FLUORESCENCE—ACTIVATED CELL SORTING, frequently referred to as FACS, allows for isolation (sorting) or enumeration (analysis) of different populations of cells and molecules based on user—defined characteristics. FACS is based on the light—scattering properties of cells as well as the detection of user—defined fluorescent markers.

First, forward scatter and side scatter of normal light are used to determine cell size and complexity, respectively. The larger the cell, the more forward scatter there is, and the more complex the cell (i.e., a cell undergoing division or apoptosis, or with more vacuoles, etc.), the higher the side scatter. Second, fluorescent markers are used to delineate specific populations of cells within the whole population. Up to 32 different markers can be simultaneously detected, although it is far more common to ...