As each cell makes contact with the laser beam, the instrument determines cellular intrinsic and extrinsic properties. These extrinsic characteristics are reflected by the presence of a fluorescent signal emitted by monoclonal antibodies that are bound to specific cellular antigens on the cell surface. The cell image below shows a cell stained with two different monoclonal antibodies, each with a different fluorochrome. Each fluorochrome will emit a different color when it intersects the laser.
The second image below is an example of a histogram display. It represents the monoclonal antibody for CD5 labeled with FITC dye. When this dye intersects a 488 nm argon ion laser beam, it emits a fluorescent signal in the green portion of the spectrum (don't be confused by the red peaks; that is simply how this particular flow cytometer is programmed to display every color on a single color histogram).
