Synthesis, Characterization and Cytotoxicity of

materials Article

Synthesis, Characterization and Cytotoxicity of Novel Multifunctional Fe3O4@SiO2@GdVO4:Dy3+ Core-Shell Nanocomposite as a Drug Carrier Bo Li, Huitao Fan *, Qiang Zhao and Congcong Wang College of Chemistry and Pharmaceutical Engineering, Nanyang Normal University, Nanyang 473061, China; [email protected] (B.L.); [email protected] (Q.Z.); [email protected] (C.W.) * Correspondence: [email protected]; Tel.: +86-139-3858-7239 Academic Editor: Dusan Losic Received: 22 January 2016; Accepted: 24 February 2016; Published: 3 March 2016

Abstract: In this study, multifunctional Fe3 O4 @SiO2 @GdVO4 :Dy3+ nanocomposites were successfully synthesized via a two-step method. Their structure, luminescence and magnetic properties were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). The results indicated that the as-prepared multifunctional composites displayed a well-defined core-shell structure. The composites show spherical morphology with a size distribution of around 360 nm. Additionally, the composites exhibit high saturation magnetization (20.40 emu/g) and excellent luminescence properties. The inner Fe3 O4 cores and the outer GdVO4 :Dy3+ layers endow the composites with good responsive magnetic properties and strong fluorescent properties, which endow the nanoparticles with great potential applications in drug delivery, magnetic resonance imaging, and marking and separating of cells in vitro. Keywords: Fe3 O4 @SiO2 @GdVO4 :Dy3+ ; nanocomposites; core-shell structure; magnetic property; luminescence property

1. Introduction In recent years, controlled drug delivery systems for modern drug therapy have been attracting increasing attention because they exhibit low toxicity, a wide therapeutic window, and ideal drug efficacy as compared to conventional drug delivery systems [1,2]. The multifunctional nanocomposites combine with magnetic and luminescent properties in one entity, and they have attracted great attention in recent years owing to their potential application in the biotechnology and nanomedicine fields including magnetic resonance imaging (MRI), cell separation, drug delivery agents, cell separation, labeling, and optical probes [3–5]. In the choice of luminescent nanomaterials for labeling, targeting and imaging, lanthanide-doped nanomaterials possess many of advantages such as high fluorescence quantum yields, low toxicity, long lifetimes, and high stability in comparison to quantum dots and organic dyes [5–8]. So far, there have been some reports of constructing multifunctional nanomaterials that were made up of Fe3 O4 and lanthanide-doped nanomaterials. In these reports [8–12], if the lanthanide-doped nanomaterials are chosen as cores, their luminescent intensity may be suppressed to some extent due to the coating of the outer layers. Meanwhile, if the lanthanide-doped nanomaterials are in direct contact with Fe3 O4 , their luminescence may be decreased as the direct contact can cause fluorescence-quenching [13–15]. Therefore, a SiO2 mid-layer between Fe3 O4 and lanthanide-doped nanomaterials is needed. To the best of our knowledge, there are no previous reports on the combination of magnetic properties with gadolinium vanadate nanophosphors. The previous investigation results indicated that Materials 2016, 9, 149; doi:10.3390/ma9030149

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Materials 2016, 9, 149

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nanosized GdVO4 :Ln3+ phosphors have a significant application in a high definition flat display panels Materials 2016, 9, 149 2 of 7 and potential applications in biology [16–19]. Compared with Ln3+ -activated YVO4 , GdVO4 :Ln3+ that nanosized GdVO 4:Ln3+ phosphors have a significant application in a high definition flat display exhibits highly efficient emitting phosphors, in which the energy transfers from the GdVO4 host to the panels and potential applications biology transfer [16–19]. (CT), Compared with Ln3+‐activated YVO4, of 3+ ´ charge incorporated Ln ions through V5+ –O2in yielding an efficient luminescence 3+ exhibits highly efficient emitting phosphors, in which the energy transfers from the GdVO 4 :Ln Ln3+ activators. GdVO4 host to the incorporated Ln3+ ions through V5+–O2− charge transfer (CT), yielding an efficient 3+ Herein, we develop, for the first time, a novel and simple route to prepare Fe3 O4 @SiO2 @GdVO4 :Dy luminescence of Ln3+ activators. core-shellHerein, we develop, for the first time, a novel and simple route to prepare Fe microspheres with excellent magnetic and luminescence properties. The good aqueous 3O4@SiO2@GdVO4:Dy3+ colloidal stability, low toxicitywith andexcellent excellentmagnetic self-heating make these novelThe magnetic, luminescent core‐shell microspheres and efficacy luminescence properties. good aqueous nanomaterials suitable for hyperthermia treatment of cancer, and the luminescent entity helps us to colloidal stability, low the toxicity and excellent self‐heating efficacy make these novel magnetic, identify the location of magnetic nanoparticles during in vitro cellular imaging [20–24]. luminescent nanomaterials suitable for the hyperthermia treatment of cancer, and the luminescent entity helps us to identify the location of magnetic nanoparticles during in vitro cellular imaging [20–24].

