MitoTracker staining per cell, as measured by flow cytometry. Similar to SDHA immunostaining, the average fluorescent intensity of MitoTracker Deep Red FM dye taken up by the cell was used to measure mitochondrial abundance. Results are expressed as mean raw intensity for each donor and show a dose-dependent decrease in intracellular mitochondrial mass in BECs treated with MWCNTs for 5 days. (N = 4, t-test, *p < 0.05, **p < 0.01)