Controlled synthesis of Au-Fe heterodimer nanoparticles and their conversion into Au-Fe3O4 heterostructured nanoparticles.

We report a facile synthesis of Au-Fe heterodimer nanoparticles (NPs) with tunable Au/Fe sizes and their sequential oxidations to Au-Fe3O4 heterostructured NPs with controllable morphologies. The size of Au in Au-Fe heterodimer NPs was tuned to be 4, 7 and 10 nm, while the Fe crystal structure was maintained as single-crystal bcc. Further oxidation of the as-synthesized Au-Fe NPs led to the formation of Au-hollow Fe3O4 yolk-shell, Au-hollow Fe3O4 heterodimer NPs and Au-porous hollow Fe3O4 yolk-shell NPs, depending on the size of the Au-Fe NPs and the oxidation conditions used. Our study has provided not only a variety of bifunctional NPs with tunable surface plasmon absorption and magnetic properties, but also a new general approach to design and synthesize multicomponent NPs with multiple heterostructures.