Palm-Size NMR
The portable but powerful magnet could be used to find archaeological artifacts or to detect contamination in products.
Room-sized nuclear magnetic resonance machines might shrink to handheld, portable devices thanks to a small, lightweight magnet design developed by German researchers.
Nuclear magnetic resonance spectroscopy is a common tool for studying the structure of proteins and identifying the chemical composition of a material. It also forms the basis of the medical imaging technique magnetic resonance imaging, or MRI. However, bulky and expensive superconducting magnets are used to generate the strong magnetic fields (about seven tesla) needed for precision NMR.
The magnet, developed by Federico Casanova and his colleagues at the RWTH Aachen University’s department of macromolecular chemistry, is about the size of a standard D battery and weighs 500 grams. While portable magnets have been made before, the new one enables NMR measurements that are just as precise as the large commercial magnets. “This is a significant additional step toward mobile high-resolution NMR,” says Alexander Pines, a chemistry professor at the University of California, Berkeley, who is developing a new type of compact MRI designs.
As the size of a permanent magnet shrinks, it generates magnetic fields that are uniform over a smaller volume because of tiny imperfections in its material and shape. This means less of a material sample can be used, making the NMR measurements almost a thousand times less sensitive than if a superconducting magnet were used. The NMR signal then becomes comparable to the electronic noise, and the device can miss chemicals that are present in very small quantities.
The new magnet generates a 0.7 tesla magnetic field, but it generates an extremely homogenous field. As a result, it is the first portable magnet that works with the conventional five-millimeter tubes in which NMR samples are placed. “The goal of our work was to take this tube, keep the volume constant, and build the smallest magnet with the desired homogeneity,” Casanova says. “The important thing we did is to correct the inhomogeneity that comes from imperfections in the magnet.”
Calling the results impressive, Louis Bouchard, a University of California Los Angeles chemistry professor, says that no previous portable magnet design has achieved such good performance. Bouchard believes the cost of the magnet should be much lower than that of present-day commercial NMR magnets. “This will likely lead to such NMR units being much more widespread,” he says. “If these guys sold this product commercially, I would probably buy one.”
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