Fluorescence-Activated Cell Sorting is an advanced flow cytometry technique that uses fluorescent markers and electrostatic deflection to isolate specific cells from heterogeneous mixtures.
How it works
In Fluorescence-Activated Cell Sorting, single cells are directed through a nozzle to form droplets that pass through a laser beam. The system measures light scatter and fluorescence to assess each cell’s size, complexity and antigen expression. When a cell meets defined criteria based on its fluorescent profile, electrodes impart a charge to the droplet containing that cell. The droplet is then deflected into a collection vessel by charged plates. This allows rapid isolation of selected cells while non-target cells continue into waste streams. The technique requires careful calibration of laser alignment, sheath fluid pressure and droplet break-off-off to maintain sorting accuracy. Fluorescent probes attached to antibodies or stains must be chosen to minimize spectral overlap and compensation is applied to separate signals. FACS instruments often include multiple lasers and detectors, enabling simultaneous measurement of many parameters. Applications span immunology, neuroscience, developmental biology and clinical diagnostics. For example, sorting of naive versus memory T cells based on CD45 isoforms, isolation of neuronal subtypes using markers such as NeuN and GAD, and separation of fetal cells from maternal blood for prenatal testing all rely on FACS.
Applications and considerations
Fluorescence-Activated Cell Sorting is widely used to obtain pure populations of hematopoietic stem cells, cancer stem cells and genetically modified cells. It enables enrichment of rare populations, such as antigen-specific B cells or virus-infected cells, for downstream sequencing or culture. Sorting can be performed under sterile conditions for subsequent in vitro experiments or transplantation. However, sorted cells may experience shear stress and exposure to high electric fields, which can affect viability. Sorting speed and purity depend on factors like nozzle size, droplet frequency and gating strategy. It is also critical to include appropriate controls and compensation to avoid contamination from autofluorescent cells. Despite these challenges, FACS remains the most versatile method for isolating cells based on multiple simultaneous markers. By combining fluorescence detection with mechanical sorting, Fluorescence-Activated Cell Sorting provides precise control over cell selection. Its ability to enrich defined populations has advanced research across many fields and supports therapeutic applications. Related Terms: FACS, Flow cytometry, Fluorescence microscope, Immunophenotyping, Cell sorting