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

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 ²⁹ 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 ²⁹ Si MR signals; the particles demonstrated long ²⁹ Si spin-lattice relaxation (T₁ ) times (∼25 mins), which suggests potential applicability for medical imaging. Furthermore, ²⁹ Si hyperpolarization levels were sufficient to allow ²⁹ 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.