Controlled torque on superparamagnetic beads for functional biosensors

Janssen, X.J.A.; Schellekens, A. J.; Ommering, Kim van; IJzendoorn, L.J. van; Prins, Mwj Menno

doi:10.1016/j.bios.2008.09.024

Cited by 121 publications

(126 citation statements)

References 28 publications

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“…Here, μ 0 ¼ 4π × 10 −7 H m −1 , m is the particle magnetic moment, and h…i denotes a time average. For high driving frequencies, ω ≳ 50 rad s −1 , the magnetic torque arises due to a finite internal relaxation time of the particle magnetization [31][32][33] t r , which in our case is t r ∼ 10 −4 s. Upon balancing T m with the viscous torque arising from the rotation in…”

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confidence: 83%

Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt

et al. 2015

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We study propulsion arising from microscopic colloidal rotors dynamically assembled and driven in a viscous fluid upon application of an elliptically polarized rotating magnetic field. Close to a confining plate, the motion of this self-assembled microscopic worm results from the cooperative flow generated by the spinning particles which act as a hydrodynamic "conveyor belt." Chains of rotors propel faster than individual ones, until reaching a saturation speed at distances where induced-flow additivity vanishes. By combining experiments and theoretical arguments, we elucidate the mechanism of motion and fully characterize the propulsion speed in terms of the field parameters. DOI: 10.1103/PhysRevLett.115.138301 PACS numbers: 82.70.Dd, 87.85.gj Propulsion in viscous fluids plays a key role in many different contexts of biology, physics, and chemistry. From a fundamental perspective, the transport of microscopic objects in a liquid medium poses the appealing challenge to find an adequate swimming strategy due to the negligible role of inertial force compared to viscous one. At low Reynolds number the Navier-Stokes equations become time reversible [1], and any strategy based on reciprocal motion, i.e., a motion composed by symmetric backward and forward displacements, will fail to produce net propulsion [2].Facing this challenge, the last few years have witnessed the theoretical propositions of several suitable geometries and procedures to propel micromachines in viscous fluids [3][4][5][6][7][8][9]. Parallel advances in miniaturization have led to the generation of new classes of chemically powered [10,11] or externally actuated [12][13][14][15] prototypes with exciting applications in emerging fields such as microsurgery [16,17] or lab-on-a-chip technology [18,19].In contrast to reaction driven microswimmers, actuated magnetic micropropellers do not present the autonomous behavior that distinguishes force-and torque-free motion of biological organisms [20], but instead avoid efficiency reduction due to fuel shortage or directional randomization. To date, three main approaches have been developed to transport microscopic particles in a viscous fluid using uniform magnetic fields [21], namely, by actuating flexible magnetic tails [12,22], by rotating helical shaped structures [23,24], or by using the close proximity to a bounding wall [25,26]. In the latter case, it is well established that in the Stokes regime the rotational motion of a body close to a surface can be rectified into net translation due to the hydrodynamic interaction with the boundary [27]. Surface rotors are optimal to work in confined geometries such as microfluidic channels or biological networks characterized by narrow pores.In this Letter we show that an ensemble of rotors dynamically self-assembled via attractive dipolar interactions can be propelled by a hydrodynamic "conveyor-belt" effect generated by the cooperative flow of the spinning particles close to a surface. Recent theoretical works [28][29][30] have addressed the rich dynamic...

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confidence: 83%

Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt

et al. 2015

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“…The magnetic moment of Dynal superparamagnetic beads drops to 1% of its maximum value in less than 10 −5 s after the field is turned off. 4 Thus these beads do not aggregate significantly by magnetic dipole-dipole attraction when the current to the magnet is zero.…”

Section: Introductionmentioning

confidence: 99%

Magnet polepiece design for uniform magnetic force on superparamagnetic beads

Fallesen

Hill

Steen

et al. 2010

Review of Scientific Instruments

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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 ‫ץ‬B x / ‫ץ‬y 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 0.5ϫ 4 mm 2 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 m 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.

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“…The magnetic susceptibility is typically anisoptropic and the particles align with their intrinsic axes along an external field [16]. The particle axis can also follow a rotating magnetic field and revolves with the same angular velocity [17]. Figure 9 shows particle distribution functions along the lateral direction for different angular velocities Ω.…”

Section: Control By Angular Velocitymentioning

confidence: 99%

Controlling inertial focussing using rotational motion

2014

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Abstract. In inertial microfluidics lift forces cause a particle to migrate across streamlines to specific positions in the cross section of a microchannel. We control the rotational motion of a particle and demonstrate that this allows to manipulate the lift-force profile and thereby the particle's equilibrium positions. We perform two-dimensional simulation studies using the method of multi-particle collision dynamics. Particles with unconstrained rotational motion occupy stable equilibrium positions in both halfs of the channel while the center is unstable. When an external torque is applied to the particle, two equilibrium positions annihilate by passing a saddle-node bifurcation and only one stable fixpoint remains so that all particles move to one side of the channel. In contrast, non-rotating particles accumulate in the center and are pushed into one half of the channel when the angular velocity is fixed to a non-zero value.

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Controlled torque on superparamagnetic beads for functional biosensors

Cited by 121 publications

References 28 publications

Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt

Colloidal Microworms Propelling via a Cooperative Hydrodynamic Conveyor Belt

Magnet polepiece design for uniform magnetic force on superparamagnetic beads

Controlling inertial focussing using rotational motion

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