Two different reaction strategies designed for core-shell structured and heterostructured Fe3O4@Au nanocomposites utilizing 50 nm polyethyleneimine coated magnetite as seeds are presented aiming at diverse applications. The polyethylenimine (PEI) coated Fe3O4 nanoparticles were firstly used as seeds to carry out the synthesis of both core-shell structured and heterostructured Fe3O4@Au nanocomposites. Results show that these two structures combined the merits of both gold and Fe3O4 nanoparticles. What is more, the distinct morphology offers diverse applications: the shell of dense gold nanoparticles coating in the core-shell structure dominates the further surface functionalization while the heterostructure offers the particles with two distinct surfaces and functionalities due to different surfactant molecules on the surface of Fe3O4 and Au nanoparticles. Furthermore, the synthesis methods presented in this paper also suggested new ways to the synthesis of multifunctional nanostructures. (C) 2012 Elsevier B. V. All rights reserved.