FRET Materials for Biosensing and Bioimaging

Förster resonance energy transfer (FRET) spectroscopy and microscopy are constantly expanding sensing techniques for analyzing biomolecular interactions. In addition to the biological recognition molecules and biological or chemical analytes, the most important components for designing FRET biosensing systems are the materials that constitute the FRET donor–acceptor pair. These FRET materials consist of small molecules, biological or chemical nanoscaffolds, or nanomaterials that function in the ultraviolet, visible, or infrared spectral range. They can absorb light, fluoresce or phosphoresce with lifetimes ranging from picoseconds to milliseconds, and can be applied for sensing in situ, in vitro, and in vivo. Organic dyes and quenchers, fluorescent or light harvesting proteins, or quantum dots are only some examples from the ever growing FRET material toolbox. A particular example are gold nanoparticles, whose strong localized surface plasmon resonance makes them frequently used as nanosurface energy transfer (NSET) acceptors. After a short recapitulation of FRET and NSET theory, we review a wide variety of FRET and NSET materials, provide representative examples of FRET/NSET systems and applications for each material, and critically discuss the benefits and drawbacks of their properties.