Single-Molecule DNA Flow-Stretching Force Spectroscopy with Higher Resolution Using Dark-Field Microscopy

Single-molecule force spectroscopy often refers to the measurement of the enzymatic activities coupled to the mechanical properties of biomolecules. We apply a simple dark-field microscope to a single-molecule flow-stretching method that quantitatively measures thermal fluctuations of the micron bead linked to DNA under a hydrodynamic force. Using various lengths of DNA attached to the bead, we measured the external force exerted on DNA immobilized on the surface and quantitatively showed the anticorrelation between the thermal fluctuation and the length of DNA. We propose a multiplexed single-molecule flow-stretching technique with better spatial resolution.