title: Video-based and interference-free axial force detection and analysis for optical tweezers.
abstract: For measuring the minute forces exerted on single molecules during controlled translocation through nanopores with sub-piconewton precision, we have developed a video-based axial force detection and analysis system for optical tweezers. Since our detection system is equipped with a standard and versatile CCD video camera with a limited bandwidth offering operation at moderate light illumination with minimal sample heating, we integrated Allan variance analysis for trap stiffness calibration. Upon manipulating a microbead in the vicinity of a weakly reflecting surface with simultaneous axial force detection, interference effects have to be considered and minimized. We measured and analyzed the backscattering light properties of polystyrene and silica microbeads with different diameters and propose distinct and optimized experimental configurations (microbead material and diameter) for minimal light backscattering and virtually interference-free microbead position detection. As a proof of principle, we investigated the nanopore threading forces of a single dsDNA strand attached to a microbead with an overall force resolution of ±0.5 pN at a sample rate of 123 Hz.
authors.affiliation: Experimental Biophysics & Applied Nanoscience, Faculty of Physics, Bielefeld University, 33615 Bielefeld, Germany. sknust@physik.uni-bielefeld.de
authors.forename: Sebastian
authors.initials: S
authors.lastname: Knust
authors.forename: Andre
authors.initials: A
authors.lastname: Spiering
authors.forename: Henning
authors.initials: H
authors.lastname: Vieker
authors.forename: André
authors.initials: A
authors.lastname: Beyer
authors.forename: Armin
authors.initials: A
authors.lastname: Gölzhäuser
authors.forename: Katja
authors.initials: K
authors.lastname: Tönsing
authors.forename: Andy
authors.initials: A
authors.lastname: Sischka
authors.forename: Dario
authors.initials: D
authors.lastname: Anselmetti