Flow cytometry is a popular and powerful analysis method in the biological sciences. The basic principle relies on laser-mediated activation of fluorescent proteins on the surface or inside a cell or particle. The huge difference compared to other laser-based analysis techniques is that the cells are not static (as in e.g. microscopy), but instead are travelling through a capillary system.
As the singularized cells pass by a laser beam, the size, granularity and fluorescence properties of each individual cell are detected by the scattered laser light as forward and sideward scatter (FSC and SSC). This signal is then translated into an electronic signal and visualized in the flow software. As most cytometers contain several different laser light sources, many different fluorophores can be recorded, referred to as multiparametric analysis. As the cells pass by the laser beams with relatively high speed, cytometers can analyze ~30.000 cells/second and still retain single cell resolution.