Click here for the video tutorial by the Beckman Coulter on cell sorting.
Sorting by deflection of charged droplets:
Most high speed cells sorters (e.g BD FACS Arias or the MoFlow) make use of the electrostatic deflection of droplets method. Fluid containing particles passes through a nozzle (between 50 and 100 µm diameter) and the stream emerges into the air. The fluid stream breaks up into droplets- with the aim being the generation of droplets big enough to contain one cell in each drop. To do this, the stream is the vibrated at a specific frequency and pressure (usually between 20 and 60 kHz kHz) to separate it into droplets by a piezoelectric transducer. These droplets are then charged (± v where v typically lies between 50 and 150 V) or not depending upon the fluorescent profile of the cell(s) within. The drops pass through an electric field allowing electrostatic or droplet deflection which sends the charged drops of interest into microcentrifuge tubes, 6-mL centrifuge tubes, 15- or 50-mL conical tubes, multiwell plates (anything up to 384-well plates) or onto a slide. Unsorted droplets go into the waste.