What is the principle of flow cytometric cell viability assays?

The principle of flow cytometric cell viability assays involves the use of fluorescent dyes to label cells, which are then excited by a laser beam. As the cells pass through the laser beam, their fluorescence intensity is measured to determine cell viability. Dead or dying cells exhibit high fluorescence because their compromised membrane integrity allows the dye to enter the cell. Live, viable cells exhibit low fluorescence because their intact membranes prevent the dye from entering the cell. 

Analyzing the fluorescence data allows researchers to identify and quantify live and dead cells, providing crucial information about cell viability. This has several applications in diverse research fields, including drug development, cancer research and immunology.