Hydrodynamic Force Compensation for Single-Molecule Mechanical Testing Using Colloidal Probe Atomic Force Microscopy

摘要

The use of colloidal probes for mechanical testing of single molecules in an atomic force microscope (AFM) provides an attractive alternative to conventional microfabricated AFM cantilever force sensors, in that they have a much greater surface area available for specific binding to a target molecule. This is of particular importance for molecules have a low binding probability or are sterically inhibited from binding in some way. There are, however, several features unique to colloidal probe force measurements performed in a fluid environment, one of which is the presence of hydrodynamic forces acting on the sphere at the tip of the cantilever as it moves through the fluid. This force must be subtracted from the total measured force to isolate the molecular interaction of interest. Herein, a method is described to perform such a correction based on Brenner's equation, and the method is demonstrated on data from the mechanical testing of a single DNA molecule.