In situ SABRE hyperpolarisation with Earth’s field NMR detection

Hyperpolarisation methods, which increase the sensitivity of NMR and MRI, have the potential to expand the range of applications of these powerful analytical techniques and to enable the use of smaller and cheaper devices. The signal amplification by reversible exchange (SABRE) method is of particular interest because it is relatively low-cost, straight-forward to implement, produces high-levels of renewable signal enhancement, and can be interfaced with low-cost and portable NMR detectors. In this work we demonstrate an in situ approach to SABRE hyperpolarisation that can be achieved using a simple, commercially-available Earth’s field NMR detector to provide 1H polarisation levels of up to 3.36 %. This corresponds to a signal enhancement over the Earth’s magnetic field by a factor of ε > 2e8. The key benefit of our approach is that it can be used to probe the polarisation transfer process at the heart of the SABRE technique directly. In particular, we demonstrate the use of in situ hyperpolarisation to observe the activation of the SABRE catalyst, the build-up of signal in the polarisation transfer field (PTF), the dependence of the hyperpolarisation level on the strength of the PTF, and the rate of decay of the hyperpolarisation in the ultra-low-field regime.