Researchers from Texas A&M University have
devised a way to magnetically levitate particles and droplets that have
volumes smaller than one billionth of a milliliter.
Scientists have levitating relatively large objects, including
live frogs, using powerful superconducting magnets. The Texas A&M researchers
scaled the process down with a computer-chip-size device that contains
permanent magnets and 25-micron-wide electrodes. Gaps between the magnets
and electrodes oriented perpendicularly to the gaps generate arrays of
magnetic wells that can levitate and contain microscopic droplets.
The method, which can move and levitate droplets with a precision
of 300 nanometers, has many potential uses, according to the researchers.
It could be used on labs-on-a-chip, and would be able to analyze
minuscule amounts of substances using very little of the way of chemicals
and power. The magnets and electrodes that make up the device are inexpensive
to mass produce, and so could be used in expendable, single-use labs-on-a-chip.
The device could also be used to manipulate droplets, nanoparticles,
cells, viruses or even single molecules in conjunction with standard microscopes,
and in conjunction with optical tweezers. Optical tweezers move and manipulate
extremely small objects using the energy of a laser beam. It could also
be used to make multilayered caplets 20 to 50 microns in diameter for
programmable drug release inside the body. A micron is one thousandth
of a millimeter.
The method could also be used in sensors. Levitated droplets and
particles are very sensitive to external forces and could therefore measure
them. The method has the potential to be on the order of a magnitude more
sensitive to force than any other method at room temperature, according
to the researchers.
Prototype levitation devices could be produced within two years,
according to the researchers. The work appeared in the September 6, 2004
issue of Applied Physics Letters.
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