On The Potential of Dynamic Nuclear Polarization Enhanced Diamonds in Solid‐State and Dissolution ¹³C NMR Spectroscopy

Abstract

Dynamic nuclear polarization (DNP) is a versatile option to improve the sensitivity of NMR and MRI. This versatility has elicited interest for overcoming potential limitations of these techniques, including the achievement of solid-state polarization enhancement at ambient conditions, and the maximization of (13) C signal lifetimes for performing in vivo MRI scans. This study explores whether diamond's (13) C behavior in nano- and micro-particles could be used to achieve these ends. The characteristics of diamond's DNP enhancement were analyzed for different magnetic fields, grain sizes, and sample environments ranging from cryogenic to ambient temperatures, in both solution and solid-state experiments. It was found that (13) C NMR signals could be boosted by orders of magnitude in either low- or room-temperature solid-state DNP experiments by utilizing naturally occurring paramagnetic P1 substitutional nitrogen defects. We attribute this behavior to the unusually long electronic/nuclear spin-lattice relaxation times characteristic of diamond, coupled with a time-independent cross-effect-like polarization transfer mechanism facilitated by a matching of the nitrogen-related hyperfine coupling and the (13) C Zeeman splitting. The efficiency of this solid-state polarization process, however, is harder to exploit in dissolution DNP-enhanced MRI contexts. The prospects for utilizing polarized diamond approaching nanoscale dimensions for both solid and solution applications are briefly discussed.

Minireview on Nuclear Spin Polarization in Optically-Pumped Diamond Nitrogen Vacancy Centers

“…Another closely related research has been done by R. Fischer et al with 14 N nuclear spin in NV center. 24 Around 90 % polarization on 14 N and 70% polarization on 13 C in the first shell were observed by using ODMR in ESLAC at low temperature (< 50 K). This polarization transfer mechanism is same as the previous work with 15 N, which can be explained in the other way that almost degenerated electronic sub-states with nucleus ( 14 N) can be mixed by the hyperfine interactions in ESLAC.…”

“…King et al obtained 13 C nuclei spin polarization by using dipolar field fluctuations including electron-electron dipole interactions in neighboring defects. 21 This system is introduced at a low temperature (5 K) and its polarization can be up to 5.2% after spin diffusion from the area of strong laser irradiation (5 W).…”

“…E. Scott et al investigated polarization mechanism of 13 C in various NV centerconcentrated diamonds by using natural abundance 13 C samples (1.1%). 22 They observed the orientation dependent 13 C polarization both in magnetic field and in electric field stemmed from the optical pumping vector. The amount of polarization in their sample was greater by the factor of 200 compared to room temperature.…”

“…12 In this context, doped diamonds have been harnessed as an alternative polarization source with a long T 1 . 13 Various diamond defects have been studied on those various physical properties, after doping with various atoms such as Nitrogen, Hydrogen, Boron, Silicon, Nickel, and Vacancy etc. 14 Their electronic properties were normally examined by Electron Paramagnetic Resonance (EPR) for using as hyperpolarization sources.…”

“…Especially, many studies described that P1 center (diamond defect, carbon is substituted by nitrogen) and surface unpaired electrons are the useful sources for polarization transfer. 13,[15][16][17][18][19] This review will be focused only on one defect, Nitrogen Vacancy Center (NV center), since we can theoretically achieve ~100 % hyperpolarized electron spin in room temperature. Its detailed physics were introduced in a review by Doherty M. et al 20 Some of its basic physics will be discussed here.…”