Multiphysics Modeling of Plasmonic Photothermal Heating Effects in Gold Nanoparticles and Nanoparticle Arrays

Induced hyperthermia has been demonstrated as an effective oncological treatment due to the reduced heat tolerance of most malignant tissues; however, most techniques for heat generation within a target volume are insufficiently selective, inducing heating and unintended damage to surrounding healthy tissues. Plasmonic photothermal therapy (PPTT) utilizes light in the near-infrared (NIR) region to induce highly localized heating in gold nanoparticles, acting as exogenous chromophores, while minimizing heat generation in nearby tissues. However, optimization of treatment parameters requires extensive in vitro and in vivo studies for each new type of pathology and tissue targeted for treatment, a process that can be substantially reduced by implementing computational modeling. Herein, we describe the development of an innovative model based on the finite element method (FEM) that unites photothermal heating physics at the nanoscale with the micron scale to predict the heat generation of both single and arrays of gold nanoparticles. Plasmonic heating from laser illumination is computed for gold nanoparticles with three different morphologies: nanobipyramids, nanorods, and nanospheres. Model predictions based on laser illumination of nanorods at a visible wavelength (655 nm) are validated through experiments, which demonstrate a temperature increase of 5 °C in the viscinity of the nanorod array when illuminated by a 150 mW red laser. We also present a predictive model of the heating effect induced at 810 nm, wherein the heating efficiencies of the various morphologies sharing this excitation peak are compared. Our model shows that the nanorod is the most effective at heat generation in the isolated scenario, and arrays of 91 nm long nanorods reached hyperthermic levels (an increase of at least 5 °C) within a volume of over 20 μm3.