(A) Cells were exposed to 0.3, 3 and 30 µg/ml MWCNT for 2, 12 and 24 h, and ROS generation was measured using MitoSOX™ Red mitochondrial superoxide indicator by Immunofluorescence microscopy. (B) Cells were exposed to the indicated concentrations of MWCNT for various times, and ROS generation was measured using 2′,7′-dichlorofluorescin diacetate (DCFH-DA) using a spectrofluorometer. ROS generation was expressed as fold increase of fluorescence compared to the control; * p<0.05, compared to PBS treated control. (C) Cells were pretreated with NAC (10 mM) for 2 h, and then exposed to 30 µg/ml of MWNCT for 24 h. * p<0.05, compared with the control. # p<0.05, compared to MWCNT treatment without NAC pre-incubation.