| Summary: | Highly fluorescent magnetic nanoparticles (Eu(TTA)<sub>3</sub>(P(Oct)<sub>3</sub>)<sub>3</sub>@mSiO<sub>2</sub>@SPION) [europium (III) chloride hexahydrate = Eu; 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione = TTA; trioctylphosphine = (P(Oct)<sub>3</sub>); mesoporous silica = mSiO<sub>2</sub>; superparamagnetic iron oxide nanoparticle = SPION] were developed as a dual-functional imaging agent. The hierarchical structure was composed of a magnetic core and mesoporous silica shell was constructed using a cationic surfactant template after coating with phosphatidylcholine of oleic acid coated SPION. Afterward, the surface and cavities of mSiO<sub>2</sub>@SPION were modified with 3-(trimethoxysilyl) propyl methacrylate (TMSPMA) as a silane coupling agent to introduce methacrylate groups. Eu(TTA)<sub>3</sub>(P(Oct)<sub>3</sub>)<sub>3</sub> molecules are penetrated, located and bonded covalently inside of the cavities/mesopores of mSiO<sub>2</sub>, it shows extremely stable anti-photobleaching properties. The emission spectra of Eu(TTA)<sub>3</sub>(P(Oct)<sub>3</sub>)<sub>3</sub>@mSiO<sub>2</sub>@SPION indicated typical hypersensitivity transition <sup>5</sup>D<sub>0</sub>→<sup>7</sup>F<sub>2</sub> at 621 nm. The concentration of Eu(TTA)<sub>3</sub>(P(Oct)<sub>3</sub>)<sub>3</sub>@mSiO<sub>2</sub>@SPION was varied between 10 and 500 μL/mL to evaluate the cytotoxicity with NCI-H460 (H460) cells using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. In addition, the presence of a strong red-emitting Eu(TTA)<sub>3</sub>(P(Oct)<sub>3</sub>)<sub>3</sub>@mSiO<sub>2</sub>@SPION in the cytoplasm was observed by fluorescence microscopy. Those results that it can be a potential candidate for dual-functional contrast agent and PL nanomaterials for fabricating the diagnostic kits to amplify the low signal.
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