Advanced hybrid nanoparticles.

Methods for the development of bifunctional magnetic and optically tunable nanoparticles with a structural design involving a magnetic iron oxide core (Fe3O4/gamma-Fe2O3) surrounded by a thick silica shell and further covered with an outer shell of optically active nanoparticles (CdTe quantum dots or gold nanoparticles) are reported. These highly fluorescent, optically tunable, and magnetic core-shell nanoparticles were synthesized from a modified Stöber method combined with the Layer-by-layer (LbL) assembly technique. Both types of particles were prepared through two main steps, including a controlled addition of tetraethoxysilane (TEOS) to a dispersion of Fe3O4/gamma-Fe,O3 nanoparticles, which were thereby homogeneously incorporated as cores into monodisperse silica spheres. The second step involved the LbL assembly of polyelectrolytes and luminescent CdTe quantum dots or Au nanoparticles onto the surface of the silica-coated magnetite/maghemite particles, which (for CdTe) were finally covered with an outer, protective silica shell. These spherical particles have a typical diameter of 220 and 230 +/- 10 nm, a saturation magnetization (Ms) of 1.34 emu/g at room temperature and a strong excitonic photoluminescence or an intense surface plasmon band.