Intracellular imaging of HeLa cells by non-functionalized NaYF4 : Er3+, Yb3+ upconverting nanoparticles.

We report on the efficient incorporation of non-functionalized NaYF(4) : Er(3+), Yb(3+) nanoparticles inside HeLa live cancer cells by direct endocytosis. The efficient two-photon excited near-infrared-to-visible upconversion fluorescence of these nanoparticles is then used to obtain high-contrast intracellular fluorescence images of single cells. These images reveal a redistribution of the nanoparticles inside the cell as the incubation time increases. Thus, non-functionalized NaYF(4) : Er(3+), Yb(3+) nanoparticles emerge as very promising fluorescence probes for real-time imaging of cellular dynamics.