FACS

Fluorescence-Activated Cell Sorting

The acronym FACS stands for Fluorescence-Activated Cell Sorting (aka. Fluorescence-Assisted Cell Sorting or Flow Cytometry). FACS is a method in which a heterogeneous population of suspended cells are characterized and separated based upon the intensity of fluorescence they emit while passing single file through an illuminated volume.

Monoclonal antibodies, tagged with a fluorescent dye (typically fluorescein or phycoerythrin), are bound specifically to receptor sites on the desired cells and then injected into the Cell Sorter apparatus. The cells then travel single file across a laser beam. As the cells pass through the light, the light is scattered, and the fluorescent dye becomes excited by the laser beam causing the tagged cells to emit fluorescence. Photocells then send signals to the CPU characterizing each of the cells. Cells that display the desired "photo characteristics" will then be electro statically charged, physically separated by attraction to one of two charged plates based upon the presence (desired) or absence of that charge, and collected in their respective collecting tubes.

Common FACS Applications

FACS can be used to distinguish living versus dead cells, different types of cells (i.e. WBC's), isolate cells for Cloning or PCR, separating sperm for gender selection, or for identifying apoptotic cells.

Separating living from dead cells by FACS

Dead cells are permeable to ethidium monoazide (EMA), a chemical that can enter the cell and bind to the DNA under a fluorescent lamp. As the FACS is run, cells containing EMA (dead) are separated out.

HI-D FACS

HI-D FACS is an upgraded method of the simple FACS. In Hi-D, up to three lasers are used to distinguish between as many as 12 dyes at one time. This process significantly increases the speed at which cells can be analyzed and sorted.