Metallic 1T Phase Enabling MoS2 Nanodots as an Efficient Agent for Photoacoustic Imaging Guided Photothermal Therapy in the Near-Infrared-II Window.

Transition metal dichalcogenide (TMD) nanomaterials, specially MoS2 , are proven to be appealing nanoagents for photothermal cancer therapies. However, the impact of the crystal phase of TMDs on their performance in photoacoustic imaging (PAI) and photothermal therapy (PTT) remains unclear. Herein, the preparation of ultrasmall single-layer MoS2 nanodots with different phases (1T and 2H phase) is reported to explore their phase-dependent performances as nanoagents for PAI guided PTT in the second near-infrared (NIR-II) window. Significantly, the 1T-MoS2 nanodots give a much higher extinction coefficient (25.6 L g-1  cm-1 ) at 1064 nm and subsequent photothermal power conversion efficiency (PCE: 43.3%) than that of the 2H-MoS2 nanodots (extinction coefficient: 5.3 L g-1  cm-1 , PCE: 21.3%). Moreover, the 1T-MoS2 nanodots also give strong PAI signals as compared to negligible signals of 2H-MoS2 nanodots in the NIR-II window. After modification with polyvinylpyrrolidone, the 1T-MoS2 nanodots can be used as a highly efficient agent for PAI guided PTT to effectively ablate cancer cells in vitro and tumors in vivo under 1064 nm laser irradiation. This work proves that the crystal phase plays a key role in determining the performance of nanoagents based on TMD nanomaterials for PAI guided PTT.