Boosting phototherapeutic efficiency with single NIR laser-activated ultrasmall bismuth sulfide quantum dots

The integration of photothermal therapy (PTT) with photodynamic therapy (PDT) has great potential to revolutionize conventional therapeutic approaches for cancers. However, most of the currently developed nanoplatforms for combinatorial phototherapy require the participation of different components or activation of separate lasers. Therefore, a desirable photoactive agent with intrinsic single laser-activated combinatorial phototherapy is still urgently needed for more efficient treatment. Here, we demonstrate a high-temperature organic synthesis, ligand exchange strategy to obtain ultrasmall, water-dispersible, and stable polylysine-bismuth sulfide quantum. dots (PLL-Bi2S3 QDs). In addition to its strong near-infrared (NIR) absorption, the ultrasmall size and sulfide-enriched surface of the obtained Bi2S3 QDs offer abundant photoelectrons with high reducing ability, promoting the rapid generation of reactive oxygen species (ROS). Therefore, excellent photothermal conversion and fast ROS generation ability can be concurrently realized upon 808 nm NIR laser irradiation. As proof of concept, the combined photothermal/photodynamic activity in single PLL-Bi2(S3) QDs was demonstrated both in vitro and in vivo, confirming that the phototherapeutic efficacy is dramatically greater than that of larger Bi2S3 nanorods. In addition, toxicity screening showed that PLL-Bi2S3 QDs possess excellent biocompatibility. Thus, the prepared PLL-Bi2S3 QDs are expected to serve as a photoactive agent for efficient cancer treatment.