MRI microscopes provide a nondestructive means to investigate the interior of small biological samples, but the volume resolution is currentlv limited to ≈40 μm~3. Christian Desen et al. have nowrndemonstrated a prototype MRI device with nanometer-level resolution, increasing the resolution by a factor of 100 million. Unlike a conventional MRI scanner that uses gradient and imaging coils, the authors' technique, called "magnetic resonance force microscopy," relies on detecting ultrasmall magnetic forces. The sample is placed on a flexible silicon can-rntilever similar to that of an atomic force microscope. Laser inter-ferometry tracks the motion of the cantilever, which vibrates slightly as nuclear spins in the sample interact with a combination of 3 external magnetic fields: A superconducting magnet provides a large static field; a tiny wire generates the rf field that drives magnetic resonance; and a nanoscale magnetic tip produces an intense, localized field. The tip is scanned in 3 dimensions, and the force signals are deconvolved to find the 3D H density. The technique is slow to produce images, but the authors say researchers could potentially use nano-MRI to image the 3D structure of large biomolecules.
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