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

Abstract

Silicon particles have garnered attention as promising biomedical probes for hyperpolarized Si-29 magnetic resonance imaging and spectroscopy. However, due to the limited levels of hyperpolarization for nanosized silicon particles, microscale silicon particles have primarily been the focus of dynamic nuclear polarization (DNP) applications, including in vivo magnetic resonance imaging (MRI). To address these current challenges, we developed a facile synthetic method for partially Si-29-enriched porous silicon nanoparticles (NPs) (160 nm) and examined their usability in hyperpolarized Si-29 MRI agents with enhanced signals in spectroscopy and imaging. Hyperpolarization characteristics, such as the build-up constant, the depolarization time (T-1), and the overall enhancement of the Si-29-enriched silicon NPs (10 and 15%), were thoroughly investigated and compared with those of a naturally abundant NP (4.7%). During optimal DNP conditions, the 15% enriched silicon NPs showed more than 16-fold higher enhancements-far beyond the enrichment ratio-than the naturally abundant sample, further improving the signal-to-noise ratio in in vivo Si-29 MRI. The Si-29-enriched porous silicon NPs used in this work are potentially capable to serve as drug-delivery vehicles in addition to hyperpolarized Si-29 in vivo, further enabling their potential future applicability as a theragnostic platform.