Fig. 1.

Excitation emission matrix (EEM) representation of three-color FRET between fluorescein, Cy3 and Cy5. (a) Photon pathways in a three-color FRET process. Six possible exciter-to-emitter photon pathways are present. (b) EEM representation of the three-color FRET as a function of both excitation and emission wavelengths. Different photon pathways occupy different regions of the EEM. For each photon pathway, the excitation spectrum follows the exciter, and the emission spectrum follows the emitter.