Cell-membrane integrity of BEAS-2B cells on exposure to CuO/Silica and MCP230 ultrafine particles. BEAS-2B cells were exposed for 4 h to 100 μg/cm2 ultrafine particles. After the exposure, cells were treated with calcein AM and ethidium homodimer-1. Calcein AM enters all cells and is enzymatically converted to calcein. Cells with an intact plasma membrane (viable cells) retain calcein in the cytoplasm and thus fluoresce green. Cells with a compromised plasma membrane (dead cells) take up ethidium homodimer-1, which fluoresces red when complexed with nucleic acid. Scale bar = 50 μm.