Silicon particles have garnered attention as promising biomedical probes for hyperpolarized 29Si 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 29Si-enriched porous silicon nanoparticles (NPs) (160 nm) and examined their usability in hyperpolarized 29Si 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 29Si-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 29Si MRI. The 29Si-enriched porous silicon NPs used in this work are potentially capable to serve as drug-delivery vehicles in addition to hyperpolarized 29Si in vivo, further enabling their potential future applicability as a theragnostic platform.

Gold nanoparticles (AuNPs) have been used widely as multifunctional materials for several biomedical applications due to their attractive characteristics. However, toxicity and aggregation of AuNPs are critical issues, and methods of effective surface modification are required to overcome these problems. In this study, porous silicon-coated gold nanoparticles (AuNP@pSi) were fabricated as a hybrid nanocomposite capable of surface-enhanced Raman scattering (SERS)sensing and drug carrier. First, size-controlled AuNPs were coated with a silica nano-shell, and the resulting silica layers were converted to porous silicon through magnesiothermic reduction. Overall results suggest that AuNP@pSi can be exploited as a SERS probe with efficient Raman signal improvement of benzenethiol as well as a drug carrier based on its high surface area (113.7 m 2 g À1 ) and porosity (13.38 nm, 0.3805 cm 3 g À1 ). Since the porous silicon possibly can serve as magnetic resonance imaging probes with DNP technology, this hybrid platform potentially can be utilized as powerful material capable of theragnosis system.

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