Hydrophilic Cu9S5 Nanocrystals: A Photothermal Agent with a 25.7% Heat Conversion Efficiency for Photothermal Ablation of Cancer Cells in Vivo

Photothermal ablation (PTA) therapy has a great potential to revolutionize conventional therapeutic approaches for cancers, but it has been limited by difficulties in obtaining biocompatible photothermal agents that have low cost, small size (<100 nm), and high photothermal conversion efficiency. Herein, we have developed hydrophilic plate-like Cu9S5 nanocrystals (NCs, a mean size of 70 nm x 13 nm) as a new photothermal agent, which are synthesized by combining a thermal decomposition and ligand exchange route. The aqueous dispersion of as-synthesized Cu9S5 NCs exhibits an enhanced absorption (e.g., similar to 1.2 x 10(9) M-1 cm(-1) at 980 nm) with the increase of wavelength in near-infrared (NIR) region, which should be attributed to localized surface plasmon resonances (SPR) arising from p-type carriers. The exposure of the aqueous dispersion of Cu9S5 NCs (40 ppm) to 980 nm laser with a power density of 031 W/cm(2) can elevate its temperature by 15.1 degrees C in 7 min; a 980 nm laser heat conversion efficiency reaches as high as 25.7%, which is higher than that of the as-synthesized Au nanorods (23.7% from 980 nm laser) and the recently reported Cu2-xSe NCs (22% from 808 nm laser). Importantly, under the irradiation of 980 nm laser with the conservative and safe power density over a short period (similar to 10 min), cancer cells in vivo can be efficiently killed by the photothermal effects of the Cu9S5 NCs. The present finding demonstrates the promising application of the Cu9S5 NCs as an ideal photothermal agent in the PTA of in vivo tumor tissues.