Designing and characterizing hyperpolarizable silicon nanoparticles for magnetic resonance imaging

Abstract

Magnetic Resonance Imaging (MRI) is one of the most powerful noninvasive tools for diagnosing human disease, but its utility is limited because current contrast agents are ineffective when imaging air-tissue interfaces, in regions with low signal-tonoise ratios, or in areas that undergo motion, like the heart and bowel. A technique called dynamic nuclear polarization can be used to hyperpolarize nuclei and achieve dramatic MRI signal enhancement with minimal background noise. It has been shown that ballmilled silicon nanoparticles have the advantageous properties of hyperpolarizability and biodegradability, but in vivo utilization requires the modification of the particle surface to prevent aggregation that leads to very fast removal from circulation through phagocytosis by the liver, spleen, and lymph nodes. This thesis describes a method to functionalize hyperpolarizable silicon nanoparticles using silane chemistry and coating by poly(ethylene glycol). The particles were characterized using dynamic light scattering, scanning electron microscopy, and laser Doppler electrophoresis. The extent of amination was quantified using a fluorescamine assay, and stability was assessed by visualizing flocculation and measuring aggregation in different solvents. The functionalized particles were stable in solutions that resemble physiological conditions. These silicon nanoparticles can potentially be used for in vivo cancer imaging to enable early diagnoses and assist with clinical decision-making through disease monitoring.