Flow cytometry fluorochromes/dyes

Fluorochrome A fluorochrome is a dye that absorbs light and then emits light of a different color (always of a longer wavelength). Fluorescein, propidium iodide, and phycoerythrin, for example, are three fluorochromes in common use in flow cytometry. Flu-orophore is an equivalent term. 

Prior to 1982, the measurement of more than one andgen amultaneously by flow cytometry required two lasers—an argon-ion laser to excite fluorescein (at 488 nm) and a krypton or a dye laser to excite rhodamine or one of its deriva-dves. The discovery of a naturally occurring fluorochrome, phycoerythrin (PE), changed this (i). PE is a phycobiloprotein found in red adgae. It can be excited efficiently at 488 nm (simultaneously with fluorescein) and has a peak fluorescence at 578 nm, sufficiently removed from the peak of 520 nm from fluorescein. There is some overlap in the emission spectra from the two dyes (in pardcular, there is sdll some emission from fluorescein above 580 nm) and this must be corrected, either electronically or by the computer software. 

Another important advantage of polychromatic flow cytometry is the measurement of rare cell populations. Multichannel detections allow applying the so-called dump channel. Undesired cells can be excluded from analysis using this dump channel after their staining by specific antibodies, labeled with the same fluorochromes. Using the other fluorescent channels (dyes), low-frequency cell subsets can be detected in a very sensitive manner. 

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