Bioimaging and toxicity assessments of near-infrared upconversion luminescent NaYF4:Yb,Tm nanocrystals

In vitro or in vivo bioimaging utilizing the upconversion (UC) luminescence of rare earth fluoride nanocrystals (NCs) has attracted much attention, especially for Yb3+/Tm3+ doped NCs with a near-infrared (NIR) UC emission at 800 nm. Herein, water-soluble NaYF4:Yb,Tm NCs with strong NIR UC emission were synthesized with a solvothermal method. In vitro and in vivo bioimaging and toxicity assessments were carried out with HeLa cell and Caenorhabditis elegans (C. elegans) cases, respectively. NaYF4:Yb,Tm NCs afforded an efficient NIR image of the HeLa cells with an incubation concentration of 10 μg mL−1, and CCK-8 assay revealed a low cytotoxicity. Fed with Escherichia coli (E. coli) and NCs together, the C. elegans showed a NIR image in the gut from the pharynx to the anus. Further, these NCs could be excreted out when those worms were then fed with only E. coli. Toxicity studies were further addressed with protein expression, life span, egg production, egg viability, and growth rate of the worms in comparison with those of the intact ones. The feeding of rare earth fluoride NCs with a dose of 100 μg does not arise obvious toxicity effect from the growth to procreation. The in vitro and in vivo studies confirm that NaYF4:Yb,Tm NCs could be served as an excellent NIR emission bioprobe with low toxicity.