FACS

FACs, commonly written FACS, stands for fluorescence-activated cell sorting. It is a specialized flow cytometry technology that analyzes and physically separates heterogeneous cell populations based on fluorescent labeling. By attaching fluorescent antibodies or dyes to cellular components, researchers can identify distinct cell types or states and collect them as purified subpopulations for further study.

In operation, cells labeled with fluorophores pass one by one through a laser beam inside a flow cytometer. Detectors measure forward and side scatter (which relate to cell size and granularity) and the emitted fluorescence across multiple channels. Based on predefined gating criteria, the instrument assigns a target phenotype to each cell. For sorting, the system converts the signal into droplets containing single cells; droplets with target cells are charged to deflect them electrostatically into separate collection receptacles, enabling isolation of specific cell populations.

FACs instruments integrate fluidics, optics, sensors, and sorting electronics. They typically feature multiple lasers, numerous optical filters, and detectors such as photomultiplier tubes, along with a droplet sorter for physical separation. The technique supports high-dimensional analysis, allowing simultaneous measurement of many parameters per cell. Researchers use FACs for immunophenotyping, rare-cell isolation, stem cell enrichment, cancer research, transplantation studies, and functional assays.

Notes on terminology and use: FACs is often used interchangeably with FACS, though some older or vendor-specific nomenclature may differ. Important considerations include proper controls, fluorescence compensation for spectral overlap, sample quality, and potential cell stress from sorting.