Preparation Of Rare Earth Doped LaF₃Upconversion Nanoparticles And Its Application In Biological Imaging

Rare earth （RE） upconverting phosphors became a hot spot in material scienceand attracted extensive attention from lots of researchers majored in chemistry,physics and biology since upconversion luminescence was reported by Auzel in1966.Because of the inherent chemical property and luminescent principle, for instance, thesatisfactory optical and chemical stability, outstanding sensitivity, deeper penetrationof excitation and emitted light during biological tissues, the various potentialapplications of upconversion nanoparticles （UCNPs） have been extensively studied inmany fields, such as material science, biomedical, optics and bioimaging in recentfive years.In this paper, we introduced a general strategy for the synthesis of UCNPs via anovel oleic acid （OA）/ionic liquid （IL） two-phase system and the roles ofcorresponding factors （OA, IL, alcohol） during reaction process. We also investigatedthe morphology, optical properties, chemical properties and biocompatibility ofas-prepared UCNPs, and then series of bioimaging experiments based on as-preparedUCNPs were performed originally. The detail content is outlined as following:1. The synthesis and functional modification of LaF₃: Yb, Er/Ho/Tm UCNPs. Weprepared hydrophobic/hydrophilic LaF₃: Yb, Er/Ho/Tm UCNPs through OA/IL two-phase system. Utilizing transmission electron microscope （TEM） and High-resolution TEM （HRTEM）, X-ray diffraction （XRD） and UC luminescent （UCL）spectra, we characterized the as-prepared LaF₃: Yb, Er/Ho/Tm UCNPs. Thesignificant function and corresponding roles of oleic acid, ionic liquid, alcohol duringreaction were discussed in great detail as well. Then we addressed the functionalmodification with hydrophilic LaF₃: Yb, Tm UCNPs via stober method, theconjugation of folic acid （FA） with the standard EDC-NHS reaction. Fouriertransform infrared spectroscopy （FTIR）, ζ-potential and UV-visible spectra wereutilized to prove the successful results in every procedure.2. The cytotoxicity assay and bioimaging experiments including in vitro humangastric cancer MGC803cells targeting imaging, in vivo CT imaging, in vivo UCL andCT dual-modality imaging, in vivo targeting imaging were carried out with the abovementioned modified LaF₃: Yb, Tm UCNPs （UCNPs@SiO₂-FA）. MGC803cellstargeting imaging and CT imaging based on UCNPs@SiO₂-FA were firstly reportedby us, and CT imaging was the biggest highlight. UCNPs have excellent X-rayattenuation coefficient, what’s more, LaF₃has the highest RE content （La=70.9%）among common host materials, so these properties make LaF₃: Yb, Tm UCNPs idealfor CT imaging. UCL imaging and CT imaging are integrated into a new form nameddual-modality imaging, we aim to offer a novel strategy for bioimaging technology.