Necrosis is most often characterized by irreversible cellular damage which includes but not limited to: cytoplasmic swelling, permanent cell membrane damage, organelle breakdown, and eventually the release of cellular contents into the surrounding medium.
In non-viable cells the loss of cellular membrane integrity allows for membrane exclusion dyes such as propidium iodide (PI), ethidium bromide (EB), 7AAD, SYTOX green/red, and others to freely diffuse into the cell and bind to its DNA. Because these dyes only enter cells with compromised cell membranes, early apoptotic and healthy cells will not be stained, while dead or dying cells will be stained. The emitted fluorescent signal is captured by the Cellometer and an image is generated. Both brightfield and fluorescent images are captured and enumerated by the Cellometer.