A Comparative Study of Copper Chalcogenide Nanocrystals as Agents for Photothermal Therapy

Abstract

In recent years, copper sulfide nanocrystals (NCs) have emerged as promising candidates for new photothermal agents due to their strong near-infrared (NIR) light absorption, high photostability, low toxicity, and suitable size for photothermal therapy.1,2 However, the low photothermal conversion efficiency of copper sulfide NCs in the tissue transparency window from 650 to 900 nm hinders further development of copper sulfide as an effective photothermal agent.3,4 Therefore, it is still necessary to improve the photothermal conversion efficiency near 800 nm for these materials to be used effectively in photothermal therapy.4 As a result, other kinds of copper chalcogenide NCs, such as copper selenide, copper telluride, and their alloys have been recently proposed.5,6,7 By changing the mix of chalcogen substituents in the NC, the localized surface plasmon resonance (LSPR) position can be tuned to more closely match the tissue transparency window, leading to a higher photothermal conversion efficiency near the excitation wavelength.8 Copper selenide-sulfide and copper telluride-sulfide alloy NCs are especially interesting candidate materials for photothermal agents, as they should have lower cytotoxicity than pure copper selenide and copper telluride NCs due to their reduced selenium and tellurium content. However, their potential use for photothermal therapy has not yet been evaluated in depth. Herein, the photothermal conversion efficiency of several copper chalcogenide alloy NCs were investigated to evaluate the potential use of each as a photothermal agent via a comparison with unalloyed copper sulfide NCs. By controlling the composition of the alloys, their localized surface plasmon resonance peaks could be tuned throughout the near-infrared region, potentially leading to materials with resonances more closely matched to ideal therapeutic windows. Moreover, it was found that the photothermal conversion efficiency increased relative to the copper sulfide NCs as the LSPR peaks were tuned more closely to the 808 nm laser wavelength used in this study – directly within the center of the tissue transparency window.