Exploiting the unique properties of lanthanide complexes as FRET probes: from quantitation to protein dynamics

Anthanide complexes have a range of photophysical properties– large pseudo-Stokes shifts, narrow line widths, long emission lifetimes– that make them ideal as emissive probes. These same properties also render them excellent donors in assays relying on Förster resonance energy transfer (FRET). Over the last 20 years these assays have increased in sophistication so that a range of biological applications has now been demonstrated. These range from easy-to-use quantitation of proteins (a practical alternative to western blotting) to sophisticated experiments which give real-time information on the movement of proteins or allow simultaneous readout of both agonist and co-activator binding to a protein. We introduce the principles and difficulties of using such assays before surveying the full scope of what they can achieve and attempting to anticipate future developments in this area.