New Views at the Nanoscale
MIT Researchers are Building a Microscope Using MRI Technology
Magnetic resonance imaging has become a standard diagnostic tool for cancer, cardiovascular disease and neurological disorders, among others. MRI is ideally suited to medical imaging because it offers an unparalleled three-dimensional glimpse inside living tissue without damaging the tissue. However, its use in scientific studies has been limited because it can't image anything smaller than several cubic micrometers. Now scientists are combining the 3-D capability of MRI with the precision of a technique called atomic force microscopy. This combination enables 3-D visualization of tiny specimens such as viruses, cells and potentially structures inside cells - a 100-million-fold improvement over MRI used in hospitals.
Last year, MIT Scientist Christian Degen used that strategy to build the first MRI device that can capture 3-D images of viruses. Now the paper reporting the ability to take an MRI image of a tobacco mosaic virus was awarded the 2009 Cozzarelli Prize by the National Academy of Sciences, for scientific excellence and originality in the engineering and applied sciences category. Researchers including Degen and his IBM colleagues have improved the technique to the point where it can produce 3-D images with resolution as low as five to 10 nm, or billionths of a meter. (A human hair is about 80,000 nm thick.) With MRFM, the sample to be examined is attached to the end of a tiny silicon cantilever (about 100 millionths of a meter long and 100 billionths of a meter wide). As a magnetic iron cobalt tip moves close to the sample, the atoms' nuclear spins become attracted to it and generate a small force on the cantilever. The spins are then repeatedly flipped, causing the cantilever to gently sway back and forth in a synchronous motion. That displacement is measured with a laser beam to create a series of 2-D images of the sample, which are combined to generate a 3-D image.