Enhancing the Plasmon Resonance Absorption of Multibranched Gold Nanoparticles in the Near-Infrared Region for Photothermal Cancer Therapy: Theoretical Predictions and Experimental Verification

Multibranched gold nanoparticles (M-AuNPs) can serve as photothermal agents for near-infrared (NIR) photothermal therapy (PTT) of cancer, but a major shortcoming is that they tend to strongly scatter NIR light, causing a significant reduction in absorption. This work addresses this issue, based on theoretical simulations and experimental determinations, to enhance the absorption and reduce the scattering of these materials by screening their structural parameters. Our finite-difference time-domain simulations predict that M-AuNPs with a core size of similar to 25 nm, a tip number of 5, and a tip height of similar to 40 nm (i.e., an aspect ratio of similar to 2) are optimal for trapping NIR light and yielding the highest light-to-heat conversion efficiency (eta) and for trapping NIR light of various polarization and incident directions. The predicted M-AuNPs were synthesized by a seed-mediated growth method, and the measured optical properties agreed well with the simulation results. The M-AuNPs were further used as photothermal agents for in vitro killing of MCF-7 cells and in vivo ablation of tumors constructed on nude mice. Nearly all cells died after they were incubated with M-AuNPs and irradiated under an 808 nm laser at a 1.0 W cm(-2) for 10 min. The tumors on the nude mice were also effectively ablated without regrowth during the observation period (20 days) after PTT.