Standard nuclear magnetic resonance (NMR) spectroscopy requires the use of a very high magnetic field created by large superconducting magnets cooled by liquid helium. Because this method is unwieldy and expensive, it cannot translate into small medical diagnostic devices. Now, however, an article posted at physicsworld.com published by the Institute of Physics (London) reports that a group of researchers at the Nuclear Science Division at the University of California, Berkeley has learned how to perform NMR spectroscopy without magnets. As a result of their work, small personalized medical spectrometers may not be so far off, after all.
|Currently the size of a room, nuclear magnetic resonance spectroscopy could eventually dispense with large magnets and accommodate small diagnostic devices.|
Conventional NMR works by bombarding a sample with radio waves and measuring the energy absorbed or emitted when nuclei flip between two states: spin-up and spin-down. Because the same nuclei in different parts of a molecule have slightly different transition frequencies, measuring these frequencies allows researchers to work out the location of particular atoms in the molecule. To resolve different frequencies, bigger magnetic fields are better.
While nuclear spins interact with the magnetic field, they also interact with one other. Known as J-coupling, this interaction results in signals that can provide a great deal of information about a sample's chemical structure.
The Berkeley scientists' achieve this type of spin coupling by employing parahydrogen-induced polarization, which transfers a special kind of polarization to the sample molecule, enhancing the signal. Uniquely, their method accomplishes this transfer in zero field. The researchers also use a technique known as an optical atomic magnetometer to measure the faint magnetic fields. This technique, which does not require refrigeration, can also be employed at zero field.
The team has demonstrated the viability of its technique by distinguishing between several similar hydrocarbon molecules. Its success points the way toward future NMR technology that is smaller and less costly than today's NMR spectrometers.