Advanced Hybrid Nanoparticles

Verónica Salgueiriño-Maceira, Miguel A. Correa-Duarte, M. Arturo López-Quintela, and José Rivas

J. Nanosci. Nanotechnol., 2009, 9, 3684–3688

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-Fe2O3 nanoparticles, which were thereby homogeneously incorporated as cores into monodis-perse 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 (M s) of 1.34 emu/g at room temperature and a strong excitonic photoluminescence or an intense surface plasmon band.