Long-T1 Silicon Nanoparticles for Hyperpolarized Magnetic Resonance Imaging

Introduction The use of nanoparticles for biomedical applications has benefited from rapid progress both in the nanoscale synthesis of materials with specific optical [1] and magnetic properties [2], and in the biofunctionalization of surfaces, allowing targeting in-vivo tracking, and therapeutic action [3]. For magnetic resonance imaging (MRI), superparamagnetic nanoparticles [2] have extended susceptibility-based contrast agents toward targeted imaging though achieving high spatial resolution with high contrast remains challenging. An alternative approach is direct MRI of hyperpolarized materials with little or no background signal. Hyperpolarized noble gases for lung imaging [4] and hyperpolarized C enhanced biomolecules [5] have demonstrated impressive image contrast, but have been limited by short in-vivo enhancement times (~ 10 s for noble gases [4], ~ 30 s for C-labeled molecules [5]). Silicon can exhibit multi-hour nuclear relaxation T1 times at room temperature [6] and can be hyperpolarized via dynamic nuclear polarization [7]. In this study, Si nanoparticles are investigated as a potential hyperpolarized, targetable MRI imaging agent.