How to measure binding affinity?

When biomolecules interact and form complexes in a solution, their diffusivity decreases, leading to slower diffusion and an extended dispersion profile. This change in diffusion behavior is quantified by analyzing the hydrodynamic radius (Rh) of the molecules. Using the Stokes-Einstein equation, FIDA software calculates the increase in Rh, providing a direct measure of the binding process. Essentially, the larger the Rh values, the stronger the binding affinity. Conducting a simple FIDA experiment by titrating the molecule of interest with its binding partners allows for the accurate determination of binding affinity (Kd), relying solely on the changes in the hydrodynamic radius. FIDA is a valuable technique for assessing molecular interactions, finding applications in fields such as drug discovery, protein-protein interactions, and various biomolecular studies.