Metal nanoshells are a class of nanoparticles with tunable optical resonances. In this article, an application of this technology to thermal ablative therapy for cancer is described. By tuning the nanoshells to strongly absorb light in the near infrared, where optical transmission through tissue is optimal, a distribution of nanoshells at depth in tissue can be used to deliver a therapeutic dose of heat by using moderately low exposures of extracorporeally applied near-infrared (

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, r 2 , and a large r 2 /r 1 ratio and therefore could be imaged by MRI to obtain T 2 -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 nanoshellmediated 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 in vivo MRI imaging of the distribution of the nanoparticles before, during, and after photo-thermal therapy.