title: Passive all-optical force clamp for high-resolution laser trapping.
abstract: Optical traps are useful for studying the effects of forces on single molecules. Feedback-based force clamps are often used to maintain a constant load, but the response time of the feedback limits bandwidth and can introduce instability. We developed a novel force clamp that operates without feedback, taking advantage of the anharmonic region of the trapping potential where the differential stiffness vanishes. We demonstrate the utility of such a force clamp by measuring the unfolding of DNA hairpins and the effect of trap stiffness on opening distance and transition rates.
authors.affiliation: Department of Applied Physics, Stanford University, Stanford, California 94305-5020, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Greenleaf
authors.forename: Michael T
authors.initials: MT
authors.lastname: Woodside
authors.forename: Elio A
authors.initials: EA
authors.lastname: Abbondanzieri
authors.forename: Steven M
authors.initials: SM
authors.lastname: Block
mesh_terms: D001360:Avidin / Q000737:chemistry; D001710:Biotin / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D004076:Digoxigenin / Q000737:chemistry; D007834:Lasers; D008863:Microspheres; D009690:Nucleic Acid Conformation; D055095:Optics and Photonics; D013314:Stress, Mechanical
chemical_list: D001360:Avidin; D001710:Biotin; D004247:DNA; D004076:Digoxigenin