An ethidium homodimer assay can be used to detect dead or dying cells.

Ethidium Ethidium bromide (or homidium bromide, chloride salt homidium chloride) is an intercalating agent commonly used as a fluorescent tag ( nucleic acid stain) in molecular biology laboratories for techniques such as agarose gel electrophoresis. It ...

homodimer is a membrane-impermeable fluorescent dye which binds to DNA. After a cell sample has been stained with ethidium homodimer, the dead cells may be viewed and counted under a

UV-light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

microscope. When cells die, the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

s of those cells becomes disrupted. Because of this, ethidium homodimer may enter those cells and bind to DNA within those cells. Because live cells don't have a compromised membrane, the ethidium homodimer can't enter. One reason for doing an ethidium homodimer assay instead of using a

TUNEL assay Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) is a method for detecting DNA fragmentation by labeling the 3′- hydroxyl termini in the double-strand DNA breaks generated during apoptosis. Method TUNEL is a method for dete ...

to measure cell death is that ethidium homodimer stains all of the dead or dying cells, while TUNEL only stains cells that have undergone programmed cell death.

References

* Laing, J.; Gober, M.; Golembewski, E.; Thompson, S.; Gyure, K.; Yarowsky P. and Aurelian, L.; ''Molecular Therapy'' (2006) 13, 870–881. Laboratory techniques