Editing Flow cytometry (section)

== Labels ==
[[File:Flow-FISH 1.JPG|thumb|upright=1.25|Use of flow cytometry to measure copy number variation of a specific DNA sequence ([[Flow-FISH]])]]Flow cytometry uses the light properties scattered from cells or particles for identification or quantitative measurement of physical properties. Labels, dyes, and stains can be used for multi-parametric analysis (understand more properties about a cell). [[Immunophenotyping]] is the analysis of heterogeneous populations of cells using labeled [[Antibody|antibodies]]<ref>{{Cite web|url=https://www.drmr.com/abcon/index.html|title=Conjugation of monoclonal antibodies|website=www.drmr.com|access-date=2018-09-18}}</ref> and other fluorophore containing reagents such as dyes and stains.

=== Fluorescent labels ===
{{Main|Fluorophore}}
A wide range of fluorophores can be used as labels in flow cytometry.<ref name="auto"/> Fluorophores, or simply "fluors",{{Citation needed|date=May 2019}} are typically attached to an antibody that recognizes a target feature on or in the cell; they may also be attached to a chemical entity with affinity for the [[cell membrane]] or another cellular structure. Each fluorophore has a characteristic peak [[excited state|excitation]] and [[Emission (electromagnetic radiation)|emission]] wavelength, and the emission spectra often overlap. Consequently, the combination of labels which can be used depends on the wavelength of the lamp(s) or laser(s) used to excite the fluorochromes and on the detectors available.<ref>{{cite book |  vauthors = Loken MR | year=1990 | title=Immunofluorescence Techniques in Flow Cytometry and Sorting | edition=2nd | publisher=Wiley | pages=341–53 }}</ref> Flow cytometry uses fluorescence as a quantitative tool; the utmost sensitivity of flow cytometry is unmatched by other fluorescent detection platforms such as [[confocal microscopy]]. Absolute fluorescence sensitivity is generally lower in [[confocal microscopy]] because out-of-focus signals are rejected by the confocal optical system and because the image is built up serially from individual measurements at every location across the cell, reducing the amount of time available to collect signal.<ref name="pmid17658411">{{cite journal | vauthors = Basiji DA, Ortyn WE, Liang L, Venkatachalam V, Morrissey P | title = Cellular image analysis and imaging by flow cytometry | journal = Clinics in Laboratory Medicine | volume = 27 | issue = 3 | pages = 653–70, viii | date = September 2007 | pmid = 17658411 | pmc = 2034394 | doi = 10.1016/j.cll.2007.05.008 }}</ref>

=== Quantum dots ===
[[Quantum dot]]s are sometimes used in place of traditional fluorophores because of their narrower emission peaks.{{cn|date=April 2022}}

=== Isotope labeling ===
{{main|Mass cytometry}}
Mass cytometry overcomes the fluorescent labeling limit by utilizing [[lanthanide]] isotopes attached to antibodies. This method could theoretically allow the use of 40 to 60 distinguishable labels and has been demonstrated for 30 labels.<ref name="JIM2010">{{cite journal |vauthors=Ornatsky O, Bandura D, Baranov V, Nitz M, Winnik MA, Tanner S |date=September 2010 |title=Highly multiparametric analysis by mass cytometry |journal=Journal of Immunological Methods |volume=361 |issue=1–2 |pages=1–20 |doi=10.1016/j.jim.2010.07.002 |pmid=20655312}}</ref> Mass cytometry is fundamentally different from flow cytometry: cells are introduced into a [[Plasma (physics)|plasma]], ionized, and associated isotopes are quantified via [[time-of-flight mass spectrometry]]. Although this method permits the use of a large number of labels, it currently has lower throughput capacity than flow cytometry. It also destroys the analysed cells, precluding their recovery by sorting.<ref name=JIM2010/>