Source- Wikipedia: In biotechnology, flow cytometry is a laser-based, biophysical technology employed in cell counting, cell sorting, biomarker detection and protein engineering, by suspending cells in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and chemical characteristics of up to thousands of particles per second.
Flow cytometry is routinely used in the diagnosis of health disorders, especially blood cancers, but has many other applications in basic research, clinical practice and clinical trials. A common variation is to physically sort particles based on their properties, so as to purify populations of interest.
Source- Bill Sosna: Flow cytometry is also used as a detection method for sorting, identifying, and quantifying specific antigens out of complex matrices. A fluorescently tagged antibody is introduced/combined to a target antigen of choice (usually via a surface protein) and passed through a cytometer. The greater the amount of fluorescence emitted the larger the source (i.e. more of the target antigen). In addition, multiple fluorescently tagged antibodies of varied colors can be used to determine if multiple antigens are present in a matrix.