flowcytometers

Flow cytometers are instruments that analyze physical and chemical characteristics of cells or particles as they flow in a fluid stream through a beam of light, usually a laser. Cells labeled with fluorescent markers are interrogated one by one, and multiple parameters are measured simultaneously.

A typical system has three main subsystems: fluidics, optics, and electronics. The fluidics subsystem forms a narrow, laminar stream so single cells pass the interrogation point. The optics subsystem provides excitation and collects forward scatter, side scatter, and fluorescence via detectors such as photomultiplier tubes.

FSC correlates with cell size; SSC relates to internal complexity or granularity. Fluorescent channels detect bound markers or dyes. Recorded signals are converted to digital data and analyzed with plots, such as scatter plots and histograms. Compensation corrects spectral overlap between fluorophores.

Flow cytometers come in conventional and high-parameter variants. Some instruments offer spectral flow cytometry, which resolves full emission spectra. Fluorescence-activated cell sorting (FACS) adds the ability to physically collect selected cells for downstream experiments.

Common applications include immunophenotyping, hematology, viability assays, cell cycle analysis, apoptosis, and rare-event detection. Sample preparation typically involves labeling with fluorophore-conjugated antibodies or dyes; controls and compensation are essential for accurate interpretation. Limitations include the need for single-cell suspensions, spectral overlap, cost, and complex data analysis. Flow cytometry has evolved since the 1960s and 1970s and remains a cornerstone in research and clinical diagnostics.