Mini Review of TiO₂ -Based Multifunctional Nanocomposites for Near-Infrared Light-Responsive Phototherapy

Phototherapy with the properties of specific spatial/temporal selectivity and minimal invasiveness has been acknowledged as one of the most promising cancer therapy types. Among all the photoactive substance for phototherapy, titanium dioxide (TiO₂ ) nanomaterials are paid more and more attention due to their outstanding photocatalytic properties, prominent biocompatibility, and excellent chemical stability. However, the wide bandgap (3.0-3.2 eV) of TiO₂ limits its absorption only to the ultraviolet (UV) light region. For a long time, UV light-stimulated TiO₂ was applied in the phototherapy researches of tumors located in the skin layer, while it is unsatisfactory for most deep-tissue tumors. Due to the maximum penetration into tissue existing in the near-infrared (NIR) region, how to use NIR light to trigger photochemical reaction of TiO₂ remains a big challenge. In this review, two strategies to develop and construct NIR-triggered TiO₂ -based nanocomposites (NCs) for phototherapy are summarized, and the relevant mechanism and background knowledge of TiO₂ -based phototherapy are also given in order to better understand the application value and current situation of TiO₂ in phototherapy. Finally, the challenges and research directions of TiO₂ in the future clinic phototherapy application are also discussed.