2. Results and Discussion 2. Results and Discussion

Figure 1 depicts the X-ray diffraction (XRD) patterns of as-synthesized Fe3 O4 , Fe3 O4 @SiO2 and 3+ nanoparticles. From Figure 1, we can find that 3there Figure 1 depicts the X‐ray diffraction (XRD) patterns of as‐synthesized Fe O4, Fe3are O4@SiO 2 and Fe3 O4 @SiO characteristic 2 @GdVO4 :Dy Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles. From Figure 1, we can find that there are characteristic diffraction peaks of Fe3 O4 , with a face-centered-cubic structure in all curves according to JCPDS card diffraction peaks of Fe3O4, with a face‐centered‐cubic structure in all curves according to JCPDS card No. 65-3107. Besides the corresponding peaks of Fe3 O4 , SiO2 (JCPDS card No. 29-0085) and GdVO4 No. 65‐3107. Besides the corresponding peaks of Fe3O4, SiO2 (JCPDS card No. 29‐0085) and GdVO4 (JCPDS card No.86-0996) can be detected in Figure 1a–c, respectively. No peaks corresponding to (JCPDS card No.86‐0996) can be detected in Figure 1a–c, respectively. No peaks corresponding to 3+ composites. impurities are detected, showing the adequate purity of the Fe O4 @SiO 2 @GdVO 4 :Dy impurities are detected, showing the adequate purity of the Fe 3O43@SiO 2@GdVO 4:Dy3+ composites.

Figure 1. X‐ray diffraction (XRD) patterns of pure Fe3O4 (a), Fe3O4@SiO2 (b) and Figure 1. X-ray diffraction (XRD) patterns of pure Fe3 O4 (a); Fe3 O4 @SiO2 (b) and Fe3 O4 @SiO2 @GdVO4 : 3+ Fe 3+ 3O4@SiO2@GdVO4:Dy (c). The diffraction peaks that are indexed in 1c correspond to GdVO4.

Dy

(c). The diffraction peaks that are indexed in 1c correspond to GdVO4 .

The morphology and size details of the composites were characterized by SEM (scanning electronic microscope) and TEM (transmission electron microscopy) images. SEM investigations, as The morphology and size details of the composites were characterized by SEM (scanning electronic displayed in Figure 2a, reveal that the magnetic cores of Fe 3O4 particles are of a rough appearance microscope) and TEM (transmission electron microscopy) images. SEM investigations, as displayed and have an average size of 290 (±20) nm. Once coated with one layer of silica, the composite in Figure 2a, reveal that the magnetic cores of Fe3 O4 particles are of a rough appearance and have microspheres are slightly larger in diameter and have a relatively smooth surface, with their size an average size of 290 (˘20) nm. Once coated with one layer of silica, the composite microspheres increased up to 320 (±30) nm, as shown in Figure 2b. The average size of the core‐shell nanocomposites are slightly larger in diameter and have a relatively smooth surface, with their size increased up finally increased up to 360 (±25) nm, as illustrated in Figure 2c. The representative TEM images in to 320 (˘30) nm, as shown in Figure 2b. The average size of the core-shell nanocomposites finally Figure 2e,f indicate that the nanocomposites exhibit a core‐shell structure. increasedTo estimate the magnetic sensitivity, the room temperature magnetization hysteresis loops of up to 360 (˘25) nm, as illustrated in Figure 2c. The representative TEM images in Figure 2e,f indicate that the nanocomposites exhibit a core-shell structure. the as‐prepared cores and core‐shell nanocomposites were collected and displayed in Figure 3. The To estimate the magnetic sensitivity, the room temperature magnetization hysteresis loops of magnetic hysteresis loops in Figure 3 indicate that they have saturation magnetizations of 83.9 emu/g 3+) as (Fe3O4), 27.8 emu/g (Fe3Ocore-shell 4@SiO2) and 20.4 emu/g (Fe3O4were @SiO2@GdVO 4:Dy well as negligible the as-prepared cores and nanocomposites collected and displayed in Figure 3. coercivity at room temperature, implying characteristics of their strong magnetism. The reduction of The magnetic hysteresis loops in Figure 3 indicate that they have saturation magnetizations of 3+ 3+). saturation could be attributed to the nonmagnetic shells (SiO2 and GdVO4:Dy 83.9 emu/g (Femagnetization 3 O4 ), 27.8 emu/g (Fe3 O4 @SiO2 ) and 20.4 emu/g (Fe3 O4 @SiO2 @GdVO4 :Dy ) as well Our study revealed that, though the magnetism of the core‐shell nanocomposites is less than that of as negligible coercivity at room temperature, implying characteristics of their strong magnetism. the bare magnetic cores, it still possesses enough magnetic response for biomedical applications The reduction of saturation magnetization could be attributed to the nonmagnetic shells (SiO2 and such as MRI, which is effectively magnetic separation. GdVO4 :Dy3+ ). Our study revealed that, though the magnetism of the core-shell nanocomposites is


