Room-temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centres in diamond

Abstract

Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ∼170,000 over thermal equilibrium. The signal of the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. Hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.

All-optical hyperpolarization of electron and nuclear spins in diamond

“…Enhancements of ≈2 × 10 5 have been observed for optically pumped microwave-driven DNP using NV − at low fields [9], and approximately 45 at high field via sample shuttling [56]: the primary advantage of the present work is projected field-insensitivity without the requirement for expensive highfrequency microwave components (>200 GHz), cryogenics, or sample shuttling at typical NMR fields.…”

“…The development of a general nuclear hyperpolarization technique at arbitrary fields would enable measurements of biomolecules and reaction dynamics that were not accessible by the present techniques while decreasing routine NMR measurement times by orders of magnitude [1]. Several approaches to dynamic nuclear polarization (DNP) processes have been demonstrated that enhance nuclear spin polarization; however, the majority are limited to specific fields [2][3][4][5], low temperatures [6,7], specific molecules [8], or require microwave irradiation of the sample [8,9]. Low temperature is particularly problematic for liquid-state biological samples, where freezing leads to a loss of spectral resolution [10].…”

Towards clinically translatable in vivo nanodiagnostics

“…However, hyperpolarization can boost magnetic resonance signals because it increases the polarization by a factor of 10 4 –10 5 compared with thermal equilibrium. For example, a 170,000-fold enhancement compared with thermal equilibrium was recently reported for bulk nuclear spin polarization of 13 C from optically pumped nitrogen-vacancy centres in diamond 14 . Other hyperpolarization methods include spin-exchange optical pumping (by 3 He and 129 Xe) 15,16 , metastability-exchange optical pumping 17 , dynamic nuclear polarization 18 and parahydrogen-induced polarization 19 .…”

Influence of magnetic field alignment and defect concentration on nitrogen-vacancy polarization in diamond

“…A difference in intersystem crossing rates between the m s =0 and m s =±1 excited state levels results in spin polarization into the m s =0 sublevel upon optical pumping [2]. NV-centers have applications in numerous fields, including magnetometry [3], nuclear spin polarization [4][5][6][7][8][9][10][11][12], and quantum information processing [13]. While many applications utilize single defects aligned with an applied magnetic field, understanding orientation dependence of NV-polarization is important for applications involving ensembles of defects in single crystals as well as defects in nanodiamonds.…”