¹³ C hyperpolarization with nitrogen-vacancy centers in micro- and nanodiamonds for sensitive magnetic resonance applications

Nuclear hyperpolarization is a known method to enhance the signal in nuclear magnetic resonance (NMR) by orders of magnitude. The present work addresses the ¹³C hyperpolarization in diamond micro- and nanoparticles, using the optically pumped nitrogen-vacancy center (NV) to polarize ¹³C spins at room temperature. Consequences of the small particle size are mitigated by using a combination of surface treatment improving the ¹³C relaxation (<i>T</i>₁) time, as well as that of NV, and applying a technique for NV illumination based on a microphotonic structure. Adjustments to the dynamical nuclear polarization sequence (PulsePol) are performed, as well as slow sample rotation, to improve the NV-¹³C polarization transfer rate. The hyperpolarized ¹³C NMR signal is observed in particles of 2-micrometer and 100-nanometer median sizes, with enhancements over the thermal signal (at 0.29-tesla magnetic field) of 1500 and 940, respectively. The present demonstration of room-temperature hyperpolarization anticipates the development of agents based on nanoparticles for sensitive magnetic resonance applications.