WS2 nanosheet as a new photosensitizer carrier for combined photodynamic and photothermal therapy of cancer cells.

We have developed a simple and efficient strategy to fabricate WS2 nanosheets with low toxicity and good water solubility via a liquid exfoliation method by using H2SO4 intercalation and ultrasonication. The as-prepared WS2 nanosheets were employed not only as an NIR absorbing agent for photothermal therapy (PTT) but also as a photosensitizer (PS) carrier for photodynamic therapy (PDT) due to their sheet like structure that offers large surface area to load PS molecules. Moreover, singlet-oxygen generation of the PSs-WS2 complex could be finely controlled by NIR irradiation that could manipulate the PSs release behavior from WS2 nanosheets. The synergistic anti-tumor effect of WS2 nanosheets mediated PDT-PTT was also evaluated carefully and the results clearly showed that the efficacy of combined PDT-PTT treatment of cancer cells is significantly higher than those of PDT-only and PTT-only treatment, indicating enhanced efficiency of the combined therapeutic system. In addition, the WS2 could be used as a computed tomography (CT) contrast agent for bio-imaging since W atoms have strong X-ray attenuation ability, making them a multifunctional theranostic platform for simultaneous imaging-guided diagnosis and therapy.