Fluorescence-Activated Cell Sorter (FACS) or flow cytometry has been
widely used for cell cycle studies.
A suspension of dead or live cells is passed single-file through a laser beam
by continuous flow of a fine stream of the suspension.
Each cell scatters some of the laser light, and also emits fluorescent light
excited by the laser. Fluorescence intensities are typically measured at several
different wavelengths simultaneously for each cell, allowing users to
mark cells with different fluorescent probes. For example, cells
can be marked with a fluorescent probe for DNA content (G1/S or G2/M phase)
and simultaneously measured for incorporation of BrdU (S phase).
A good starting point for FACS
resources, tips, and protocols is
Scripps FACS Core Facility.