Real-time tracking of Yb³⁺, Tm³⁺ doped NaYF₄ nanoparticles in living cancer cells

The aim of the study was to demonstrate the possibility of real-time tracking of polyethylenimine-coated NaYF₄ :Yb,Tm upconversion nanoparticles (UCNPs) in living cancer cells using wide-field microscopy technique.

Materials and Methods. Human breast adenocarcinoma SK-BR-3 cells and Yb³⁺ , Tm³⁺ doped NaYF₄ nanoparticles with anti-Stokes photoluminescence were used in the study. The nanoparticles were visualized using wide-field microscope with excitation at 975 nm and signal detection in 420–842 spectral range. The analysis of the displacement of UCNPs was performed by fitting the point spread function of the photoluminescent spots corresponding to UCNP location by the Gaussian function, and calculation of mean square displacement. 

Results. UCNPs were rapidly internalized by SK-BR-3 cells and retained in the cells for at least 12 h. Two types of the particles motion were registered: (i) isotropic random spatial fluctuations with relatively small amplitudes and low rate of displacement, and (ii) flick and directional movements with rates up to 1.2 µm/s and total displacement up to tens of microns. The registered types of motion can be attributed to diffusion in local area and intracellular transport of nanoparticles encapsulated in vesicles, respectively.

Conclusion. The demonstrated tracking of UCNPs in human breast adenocarcinoma cells showed that Yb³⁺ , Tm³⁺ doped NaYF₄ nanoparticles are an advanced agent for dynamic studies of intracellular processes. The implemented scheme for UCNPs tracking provides long-term observation with preservation of cell viability for at least several hours. In total, almost complete absence of cell autofluorescence and UCNPs photobleaching, low invasiveness, fast rate of image acquisition allow us to consider the proposed approach as useful for a variety of tasks in biomedical research.