Suitability of different cell viability assays for nanotoxicity testing. Cytotoxicity of different NPs (suspended from dry powders) on THP-1 cells was tested after 48 h incubation using the Cytotox-96 assay from Promega (left panel) and the Toxilight assay from Lonza (center panel). In addition, the CellTiter-Blue assay from Promega was used to determine the cell viability (right panel). Data were normalised to the PBS control (9.1% v/v PBS) and mean values ± SD are shown. The dotted lines represent the values in control cells with PBS (taken as 0% cytotoxicity in left and centre panels, and as 100% viability in the right panel). The shaded areas represent the SD above and below the control values. * p < 0.05 vs. untreated control.