Figure 3. In vitro cytotoxicity of different sizes of CdSe QDs on A549 lung cancer cells by MTT assay. (A) Cellular morphology of A549 cells after 24 h treatment at different concentration (0.5-25 μM) of QDs by inverted phase contrast microscopy and (B) Dose-response effects of QDs on cytotoxicity against A54 cells. Scale bar=100 μm. Values are expressed as mean ± SEM of at least three independent experiments. *p < 0.05 as compared with their respective control.