Hydrothermal synthesis of defective TiO2 nanoparticles for long-wavelength visible light-photocatalytic killing of cancer cells

Defective TiO2 nanoparticles (d-TiO2 NPs) were successfully synthesized using a simple hydrothermal technique through the formation of liposome–TiO2 composites using P25 TiO2 powder as the starting material. The morphology and vibrational structures of the d-TiO2 NPs were characterized by various techniques, including X-ray diffraction, transmission electron microscopy, and Fourier transform-infrared and Raman spectroscopic analyses. The synthesized d-TiO2 NPs were composed of both the rutile and anatase phases of TiO2 with a diameter of approximately 25 nm, and they exhibited absorption of broad visible light including near-infrared wavelengths, from 400 nm to 1000 nm, which was confirmed by diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The agglomeration size of the d-TiO2 NPs in aqueous solution was lesser (224 nm) than that of P25 TiO2 (1440 nm). Therefore, the synthesized d-TiO2 NPs could more easily infiltrate the membrane and cytoplasm of cancer cells via endocytosis than could P25 TiO2. Consequently, upon irradiation with long-wavelength visible light (400–800 nm), the d-TiO2 NPs could generate reactive oxygen species, including singlet oxygen, leading to the destruction of cancer cells. These results suggest that the newly fabricated d-TiO2 NPs are promising nanomaterials for future in vivo photodynamic therapy of cancer.