagnets in the matrix. Our results indicate that this material could be adequate for biotechnology applications.