Fig. 3
a Cytotoxicity assays showing viability of tested neuroblastoma cells after incubation with Ln-doped QDs (0.001–1 mM, 24 h). b MTT assay of green CdTe QDs illustrating their pronounced cytotoxicity in comparison to Ln-doped QDs. Inserted are basic characteristics of CdTe and image depicting their endocytosis (red, 10,000 MW pHrodo Red) in UKF-NB-4 cells. Scale bar, 20 μm. Red line indicates approximate 24IC50 values. The values are expressed as the mean of six independent replicates (n = 6). Vertical bars indicate standard error. *p < 0.05, **p < 0.01 related to control non-treated cells. c Living cells fluorescence microscopy showing Ln-doped QDs-induced endocytosis (10,000 MW pHrodo Green). Scale bars, 200 μm. BF bright field image. d Cytoplasmic accumulation of YbQDs and TbQDs in UKF-NB-4 cells. Scale bars, 40 μm. In all microscopic analyses, nuclei were counterstained with Hoechst 33342. Prior to microscopy, cells were incubated with 2 μM QDs for 6 h