title: A high-resolution magnetic tweezer for single-molecule measurements.
abstract: Magnetic tweezers (MT) are single-molecule manipulation instruments that utilize a magnetic field to apply force to a biomolecule-tethered magnetic bead while using optical bead tracking to measure the biomolecule's extension. While relatively simple to set up, prior MT implementations have lacked the resolution necessary to observe sub-nanometer biomolecular configuration changes. Here, we demonstrate a reflection-interference technique for bead tracking, and show that it has much better resolution than traditional diffraction-based systems. We enhance the resolution by fabricating optical coatings on all reflecting surfaces that optimize the intensity and contrast of the interference image, and we implement feedback control of the focal position to remove drift. To test the system, we measure the length change of a DNA hairpin as it undergoes a folding/unfolding transition.
authors.affiliation: Materials Department, University of California, Santa Barbara, CA 93106, USA.
authors.forename: Kipom
authors.initials: K
authors.lastname: Kim
authors.forename: Omar A
authors.initials: OA
authors.lastname: Saleh
mesh_terms: D004247:DNA / Q000737:chemistry*; D052898:Optical Tweezers; D015203:Reproducibility of Results
chemical_list: D004247:DNA