Fig. 1: The mechanism and detection of energy migration via homoFRET.

a Principle of homoFRET. At a lower fluorescent protein (eGFP) density, the emission is polarized, whereas, at a higher density, the emission is depolarized due to energy migration to proximal neighboring molecules. The overlap between the excitation and the emission spectra of eGFP is shown. The fast depolarization of fluorescence anisotropy due to homoFRET is also schematically depicted. b A confocal time-resolved fluorescence microscopy setup (MicroTime 200, PicoQuant) used for our single-droplet anisotropy imaging and time-resolved measurements. Representative anisotropy images and decay profiles shown here are the same as shown in Figs. 3f, 5o, and 2f. See “Methods” for more details.