Fig. 6

N-GQDs caused oxidative stress and dysfunction in mitochondria of BV2 cells. a Representative fluorescent images of internalization of N-GQDs (blue) in BV2 cells treated with 100 μg/mL N-GQDs for 24 h. Nuclei are stained by AO (green). Mitochondria are stained by MitoTracker (red). Scale bars: 10 μm; b TEM images showing the ultrastructure of BV2 cells treated with 100 μg/mL N-GQDs for 24 h. The asterisks indicate aggregated GQDs in endosomes/lysosomes. The red boxes indicate aggregated GQDs. The white arrows indicate normal mitochondria, the red arrows indicate mitochondrial shrinkage, the yellow arrows indicate broken mitochondrial ridge, and the blue arrows indicate collapse of mitochondrial membrane; Representative fluorescent images of mitochondrial iron level (c), mitochondrial ROS (mtROS) production (d) and mitochondrial lipid peroxidation (e) in BV2 cells treated with 25, 50 and 100 μg/mL N-GQDs for 24 h. Nuclei are stained by DAPI (blue). Iron levels are detected by Mito-FerroGreen (green). mtROS are detected by MitoSOX (red). Oxidative lipid are detected by LiperFluo (green). Mitochondria are marked by MitoTracker (red) and MitoTracker (green), respectively. Merging of the red and green color results in a yellow signal. Scale bars: 20 μm; f Representative flow cytometer dot plot of mitochondrial transmembrane potential (Δψ_mt) in BV2 cells treated with 25, 50 and 100 μg/mL N-GQDs for 24 h were identified by using JC-1; g Quantitative results of red fluorescence positive cells from flow cytometer analysis. Data are expressed as the mean ± SE of three independent experiments, performed in triplicate. Statistical significance was determined by one-way ANOVA and Dunnett’s t test (*P < 0.05, **P < 0.01, ***P < 0.001 vs. the control group)