The FluoroMax-4 from HORIBA Scientific has extremely high sensitivity for all your steady-state applications including protein-protein interactions, protein-DNA interactions and protein folding.
Fluorescence Resonance Energy Transfer (FRET) is a powerful tool for these applications and is used in biophysics, biochemistry and cell biology to quantify molecular dynamics.
It’s very efficient in measuring distance or changes of distance in molecules.
Works best in the range of 1-10 nm and can measure the proximity within a single molecule.