What is the advantage of tandem dyes in flow cytometry?

Tandem dyes largely expand the pool of fluorophores that are suitable for flow cytometry, increasing the number of colors that can be detected in a single experiment.

The number of fluorophores one can use at the same time is limited by the number of lasers and detectors on a flow cytometer. With traditional non-tandem fluorophores, each laser could only discretely excite a small number of fluorophores. Tandem dyes, on the other hand, could further expand the number of detectors off of each laser because multiple acceptors can be excited by the same laser. For example, by staining cells with PE, and its tandems PE-Cy5 and PE-Cy7, three different emissions could be detected simultaneously in one experiment, greatly increasing the capacity and flexibility of research.