Calcium Fluoride Nanocrystals: Tracers for In Vivo ¹⁹F Magnetic Resonance Imaging

Inorganic nanocrystals (NCs) have been extensively developed for a variety of uses. The ability to obtain high-resolution NMR signals from the core nuclei of NCs in solution could offer new opportunities in materials sciences and MR imaging. Herein, we demonstrate that small, water-soluble ¹⁹F-ionic NCs can average out homonuclear dipolar interactions, enabling one to obtain high-resolution ¹⁹F NMR signals in solution that reflect the MR properties of F ⁻ in the crystal core. Decorating ¹⁹F-NC surfaces with a biocompatible poly(ethylene glycol) coating maintains colloidal stability in water while preserving the NC high-resolution ¹⁹F NMR properties, even after further functionalization. The high content and magnetic equivalence of the fluorides within the NCs enable their use as imaging tracers for in vivo ¹⁹F MRI by facilitating a “hot-spot” display of their distribution.