Magnetically inducible particles, such as paramagnetic
microspheres, when placed in an external magnetic field align along the magnetic
flux lines, to form aggregates in the form of long chains. This phenomenon has
been the topic of interest in recent years due to its possible applications in
microfluidics and rheology.
Until now the preferred method of magnetic field generation
has been via the electromagnetic technique, in which Helmholtz coils placed
across the fluid cell are used to generate an external field. At small
distances, the field is uniform and unidirectional, and the flux lines pass
through the fluid cell, all in the same direction from one end to the other.
Researchers at ASU, in a recent study, have used a strong
rare-earth magnet to provide the external magnetic field. When placed over a
fluid sample containing the magnetically inducible particles a unidirectional
magnetic field is created in the fluid suspension and causes the microspheres to
form chains. When the field is rotated, by revolving the magnet, the particle
chains also rotate about their centers. This produces a micro-rotor mixing
effect. This device is much simpler than the Helmholtz coil arrangement that
requires function generators, power amplifiers and cooling systems for
generating and rotating the magnetic field.
Potential Applications
- Liquid Mixing in DNA Sequencing Chips
- Medical Diagnostic Testing
- Microflow Cytometry
- Mass Spectroscopy
- Microfluidic Electrophoresis
- Lab-On-A-Chip
- Micro Cell Culture
Benefits and Advantages
- Increased mixing in micro and macro devices and reactors
- Non-turbulent mixing - Low Reynolds number
- Technology does not rely on a specialized chamber design
- Mixing can be performed within any micro-well or micro-channel
- Compatible with cells and other shear sensitive
components in solution - The micro-rotors impart very low levels of
hydrodynamic shear stress
- Magnetic field external to the fluid sample
- Mobile - Can be located to any area of interest
- Magnets can be arranged to produce fields that are either
uniform or non-uniform
- Combination of magnet and motor arrangement can be used
to produce particle rotation about various axes
- Increased effective heat and mass diffusivities in the
local area around the particles
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