FACS - fluorescence activated cell sorting
The ability to select any population, defined by a logical combination of regions, and isolate that population from the sample.
How to sort cells?
The initial processes are the same as for cytometric analysis:
- hydrodynamic focusing of the cell or particle mixture to form a central core in the fluid coating;
- passing the cells through the laser beam with subsequent analysis of the scattering and fluorescence signals;
- using regions and gates to define subpopulations;
Electrostatic sorting: course of events in the sorting chamber?
1) Vibration of the nozzle under the influence of the transducer causes the stream to break down into droplets containing sorted cells / particles;
2) At the interrogation point level (where the laser beam runs), the signal is processed and the decision made: sort to the left, sort to the right, discard;
3) Stream loading: negative charge when the drop goes left; positive when right;
4) Bending of the stream in the electrostatic field created by the deflection plates maintained at high voltage (+/- 5000 V): the charged drops are attracted to the appropriate plates, forming side fluxes;
5) Collecting sorted droplets of fluid containing cells / particles into tubes or onto a plate.