Thiol-capped Bi nanoparticles as stable and all-in-one type theranostic nanoagents for tumor imaging and thermoradiotherapy.

Bismuth (Bi)-based semiconductors and composites have been well developed for cancer treatments due to their multimodal diagnostic and therapeutic functions, while the development of metallic Bi nanocrystals is rather hindered by the easy-oxidation and unsatisfactory near-infrared photoabsorption. Herein, we prepared uniform Bi nanoparticles (∼40 nm) capped with thiol ligands (Bi-SR) through the chemical reduction method and then surface-modified them with PEGylated phospholipids. The resulting Bi-SR-PEG has strong NIR absorbance and high photothermal conversion efficiency of 45.3%. Importantly, thiol ligands on the surface of Bi-SR-PEG can significantly prevent the metal Bi core from oxidation because of the strong chemisorption energy between sulfur and metal, thus maintaining the high stability and long-term near-infrared photoabsorption. More importantly, given the low toxicity, good blood compatibility and high X-ray attenuation coefficient, Bi-SR-PEG can passively accumulatein the tumor area through intravenous injection, endowing them with the simultaneous tumor CT imaging and thermoradiotherapy, and thereafter they can be metabolized and excreted from the mice body overtime. Therefore, the satisfying therapeutic effect of tumors can be achieved, undoubtedly verifying that Bi-SR-PEG can be used as a novel, stable and all-in-one type theranostic nanoagent for cancer treatment.