Europium and Calcium-Co-Doped TiO2 Nanocrystals: Tuning the Biocompatibility and Luminescent Traceability of Drosophila melanogaster

We explored the TiO2 nanocrystals (NCs) by introducing red luminescence via europium (Eu) ion doping (TiO2:Eu). Our objective was to optimize their biocompatibility and luminescence through calcium (Ca) co-doping. To achieve this, nanomaterials were synthesized, and physical characterizations were performed by investigating the effects of the crystalline phase of TiO2 on the doping, morphology, zeta potential, hydrodynamic diameter, and photocatalytic properties. Biological assessments were conducted using in vitro assays with human osteosarcoma cells (SAOS-2) through cytotoxicity assays and in vivo assays with Drosophila melanogaster, where we evaluated the mortality rate during postembryonic development and the luminescence of nanomaterials in vivo. Our results demonstrated the successful integration of Ca ions into the TiO2:Eu crystal (TiO2:Eu:xCa) structure without the emergence of additional phases or compounds. The co-doping of Ca led to a reduction of approximately 70% in photocatalytic activity. Moreover, co-doping with Ca was not cytotoxic to SAOS-2 cells. Our in vivo analysis showed no delays in postembryonic development and no larval or pupal lethality. The larval mortality rate and pupal formation rate were comparable to the control group when Drosophila were exposed to nanomaterials at concentrations of 1 mg/mL or lower. Luminescence of the NCs was detected in confocal microscopy images, indicating the presence of NCs in the larval brain and intestines. This luminescence was observed in Europium and Calcium-Co-Doped TiO2 (TiO2:Eu:xCa). These results showed that Ca doping improved the biocompatibility and enhanced the luminescence of these materials, making them traceable in biological tissues. Therefore, our research provides valuable insights into the tailored properties of TiO2 for potential applications in various fields of biomedicine.