Titanium dioxide is well-known material mainly due to its interesting photocatalytical activity. Due to properties such as strong light absorption in UV range, low toxicity, biocompatibility and chemical stability, TiO₂ is widely used not only in the field of photochemistry, but also in biomedicine [1]. Particular focus is on its photocatalytical properties that can greatly benefit the photodynamic therapy (PDT) in cancer treatment, by acting as a photosensitizer (PS) and/or as carrier of other photosensitizing molecules or biologically active molecules (e.g. antibodies). The predominant role of TiO₂ NPs in PDT is a generation of Reactive Oxygen Species (ROS) upon light exposure and with the contribution of the molecular oxygen, which exhibit cytotoxicity towards cell located in their vicinity [2].
In order to maximize photosensitizing properties, nanocrystalline particles of TiO₂ doped with acceptor Fe³⁺ ions (1-10 wt. %) have been prepared with the sol-gel method. The synthesis procedure included modification with polyethylene glycol (PEG400) after nanoparticles formation. The morphology and phase composition of as-prepared NPs have been investigated with XRD and TEM. According to results, TiO₂ NPs, crystallize in the predominant anatase phase over the rutile and brookite trace contribution, what has been also evidenced with Raman spectroscopy. UV-Vis studies have shown significant changes of the band gap structure and light absorption properties upon Fe-doping and PEG modification. The cellular response to as-prepared NPs treatment have been studied in vitro on cervical cancer cells (HeLa) and normal fibroblasts (Detroit 551) with Live/Dead (Calcein/Ethidium homodimer-1) fluorescent assay. In turn, the photo-induced cytotoxic activity of HeLa in comparison to normal fibroblasts have been investigated with WST-1 assay using near-visible (405 nm) light irradiation. Finally, the cellular uptake of TiO₂ NPs and their effect on the cell viability and morphology have been observed with fluorescence and confocal microscopy using fluorescent labeling method with FITC dye (fluorescein isothiocyanate) and specific cross-staining of mitochondria (Mito-Tracker green), lysosomes (Lyso-Tracker red) and nuclei (Hoechst).

Acknowledgements
The work was supported by the International PhD Projects Programme of Foundation for Polish Science operated within the Innovative Economy Operational Programme (IE OP) 2007-2013 within European Regional Development Fund.

References
[1]  Fei Yin, Z., Wu, L., Gui Yang, H., Hua Su, Y., Physical Chemistry Chemical Physics, 2013, 15, 4844-4858.
[2] Jańczyk, A., et al., Free Radical Biology and Medicine, 2008, 44, 1120-1130.

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