Silicon-based micro- and nanoparticles: preparation, functionalization and hyperpolarized magnetic resonance imaging

In this thesis, we focus on two silicon based ceramic materials: non porous silicon particles (> 10 nm) and silicon carbide (SiC) due to their potential for MRI via hyperpolarization. Hyperpolarization is a process in which nuclear spins are redistributed in energy states to produce a much stronger signal than thermal (Boltzmann) state polarization. The isotope 29Si is magnetic resonance (MR) active and some reports have demonstrated that silicon particles can be used for hyperpolarized MRI. However, there are still important challenges to the widespread use of SiNPs in hyperpolarization MRI, such as the lack of large scale synthetic strategies towards non agglomerated particles, limited colloidal stability of SiNPs and poor size control. The prospect of silicon based particles as MRI probes with high sensitivity, long relaxation time and excellent polarizability is highly appealing. Therefore, the research described in this thesis aims at promoting the feasibility and versatility of silicon based particles for hyperpolarized MRI. Specifically, for SiNPs with demonstrated hyperpolarization potential, we improve their stability by surface modification such as polymer grafting or lipid coating (Chapter 3 and Chapter 4), as well as explore available methods for the preparation of non agglomerated silicon particles (Chapter 5). For silicon carbide, optical pumping has been demonstrated to polarize SiC nuclear spins. SiC provides paramagnetic impurities and unpaired electrons that might also be used for hyperpolarization. Besides, both 13C and 29Si are MR visible and within the tuning ranges of commercial multinuclear MRI systems. SiC therefore presents an interesting yet hardly explored material for hyperpolarization via DNP. Factors that may affect DNP enhancements and T1 relaxation times such as crystal structure, size, and chemical composition are under consideration (Chapter 6).