Photocatalytic and Cytotoxic Effects of Nitrogen-Doped TiO₂ Nanoparticles on Melanoma Cells

Titanium dioxide (TiO₂) has attracted attention as a photosensitizer in the field of photodynamic therapy (PDT) due to its low toxicity and high photostability. In the present work, nitrogen-doped TiO₂ (N–TiO₂) nanoparticles had their photokilling efficiency evaluated on a murine melanoma cell line (B16-F10) and fibroblasts (NIH 3T3). The N–TiO₂ nanoparticles were prepared by a modified hydrogen peroxide sol–gel process using triethylamine as nitrogen precursor. XRD measurements showed that all TiO₂ and N–TiO₂ samples consisted of an anatase crystalline phase and no trace of rutile was detected. N–TiO₂ nanoparticles showed higher absorbance in the visible region than pure TiO₂. Nanoparticle dosage increase from 0.1 mg/ml to 0.5 mg/ml played a role in cell viability, causing high cytotoxicity in melanoma and fibroblast cells. The cytotoxic potential of N–TiO₂ on cells was analyzed using visible light, UV-A irradiation and dark conditions. All samples were cytotoxic in a PDT test, and N–TiO₂ caused 93% death in melanoma cells under UV irradiation treatment at 0.5 mg/ml. Gene expression analysis of this sample showed, under ultraviolet photoexcitation, an increase of pro-apoptotic BAX gene expression, suggesting cell death by apoptosis.