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.