The FACS fluidics system transports cells in a stream to the laser beam for interrogation. You can see a schematic view of it in Figure 1.

The fluidics system is composed by:

  • Sheath fluid: It is the liquid that goes through the system. It could be flow buffer, which transports the sample, or ethanol, which is used in the cleaning and shutdown procedure.

  • Tanks: The main tanks are those destined to store the flow buffer and ethanol (used in the cleaning procedure, not depicted on the image), but also to collect the non-sorted cells as waste.

  • Tubing: Used to connect the whole system, starting in the tank with flow buffer until the waste tank.

  • Valves and pressure regulators: Pressure is a very important parameter in the fluidics system, as it allows both the flow buffer and sample to go through it and create a consistent stream in the flow chamber. To do so, the sample pressure is usually higher than the one for the flow buffer. Changes in both pressures control the sample flow rate, which is the amount of sample that goes through the interrogation point.

  • Flow chamber: Here, the sample is mixed with the flow buffer to create the steady stream before it goes through the interrogation point.

  • Nozzle: It is placed right after the flow chamber, and since it determines how ‘thick’ the stream is, different nozzle sizes are available depending on the cell size to sort. The nozzle size should be about four to five times that of the cells that are being sorted. The most common size used for bacteria is the 70 µm nozzle. Furthermore, there is a special nozzle, called closed-loop nozzle.

Figure 1: FACS fluidics system.