Two-dimensional TiS₂ Nanosheets For In Vivo Photoacoustic Imaging And Photothermal Cancer Therapy

Recently, two-dimensional(2D) nanomaterials with unusual physical and chemical properties have been extensively explored in materials science and engineering. Graphene, a 2D single layer of carbon atoms of honeycomb lattice structure, as a typical example, has shown exceptional electronic, optical, thermal, and mechanical properties. As the analogues of graphene, transition-metal dichalcogenides(TMDCs) such as MoS2, MoSe2, WS2, WSe2 and Bi2Se3, consisting of hexagonal layers of metal atoms sandwiched between two layers of chalcogen atoms, have also become a star in materials science in recent years, showing promising applications in many different areas including nanomedicine.Titanium dichalcogenides(TiS2) is a typical class of TMDC materials and has also been studied recently in electronic devices or as a hydrogen-storage material. In this study, TiS2 nanosheets, are synthesized by a bottom-up solution-phase method and then modified with polyethylene glycol(PEG), obtaining TiS2-PEG with high stability in physiological solutions and no appreciable in vitro toxicity. Due to their high absorbance in the near-infrared(NIR) region, TiS2-PEG nanosheets could offer strong contrast in photoacoustic imaging, which uncovers the high tumor uptake and retention of those nanosheets after systemic administration into tumor-bearing mice. We further apply TiS2-PEG nanosheets for in vivo photothermal therapy, which is able to completely eradicate the tumors on mice upon intravenous injection of TiS2-PEG and the followed NIR laser irradiation. Our work indicates that TiS2 nanosheets with appropriate surface coating(e.g. PEGylation) would be promising new class of photothermal agent for imaging-guided cancer therapy.