Uniform Ln3+:CeF3 (Ln= Nd; Tb) nanoparticles synthesized in polyol media as bimodal bioprobes for fluorescence and CT bio-imaging

Lanthanide-based inorganic nanoparticles (Ln-NPs) are an excellent choice for potential use as phosphors in luminescent bioimaging and as contrast agents in X-rays computed tomography (CT). Among the different Ln salts, Ln fluorides are preferred as phosphors matrices because of the low phonon energy of the fluoride lattice, which provides improved quantum efficiency to the phosphor. Cerium fluoride (CeF3), in particular, benefits from the well-known Ce3+ capacity to absorb ultraviolet (UV) radiation and efficiently transfer it to several active lanthanide ions like Tb3+. To date, different approaches have been developed for the synthesis of Ln:CeF3 NPs (e.g. hydrothermal synthesis, microemulsion, sonochemistry, etc.), most of which produce either aggregated NPs or micrometric particles, which are useless in biotechnology. The few procedures that yield highly uniform and well dispersed Ln:CeF3 nanoparticles suffer a number of drawbacks including high temperature synthesis, need of additives, use of hydrofluoric acid or hydrophobicity of the obtained NPs. Therefore, developing an effective, commercially attractive procedure working at mild or low temperatures, in the absence of surfactants, dispersing agents or corrosive precursors, to obtain uniform, hydrophilic Ln:CeF3 NPs is still a challenge. Herein we present an effective and commercially attractive procedure that renders uniform, hydrophilic Ln3+:CeF3 (Ln=Tb, Nd) nanoparticles at room temperature. The method consists of the homogeneous precipitation, in a mixture of polyol and water, of cations and anions using precursors that allow the controlled release of the latter. Different morphologies (lentils and disks) and sizes (from 40 nm to 80 nm diameter) are obtained depending on the polyol used as reaction medium (Figure 1). The Nd3+:CeF3 NPs are good candidates for in-vivo imaging because their excitation and emission wavelengths lie in the biological windows (Figure 2a). The Tb3+:CeF3 NPs produce an intense gr