Lanthanide Complexes in FRET Applications

Abstract

In this article, the main principles of Forster resonance energy transfer (FRET) are described with special emphasis on luminescent lanthanide complexes (LLCs) in modern fluorescence spectroscopy and microscopy and their use in biomolecular analysis. The theoretical fundamentals of FRET are explained and the unique photophysical properties of LLCs are presented. Their narrow emission bands, long excited-state lifetimes and large “Stokes shifts” make LLCs very promising energy donors for various FRET systems. Numerous recent literature examples as well as commercial applications, demonstrating the particular advantages of LLCs in FRET spectroscopy and microscopy, are reported. Afterwards, the benefits of multi-parametric FRET measurements using LLC donors are emphasized. The multiplexed approach allows the simultaneous detection of several analytes or binding events, which makes it especially important for modern high-throughput-screening as well as low-cost lab-on-a-chip devices. Finally, semiconductor quantum dots (QDs) and the advantages of their use as novel FRET acceptors are presented. A combination of LLCs and QDs in FRET provides extraordinary donor-acceptor pairs with outstanding properties, and long biomolecular distances of up to 20 nm become accessible. Extremely high sensitivity combined with multiplexed detection make the LLC-QD FRET pairs substantial for application in modern time-resolved fluoroimmunoassays (TR-FIA). Luminescent lanthanide complexes have been very efficient tools in various FRET applications and regarding the ever increasing amount of newly arising biomolecular questions and the development of novel fluorescent materials the future of LLC-based FRET is still wide open and highly promising.