Flow cytometry is a technique for counting, examining and sorting microscopic particles suspended in a stream of fluid. It allows simultaneous multiparametric analysis of the physical and/or chemical characteristics of single cells flowing through an optical/electronic detection apparatus.
Modern flow cytometers can analyse several thousand particles every second in "real time" and can actively separate out and isolate particles having specified properties. A flow cytometer is similar to a microscope, except it doesn't produce an image of the cell but offers high-throughput automated quantification of the set parameters for high number of single cells during each analysis session.
The data coming from flow-cytometers can be plotted in 1-D to produce histograms or seen in 2D as dot plots or in 3D with newer software and then studied.