Increase in signal-to-noise ratio of > 10,000 times in liquid-state NMR.
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-to-noise 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 ball-milled 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. Acknowledgments I would like to thank several people who have helped me tremendously with completing this thesis. First and foremost, I am very grateful to Professor Sangeeta Bhatia for her constant support throughout the year and for the privilege of working in the Laboratory for Multiscale Regenerative Technology. It has been a wonderful to learn so much about nanotechnology and tissue engineering, while enjoying the company of all the fun and inspiring people in the lab, including the many talented undergraduates. In particular, I would like to thank Yin Ren for his guidance, assistance with getting the project off the ground, and for proofreading this thesis, Geoff von Maltzahn for his patience and willingness to answer my never-ending list of questions, and Amit Agrawal for his advice and discussions. Additionally, I would like to thank several collaborators at Harvard University-Vo-whose expertise in physics and material science made this project possible. Also, thanks to Ji Ho Park at the University of California San Diego for sharing his knowledge of silicon nanoparticles.