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13 Jun 2005

Volume 86, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 86, 241913 (2005); http://dx.doi.org/10.1063/1.1946181 (3 pages)

E. Placidi, F. Arciprete, V. Sessi, M. Fanfoni, F. Patella, and A. Balzarotti
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Manipulation and sorting of magnetic particles by a magnetic force microscope on a microfluidic magnetic trap platform

Elizabeth Mirowski, John Moreland, Arthur Zhang, Stephen E. Russek, and Michael J. Donahue

Appl. Phys. Lett. 86, 243901 (2005); http://dx.doi.org/10.1063/1.1947368 (3 pages) | Cited 15 times

Online Publication Date: 6 June 2005

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We have integrated a microfluidic magnetic trap platform with an external magnetic force microscope (MFM) cantilever. The MFM cantilever tip serves as a magnetorobotic arm that provides a translatable local magnetic field gradient to capture and move magnetic particles with nanometer precision. The MFM electronics have been programmed to sort an initially random distribution of particles by moving them within an array of magnetic trapping elements. We measured the maximum velocity at which the particles can be translated to be 2.2 mm/s±0.1 mm/s, which can potentially permit a sorting rate of approximately 5500 particles/min. We determined a magnetic force of 35.3±2.0 pN acting on a 1 μm diameter particle by measuring the hydrodynamic drag force necessary to free the particle. Release of the particles from the MFM tip is made possible by a nitride membrane that separates the arm and magnetic trap elements from the particle solution. This platform has potential applications for magnetic-based sorting, manipulation, and probing of biological molecules in a constant-displacement or a constant-force mode.
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75.50.Tt Fine-particle systems; nanocrystalline materials
07.79.Pk Magnetic force microscopes

Open-type magnetocardiograph with cylindrical magnetic shield

Yusuke Seki, Akihiko Kandori, Daisuke Suzuki, and Mitsuru Ohnuma

Appl. Phys. Lett. 86, 243902 (2005); http://dx.doi.org/10.1063/1.1946203 (3 pages) | Cited 8 times

Online Publication Date: 9 June 2005

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We have developed an open-type magnetocardiograph (MCG) with a cylindrical magnetic shield—having an auxiliary magnetic shield—and 64 gradiometers based on low-transition temperature (Tc) superconducting quantum interference devices (SQUIDs). A revolving door is applied to the magnetic shield with the aim of providing easy access to a subject and easy operation. The cryostat attached to the MCG contains 64 low-Tc SQUIDs and is about 1 m in height, so there must be an opening through the cylindrical surface of the magnetic shield. The properties of the magnetic shield were simulated using finite-element-method simulations and experiments. The results of the simulations indicated that the auxiliary magnetic shield recovers enough of the shielding performance of a magnetic shield with an opening that it performs like a magnetic shield without an opening. The shielding factor of the developed magnetic shield is above 46 dB in the vicinity of the magnetic shield. Accordingly, the open-type MCG can clearly measure magnetocardiograms.
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87.80.-y Biophysical techniques (research methods)
85.25.Dq Superconducting quantum interference devices (SQUIDs)
02.70.Dh Finite-element and Galerkin methods
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