Orientation Effects on Plasmonic Heating of Near-Infrared Colloidal Gold Nanostructures

Abstract

Photothermal therapy assisted by plasmonic nanostructure relies on the absorption of light energy by the metallic nanoparticle. The manifestation of a rational use of plasmonic-assisted superficial laser thermal therapy procedures requires the analyses of the thermoplasmonic behavior of colloidal nanostructures in random orientation. A quantitative analysis of orientation effect on optically heating metallic nanostructures still unrevealed. Here, we evaluate the thermal properties of metallic nanoparticles (SiO2/Au core-shell particles, Au nanotriangles, Au nanorods, and Au nanocages) irradiated by polarized light. We perform 3D full-wave field analysis to compare absorption properties and temperature rise of these nanoparticles as a function of the nanostructure orientation with respect to applied field polarization. The analysis shows a major variation in joule number of asymmetrical nanostructures (up to 50%) due to orientation effects, which may limit its performance on colloidal photothermal applications. In contrast, the high degree of rotational symmetry of core-shell nanoparticles and nanocages provide greater potential in thermal-assisted phototherapy applications, as their absorption is largely independent (less than 2%) of their orientation in colloid. Our computational results establish new insights for the use of gold nanocages, as a high performance plasmonic structure for thermal applications with colloidal samples.