ROS levels in BEAS-2B cells after exposure to AgNPs. ROS formation after exposure to AgNPs was investigated using the DCFH-DA assay. Cells were incubated with AgNPs (5, 10, 20 μg/mL) for 24 h and then with 20 μM DCF-DA probe for 40 min. Readings (Ex485 nm/Em535 nm) were performed every 5 min over 30 min. Tert-butyl hydroperoxide (TBP, 15 μM) was used as positive control. ROS increase was calculated as mean slope per min and normalized to the unexposed control. Results are presented as mean ± standard deviation of 4 independent experiments.