Basic principles of flow cytometry.

Although the basic principles of flow cytometry have changed little in the past quarter century, the applications of this technology have evolved substantially. As in the past, cytometers interrogate individual cells or particles in a stream with a laser as the cells move past a set of stationary detectors. Increasingly, more colors of fluorescence are being detected by cytometers, faster analysis and sorting rates are becoming possible, cytometers capable of multidirectional sorting are being marketed, and more reagents are becoming available for a wide variety of applications. Furthermore, flow cytometry has not stopped evolving. The development of narrow spectrum flourescent probes, the integration of molecular biologic techniques with flow cytometry, and the evaluation of cell-free markers such as cytokines will be key components in the continuing evolution of flow cytometry.