⁷⁷Se Hyperpolarization Enabled by Reversible Parahydrogen Exchange and Audio-Frequency Magnetic Fields at 0.1 mT

Nuclear spin hyperpolarization boosts NMR sensitivity but typically requires complex infrastructure. Signal Amplification by Reversible Exchange (SABRE), a parahydrogen-based hyperpolarization technique, can be conducted using a remarkably low-cost polarizer (<$100) comprising only magnetic coils and a standard PC sound card, avoiding magnetic shielding. However, under these conditions SABRE requires direct spin-coupling between parahydrogen and the target nucleus, limiting its application to distant heteronuclear spins such as ⁷⁷Se in biologically relevant selenium-nitrogen heterocycles (e.g. antioxidant, antiviral, and anticancer agents). Here, we overcome the distance restrictions by developing the ¹⁵N-mediated polarization transfer driven by optimized oscillating magnetic fields of the audio frequency. This enables a significant ⁷⁷Se NMR signal enhancement of 11,600-fold at 9.4 T in a shielding-free setup within several seconds, corresponding to over 6% of net 77Se polarization. Thus, our approach makes hyperpolarized ⁷⁷Se NMR widely accessible for biomolecular investigations.