Genotoxicity of AgNPs in BEAS-2B cells. Comet assay was performed after 4 h (A) and 24 h (B) exposure to AgNPs. The induction of DNA damage was evaluated after 4 and 24 h incubation with 10 μg/mL AgNPs. DNA damage was expressed as % DNA in tail. Results are presented as mean ± standard deviation of at least 3 independent experiments. Significant results as compared to the control are marked with asterisks (* for P-value < 0.05, ** for P-value < 0.01). Immunocytochemistry of γH2AX foci in BEAS-2B cells was performed after exposure to AgNPs for 24 h (C). Cells were treated for 24 h with 10 μg/mL AgNPs (10 nm and 75 nm citrate coated) and etoposide 10 μM (positive control). After exposure, cells were fixed and stained for γH2AX foci (FITC conjugated anti-phospho-histone H2AX-Ser 139 antibody, green) and nucleus (DAPI, blue). Pictures were taken with a confocal laser scanning microscope, 40X, oil objective. Images are representative for 3 independent experiments.