Magnetic attraction: Microchip demonstrates concept of 'MRAM for biomolecules'

ScienceDaily (Oct. 19, 2011) — Researchers from the National Institute of Standards and Technology (NIST) and University of Colorado Boulder (CU) have developed a low-power microchip that uses a combination of microfluidics and magnetic switches to trap and transport magnetic beads. The novel transport chip may have applications in biotechnology and medical diagnostics.

A key innovation in the new chip is the use of magnetic switches like those in a computer random access memory. As described in a new paper, the NIST/CU team used the chip to trap, release and transport magnetic beads that potentially could be used as transport vehicles for biomolecules such as DNA.

Conventional microfluidics systems use pumps and valves to move particles and liquids through channels. Magnetic particle transport microchips offer a new approach to microfluidics but generally require continuous power and in some cases cooling to avoid sample damage from excessive heating. The NIST/CU 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, commonly 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 (see video clip at: http://www.nist.gov/pml/electromagnetics/magnetics/magnetic-101311.cfm). The beads start out suspended in salt water above the valves before being trapped in the array.

"It's a whole new way of thinking about microfluidics," says NIST physicist 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 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.

Magnetic tags are used 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 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.

The lead author of the new paper, Wendy Altman, 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.

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The above story is reprinted from materials provided by National Institute of Standards and Technology (NIST).

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Journal Reference:

Wendy R. Altman, John Moreland, Stephen E. Russek, Bruce W. Han, Victor M. Bright. Controlled transport of superparamagnetic beads with spin-valves. Applied Physics Letters, 2011; 99 (14): 143703 DOI: 10.1063/1.3645615

Note: If no author is given, the source is cited instead.

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View the original article here

Tuning 'metasurface' with fluid in new concept for sensing and chemistry

ScienceDaily (June 8, 2011) — Like an opera singer hitting a note that shatters a glass, a signal at a particular resonant frequency can concentrate energy in a material and change its properties. And as with 18th century "musical glasses," adding a little water can change the critical pitch. Echoing both phenomena, researchers at the National Institute of Standards and Technology (NIST) have demonstrated a unique fluid-tuned "metasurface," a concept that may be useful in biomedical sensors and microwave-assisted chemistry.

A metasurface or metafilm is a two-dimensional version of a metamaterial, popularized recently in technologies with seemingly unnatural properties, such as the illusion of invisibility. Metamaterials have special properties not found in nature, often because of a novel structure. NIST's metasurface is a small piece of composite circuit board studded with metal patches in specific geometries and arrangements to create a structure that can reflect, store, or transmit energy (that is, allow it to pass right through).

As described in a new paper,  NIST researchers used purified water to tune the metasurface's resonant frequency -- the specific microwave frequency at which the surface can accumulate or store energy. They also calculated that the metasurface could concentrate electric field strength in localized areas, and thus might be used to heat fluids and promote microwave-assisted chemical or biochemical reactions.

The metasurface's behavior is due to interactions of 18 square copper frame structures, each 10 millimeters on a side (see photo). Computer simulations help design the copper squares to respond to a specific frequency. They are easily excited by microwaves, and each one can store energy in a T-shaped gap in its midsection when the metasurface is in a resonant condition. Fluid channels made of plastic tubing are bonded across the gaps. The sample is placed in a waveguide, which directs the microwaves and acts like a kaleidoscope, with walls that serve as mirrors and create the electrical illusion that the metasurface extends to infinity.

Researchers tested the metasurface properties with and without purified water in the fluid channels. The presence of water shifted the resonant frequency from 3.75 to 3.60 gigahertz. At other frequencies, the metasurface reflects or transmits energy. Researchers also calculated that the metasurface, when in the resonant condition, could concentrate energy in the gaps at least 100 times more than the waveguide alone.

Metasurface/fluid interactions might be useful in tunable surfaces, sensing and process monitoring linked to changes in fluid flow, and catalysis of chemical or biochemical reactions in fluid channels controlled by changes in microwave frequency and power as well as fluid flow rates. NIST researchers are also looking into the possibility of making metamaterial chips or circuits to use for biomedical applications such as counting cells.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

J. Gordon, C. Holloway, J.C. Booth, J.R. Baker-Jarvis, D. Novotny, S. Kim and Y. Wang. Fluid interactions with metafilm/metasurfaces for tuning, sensing, and microwave assisted chemical processes. Physical Review B, 83, 205130 (2011) DOI: 10.1103/PhysRevB.83.205130

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Tuning 'metasurface' with fluid in new concept for sensing and chemistry

ScienceDaily (June 8, 2011) — Like an opera singer hitting a note that shatters a glass, a signal at a particular resonant frequency can concentrate energy in a material and change its properties. And as with 18th century "musical glasses," adding a little water can change the critical pitch. Echoing both phenomena, researchers at the National Institute of Standards and Technology (NIST) have demonstrated a unique fluid-tuned "metasurface," a concept that may be useful in biomedical sensors and microwave-assisted chemistry.

A metasurface or metafilm is a two-dimensional version of a metamaterial, popularized recently in technologies with seemingly unnatural properties, such as the illusion of invisibility. Metamaterials have special properties not found in nature, often because of a novel structure. NIST's metasurface is a small piece of composite circuit board studded with metal patches in specific geometries and arrangements to create a structure that can reflect, store, or transmit energy (that is, allow it to pass right through).

As described in a new paper,  NIST researchers used purified water to tune the metasurface's resonant frequency -- the specific microwave frequency at which the surface can accumulate or store energy. They also calculated that the metasurface could concentrate electric field strength in localized areas, and thus might be used to heat fluids and promote microwave-assisted chemical or biochemical reactions.

The metasurface's behavior is due to interactions of 18 square copper frame structures, each 10 millimeters on a side (see photo). Computer simulations help design the copper squares to respond to a specific frequency. They are easily excited by microwaves, and each one can store energy in a T-shaped gap in its midsection when the metasurface is in a resonant condition. Fluid channels made of plastic tubing are bonded across the gaps. The sample is placed in a waveguide, which directs the microwaves and acts like a kaleidoscope, with walls that serve as mirrors and create the electrical illusion that the metasurface extends to infinity.

Researchers tested the metasurface properties with and without purified water in the fluid channels. The presence of water shifted the resonant frequency from 3.75 to 3.60 gigahertz. At other frequencies, the metasurface reflects or transmits energy. Researchers also calculated that the metasurface, when in the resonant condition, could concentrate energy in the gaps at least 100 times more than the waveguide alone.

Metasurface/fluid interactions might be useful in tunable surfaces, sensing and process monitoring linked to changes in fluid flow, and catalysis of chemical or biochemical reactions in fluid channels controlled by changes in microwave frequency and power as well as fluid flow rates. NIST researchers are also looking into the possibility of making metamaterial chips or circuits to use for biomedical applications such as counting cells.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

J. Gordon, C. Holloway, J.C. Booth, J.R. Baker-Jarvis, D. Novotny, S. Kim and Y. Wang. Fluid interactions with metafilm/metasurfaces for tuning, sensing, and microwave assisted chemical processes. Physical Review B, 83, 205130 (2011) DOI: 10.1103/PhysRevB.83.205130

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here