Dr Philip Norcott | Improving Nuclear Magnetic Resonance with SABRE-DREAM

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Dr Philip Norcott | Improving Nuclear Magnetic Resonance with SABRE-DREAM

Mar 22, 2023 | engineering and tech, physical sciences

About this episode

Nuclear magnetic resonance, or NMR, is an excellent technique for studying molecules, and is also the process behind hospital MRI machines. NMR works by exposing a sample to a strong, constant magnetic field. Then, a weak, oscillating magnetic field is also applied, and the atomic nuclei in the sample respond by emitting electromagnetic signals. These signals have particular frequencies, which scientists use to identify molecules in the sample. As useful as it is, NMR has weaknesses. Dr Philip Norcott at the Australian National University identifies two fundamental flaws and proposes a technique to overcome them.

The first weakness is NMR’s low sensitivity. This low sensitivity means you need a large number of detectable atomic nuclei in your sample to generate a coherent signal. This is a problem if you want to study trace amounts of a molecule: for example, identifying impurities in a chemical mixture.

As Dr Norcott explains, this sensitivity problem can be mitigated with hyperpolarisation. This technique increases the proportion of nuclei that respond to the magnetic field, boosting the signals they produce.

The second weakness is that different signals from different atoms can overlap. NMR signals are often very close together, and stronger signals can hide weaker signals. This is a problem if your sample contains a mixture of lots of different molecules.
Dr Norcott explains that there is a partial solution to this problem. A technique called DREAMTIME lets scientists filter the data, so that the signals from unwanted components are removed.

However, this doesn’t solve the problem of low sensitivity. In fact, this technique reduces the signal intensity, worsening the sensitivity problem.

Dr Norcott proposes combining a hyperpolarisation technique called SABRE with DREAMTIME. He calls this approach SABRE-DREAM, which can reduce signal overlap while increasing sensitivity. Essentially, SABRE-DREAM allows individual hyperpolarised components to be visualised independently.

Dr Norcott tested this approach, comparing SABRE-DREAM to each technique in isolation, while monitoring the progress of a chemical reaction. SABRE-DREAM achieved a similar level of signal enhancement to SABRE, but filtered the data to eliminate unwanted signals from the chemical mixture.

This experiment shows that the two major weaknesses of NMR – low sensitivity and signal overlap – can both be mitigated at the same time. This offers scientists new and improved ways to use NMR in their work. SABRE-DREAM could also be useful in medical imaging, for monitoring markers such as glucose levels in people with diabetes.

Original Article Reference

Summary of the paper ‘Selective NMR detection of individual reaction components hyperpolarised by reversible exchange with para-hydrogen’, in Physical Chemistry Chemical Physics. doi.org/10.1039/d2cp01657e

Dr Norcott gratefully acknowledges an Australian Research Council Discovery Early Career Researcher Award (DE210100065)