278 - Hematology flow analyzers: history of continuously evolving technology. Part 2: the optical method

In flow cytometry the optical method was developed before the impedance method and the first application dates back to 1934 by A.Moldavan. The use of dark field analysis and the introduction of sheath flow by P.Crosland-Taylor in 1953 represent two fundamental steps toward obtaining relatively accurate cell counts. Following these developments the first commercial instruments based on optical method to perform the blood cell counts were produced. Specifically Technicon (now Bayer) introduced the SMA4A/7A in 1965. The next decade was characterized by theoretical and experimental research on the effects of interaction between narrow light beams (diameters 100-300 µ) and individual cells while they pass through a flow cell. The goal was to obtain the greatest amount of information on cell characteristics. The amplitude of scattered light collected at narrow angle (forward scatter) was found to be correlated to cell volume while at greater angles refraction index and the structural complexity became more important......