Bifunctional Gold Nanoshells with a Superparamagnetic Iron Oxide−Silica Core Suitable for Both MR Imaging and Photothermal Therapy

We describe the synthesis, characterization, and use of hybrid nanoparticles with a superparamagnetic iron oxide (SPIO) core and a gold nanoshell. These multifunctional nanoparticles, designated SPIO-Au nanoshells, displayed superparamagnetic characteristics and a significant absorbance in the near-infrared (NIR) region of the electromagnetic spectrum. In addition, they exhibited high transverse relaxivity, <i>r₂</i> , and a large <i>r₂/r₁</i> ratio and therefore could be imaged by MRI to obtain T₂-weighted images. Moreover, SPIO-Au nanoshells showed efficient photo-thermal effect when exposed to NIR light. The use of SPIO-Au nanoshells, with their combination of unique magnetic and optical properties, should enhance the efficacy of nanoshell-mediated photo-thermal therapy by making it possible to direct more nanoparticles to tumors through the application of external magnetic field and by permitting real-time <i>in vivo</i> MRI imaging of the distribution of the nanoparticles before, during, and after photo-thermal therapy.