Dynamics of breaking intermolecular bonds in high-speed force spectroscopy

Atomic force microscope based single-molecule force spectroscopy provides a description of a variety of intermolecular interactions such as those occurring between receptor molecules and their ligands. Advances in force spectroscopy have enabled performing measurements at high-speeds and sub-microsecond resolutions. We report experiments performed on a biotin-avidin system that reveal that the measured force decreases with the loading rate at high rates. This result is at odds with the established Bell-Evans theory that predicts a monotonic increase of the rupture force with the loading rate. We demonstrate that inertial and hydrodynamic forces generated during the breaking of the bond dominate the measured force at high loading rates. We develop a correction factor to incorporate those effects into the Bell-Evans theory. The correction is necessary to obtain accurate values of the intermolecular forces at high speeds.