Dynamic Nuclear Polarization of Silicon Carbide Micro- and Nanoparticles

Abstract

Two dominant crystalline phases of silicon carbide (SiC): α-SiC and β-SiC, differing in size and chemical composition, were investigated regarding their potential for dynamic nuclear polarization (DNP). 29 Si nuclei in α-SiC micro- and nanoparticles with sizes ranging from 650 nm to 2.2 μm and minimal oxidation were successfully hyperpolarized without the use of free radicals, while β-SiC samples did not display appreciable degrees of polarization under the same polarization conditions. Long T 1 relaxation times in α-SiC of up to 1600 s (∼27 min) were recorded for the 29 Si nuclei after 1 h of polarization at a temperature of 4 K. Interestingly, these promising α-SiC particles allowed for direct hyperpolarization of both 29 Si and 13 C nuclei, resulting in comparably strong signal amplifications. Moreover, the T 1 relaxation time of 13 C nuclei in 750 nm-sized α-SiC particles was over 33 min, which far exceeds T 1 times of conventional 13 C DNP probes with values in the order of 1–2 min. The present work demonstrates the feasibility of DNP on SiC micro- and nanoparticles and highlights their potential as hyperpolarized magnetic resonance imaging agents.

Spin Hyperpolarization in Modern Magnetic Resonance

“…For the 4H polymorph SiC wafer, these two conditions were revealed as two prominent maxima in the B 0 field dependence of 29 Si polarization at B 0 = 30.0–33.5 mT and 46.5–49.0 mT, respectively, with the highest polarization reaching 99 ± 1% . Potential application of hyperpolarized SiC in MRI was demonstrated . Similar electronic spin states are associated with nitrogen-vacancy defects in diamond.…”

“…628 Potential application of hyper- polarized SiC in MRI was demonstrated. 629 Similar electronic spin states are associated with nitrogen-vacancy defects in diamond. These states can be interrogated and manipulated at either ensemble or single-spin level, making them useful for a range of fundamental and practical applications.…”

29Si Isotope-Enriched Silicon Nanoparticles for an Efficient Hyperpolarized Magnetic Resonance Imaging Probe

“…This typically limits clinical MRI to detecting protons ( 1 H) due to their high prevalence, isotopic abundance, and gyromagnetic ratio. From this perspective, there have been many efforts to increase the sensitivity − by hyperpolarization techniques, especially dynamic nuclear polarization (DNP), to amplify the signals of inherently low-sensitivity nuclei, such as 13 C, 15 N, and 29 Si. − In DNP, hyperpolarization occurs at cryogenic temperatures (typically <4 K) in a moderate magnetic field of a few Tesla, where high electron spin polarization is transferred to target nuclei by saturating nearby electron spin resonance frequencies. Through the DNP technique, hyperpolarization of 29 Si nuclear spins in micro- and nanoparticles (NPs) has recently been demonstrated; − 29 Si MR signals were temporarily enhanced by several orders of magnitude, which is far beyond polarization levels in thermal equilibrium conditions.…”

Background free in vivo29Si MR imaging with hyperpolarized PEGylated silicon nanoparticles

“…Silicon nanoparticles (Si NPs) have recently attracted significant attention as potential probes for magnetic resonance (MR) imaging owing to their high biocompatibility, biodegradability, and background-free positive-contrast imaging capabilities. 1 However, the scarcity of NMR-active 29 Si nuclei has hampered the development of high-resolution magnetic resonance (MR) images. Fortunately, this obstacle can be overcome by employing hyperpolarization techniques such as dynamic nuclear polarization (DNP), which dramatically boosts the MR signal sensitivity.…”