Real-Space Investigation of Energy Transfer through Electron Tomography

We herein report the first real-space investigation of Förster resonance energy transfer (FRET) in two different types of quantum dot (QD) supramolecular assemblies by observing their three-dimensional (3D) configurations through high-resolution electron tomography. Owing to its critical role in photosynthesis, artificial light-harvesting antennas, and investigation of protein–protein interactions, the mechanism of FRET has been intensively studied by monitoring its excited-state dynamics via various spectroscopic techniques. The utilized electron tomography technique allowed the direct localization of 3D coordinates of individual QDs in self-assembled nanostructures and theoretical estimation of the FRET efficiency of a single fluorophore, domain, or supramolecular assembly. Moreover, the experimental value of the FRET efficiency determined by fluorescence spectroscopy was in good agreement with the magnitude obtained via electron tomography. We believe that the described strategy can be used in single-molecule FRET studies and will help to create a new bridge between material science and molecular/supramolecular photochemistry.