Figure 2: Representative images of randomly selected microscopic fields of A549 cells stained with calcein-AM/PI after 24 h exposure to increasing concentration (1–100 μg/mL) of Cd-SiO2NPs (a), CdCl2 (b), and SiO2NPs (c). Dose-dependent cytotoxic effect in both Cd-SiO2NP and CdCl2 treatment groups: there was a strong decrease of viability at higher concentrations ranging from 50 to 100 μg/mL (low or no green fluorescence and red fluorescence indicating cell death). SiO2NPs treated cells showed uniformly diffused green fluorescence at all tested doses similarly to cell controls. Quantitative analysis of the cell loss is shown for each treatment (Green Square Cell Live; Red Square Cell Death). Data are mean ± DS of three separate experiments, error bars: ±SD. (Scale bar: 100 μm).