title: Skewed brownian fluctuations in single-molecule magnetic tweezers.
abstract: Measurements in magnetic tweezers rely upon precise determination of the position of a magnetic microsphere. Fluctuations in the position due to Brownian motion allows calculation of the applied force, enabling deduction of the force-extension response function for a single DNA molecule that is attached to the microsphere. The standard approach relies upon using the mean of position fluctuations, which is valid when the microsphere axial position fluctuations obey a normal distribution. However, here we demonstrate that nearby surfaces and the non-linear elasticity of DNA can skew the distribution. Through experiment and simulations, we show that such a skewing leads to inaccurate position measurements which significantly affect the extracted DNA extension and mechanical properties, leading to up to two-fold errors in measured DNA persistence length. We develop a simple, robust and easily implemented method to correct for such mismeasurements.
authors.affiliation: Delft University of Technology, Kavli Institute of Nanoscience, Department of Bionanoscience, Delft, The Netherlands.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Burnham
authors.affiliation: Delft University of Technology, Kavli Institute of Nanoscience, Department of Bionanoscience, Delft, The Netherlands.
authors.forename: Iwijn
authors.initials: I
authors.lastname: De Vlaminck
authors.affiliation: Delft University of Technology, Kavli Institute of Nanoscience, Department of Bionanoscience, Delft, The Netherlands.
authors.forename: Thomas
authors.initials: T
authors.lastname: Henighan
authors.affiliation: Delft University of Technology, Kavli Institute of Nanoscience, Department of Bionanoscience, Delft, The Netherlands.
authors.forename: Cees
authors.initials: C
authors.lastname: Dekker
mesh_terms: D004247:DNA / Q000032:analysis*; D005434:Flow Cytometry; D060328:Magnetic Phenomena; D008280:Magnetics; D059346:Magnets; D008846:Micromanipulation / Q000295:instrumentation* / Q000379:methods*; D008863:Microspheres; D036103:Nanotechnology
chemical_list: D004247:DNA