What is flow cytometry?
It is a technology that allows the simultaneous measurement of several physical characteristics of a particle (cell) in suspension.

What information about the cell does flow cytometry (FC) provide?
Its relative size (Forward Scatter),
Its granularity or relative internal complexity (Side Scatter),
Its relative fluorescence intensity.

Single cell analysis methods are essential for understanding the functions of normal cells and the possibility of modulating pathological cells. Flow cytometry (FCM) was born out of the need to automate the counting of cellular constituents in blood.
The origins of FCM go back to 1934 when Moldavan designed the first device with which he performed cell counts by passing cells through a thin capillary where they were viewed by a photoelectric sensor. In the 1970s, researchers at Los Alamos and Stanford combined methods of measuring the individual volume or fluorescence of flowing cells with electrostatic methods for cell sorting under life-saving conditions. Light scattering soon completed the list of properties capable of discriminating between cell types. The simultaneous development of commercially available multipurpose instruments and the appearance of hybridomas for the production of monoclonal antibodies led to an explosion of activities involving flow cytometry. The use of intrinsic cellular properties (scattering, auto fluorescence) and the continuous development of fluorochromes capable of translating numerous cellular properties and functions have led to the implementation of increasingly fine methods for the analysis of heterogeneous cell population.

CMF is defined as the precise study of isolated cells entrained in a liquid flow. It is a technique for individual, quantitative and qualitative characterization of particles suspended in a liquid.
It consists in analyzing the optical or physical signals emitted by a particle cutting the light beam of a laser or an arc lamp. The measured signals are essentially related to:
-the intrinsic optical properties of the particles which correspond to the phenomena of light scattering related to the dimensions of the particle, their internal structure, or the auto fluorescence of certain cells such as plants, phytoplankton...
-the induced optical properties of fluorescence obtained by specific markings of structures or cellular functions.
These signals separated by optical filters are collected by photomultipliers, amplified, digitized, processed and stored by a computer.
This process of individual analysis (cell by cell) is multiparametric and can be performed at the speed of several thousand events per second. The computer calculates the statistical data associated with the distributions of the measured parameters and represents them in the form of histograms (1 parameter) or cytograms (2 parameters) on one or more populations whose cellular properties are thus evaluated.
The sorting function of the most advanced flow cytometers allows to physically sort several cell populations defined by their optical properties.