Spin polarization transfer from laser-polarized 129Xe to oxygen-sensitive perfluorocarbons at ultra-low magnetic field

The spin polarization-induced nuclear Overhauser effect (SPINOE), particularly at low field strengths, can increase nuclear spin polarization by several orders of magnitude relative to its thermal equilibrium value and offers a promising route to offset the inherently low polarization that limits ultra-low field nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI). In this study, we demonstrate the SPINOE-mediated polarization of oxygen-sensitive perfluorocarbons (PFC) by laser-polarized ¹²⁹Xe gas at ultra-low magnetic field strengths. Low field provides several distinct advantages for SPINOE, such as more efficient polarization transfer in systems with slow molecular dynamics, and the ability to simultaneously detect both spin species, which enables a more direct and accurate observation of the spin polarization dynamics and its modulation by molecular oxygen. We begin by outlining the theoretical framework describing how SPINOE efficiency depends on field strength, correlation time, and the relaxation times of the involved nuclei, followed by experimental results demonstrating long-lasting polarization enhancement of oxygen-sensitive PFCs. Using a straightforward bubbling protocol to introduce hyperpolarized ¹²⁹Xe into a PFC solution, we observed a 53-fold enhancement of the ¹⁹F NMR signal. This enhancement persisted for tens of seconds, well beyond the ¹⁹F relaxation time (< 10 s), enabling prolonged detection of ¹⁹F signals from oxygen-sensitive PFCs at ultra-low field.