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Magnet polepiece design for uniform magnetic force on superparamagnetic beads

Source: Rev. Sci. Instrum. 81, 074303 (2010); doi:10.1063/1.3469792

Published 29 July 2010

KEYWORDS and PACS
Keywords
PACS
  • 07.55.Db
    Generation of magnetic fields; magnets
  • 75.20.-g
    Diamagnetism, paramagnetism, and superparamagnetism
  • YEAR: 2010
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PUBLICATION DATA
ISSN:
1553-9628 (online)
Publisher:
AIP is a member of CrossRef AIP
Todd Fallesen,1 David B. Hill,1,2 Matthew Steen,1 Jed C. Macosko,1 Keith Bonin,1 and George Holzwarth1
1Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109, USA
2Cystic Fibrosis Pulmonary Treatment/Research Center, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
Here we report construction of a simple electromagnet with novel polepieces which apply a spatially uniform force to superparamagnetic beads in an optical microscope. The wedge-shaped gap was designed to keep [partial-derivative]Bx/[partial-derivative]y constant and B large enough to saturate the bead. We achieved fields of 300–600 mT and constant gradients of 67 T/m over a sample space of 0.5×4  mm2 in the focal plane of the microscope and 0.05 mm along the microscope optic axis. Within this space the maximum force on a 2.8  µm diameter Dynabead was 12 pN with a spatial variation of approximately 10%. Use of the magnet in a biophysical experiment is illustrated by showing that gliding microtubules propelled by the molecular motor kinesin can be stopped by the force of an attached magnetic bead. ©2010 American Institute of Physics
History: Received 4 May 2010; accepted 2 July 2010; published 29 July 2010
Permalink: http://link.aip.org/link/?RSINAK/81/074303/1

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