Maja Clare Cassidy1, Jacob Webster Aptekar1, Alexander C. Johnson1, Robert A. Barton1, Menyoung Lee1, Chinh Vo1, Alison L. Hill2, Ross Webster Mair2, Matthew S. Rosen1,2, Ronald L. Walsworth1,2, Charles M. Marcus1
1Department of Physics, Harvard University, Cambridge, MA, USA; 2Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Nanoparticles are currently being widely investigated as targetable contrast agents for magnetic resonance imaging (MRI). For these applications, the action of the nanoparticle is to alter the nuclear relaxation properties, as in traditional (untargeted) contrast agents. An alternative imaging modality is to use MRI to image the particles directly, without a background signal. Bulk silicon exhibits multi-hour nuclear relaxation T1 times at room temperature and can be hyperpolarized via dynamic nuclear polarization. Here we demonstrate the production and functionalization of silicon nanoparticles for use as hyperpolarized targeted imaging agents. The NMR properties are studied as a function of nanoparticle size, dopant concentration and synthesis method. Nuclear T1 times are found to be remarkably long, allowing for hyperpolarized particles to be transported and administered on practical time scales without significant polarization loss.