Synthesis and properties of a novel Fe<sub>3</sub>O<sub>4</sub>@MoO<sub>3</sub>@GdF<sub>3</sub>:Eu<sup>3+</sup> magnetic-luminescent bi-model imaging materials

The probe plays a key role in the process of the tumor diagnosis and image guided accuracy surgery, but its single-function, weaker luminescent intensity and high cost limitits application. Therefore, development of new type high-performance and multi-functional imaging materials has become an important research topic in the field of chemistry, materials science, life science and medicine. In recent years, researchers have found that magnetic-luminescent bi-functional nanoparticles can provide high-resolution, high-contrast images for precision medicine and are crucial for imaging applications. Among them, the design and synthesis of Fe3O4@REL (rare earth luminescence) magnetic-luminescent bi-functional nanoparticles have become the focus of current research. In this work, we demonstrated the nonmetallic plasmon induced enhancement of luminescence in a core-shell structured material, consisting of Fe3O4 as the core, GdF3: Eu3+ as the luminescence layer and MoO3 as the plasmonic layer. The novel Fe3O4@MoO3@GdF3:Eu3+ nanoparticles of MoO3 intermediate with local surface plasmon resonance (LSPR) effect were synthesized by solvothermal and precipitation method. And their structures, compositions and properties were analyzed. Enhancement mechanism of luminescence property and the interaction factors between the oxide layer and luminescence shell had been illuminated. The results of X-ray diffraction (XRD) analysis showed that the nanoparticles are composed of Fe3O4, single monoclinic MoO3 and orthorhombic GdF3:Eu3+. Transmission electron microscope (TEM) images showed that the obvious nanoparticles and MoO3 and GdF3:Eu3+ are deposited on the surface of Fe3O4 layer by layer. It showed that the shielding effect of homogeneous coating MoO3 spacer and the MoO3 with LSPR plays a role in enhancing the luminescence properties of the shell GdF3:Eu3+. The emission spectra showed that the strongest emission (593 nm) is due to the 5D0→7F1 forced electric dipole transition, and the other emission bands are observed at 556, 616 and 692 nm for 5D0 →7Fn, 5D0→7F2 and 5D0→7F4, respectively. The magnetic measurement results showed that the Fe3O4@MoO3@GdF3:Eu3+ nanoparticles possess excellent magnetic responsivity (25.9 emu/g) and redispersibility. MTT assays showed that the nanoparticles almost have no cytotoxicity or side effects in living cells. The magnetic resonance imaging of the sample gradually enhanced with the increase of the concentration, indicating that the effect of magnetic resonance imaging was corresponding to the concentration. The T 2 magnetic resonance imaging relaxation rate of the material was 0.9813 mg−1 m−1 s−1. In summary, the core-shell structured Fe3O4@MoO3@GdF3:Eu3+ nanoparticles have been prepared by a facile method. The nanoparticles have high emission intensity and magnetisation saturation value. Compared with Fe3O4@GdF3:Eu3+, luminescence intensity of Fe3O4@MoO3@GdF3:Eu3+ nanoparticles increased significantly. Therefore, the as-prepared core-shell structured bifunctional nanoparticles are feasibly applicable to simultaneous cell imaging and target drug delivery. This work can solve the property problem of the magnetic-luminescent bimodal imaging material and promote this kind of composite material applications in imaging and therapy of tumor, and optical confocal microscopy technology.