Fig. 1

The uptake of ZnO NPs and the release of zinc ions from ZnO NPs. a TEM image of ZnO NPs internalized in PC12 cells. PC12 cells were treated with 15 μg/mL ZnO NPs for 6 h. Red arrows indicated that ZnO NPs were wrapped into cells. Scale bar, 1 μm. b Exposure to different doses (5, 10, 15 and 20 μg/mL) of ZnO NPs for 2 h showed a particle-specific internalization. The mean SSC-A was analyzed by flow cytometry to represent the uptake of ZnO NPs. c AAS quantification of the uptake of ZnO NPs. PC12 cells were exposed to various concentrations of ZnO NPs for 24 h. Total cellular zinc content was detected as described in “Materials and Methods” and expressed as μg zinc element per mg of cellular proteins. d Fluor™ Zn-520 probe for measurement of intracellular free Zn²⁺ concentrations. After incubation of PC12 cells with 15 μg/mL ZnO NPs for the indicated times, the cells were loaded with Fluor™ Zn-520, then the fluorescence intensity was measured by flow cytometry. e Distribution of labile zinc ions in PC12 cells. Cells were treated with 15 μg/mL ZnO NPs for 12 h. Intracellular co-localization of zinc ions (TSQ probe, blue) with lysosomes (Lyso tracker, red) was imaged using the confocal microscopy and determined by calculation of Pearson’s correlation coefficient (P coloc) of 27 cells. Scale bar, 20 μm. Data from at least three independent experiments were expressed as the means ± SD. *p < 0.05, **p < 0.01, ***p < 0.001 compared with the untreated control