Direct measurement of compression spring constant of single DNA molecule with AFM

In this paper, a new approach is demonstrated to measure the compression elasticity of single biomolecule in small force regime (<0.5 nN) using vibrating mode scanning polarization force microscopy (VSPFM). With this method we investigate the compression elasticity of a single DNA molecule in the radial direction (perpendicular to DNA strands). The radial deformation of DNA molecules deposited on mica surface is shown to be able to reach about 50% un der external load, and this remarkable deformation is re- versible. In addition, the compression spring constant of DNA molecules is estimated to be about 0.6 nN/nm according to the height-force curves.