Microchip Demonstrates Biomolecules’ Magnetic Attraction

Scientists have developed a low-power microchip that uses a combination of magnetic switches and microfluidics to trap and transport magnetic beads. The innovative transport chip may have applications in biotechnology and medical diagnostics.

A major advance in the new chip is the use of magnetic switches similar to those in a computer random access memory. As described in an article published October 3, 2011, in the journal Applied Physics Letters, the investigators, from the US National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA) and University of Colorado Boulder (CU; USA), used the chip to trap, release, and transport magnetic beads that potentially could be used as transport vehicles for biomolecules such as DNA.


Traditional microfluidics systems use pumps and valves to move particles and liquids through channels. Magnetic particle transport microchips provide a new application for microfluidics, but typically require continuous power, and in some instances, cooling to avoid sample damage from excessive heating. The technology eliminates these drawbacks while offering the possibility for random access two-dimensional control and a memory that lasts even with the power off.

The demo chip features two adjacent lines of 12 thin-film magnet switches called spin valves, usually used as magnetic sensors in read heads of high-density computer disk drives. In this case, however, the 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, and thereby move the bead down a ladder formed by the two lines. The beads begin suspended in salt water above the valves before being trapped in the array.

“It’s a whole new way of thinking about microfluidics,” said NIST physicist Dr. John Moreland. “The cool thing is it’s a switchable permanent magnet--after it’s turned on it requires no power. You beat heat by switching things quickly, so you only need power for less than a microsecond.”

NIST researchers previously shown 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.

Magnetic tags are utilized in bioassays such as protein and DNA purification and cell breakdown and separation. 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 regulate a large number of beads, and the attached molecules or cells, to assemble “smart” tags with specified characteristics, 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) research in which individual cells, such as stem cells or cancer cells, would be tagged with a smart magnetic biomarker that can be monitored remotely in an MRI scanner, according to Dr. Moreland. Automated spin valve chips might also be used in portable instruments for rapid medical diagnosis or DNA sequencing.

Related Links:
The US National Institute of Standards and Technology
University of Colorado Boulder
Video NIST CU Magnetic Microfluidic Chip