Flow cytometry stems from a collection of scientific discoveries in the fields of biology, physics and chemistry. A flow cytometer simultaneously measures and then analyzes multiple characteristics of particles, usually cells, as they flow, ideally in single file, within a fluid stream and through a beam of light. The properties measured include a particle’s relative size, its granularity, and fluorescence intensity. These characteristics are determined using an optical system coupled to an electronic system that simultaneously records this information in a correlated manner. A flow cytometer is made up of three main systems: fluidics, optics, and electronics.
• The fluidics system transports particles in a stream to the laser beam for interrogation.
• The optics system consists of lasers to illuminate the particles in the sample stream and optical filters to direct the resulting light signals to the appropriate detectors.
• The electronics system converts the detected light signals into electronic signals that can be processed by the computer. For sorting instruments, the electronics are also capable of initiating sorting decisions to charge and deflect particles for collection.
In a flow cytometer, particles are carried single file through a laser intercept. Any suspended particle or cell from approximately 0.2–150 um in size can be analyzed. As particles pass through the laser intercept, they scatter laser light. Any fluorescent molecules present on the particle are excited by an appropriate laser and fluoresce. A combination of beam splitters and filters steer the scattered and fluorescent light to the appropriate detectors. The detectors produce electronic signals proportional to the photons of light striking them which are in turn recorded by the computer for analysis.