Hyperpolarized Porous Silicon Nanoparticles: Potential Theragnostic Material for ²⁹Si Magnetic Resonance Imaging

Abstract

Porous silicon nanoparticles have recently garnered attention as potentially-promising biomedical platforms for drug delivery and medical diagnostics. Here, we demonstrate porous silicon nanoparticles as contrast agents for Si magnetic resonance imaging. Size-controlled porous silicon nanoparticles were synthesized by magnesiothermic reduction of silica nanoparticles and were surface activated for further functionalization. Particles were hyperpolarized via dynamic nuclear polarization to enhance their Si MR signals; the particles demonstrated long Si spin-lattice relaxation (T ) times (∼25 mins), which suggests potential applicability for medical imaging. Furthermore, Si hyperpolarization levels were sufficient to allow Si MRI in phantoms. These results underscore the potential of porous silicon nanoparticles that, when combined with hyperpolarized magnetic resonance imaging, can be a powerful theragnostic deep tissue imaging platform to interrogate various biomolecular processes in vivo.

Direct hyperpolarization of micro- and nanodiamonds for bioimaging applications – Considerations on particle size, functionalization and polarization loss

“…Such an approach is particularly attractive to study surface phenomena, but fails to provide significant enhancement for bulk 29 Si nuclei due to weak dipole-dipole 1 H- 29 Si coupling with the surface protons. Similarly, doping the sample with an exogenous radical was used to directly enhance the 29 Si polarization in a suspension of small, nanometre-size silicon particles, which exhibited an insufficient endogenous surface defect concentration 42,43 .…”

Spin-Dependent Phenomena in Semiconductor Micro-and Nanoparticles—From Fundamentals to Applications

“…A variety of particle sizes (20 nm to 2 µm) were found to have hyperpolarized relaxation times ranging from ∼10 to 50 min [54,55]. The addition of different functional groups to the Si particle surface was shown to provide no effect on the hyperpolarization buildup or decay rates and allowed for in vivo imaging over long time-scales.…”

“…The addition of different functional groups to the Si particle surface was shown to provide no effect on the hyperpolarization buildup or decay rates and allowed for in vivo imaging over long time-scales. Hyperpolarized Si particles were demonstrated to be available agents for targeted, noninvasive and nonradioactive molecular imaging of various cancer systems [54] and a powerful theragnostic deep tissue imaging platform [55]. In vivo studies examined diverse particle administration routes in mice, including intraperitoneal injection, rectal enema and oral gavage [54].…”

Acquisition strategies for spatially resolved magnetic resonance detection of hyperpolarized nuclei

“…By various means, these methods induce a transient state of increased nuclear polarization that decays with the spin-lattice relaxation time T 1 . Five different 1 3 approaches are currently used to create a hyperpolarized spin state for various nuclear isotopes, which currently include 1 H (protons), and various others (X-nuclei): 3 He, 6 Li, 13 C, 15 N, 29 Si, 31 P, 129 Xe, 83 Kr, and 107,109 Ag:…”