Optimal design of gold nanoshells for optical imaging and photothermal therapy

Gold nanoshells are of great interest in optical imaging based on their light scattering properties and photothermal therapy due to their light absorption properties. Strong light scattering is essential for optical imaging, while effective photothermal therapy requires high light absorption. In this article, the optimal core radii and shell thicknesses of silica–gold and hollow gold nanoshells, possessing maximal light scattering and absorption at wavelengths between 700 and 1100 nm, are obtained using the Mie theory of a coated sphere. The results show that large-sized gold nanoshells of high aspect ratios (the aspect ratio is defined as the ratio of core radius to shell thickness) are the efficient contrast agents for optical imaging, while smaller gold nanoshells of high aspect ratios are the ideal therapeutic agents for photothermal therapy. From the comparison of the numerical results for silica–gold and hollow gold nanoshells, the latter are seen to offer a little superior light scattering and absorption at smaller particle size. Fitting expressions for the optimal core radii and shell thicknesses are also obtained, which can provide design guidelines for experimentalists to optimize the synthetic process of gold nanoshells.