Cytometer

A cytometer is an instrument used to count and analyze microscopic particles, particularly cells, in a fluid or fixed sample. It measures physical and chemical characteristics and renders quantitative data about individual particles in a population.

The term covers several instrument classes, most notably flow cytometers and image cytometers. Flow cytometers analyze cells in a fluid stream as they pass through one or more laser beams, recording light scatter and fluorescence signals to derive counts, viability, immunophenotype, and other markers. Image cytometers capture high-resolution images of cells or tissue sections and analyze morphology, staining patterns, and spatial relationships.

Core components include a fluidics system to align cells, an optical system with lasers and detectors, and an electronics/data system to convert signals to measurements. Common detectors are photomultiplier tubes or avalanche photodiodes; data are usually presented as scatter plots and histograms, with compensation and gating used to isolate populations.

Applications span clinical hematology (cell counts, reticulocytes), immunology (surface markers, cytokine assays), cancer biology (cell cycle, DNA content, rare-event detection), microbiology, and plant biology. Image cytometry provides morphological analysis and image-based quantification. Calibration, standardization, and proper sample preparation are essential for reproducibility. Limitations include the need for appropriate sample preparation to achieve single-cell suspensions for flow cytometry and potential biases introduced by instrument settings and data analysis strategies.