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.