October 24, 2011 — Researchers from the National Institute of Standards and Technology (NIST) and University of Colorado Boulder (CU) developed a low-power microchip combining microfluidics and magnetic switches to trap and transport magnetic beads.
The magnetic particle microfluidics approach has traditionally required continuous power, and heat can be an issue. The demo chip features two adjacent lines of 12 thin-film magnet switches called spin valves, commonly used as magnetic sensors in read heads of high-density computer disk drives. These spin valves have been optimized for magnetic trapping. Pulses of electric current are used to switch individual spin valve magnets “on” to trap a bead, or “off” to release it, moving the bead down a ladder formed by the two lines. The beads start out suspended in salt water above the valves before being trapped in the array.
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| Figure. Micrograph of magnetic microfluidic chip developed by the NIST and CU. Brief pulses of electrical current in the two orange lines generate a magnetic field to turn individual spin valves (blue bars) on and off, moving a magnetic bead up or down the “ladder.” SOURCE: W. Altman/CU and NIST. |
This design creates a "switchable permanent magnet" that requires power only to switch on (for less than a microsecond), said NIST physicist John Moreland.
NIST researchers previously demonstrated that spin valves could be used to trap and rotate particles and recently were awarded two patents related to the idea of a magnetic chip. (U.S. Patent 7,981,696 B2, awarded July 19, 2011, and U.S. Patent 7,985,599 B2, awarded July 26, 2011. Inventors John Moreland, Elizabeth Mirowski, and Stephen Russek. Microfluidic platform of arrayed switchable spin-valve elements for high-throughput sorting and manipulation of magnetic particles and biomolecules.)
Biotechnology and medical diagnostics applications could use the chip in bioassay magnetic tags. The chip demonstration provides a conceptual foundation for a more complex magnetic random access memory (MRAM) for molecular and cellular manipulation. For example, programmable microfluidic MRAM chips might simultaneously control a large number of beads, and the attached molecules or cells, to assemble “smart” tags with specified properties, such as an affinity for a given protein at a specific position in the array. NIST is also interested in developing cellular and molecular tags for magnetic resonance imaging (MRI) studies in which individual cells, such as cancer cells or stem cells, would be tagged with a smart magnetic biomarker that can be tracked remotely in an MRI scanner, Moreland says. Automated spin valve chips might also be used in portable instruments for rapid medical diagnosis or DNA sequencing.
Results were published by lead author Wendy Altman, who did the research at NIST as a CU graduate student working on her doctoral thesis. Another author, Bruce Han, was a CU student in NIST’s Summer Undergraduate Research Fellowship (SURF) program. See: W.R. Altman, J. Moreland, S.E. Russek, B.W. Han and V. M. Bright. 2011. Controlled transport of superparamagnetic beads with spin-valves. Applied Physics Letters, Vol. 99, Issue 14, Oct. 3.
The National Institute of Standards and Technology (NIST) is an agency of the U.S. Department of Commerce. Learn more at www.nist.gov.