What is the principle of fluorometric cell viability assays?

Fluorometric cell viability assays are used to determine the number of viable cells in a population. It is based on the nonspecific cleavage of a non-fluorescent compound such as fluorescein diacetate. These compounds fluoresce after they have been cleaved by cellular esterases. The fluorescence intensity or ratio of different fluorophores can be quantified and used to determine the percentage of viable cells in the population.