Energy transfer with semiconductor nanocrystals

Fo¨ rster (or fluorescence) resonant energy transfer (FRET) is a powerful spectroscopic technique to study interactions, conformational and distance changes, in hybrid nanosystems. Semiconductor nanocrystals, also known as colloidal quantum dots, are highly efficient fluorophores with a strong band-gap luminescence tuneable by size as a result of the quantum confinement effect. Starting from a short summary on the FRET formalism and on the basic properties of semiconductor nanocrystals, this Feature Article provides an overview of the major classes of hybrid FRET systems with semiconductor nanocrystals as at least one component. Systems under consideration include thin solid films containing differently sized semiconductor nanocrystals, solution-based complexes of differently sized semiconductor nanocrystals, nanocrystal-based bioconjugates, and hybrid structures of semiconductor and gold nanoparticles. We focus in particular on the directional energy transfer in layer-by-layer assembled multilayers of differently sized CdTe semiconductor nanocrystals and on the energy transfer from individual rod-like semiconductor CdSe/CdS nanoantennae to single dye molecules, which can be efficiently controlled by external electric fields leading to the realisation of the FRET optical switch.