title: Biological magnetometry: torque on superparamagnetic beads in magnetic fields.
abstract: Superparamagnetic beads are widely used in biochemistry and single-molecule biophysics, but the nature of the anisotropy that enables the application of torques remains controversial. To quantitatively investigate the torques experienced by superparamagnetic particles, we use a biological motor to rotate beads in a magnetic field and demonstrate that the underlying potential is π periodic. In addition, we tether a bead to a single DNA molecule and show that the angular trap stiffness increases nonlinearly with magnetic field strength. Our results indicate that the superparamagnetic beads' anisotropy derives from a nonuniform intrabead distribution of superparamagnetic nanoparticles.
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Maarten M
authors.initials: MM
authors.lastname: van Oene
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Dickinson
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.|Department of Single-Molecule Biophysics, Centre de Biochimie Structurale, UMR 5048 CNRS, Montpellier, France.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pedaci
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Mariana
authors.initials: M
authors.lastname: Köber
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: David
authors.initials: D
authors.lastname: Dulin
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.|Department of Physics, Nanosystems Initiative Munich, and Center for NanoScience, Ludwig-Maximilian-University, Amalienstrasse 54, 80799 Munich, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Lipfert
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Nynke H
authors.initials: NH
authors.lastname: Dekker
mesh_terms: D016880:Anisotropy; D004247:DNA / Q000737:chemistry*; D060526:Magnetic Fields; D060306:Magnetometry / Q000379:methods*; D008863:Microspheres; D008962:Models, Theoretical; D019415:Torque
chemical_list: D004247:DNA