As described in a recent paper, NIST researchers found that arrays of switches called "spin valves"—commonly used as magnetic sensors in the read heads of high-density disk drives—also show promise as tools for controlled trapping of single biomolecules.
The arrays might be used in chip-scale, low-power microfluidic devices for stretching and uncoiling, or capturing and sorting, large numbers of individual biomolecules simultaneously for massively parallel medical and forensic studies—a sort of magnetic random access memory (MRAM) for biosciences.
Spin valves are made by stacking thin layers of materials with different magnetic properties. Their net magnetization can be switched on and off by applying an external magnetic field of sufficient strength to align the electron "spins" in the magnetic layers in the same (on) or opposite (off) directions. NIST researchers made an array of spin valves, each about one by four micrometers in size, patterned on a 200-nanometer-thick silicon nitride membrane in fluid. When the spin valves are turned on, a local magnetic field is created that is strongest near the ends of the magnetic stack below the membrane—a field strong enough to trap nanoscale magnetic particles.
The NIST experiments demonstrated that the spin valves not only can trap magnetic particles, but also can be used as the pivot point for rotating strands of particles when a rotating magnetic field is applied. According to the researchers, these experimental results, combined with computer modeling, suggest that if biomolecules such as proteins or DNA strands were attached to the magnetic particles, the spin-valve array could apply torsional forces strong enough to alter the structure or shape of the biomolecules. The NIST group is now working on a microfluidic chip that will accomplish this electronically, which would be a significant milestone for applications.
Parallel processing of single biomolecules would be a significant advance over existing techniques limited to studying one molecule at a time. Optical tweezers, which use lasers to trap and manipulate biomolecules, tend to be slow and limited in force, and the particles need to be micrometer sized or larger. Existing magnetic tweezers can trap smaller particles and apply torque, but typically require permanent immobilization of biomolecules, which is time consuming and prevents subsequent analysis.
To view short video clip of the device in use, see:
http://www.nist.gov/public_affairs/images/spin_valve_array.avi
Citation: E. Mirowski, J. Moreland, S. Russek, M. Donahue and K. Hsieh. Manipulation of magnetic particles by patterned arrays of magnetic spin-valve traps.
Journal of Magnetism and Magnetic Materials, Vol. 311, pp. 401-404, (2007).
Source: National Institute of Standards and Technology
Related stories:
DNA technique yields 3-D crystalline organization of nanoparticles
In an achievement some see as the "holy grail" of nanoscience, researchers at the U.S. Department of Energy's Brookhaven National Laboratory have for the first time used DNA to guide the creation of three-dimensional, ordered, crystalline structures of nanoparticles (particles with dimensions measured in billionths of a meter). The ability to engineer such 3-D structures is essential to producing functional materials that take advantage of the unique properties that may exist at the nanoscale - for example, enhanced magnetism, improved catalytic activity, or new optical properties. The research will be published in the January 31, 2008, issue of the journal
Nature.
New technique captures chemical reactions in a single living cell at unprecedented resolution
Bioengineers at the University of California, Berkeley, have discovered a technique that for the first time enables the detection of biomolecules' dynamic reactions in a single living cell.
Magnetic particles act as ink in new printer
By using a laser beam to focus and push particles against a substrate, scientist Lars Helseth of Nanyang Technological University in Singapore has designed and built a unique type of colloidal printer. Taking advantage of the electrical and paramagnetic properties of tiny beads, Helseth’s printer provides a new printing method that may have applications in printing chemical and biological patterns.
Nanoparticles Designed for Dual-Mode Imaging
Nanoscale, inorganic fluorescent imaging agents such as quantum dots have become an important tool for researchers studying key biomolecules involved in cancer. At the same time, magnetic iron oxide nanoparticles are proving to be useful in detecting tumors and metastatic lesions thanks to their ability to act as powerful contrast agents for use with magnetic resonance imaging (MRI).
Electromagnetic miniatures
Magnetic components that can be controlled by the application of an external electric field are useful in many different applications. They can serve as microfluidic pumps, mixers, or valves in miniature lab-on-chip systems, or they can help in sorting and arranging magnetic particles.
Nanoparticles Make Cancer Cells Visible
Wouldn’t it be nice if we could detect tumors and their metastases as easily as we find broken bones with X-rays? A team of scientists headed by S. Bhatia in Boston has been working on this problem. They have found a way to make a tumor-specific protease visible by using Fe
3O
4 nanoparticles and magnetic resonance imaging (MRI).
MIT instrument studies edge of sun's bubble
The Voyager 1 and 2 spacecraft have traveled beyond the edges of the bubble in space where the sun's constant outward wind of particles and radiation slams into the interstellar medium that pervades our galaxy. The first scientific reports on what the Voyagers found there appears this week in the journal
Nature.
First images of solar system's invisible frontier
NASA's sun-focused STEREO spacecraft unexpectedly detected particles from the edge of the solar system last year, allowing University of California, Berkeley, scientists to map for the first time the energized particles in the region where the hot solar wind slams into the cold interstellar medium.
