Rare-Earth-Metal (Nd3+, Ce3+ and Gd3+)-Doped CaF2: Nanoparticles for Multimodal Imaging in Biomedical Applications.

ABSTRACT

Here, we describe the synthesis of a novel type of rare-earth-doped nanoparticles (NPs) for multimodal imaging, by combining the rare-earth elements Ce, Gd and Nd in a crystalline host lattice consisting of CaF2 (CaF2 Ce, Gd, Nd). CaF2 Ce, Gd, Nd NPs are small (15-20 nm), of uniform shape and size distribution, and show good biocompatibility and low immunogenicity in vitro. In addition, CaF2 Ce, Gd, Nd NPs possess excellent optical properties. CaF2 Ce, Gd, Nd NPs produce downconversion emissions in the second near-infrared window (NIR-II, 1000-1700 nm) under 808 nm excitation, with a strong emission peak at 1056 nm. Excitation in the first near- infrared window (NIR-I, 700-900 nm) has the advantage of deeper tissue penetration power and reduced autofluorescence, compared to visible light. Thus, CaF2 Ce, Gd, Nd NPs are ideally suited for in vivo fluorescence imaging. In addition, the presence of Gd3+ makes the NPs intrinsically monitorable by magnetic resonance imaging (MRI). Moreover, next to fluorescence and MR imaging, our results show that CaF2 Ce, Gd, Nd NPs can be used as imaging probes for photoacoustic imaging (PAI) in vitro. Therefore, due to their biocompatibility and suitability as multimodal imaging probes, CaF2 Ce, Gd, Nd NPs exhibit great potential as a traceable imaging agent in biomedical applications.