Magnetic resonance force microscopy

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Magnetic resonance force microscopy (MRFM) is an imaging technique that acquires magnetic resonance images (MRI) at nanometer scales, and possibly at atomic scales in the future. MRFM is potentially able to observe protein structures which cannot be seen using X-ray crystallography and protein nuclear magnetic resonance spectroscopy. Detection of the magnetic spin of a single electron has been demonstrated using this technique. The sensitivity of a current MRFM microscope is 10 billion times better than a medical MRI used in hospitals.

Contents 1 Basic principle 2 Milestones 3 External links 4 References

[edit] Basic principle

Magnetic Resonance Force Microscopy (MRFM) is a measurement technique conceived to observe the three-dimensional atomic structures of single molecules. The concept combines the ideas of magnetic resonance imaging (MRI) and atomic force microscopy (AFM). Conventional MRI employs an inductive coil as an antenna to sense resonant nuclear or electronic spins in a magnetic field gradient. MRFM uses a cantilever tipped with a ferromagnetic particle to directly detect a modulated spin gradient force between sample spins and the tip. The motion of the cantilever - in particular the change in its resonant frequency - is detected by an interferometer. Smaller ferromagnetic particles and softer cantilevers increase the signal to noise ratio. Unlike the inductive coil approach, MRFM sensitivity scales favorably as device and sample dimensions are reduced.

Because the signal to noise ratio is inversely proportional to the sample size, Brownian motion is the primary source of noise at the scale in which MFRM is useful. Accordly, MFRM devices are cryogenically cooled. MFRM was specifically devised to determine the structure of proteins in situ.

[edit] Milestones

The basic principles of MRFM imaging and the theoretical possibility of this technology were first described in 1991^[1]. The first MRFM image was obtained in 1993 at the IBM Almaden Research Center with 1-μm vertical resolution and 5-μm lateral resolution using a bulk sample of the paramagnetic substance diphenyipicrylhydrazil^[2]. The spatial resolution reached nanometer-scale in 2003^[3]. Detection of the magnetic spin of a single electron was achieved in 2004^[4].

[edit] External links

• University of Washington Quantum System Engineering and MRFM Home Page, http://courses.washington.edu/goodall/MRFM/.
• Magnetic-Resonance Force Microscopy, http://www.medgadget.com/archives/2005/04/magneticresonan.html.

[edit] References

1. ^ J. A. Sidles. "Noninductive detection of single-proton magnetic resonance." Applied Physics Letters, 58(24):2854–6, 1991.
2. ^ O. Z¨uger and D. Rugar. "First images from a magnetic resonance force microscope." Applied Physics Letters, 63(18):2496–8, 1993.
3. ^ S. Chao, W. Dougherty, J. Garbini, J. Sidles. "Nanometer-scale magnetic resonance imaging." Review of Scientific Instruments, 75 (5):1175-81, 2003.
4. ^ D. Rugar, R. Budakian, H. Mamin, B. Chui, "Single spin detection by magnetic resonance force microscopy", Nature, 430, 329-32, 2004.

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