“…While single particlesas small as 1 nm [5][6][7] are trapped, they experience uniform illumination intensity and rotate freely, enabling an isotropic view of the molecule and simultaneous high-precision acquisition of multiple spectroscopic parameters including brightness, fluorescence lifetime, anisotropy, and emission spectrum. Such high information-content data have proved useful for single-molecule studies of systems which exhibit photophysical heterogeneity, such as photosynthetic antenna complexes [8][9][10][11][12][13][14] , other proteins 15,16 , aggregates and nano-compartments 17,18 , and individual nanoparticles 19,20 . ABEL trap measurements of molecules labeled with multiple dyes that undergo Förster resonance energy transfer (FRET) have demonstrated exceptional utility and future potential for generating biological insights on protein conformations 21 including enzyme motions [22][23][24][25] , protein-protein interactions 26 , and DNA structure and conformation [27][28][29][30][31] .…”