Formation of gold-coated magnetic nanoparticles using TiO₂ as a bridging material

TiO₂ nanoparticles with embedded magnetite were suspended in aqueous HAuCl₄ and ultraviolet irradiated to photodeposit gold on the surface. The degree of gold coating and the wavelength of absorbance could be controlled by adjusting [HAuCl₄]. Absorbance maxima were between 540-590 nm. Particles exhibited superparamagnetic properties (blocking temperature ∼170 K) whether or not coated with gold. These particles have potential applications as drug delivery agents, magnetic imaging contrast agents, and magnetically separatable photocatalysts with unique surface properties.