Time-resolved fluorescence energy transfer (TR-FRET) works on the principles that when suitable pairs of fluorophores are in close proximity of one another, excitation of a lanthanide donor fluorophore results in energy transfer to an acceptor fluorophore. These assays, commonly used in drug discovery applications, combine the use of time-resolved fluorescence (TRF) and Förster resonance energy transfer (FRET). The benefit of this combination of technologies is the long fluorescence lifetime of the lanthanide donor fluorophore. This lifetime allows measurement of the signal long after the background fluorescence has dissipated. The time-resolved measurement reduces assay interference (e.g. fluorescent compounds) and increases data quality.

The laser-based optical system in the Agilent BioTek Synergy Neo2 provides a powerful and fast excitation source for TR-FRET assays.  The Xenon lamp based optical systems in the Agilent BioTek Synergy H1 and Agilent BioTek Cytation multi-mode readers enable the speed and sensitivity required for TR-FRET assays at an affordable price point.



Assay principal for AlphaScreen® SureFire®  STAT3 assay
 Figure 1. TR-FRET energy transfer.

TR-FRET assay principle

  • When excited, the TR donor emits light over a few milliseconds.

  • When excited directly, the acceptor emits light over a few nanoseconds.

  • When FRET occurs, the energy transfer occurs over a few milliseconds, thus the emission of the acceptor occurs in the same time-frame.


TR-FRET is available in:k