Activating Layered Metal Oxide Nanomaterials via Structural Engineering as Biodegradable Nanoagents for Photothermal...

Layered metal oxides including MoO₃ and WO₃ have been widely explored for biological applications owing to their excellent biocompatibility, low toxicity, and easy preparation. However, they normally exhibit weak or negligible near-infrared (NIR) absorption and thus are inefficient for photo-induced biomedical applications. Herein, the structural engineering of layered MoO₃ and WO₃ nanostructures is first reported to activate their NIR-II absorption for efficient photothermal cancer therapy in the NIR-II window. White-colored micrometre-long MoO₃ nanobelts are transformed into blue-colored short, thin, defective, interlayer gap-expanded MoO_3-x nanobelts with a strong NIR-II absorption via the simple lithium treatment. The blue MoO_3-x nanobelts exhibit a large extinction coefficient of 18.2 L g^-1  cm^-1 and high photothermal conversion efficiency of 46.9% at 1064 nm. After surface modification, the MoO_3-x nanobelts can be used as a robust nanoagent for photoacoustic imaging-guided photothermal therapy to achieve efficient cancer cell ablation and tumor eradication under irradiation by a 1064 nm laser. Importantly, the biodegradable MoO_3-x nanobelts can be rapidly degraded and excreted from body. The study highlights that the structural engineering of layered metal oxides is a powerful strategy to tune their properties and thus boost their performances in given applications.