A method for the development of bifunctional magnetic and optically tunable nanoparticles with a structural design involving a magnetic iron oxide core (Fe3O4/γ-Fe2O3) surrounded by a thick silica shell and further covered with an outer shell of gold is reported. These gold-coated magnetic silica spheres take advantage of the strong resonance absorption they show in the visible and near-infrared (NIR) range and can be controlled by using an external magnetic field, which makes them very promising in biomedical applications.