Nano–bio interactions of upconversion nanoparticles at subcellular level: biodistribution and cytotoxicity

Background: Modern medicine requires intensive research to find new diagnostic and therapeutic
solutions. Recently, upconverting nanoparticles (UCNPs) doped with lanthanide ions have attracted
significant attention. Methods: The efficient internalization of UCNPs by cells was confirmed, and their
precise cellular localization was determined by electron microscopy and confocal studies. Results: UCNPs
colocalized only with specific organelles, such as early endosomes, late endosomes and lysosomes.
Furthermore, experiments with chemical inhibitors confirmed the involvement of endocytosis in
UCNPs internalization and helped select several mechanisms involved in internalization. Exposure to
selected UCNPs concentrations did not show significant cytotoxicity, induction of oxidative stress or
ultrastructural changes in cells. Conclusion: This study suggests that UCNPs offer new diagnostic options
for biomedical infrared imaging.