Flow cytometry is a technique used to detect and measure physical and chemical characteristics of a population of cells and particles.

A sample containing cells is suspended in a fluid (sheath) and injected into a flow cytometer; the sample is then focused to ideally flow one cell at a time through a laser beam. The light scattered by each cell is characteristic to that individual cell’s size and its intracellular components.

Cells are often labeled with fluorescent markers so that the light is first absorbed and then emitted in a band of wavelengths specific to the given marker.