Magnetic Tweezers for Single-Molecule Experiments

Vilfan, Igor D.; Lipfert, Jan; Köster, Daniel; Lemay, Serge G.; Dekker, Nynke H.

doi:10.1007/978-0-387-76497-9_13

Cited by 72 publications

(97 citation statements)

References 85 publications

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“…An important advantage of single-cell and single-molecule data compared to ensembleaveraging measurements is that high sensitivities are achieved and that deeper insights are gained into the biological processes, e.g., into the development of population heterogeneities in space and/or in time. 4 Superparamagnetic particles are a potent component in many single molecule analysis technologies [5][6][7][8] because such particles can be manipulated and interrogated by magnetic fields without perturbing the biological matter under study. To be able to use magnetic particles in high-throughput methods with single-particle and single-molecule resolution, it is important that the size as well as the magnetic properties of the particles are accurately known.…”

mentioning

confidence: 99%

Accurate quantification of magnetic particle properties by intra-pair magnetophoresis for nanobiotechnology

Reenen

Gao

Bos

et al. 2013

Applied Physics Letters

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The application of magnetic particles in biomedical research and in-vitro diagnostics requires accurate characterization of their magnetic properties, with single-particle resolution and good statistics. Here, we report intra-pair magnetophoresis as a method to accurately quantify the field-dependent magnetic moments of magnetic particles and to rapidly generate histograms of the magnetic moments with good statistics. We demonstrate our method with particles of different sizes and from different sources, with a measurement precision of a few percent. We expect that intra-pair magnetophoresis will be a powerful tool for the characterization and improvement of particles for the upcoming field of particle-based nanobiotechnology.

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mentioning

confidence: 99%

Accurate quantification of magnetic particle properties by intra-pair magnetophoresis for nanobiotechnology

Reenen

Gao

Bos

et al. 2013

Applied Physics Letters

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“…Further details of this setup were reported previously. 3,12,15,22 Experiments used either a conventional magnet configuration (referred to as "conventional MT") with a pair of 5 mm × 5 mm × 5 mm magnets (Supermagnete, W-05-N50-G) in horizontal configuration with an iron yoke 12 or a cylindrical permanent magnet with a central aperture (Supermagnete, R-06-02-02-G) and an attached side magnet (Supermagnete, S-04-07-N) in the geometry described previously 15 (referred to as "MTT"). CCD images are either analyzed in real time or recorded at frequencies up to 100 Hz.…”

Section: A Magnetic Tweezers Experimental Configurationmentioning

confidence: 99%

“…[1][2][3][4] MT assays have provided unique insights into the function and dynamics of biological macromolecules. Examples include studies of the properties of bare DNA, 5,6 RNA, 7 and of enzymes that act on DNA or RNA, such as topoisomerases, 8 helicases, 4, 9 and polymerases.…”

Section: Introductionmentioning

confidence: 99%

A method to track rotational motion for use in single-molecule biophysics

Lipfert

Kerssemakers

Rojer

et al. 2011

Review of Scientific Instruments

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The double helical nature of DNA links many cellular processes such as DNA replication, transcription, and repair to rotational motion and the accumulation of torsional strain. Magnetic tweezers (MTs) are a single-molecule technique that enables the application of precisely calibrated stretching forces to nucleic acid tethers and to control their rotational motion. However, conventional magnetic tweezers do not directly monitor rotation or measure torque. Here, we describe a method to directly measure rotational motion of particles in MT. The method relies on attaching small, non-magnetic beads to the magnetic beads to act as fiducial markers for rotational tracking. CCD images of the beads are analyzed with a tracking algorithm specifically designed to minimize crosstalk between translational and rotational motion: first, the in-plane center position of the magnetic bead is determined with a kernel-based tracker, while subsequently the height and rotation angle of the bead are determined via correlation-based algorithms. Evaluation of the tracking algorithm using both simulated images and recorded images of surface-immobilized beads demonstrates a rotational resolution of 0.1• , while maintaining a translational resolution of 1-2 nm. Example traces of the rotational fluctuations exhibited by DNA-tethered beads confined in magnetic potentials of varying stiffness demonstrate the robustness of the method and the potential for simultaneous tracking of multiple beads. Our rotation tracking algorithm enables the extension of MTs to magnetic torque tweezers (MTT) to directly measure the torque in single molecules. In addition, we envision uses of the algorithm in a range of biophysical measurements, including further extensions of MT, tethered particle motion, and optical trapping measurements.

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“…5,6 Techniques to actively manipulate the height of a bound particle are optical tweezers, 7-9 magnetic tweezers, [10][11][12][13] fluidic forces, 14,15 or methods in which the particle is attached to larger objects such as in atomic force microscopy or in a bioforce probe. 16 The challenge in manipulating particle height in a biosensor lies in exerting high, well-defined and uniform forces, preferably perpendicular to the surface, on large ensembles of particles.…”

Section: Introductionmentioning

confidence: 99%

“…16 The challenge in manipulating particle height in a biosensor lies in exerting high, well-defined and uniform forces, preferably perpendicular to the surface, on large ensembles of particles. Although magnetic tweezers have been shown to be successful, 12,13 magnetic manipulation is limited, for example, by the force magnitude, 12 by magnetic interactions between particles, or by particle alignment due to magnetic anisotropy. 17 It has been shown that the height of bound particles depends, among others, on the electrostatic force between the particle and the surface, 15 which in turn depends on the properties of the fluid in which they are immersed.…”

Section: Introductionmentioning

confidence: 99%

Electrostatic height modulation of bound particle labels by buffer exchange in an evanescent wave biosensor

Ommering

Paesen

Zon

et al. 2010

Journal of Applied Physics

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We introduce a technique to electrostatically modulate the height of bound particle labels on a biosensor surface by exchanging the buffer. In an evanescent wave biosensor, height modulation leads to a modulation of the scattered and reflected light intensity. We measured a lower scattering and, therefore, a higher reflection for a decreasing ionic strength, which can be explained by an increasing electrostatic force repelling bound particles from the surface. By comparing bonds with troponin, 105 base pair ͑bp͒ DNA and 290 bp DNA, we found that the signal change for an ensemble of bound particles was related to the length of the analyte. Additionally, we observed for individual particles that the thermal fluctuations of scattered light intensity became smaller for decreasing ionic strength and that the average intensity shifted toward lower values, corresponding to larger particle heights. A quantitative model comprising electrostatic repulsion and van der Waals interaction could fit the measured height displacements for four different DNA lengths ͑105 bp to 590 bp͒ as analytes. Height manipulation of bound particle labels thus reflects analyte-specific properties and may lead to biosensors with enhanced specificity.

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Magnetic Tweezers for Single-Molecule Experiments

Cited by 72 publications

References 85 publications

Accurate quantification of magnetic particle properties by intra-pair magnetophoresis for nanobiotechnology

Accurate quantification of magnetic particle properties by intra-pair magnetophoresis for nanobiotechnology

A method to track rotational motion for use in single-molecule biophysics

Electrostatic height modulation of bound particle labels by buffer exchange in an evanescent wave biosensor

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