Figure 7.

Synthetic scheme for the preparation of the three-layer NPs (left); TEM images of colloids after each synthetic step. ab SiO2 particles covered with silica-primed Fe3O4 NPs (SiO2–Fe3O4). cd SiO2 particles covered with silica-primed Fe3O4 NPs and heavily loaded with Au nanoparticle seeds (SiO2–Fe3O4–Au seeds). e Three-layer magnetic NPs synthesized in a single-step process from particles presented in (c) and (d). Note the uniformity of the gold shell. The inset shows the three-layer magnetic NPs drawn to the wall with a magnet. From [125]

Wu et al. Nanoscale Research Letters 2008 3:397-415   doi:10.1007/s11671-008-9174-9