Magnetic, luminescent and core–shell structured Fe3O4@YF3:Ce3+,Tb3+ bifunctional nanocomposites
Graphical abstract
The Fe3O4@YF3:Ce3+,Tb3+ nanoparticles have a particle size ranging from 160 to 220 nm and still keep the spherical morphology, non-aggregation and rough surface. The shell shows a gray color with an average thickness of about 25 nm. The as-prepared nanoparticles displayed a strong green light emission and superparamagnetic behavior at room temperature.
Highlights
► Bifunctional magnetic–luminescent nanocomposites with Fe3O4 nanoparticles as the core and YF3:Ce3+,Tb3+ as the shell. ► A cubic spinel structure of Fe3O4 core and an orthogonal phase of YF3 shell. ► The nanocomposites displayed a strong green emission and superparamagnetic behavior at room temperature.
Introduction
Magnetic and luminescent materials are of great importance in the fields of chemistry, biology, and medical sciences as well as in biotechnology [1], [2], [3]. Magnetic nanoparticles have widely been studied for biomedical applications, such as magnetic biosensing, targeted drug delivery, cell separation and contrast enhancement in magnetic resonance imaging [4], [5], [6]. Fe3O4 was chosen in this study because of its nontoxicity and good biocompatibility. Whereas high-photostability luminescent nano-materials have attracted much attention in biological labeling [7], [8], [9], [10], [11], [12], [13]. The combination of magnetic and luminescent properties of different materials into a single nanocomposite system might greatly enhance their applications in the biomedical fields [14], [15]. Bifunctional magnetic and luminescent nanocomposites provide a new platform for both diagnostics and treatment of disease due to their enhanced functionality and multifunctional properties in contrast with their single counterparts, which can enable “find-detect-treat” in one body [16], [17]. The use of bifunctional magnetic and luminescent nanoplatforms will improve further diagnostic effectiveness and reduce side effects [18], [19], [20], [21].
Recently, many different kinds of bifunctional luminescent–magnetic nanoparticles with Fe3O4 nanoparticles as the core and QDs as the shell had been synthesized by several different research groups with different methods [22], [23], [24], [25]. However, QDs (generally made from heavy metal ions such as Pb2+ or Cd2+) release Cd over time by UV light, they are less promising due to aggressive biological environment in vivo studies [26], [27]. Such problems would hinder their applications on biological detections and medical diagnosis.
To solve this issue, it is important to develop new photostable and nontoxic or lower toxicity luminescent markers. Lanthanide-doped nanoparticles are very promising due to their large stokes shift, sharp emission spectra, a high luminescence quantum yield, long lifetime, multiphoton and up-conversion excitation, superior photostability, low toxicity, thus they offer tremendous potential for future medical diagnosis and therapy [28]. Fang et al. employed a facile one-pot method to fabricate the Fe3O4@SC[6]-LaPO4:Ce3+:Tb3+ superparamagnetic and fluorescent nanocomposites [29]. Zhang et al. had prepared Fe3O4@SiO2/Y2O3:Tb bifunctional nanocomposites by homogeneous precipitation method [30]. Sun et al. had synthesized Fe3O4/SiO2/YVO4:Eu3+ magnetic/luminescent nanocomposites by a hydrothermal method [31]. Lu et al. employed a modified Stöber method combined with a layer-by-layer assembly technique to fabricate the core–shell structured luminomagnetic microsphere composed of a Fe3O4 magnetic core and a continuous SiO2 nanoshell doped with Eu(DBM)3·2H2O fluorescent molecules [32]. YF3 is an important host crystal for lanthanide-doped phosphors. It provides a wide band gap (> 10 eV) and suitable Y3+ sites where trivalent rare earth ions can be easily substituted without additional charge compensation [33]. The terbiumion (Tb3+) is one of the most strongly emitting ions in lanthanide ions. It is resistant to photobleaching, nontoxic, biocompatible, monochromatic, highly luminescent, most importantly, ultrasensitive both in vitro and in vivo bioassays, therefore Tb3+ could serve as a more efficient biological label than traditional organic fluorescent compounds or QDs [34]. Ce3+ ions can absorb the energy and then effectively transfer it to Tb3+ ions, so it is an efficient luminescent sensitizer [35].
In this work, we select Fe3O4 as magnetic cores and YF3:Ce3+,Tb3+ as luminescent shells, using a facile direct precipitation method to synthesize the Fe3O4@YF3:Ce3+,Tb3+ bifunctional magnetic–luminescent nanocomposites. The synthetic strategy as schematically illustrated in Scheme 1. With the excellent magnetic properties and surface amino-functional groups of Fe3O4 cores, YF3:Ce3+,Tb3+ can be successfully coated. Compared with the reference [29], [30], [31], our method is simple and the cost is low. In addition, without the coated SiO2 layer, the as-prepared product has a good green emission and strong magnetic property.
Section snippets
Reagents and characterization
Yttrium oxide (Y2O3, purity:99.99%), Cerium oxide (CeO2, purity: 99.99%) and Terbium oxide (Tb4O7, purity: 99.99%) were purchased from Shanghai Yuelong Non-Ferrous Metal Limited China, ammonium fluoride (NH4F, purity:96.0%), Ferric chloride hexahydrate (FeCl3·6H2O, purity ≥ 99.0%), ethylenediamine (C2H8N2, purity ≥ 98.0%), sodium acetate (NaAc, purity ≥ 99.0%), Ethylene glycol (EG, purity 96.0%) were purchased from Beijing Chemical Reagent Limited China. All chemicals were used without any further
XRD patterns
The structure of Fe3O4 particles and Fe3O4@YF3:Ce3+,Tb3+ nanocomposites has been examined by XRD. As shown in Fig. 1a, the position and relative intensity of all diffraction peaks match well with standard Fe3O4 powder diffraction data (PDF 75–1610), which indicates that the Fe3O4 particles are pure phase and belong to cubic spinel structure. As shown in Fig. 1b, besides the characteristic diffraction peaks of YF3 (PDF 70–1935) with orthogonal phase, the obvious diffraction peaks at 2θ = 35.0° and
Conclusion
In summary, we reported the synthesis of the Fe3O4@YF3:Ce3+,Tb3+ magnetic–luminescent bifunctional nanocomposites. The as-prepared nanocomposites combined the advantages of magnetism and luminescence, which would find extensive applications in biomedical fields. Further investigation about the diagnostic and therapeutic potentials of these bifunctional magnetic luminescent nanocomposites is in process.
Acknowledgment
This work was supported by the National Natural Science Foundation of P.R. China (NSFC) (Grant No. 51072026) and the Development of Science and Technology Plan projects of Jilin Province (Grant No. 20090528).
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