Cell Sorting

Fluorescence activated cell sorting (FACS) is a special technology for identifying and separating rare cell populations with high purity.

Large-size fat particle sorting is widely used to isolate cells up to 200 μm in diameter. Single-cell flow sorting will allow greater insight into adipocyte heterogeneity by identifying gene expression, protein composition, and metabolic signatures at the single-cell level.

Flow cytometry (FC) is a technique for high-speed, step-by-step quantitative analysis and sorting of single cells or other biological particles in a suspension by detecting labeled fluorescent signals.

Fluorescence-Activated Cell Sorting (FACS) separates cells in suspension after flow-cytometric measurement of light scatter and fluorescence; classic droplet-based instruments interrogate cells with a laser, convert optical signals into electronic signals, charge droplets containing target cells, and electrostatically deflect them into collection vessels. FACS detects phenotypes defined by fluorescent antibodies, fluorescent proteins, viability dyes, or intracellular markers, and the readout is the sorted fraction, purity, recovery, and post-sort viability of the gated population.

Immunoaffinity-based positive/negative selection without magnetic or flow cytometric separation is implemented as immunopanning, in which dissociated cells bind to antibody-coated plastic surfaces through specific cell-surface antigens; negative-selection plates remove unwanted antigen-positive cells, and positive-selection plates retain the desired antigen-positive population for recovery and downstream culture or analysis. The readout is the recovered cell fraction after sequential plate binding and washing: depleted non-adherent cells represent the negative-selection output, while cells retained on the final antibody-coated surface represent the positive-selection output; published examples include T-cell subpopulation purification, mouse and rat oligodendrocyte-lineage cell isolation, and mouse marrow progenitor enrichment.

Density gradient centrifugation enriches cells by buoyant density: cells sediment during centrifugation until they reach a medium layer or interface compatible with their density, allowing mononuclear cells, granulocytes, erythrocytes, and density-defined subpopulations to be recovered from separate bands or layers. Classic blood-cell applications include Ficoll/sodium-metrizoate or Ficoll-Hypaque enrichment of peripheral blood mononuclear cells, Percoll subfractionation of PBMC and T-cell populations, and Percoll-based neutrophil isolation from whole blood or leukocyte-enriched suspensions. The readout is the physical recovery of enriched cell bands, followed by cell counting, morphology, viability, and immunophenotyping to determine yield, purity, and suitability for downstream assays.

Dielectrophoresis-based electrical cell sorting separates suspended cells by the motion generated when polarizable cells experience a non-uniform electric field; cell trajectory depends on cell size, medium conductivity, applied AC frequency, electric-field gradient, and cell dielectric properties, so cells with different DEP responses can be routed, trapped, levitated, or released without biochemical labeling. In practical DEP sorters, the readout is the spatial redistribution of cells into different outlets, traps, or recovered fractions; reported examples include DEP field-flow fractionation of leukocytes, breast cancer cells, CD34+ cells, and blood cells, continuous-flow hMSC/osteoblast sorting, and image-based single-cell recovery after DEP manipulation.

Microfluidic cell sorting separates target cells in microscale channels by either intrinsic physical properties or specific molecular binding. Label-free platforms use size, deformability, hydrodynamic behavior, acoustic contrast, dielectric properties, or inertial migration to alter cell trajectories without antibody labeling, while affinity-based platforms immobilize antibodies, selectins, aptamers, or ligand-bearing nanoparticles to capture cells expressing corresponding surface markers. Classic label-free examples include deterministic lateral displacement arrays, inertial focusing systems, acoustophoresis devices, dielectrophoresis systems, and physical cluster-capture devices. Classic affinity-based examples include EpCAM-coated micropost or herringbone chips, PSMA-GEDI devices, E-selectin/anti-EpCAM biomimetic surfaces, and nanoparticle-mediated capture-and-release chips.

MACS enriches or depletes cells by binding antibody-targeted magnetic particles to surface antigens; labeled cells are retained in a high-gradient magnetic column, while unlabeled cells pass through, and retained cells are eluted after removal from the magnetic field. In ovalbumin-induced allergic airway inflammation, MACS can enrich immune populations such as CD4+ T cells, CD8+ T cells, dendritic cells, eosinophils, or marker-defined leukocytes for downstream analysis of airway inflammation, antigen presentation, and type 2 immune responses.