Optimal dimensions of gold nanoshells for light backscattering and absorption based applications

•Resonance intensity of nanoshells strongly depends on the core and shell sizes.•Resonance wavelength of nanoshells can be tuned to the near-infrared region.•We obtain the optimal dimensions of nanoshells for biological imaging.•We obtain the optimal dimensions of nanoshells for photothermal therapy.•We optimize nanoshells for combined biological imaging and photothermal therapy.

Gold nanoshells, a novel type of composite spherical nanoparticle consisting of a spherical dielectric core covered by an ultrathin gold shell, have been used as contrast agents for biological imaging as well as therapeutic agents for photothermal therapy based on their strong backscattering and absorption properties. In this paper, we investigate the dependence of the backscattering and absorption properties of silica core-gold nanoshells on the core radius and shell thickness by using the Mie theory for a coated sphere with the size-dependent dielectric function of metal nanoparticles. Our results show that, by varying the core radius and shell thickness, the position and intensity of the backscattering and absorption resonance peak can be tuned within the visible and near-infrared regions. We obtain the optimal dimensions of silica core-gold nanoshells for light backscattering and absorption based applications: biological imaging, photothermal therapy, and combined biological imaging and photothermal therapy. The optimized gold nanoshells can be used as ideal contrast and therapeutic agents.