PEG-capped, lanthanide doped GdF3 nanoparticles: Luminescent and T2 contrast agents for optical and MRI multimodal imaging

A facile method for the synthesis of water dispersible Er 3+/Yb3+ and Tm3+/Yb3+ doped upconverting GdF3 nanoparticles is reported. Strong upconversion emissions are observed in the red (for Er/Yb doped) and near-infrared (for Tm/Yb doped) regions upon laser excitation at 980 nm. The PEG coating ensures a good dispersion of the system in water and reduces the radiationless de-excitation of the excited states of the Er3+ and Tm3+ ions by water molecules. The r2 relaxivity values are quite high with respect to the common T2-relaxing agents (22.6 ± 3.4 mM-1 s-1 and 15.8 ± 3.4 mM-1 s-1 for the Tm/Yb and Er/Yb doped samples, respectively), suggesting that the present NPs can be interesting as T2 weighted contrast agents for proton MRI purpose. Preliminary experiments conducted in vitro, in stem cell cultures, and in vivo, after subcutaneous injection of the lanthanide-doped GdF3 NPs, indicate scarce toxic effects. After an intravenous injection in mice, the GdF3 NPs localize mainly in the liver. The present results indicate that the present Er3+/Yb3+ and Tm3+/Yb 3+ doped GdF3 NPs are suitable candidates to be efficiently used as bimodal probes for both in vitro and in vivo optical and magnetic resonance imaging. © 2012 The Royal Society of Chemistry.