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.