Lanthanide metals such as Europium and Terbium have been used successfully in a variety of time-resolved fluorescence assays and time-resolved fluorescence resonance energy transfer (TR-FRET) assays. Their long fluorescent lifetimes, sharp emission peaks, and large Stokes shifts make them ideal for reducing background fluorescence thus increasing sensitivity and lowering the variance of intra- and inter-assay signal measurements.
Both Europium and Terbium are amenable for use in TR-FRET assays using the phycobiliproteins allophycocyanin (APC) and phycoerythrin (PE), respectively. The implementation of TR-FRET in assays further decreases signal background by making the separation between excitation and emission even greater (320nm for Europium:APC and 252nm for Terbium:PE). Additionally, the use of TR-FRET allows for interrogation of binding events as there is no emission from the phycobiliprotein acceptor if the lanthanide donor is not in very close proximity.
Chelate |
Excitation (nm) |
Emission (nm) |
Stokes Shift (nm) |
Fluorescence Lifetime (τ)(μsec) |
| Europium (Eu) | 340 |
615 |
275 |
730 |
| Terbium (Tb) | 320 |
545 |
225 |
1050 |
Excitation and emission of Europium chelate
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