A vital
dye used in
biological research. One use is in determining the
viability of
pollen grains; grains which are alive take up the fluorescein diacetate and
hydrolyze
it
intracellularly; the released
fluorescein will
fluoresce, and can be detected
with a
microscope
using
filters that allow only the longer-wavelength light to pass.
My guess is that the same principle can be used with other types of cells to determin their viability.