Attachment of gold nanograins onto colloidal magnetite nanocrystals

The successful attachment of 2-3 nm gold particles to similar to 10 nm Fe3O4 nanocrystals through a simple, two-step chemically controlled procedure is reported. The surface of individual, relatively monodisperse, Fe3O4 nanospheres forming a stable colloidal methanolic solution is coated with an amino-terminated silane, peptized to induce positive charges on the particles' surfaces and then treated with a colloidal solution of negatively charged An nanoparticles. A detailed investigation by transmission electron microscopy, X-ray diffraction, UV-vis, inductively coupled plasma, and superconducting quantum interference device magnetometry was performed in order to elucidate the morphology and properties of the nanocomposites. Due to their low concentration and small size of the attached Au particles, the optical properties are not observable in the case of the Fe3O4/Au nanocomposites. Additionally, the colloidal Fe3O4/Au nanocomposites are highly stable against separation and exhibit magnetic properties similar to those of the parent Fe3O4 nanocrystals. These novel nanoarchitectures open up new opportunities for the use of magnetite nanoparticles for in-vivo biomedical applications through chemical bonding of bioactive molecules to the attached Au nanoparticles.