Rare-Earth-Metal (Nd 3+ , Ce 3+ and Gd 3+ )-Doped CaF 2 : Nanoparticles for Multimodal Imaging in Biomedical Applications.

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 CaF 2 (CaF 2 : Ce, Gd, Nd). CaF 2 : 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, CaF 2 : Ce, Gd, Nd NPs possess excellent optical properties. CaF 2 : 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, CaF 2 : Ce, Gd, Nd NPs are ideally suited for in vivo fluorescence imaging. In addition, the presence of Gd 3+ makes the NPs intrinsically monitorable by magnetic resonance imaging (MRI). Moreover, next to fluorescence and MR imaging, our results show that CaF 2 : 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, CaF 2 : Ce, Gd, Nd NPs exhibit great potential as a traceable imaging agent in biomedical applications.