Breaking bonds in the atomic force microscope: extracting information

A theoretical framework is developed to analyze molecular bond breaking in dynamic force spectroscopy using atomic force microscopy (AFM). An analytic expression of the observed bond breaking probability as a function of force is obtained in terms of the relevant physical parameters. Three different experimental realizations are discussed, in which (i) the force is increased linearly in time, and (ii) the AFM cantilever is moved at constant speed, and (iii) the force is held constant. We find that unique fitting of the bond parameters such as the potential depth and its width is possible only when data from rather different force-loading rates is used. The complications in the analysis of using the constant velocity mode arising from the intermediate polymer spacer are discussed at length.