Scientists at UC Berkeley, Lawrence Berkeley National Lab, and National Institute of Standards and Technology demonstrated the detection of nuclear magnetic resonance (NMR) signals without setting up a magnetic field at all. Not having to use powerful superconducting magnets in future NMR devices will allow them to be considerably smaller, more portable, cheaper, and safer.
First, the problem of spin coupling without an applied magnetic field can be overcome by employing a technique known as “parahydrogen-induced polarization”. Parahydrogen is a spin isomer form of hydrogen with the anti-parallel spin alignment, forming a “singlet state” (see image above). The technique used by them transfers a special kind of polarization from to the sample molecule, resulting in enormous signal enhancement. While the phenomenon of parahydrogen-induced polarization has been known for some time, the current work is the first to successfully use it in zero-field.
The researchers then used an innovative technique to measure the faint magnetic fields. The detectors used in early experiments with low-field NMR needed to be cooled to near absolute zero, which defeated the purpose of removing the applied field in the first place. Instead, the researchers modified a different type of detector called an “optical atomic magnetometer” – which requires no refrigeration – for use at zero-field.
Link @ PhysicsWorld: NMR spectroscopy without the ‘M’
Study abstract in Nature Physics: Parahydrogen-enhanced zero-field nuclear magnetic resonance