MRI On The Nanoscale

Scientists at IBM’s Almaden Research Center, in San Jose, Calif., report the first nanometer-scale magnetic resonance imaging of a biological sample. At such length scales, MRI could be used to image the three-dimensional structure of individual macromolecules and complexes, they note. Conventional MRI microscopy is limited to the micrometer scale. The IBM team, led by Dan Rugar, manager of nanoscale studies, improved the spatial resolution by combining magnetic resonance force microscopy (MRFM) with 3-D image reconstruction (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0806062106). MRFM is based on the mechanical measurement of ultrasmall magnetic forces between the nuclear spins in a sample and a nearby magnetic tip, which is scanned in three dimensions over the sample. The best spatial resolution previously achieved was 90 nm in ¹⁹F MRFM of inorganic samples. The IBM researchers extended the technology to biological samples and obtained ¹H MRI images of tobacco mosaic virus particles with 4-nm resolution. Such a technique “would be complementary to other techniques, such as cryo-electron microscopy, and could develop into a powerful tool for structural biology,” the researchers write.