A) U87, U373, and D54 GBM cells or NHA cells were treated for 24 h with increasing doses of acid oxidized MWCNTs dispersed in the indicated surfactants. After 24 h, cells were lysed, pelleted and the supernatant was analyzed for ATP content as a measure of cell viability using the CellTiter-Glo assay. Samples were prepared and measured in sextuplicate and are displayed as the mean ± standard deviation of each measurement. Significant differences in viability between cells treated with 1% or 2% DSPE-PEG coated MWCNTs and uncoated or Pluronic F-127 coated MWCNTs (determined by ANOVA followed by Student’s T-Test when appropriate) are indicated by (*; p<0.05) or (**; p<0.01). B) U87, U373, and D54 GBM cells or NHA cells were treated for 24 h with 2% DSPE-PEG MWCNTs (50 μg/ml). Cells were co-stained with propidium iodide and Annexin V and then evaluated by flow cytometry. the percentages of cells characterized as viable (lower-left quadrant), early apoptotic (lower-right quadrant), late-apoptotic (upper-right quadrant), and necrotic (upper-left quadrant) are shown within each quadrant. At least 10,000 cells were counted for each measurement and the experiments were repeated 2–3 times for each cell line with similar results.