Application of titanium dioxide nanoparticles in photothermal and photodynamic therapy of cancer: An updated and comprehensive review

The usage of nanoparticles (NPs) in treating and diagnosing many diseases, especially cancer, has been investigated in recent studies. The primary purpose of using nanotechnology in cancer treatment is to design a specific NPs-based drug delivery system to target cells. Thanks to their slow degradation, controlled release, optimum surface functionaity, and high optical absorbance, NPs can be used as agents for photothermal therapy (PTT) and photodynamic therapy (PDT). In this connection, the efficiency of the treatment increases, and the side effects are reduced. Titanium dioxide (TiO2) is one of the most basic materials in daily life that represents tremendous photocatalyst activity. Recently, several functionalized biodegradable polymers were recently designed for TiO2 NP-based photothermal and photodynamic therapies. These photosensitizers can be modified by attaching dyes, targeting molecules, and drug molecules. Although these modifications resulted in and have shown enhanced water dispersibility and biocompatibility, TiO2 NPs possess the disadvantage of inducing oxidative stress, leading to the diminution of cellular antioxidants. The wide bandgap of TiO2 limits its absorption merely to the ultra-violet (UV) and not the NIR light region, which provides deep optical imaging of cancer tissue. In addition, the UV-stimulated TiO2 was successfully applied for phototherapy of skin cancers and yielded undesirable outcomes when applied to most deep-tissue tumors. This updated review contains numerous reports on the PDT and PTT applications of TiO2 NPs. More highly efficient functionalized biodegradable polymers exhibiting a non-toxic profile should be prepared regarding the TiO2 NP-based photothermal and photodynamic therapies to overcome the obstacles of traditional TiO2 NPs and, therefore, broaden the use of these nanostructures for further biomedical purposes.