NMR measurements without strong magnetic fields

Nuclear magnetic resonance (NMR) is an analytical tool with a wide range of applications, including magnetic resonance imaging in medicine. However, NMR often requires powerful magnetic fields to be generated, which limits the scope of its use. Researchers at Johannes Gutenberg University Mainz (JGU) and the Helmholtz Institute Mainz (HIM) have now discovered a way to reduce the size of the corresponding devices — and also the associated risk — by eliminating the need for strong magnetic fields.

The current generation of NMR devices is — because of the magnets — extremely heavy and expensive. Another complicating factor is the present shortage of liquid helium that is employed as a coolant. To make magnets redundant in this context, JGU/HIM researcher Dr Danila Barskiy came up with the idea of combining zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) with a special technique that makes it possible to hyperpolarise atomic nuclei.

ZULF NMR is itself a recently developed form of spectroscopy that provides abundant analytical results without the need for large magnetic fields. Another advantage over high-field NMR is the fact that its signals can also be readily detected in the presence of conductive materials, such as metals. The sensors employed for ZULF NMR, typically optically pumped magnetometers, are highly sensitive, easy to use and commercially available. Thus, it is relatively straightforward to assemble a ZULF NMR spectrometer.

However, the generated NMR signal is an issue to be dealt with. The methods that have been used to date to generate the signal are suitable only for the analysis of a limited selection of chemicals or are otherwise associated with exorbitant costs. For this reason, Barskiy decided to exploit the hyperpolarisation technique known as SABRE, which allows for aligning nuclear spins at large numbers in solution.

There are a number of such techniques that would produce a signal sufficient for detection in ZULF conditions; SABRE, short for Signal Amplification by Reversible Exchange, has proved to be particularly well suited. Central to SABRE is an iridium metal complex that mediates the transfer of the spin order from parahydrogen to a substrate. Barskiy managed to sidestep the disadvantages resulting from the temporary binding of the sample to the complex by employing SABRE-Relay, a recent improvement of the SABRE technique. In this case, SABRE is used to induce polarisation which is then relayed to a secondary substrate.

In their paper published in the journal Science Advances, Barskiy and colleagues reported on how they were able to detect the signals for methanol and ethanol extracted from a sample of vodka.

“This simple example demonstrates how we have been able to extend the application range of ZULF NMR with the help of an inexpensive, rapid and versatile method of hyperpolarisation,” Barskiy said. “We hope that we’ve managed to get a little closer to our objective of making feasible the development of compact, portable devices that can be used for the analysis of liquids such as blood and urine and in future, possibly endowing discrimination of particular chemicals such as glucose and amino acids.”

Image caption: Dr Danila Barskiy conducting an experiment. Photo ©Danila Barskiy

Please follow us and share on Twitter and Facebook. You can also subscribe for FREE to our weekly newsletters and bimonthly magazine.