Figure 1.

Excitation and emission spectra of a commonly used FRET pair. The scheme depicts simplified absorbance and emission spectra of CFP (cyan fluorescent protein; donor; D) and YFP (yellow fluorescent protein; acceptor, A). Overlap between CFP emission and YFP absorption (shaded region) is a prerequisite for FRET. D_abs – Donor absorbance; D_em – Donor emission; A_abs – Acceptor absorbance; A_em – Acceptor emission.