Passive all-optical force clamp for high-resolution laser trapping |
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Authors: | Greenleaf William J Woodside Michael T Abbondanzieri Elio A Block Steven M |
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Institution: | Department of Applied Physics, Stanford University, Stanford, California 94305-5020, USA. |
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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. |
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