Solid and Hollow Gold Nanostructures for Nanomedicine: Comparison of Photothermal Properties

The photothermal properties of solid and hollow gold nanostructures represented by colloidal solutions of spherical nanoparticles, nanoshells, and nanocages upon irradiation with a 100 mW 808 nm continuous-wave laser for the first time were experimentally compared under identical optical density and nanoparticle concentration conditions. Accompanying computer modeling of light absorption by the studied gold nanostructures revealed the general parameters influencing the photothermal efficiency, which is of significance for nanomedical applications. The spectral position of localized plasmonic excitations of the studied nanostructures ranged from 518 nm for solid gold nanoparticles to 718 nm for gold nanocages, which provided a possibility to observe a direct influence of the wavelength proximity between the localized surface plasmon resonance and laser line on the heat generation capability of the nanostructures. As a result, the best photothermal efficiency was registered for gold nanocages, which proves them as an efficient photothermal treatment agent and a possible candidate to build a nanocarrier platform for drug delivery with a controlled release. Light absorption modeling demonstrated an existence of optimal wall thickness for gold nanoshells that should lead to the maximum photothermal efficiency when irradiated with 808 nm light, which varied from about 0.1 to 0.4 in units of external nanoshell radius with an increase of the wall porosity. Additionally, computer modeling results show that increased wall porosity should lead to enhanced photothermal efficiency of polydisperse colloidal solutions of hollow gold nanostructures.