Synthesis of Long T1 Silicon Nanoparticles for Hyperpolarized 29Si Magnetic Resonance Imaging

We describe the synthesis, materials characterization, and dynamic nuclear polarization (DNP) of amorphous and crystalline silicon nanoparticles for use as hyperpolarized magnetic resonance imaging (MRI) agents. The particles were synthesized by means of a metathesis reaction between sodium silicide (Na4Si4) and silicon tetrachloride (SiCl4) and were surface functionalized with a variety of passivating ligands. The synthesis scheme results in particles of diameter similar to 10 nm with long size-adjusted Si-29 spin-lattice relaxation (T-1) times (>600 s), which are retained after hyperpolarization by low-temperature DNP.