Optical trapping of NaYF4:Er3+,Yb3+ upconverting fluorescent nanoparticles

Patricia Haro, Blanca del Rosal, Laura Martínez Maestro, Rafik Naccache, John A. Capobianco, Kishan Dholakia, José García Solé, Emma Martín Rodríguez and Daniel Jaque García
We report on the first experimental observation of stable optical trapping of dielectric NaYF4:Er3+,Yb3+ upconverting fluorescent nanoparticles (~26 nm in diameter) using a continuous wave 980 nm single-beam laser. The laser serves both to optically trap and to excite visible luminescence from the nanoparticles. Sequential loading of individual nanoparticles into the trap is observed from the analysis of the emitted luminescence. We demonstrate that the trapping strength and the number of individual nanoparticles trapped is dictated by both the laser power and nanoparticle density. The possible contribution of thermal effects has been investigated by performing trapping experiments in heavy water in addition to distilled water. For the case of heavy water, thermal gradients are negligible and optical forces dominate the trap loading behaviour. The results provide a promising path towards real three dimensional manipulation of single NaYF4:Er3+,Yb3+ nanoparticles for precise fluorescence sensing in biophotonics experiments.
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