Photothermal therapy of single cancer cells mediated by naturally created gold nanorod clusters.

Gold nanorods (GNRs) are generally considered to be nontoxic to normal and cancer cells. They are usually accumulated at lysosomes after entering into cells, forming GNR clusters in which strong plasmonic coupling between GNRs is expected. We investigated the photothermal therapy of single cancer cells by exploiting the significantly enhanced two-photon-induced absorption of GNR clusters naturally created in the lysosomes of cancer cells. It was revealed numerically that the plasmonic coupling between GNRs in GNR clusters can effectively enhance the photothermal conversion efficiency. As a result, the thermal damage of single cancer cells can be induced by using pulse energy as low as ~70 pJ. In experiments, the locations of GNR clusters can be accurately determined through the detection of the two-photon-induced luminescence, which is also significantly enhanced, by using a confocal laser scanning microscope. The photothermal therapy was conducted by focusing femtosecond laser light on the targeted GNR clusters, generating bubbles and deforming cell membranes. The photothermal therapy proposed in this work can lead to the rapid and acute injury of single cancer cells. The dependence of the apoptosis time on the pulse energy of femtosecond laser light was also examined. Our findings suggest a novel strategy for the photothermal therapy of single cancer cells with ultralow energy.