Luminescence Enhanced Eu(3+)/Gd(3+) Co-Doped Hydroxyapatite Nanocrystals as Imaging Agents In Vitro and In Vivo

Biocompatible, biodegradable, and luminescent nano material can be used as an alternative bioimaging agent for early cancer diagnosis, which is crucial to achieve successful treatment. Hydroxyapatite (HAP) nanocyrstals have good biocompatibility and biodegradability, and can be used as an excellent host for luminescent rare earth elements. In this study, based on the energy transfer from Gd(3+) to Eu(3+), the luminescence enhanced imaging agent of Eu/Gd codoping HAP (HAP:Eu/Gd) nanocrystals are obtained via coprecipitation with plate-like shape and no change in crystal phase composition. The luminescence can be much elevated (up to about 120%) with a nonlinear increase versus Gd doping content, which is due to the energy transfer ((6)PJ of Gd(3+) → (5)HJ of Eu(3+)) under 273 nm and the possible combination effect of the cooperative upconversion and the successive energy transfer under 394 nm, respectively. Results demonstrate that the biocompatible HAP:Eu/Gd nanocrystals can successfully perform cell labeling and in vivo imaging. The intracellular HAP:Eu/Gd nanocrystals display good biodegradability with a cumulative degradation of about 65% after 72 h. This biocompatible, biodegradable, and luminescence enhanced HAP:Eu/Gd nanocrystal has the potential to act as a fluorescent imaging agent in vitro and in vivo.

Quantitative Detection Method of Hydroxyapatite Nanoparticles Based on Eu(3+) Fluorescent Labeling in Vitro and in Vivo

One major challenge for application of hydroxyapatite nanoparticles (nHAP) in nanomedicine is the quantitative detection method. Herein, we exploited one quantitative detection method for nHAP based on the Eu(3+) fluorescent labeling via a simple chemical coprecipitation method. The trace amount of nHAP in cells and tissues can be quantitatively detected on the basis of the fluorescent quantitative determination of Eu(3+) ions in nHAP crystal lattice. The lowest concentration of Eu(3+) ions that can be quantitatively detected is 0.5 nM using DELFIA enhancement solution. This methodology can be broadly applicable for studying the tissue distribution and metabolization of nHAP in vivo.