NaGdF4:Eu 3+ Nanoparticles for Enhanced X‑ray Excited Optical Imaging

ABSTRACT: X-ray luminescent nanoparticles (NPs), including lanthanide fluorides, have been evaluated for application to deep tissue in vivo molecular imaging using optical tomography. A combination of high material density, higher atomic number and efficient NIR luminescence from compatible lanthanide dopant ions indicates that particles that consist of ALnF4 (A = alkaline, Ln = lanthanide element) may offer a very attractive class of materials for high resolution, deep tissue imaging with X-ray excitation. NaGdF4:Eu 3+ NPs produced an X-ray excited luminescence that was among the most efficient of nanomaterials that have been studied thus far. We have systematically studied factors such as (a) the crystal structure that changes the lattice environment of the doped Eu3+ ions within the unit cell; and extrinsic factors such as (b) a gold coating (with attendant biocompatibility) that couples to a plasmonic excitation, and (c) changes in the NPs surface properties via changes in the pH of the suspending mediumall with a significant impact on the X-ray excited luminescence of NaGdF4:Eu3+NPs. The luminescence from an optimally doped hexagonal phase NaGdF4:Eu 3+ nanoparticle was 25 % more intense compared to that of a cubic structure. We observed evidence of plasmonic reabsorption of midwavelength emission by a gold coating on hexagonal NaGdF4:Eu 3+ NPs; fortunately, the NaGdF4:Eu 3