Gold Nanoparticles for Photothermal and Photodynamic Therapy

Cancer cells exposed to 13 nm gold nanoparticles and irradiated with cw laser light at 532 nm are shown to undergo cell death via two competing causes. When cells contain relatively high quantities of gold nanoparticles and/or receive a high dose of light, photothermal effects dominate, which are independent of the cellular location of the gold nanoparticles and affect all cells in the irradiated area due to the rapid diffusion of heat. In contrast, at lower doses of nanoparticles and light, the photogeneration of singlet oxygen triggers cell death only in cells that contain a sufficient number of nanoparticles. The parallel occurrence of both effects will need to be considered carefully when designing practical therapy applications. In particular, the photodynamic effect should allow for a cell-type-specific treatment modality that can distinguish between cancer and normal cells using suitable targeting ligands on the nanoparticle surface, providing a highly selective route for cancer therapy.