Controlled killing of human cervical cancer cells by combined action of blue light and C-doped TiO2 nanoparticles

Abstract

In this study, C-doped TiO₂ nanoparticles (C-TiO₂) were prepared and tested as a photosensitizer for visible-light-driven photodynamic therapy against cervical cancer cells (HeLa). X-ray diffraction and Transmission Electron Microscopy confirmed the anatase form of nanoparticles, spherical shape, and size distribution from 5 to 15 nm. Ultraviolet-visible light spectroscopy showed that C doping of TiO₂ enhances the optical absorption in the visible light range caused by a bandgap narrowing. The photo-cytotoxic activity of C-TiO₂ was investigated in vitro against HeLa cells. The lack of dark cytotoxicity indicates good biocompatibility of C-TiO₂. In contrast, a combination with blue light significantly reduced the survival of HeLa cells: illumination only decreased cell viability by 30% (15 min of illumination, 120 µW power), and 60% when HeLa cells were preincubated with C-TiO₂. We have also confirmed blue light-induced C-TiO₂-catalyzed generation of reactive oxygen species in vitro and intracellularly. Oxidative stress triggered by C-TiO₂/blue light was the leading cause of HeLa cell death. Fluorescent labeling of treated HeLa cells showed distinct morphological changes after the C-TiO₂/blue light treatment. Unlike blue light illumination, which caused the appearance of large necrotic cells with deformed nuclei, cytoplasm swelling, and membrane blebbing, a combination of C-TiO₂/blue light leads to controlled cell death, thus providing a better outcome of local anticancer therapy.

Keywords: Autophagy; Blue light; C-doped TiO2; HeLa; Photodynamic therapy; Reactive oxygen species.