Upconversion luminescent hollow Er³⁺,Yb³⁺ co-doped Y₂SiO₅ spheres for biophotonics: In vitro cytotoxicity and cellular sub-locality evaluation in glioblastoma cells

Nanostructures that can perform upconversion have been used in several research fields including bioimaging, energy conversion, sensors, and catalysis. In this study, we present the synthesis and comprehensive characterization of Er³⁺, Yb³⁺-co-doped Y₂O₃, and Y₂SiO₅ nanoparticles designed for upconversion applications in the biomedical field. The synthesized nanoparticles were morphologically, structurally, and spectroscopically characterized to investigate their potential for bioimaging and in vitro assays in glioblastoma cells. We evaluated Y₂SiO₅ crystallization by varying the SiO₂ layer thickness on the surface of the Y(OH)CO₃ cores and observed the formation of dispersed hollow spheres using transmission electron microscopy. The X-ray diffraction patterns confirmed the highly crystalline nature of the nanoparticles, showing both cubic Y₂O₃ and monoclinic X1– Y₂SiO₅ crystalline patterns. The vibrational spectroscopy results further supported the structural analysis, revealing specific vibrational modes related to tetrahedral SiO₄ stretching in the X1-Y₂SiO₅ nanoparticles. Photoluminescence studies demonstrated intense green emissions at 525–545 nm and red emission at 650 nm under excitation with a continuous-wave laser at 980 nm. The upconversion processes were analyzed and explained. In vitro studies with the high-grade glioblastoma cell lines U87MG and KNS42 showed promising results with minimal cytotoxic effects, and the subcellular localization of the nanoparticles in the cytoplasm was verified by luminescence, indicating their potential for glioblastoma multiforme diagnosis and phototherapeutic applications in nanomedicine. This work highlights the significant promise of these multifunctional nanoparticles for the advancement of biophotonics and development of safer and more efficient therapeutic approaches in nanomedicine.