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less than that of the bare magnetic cores, it still possesses enough magnetic response for biomedical applications such as MRI, which is effectively magnetic separation. Materials 2016, 9, 149 3 of 7 Materials 2016, 9, 149

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Figure 2. Scanning electronic microscope (SEM) images of Fe3O4 (a); Fe3O4@SiO2 (b);

Figure 2. Scanning electronic microscope (SEM) images of Fe3 O4 (a); Fe3 O4 @SiO2 (b); images of Fe3O4 (d); Fe3O4@SiO2@GdVO4:Dy3+ (c); and transmission electron microscopy (TEM) 3+ (c); and transmission electron microscopy (TEM) images of Fe O (d); Fe3 O4Fe @SiO @GdVO 2 4 3:Dy 3 4 3O4@SiO O4@SiO 2@GdVO4microscope :Dy3+ (f). Figure 2. 2 (e); Fe Scanning electronic (SEM) images of Fe 3O4 (a); Fe3O4@SiO2 (b); 3+ (f). Fe3 O4 @SiO (e); Fe O @SiO @GdVO :Dy 2 3 4 2 4 Fe3O4@SiO2@GdVO4:Dy3+ (c); and transmission electron microscopy (TEM) images of Fe3O4 (d); Fe3O4@SiO2 (e); Fe3O4@SiO2@GdVO4:Dy3+ (f).

Figure 3. The magnetic hysteresis loops of pure Fe3O4 (a); Fe3O4@SiO2 (b); and Fe3O4@SiO2@GdVO4:Dy3+ (c).

The photoluminescence spectra of Fe3O4@SiO 2@GdVO4:Dy3+ are shown in Figure 4. In the Figure 3. The magnetic hysteresis loops of pure Fe 3O4 (a); Fe3O4@SiO2 (b); and Fe3O4@SiO2@GdVO4:Dy3+ (c). Figure 3. The magnetic hysteresis loops of pure Fe3 O4 (a); Fe3 O4 @SiO2 (b); and excitation spectra (Figure 4A), the excitation band at 300–350 nm monitored with a 571 nm emission 3+ (c). Feof @SiO 4F 3O 49/2 2 @GdVO 4 :Dy transition –6H1 3/2 electronic of Dy can be attributed a 3+charge transfer the The photoluminescence spectra of 3+Fe 3O4@SiO 2@GdVO4to :Dy are shown in through Figure 4. In V–O the 3+ are shown in bond overlay of the Dy–O charge transfer band. The emission spectra of GdVO 4 :Dy excitation spectra (Figure 4A), the excitation band at 300–350 nm monitored with a 571 nm emission 3+ are 4F9/2–6H15/2 transition and Figure 4B. The main emission peaks at 481 nm and 571 nm are results of the of 4Fphotoluminescence 9/2–6H13/2 electronic transition be attributed to 4 :Dy a charge transfer the V–O The spectraof ofDy Fe3+3 can O4 @SiO shownthrough in Figure 4. In the 2 @GdVO 4F9/2–6H13/2 transition of Dy3+ ions. Moreover, Figure 4 shows the excitation spectra and bond overlay of the Dy–O charge transfer band. The emission spectra of GdVO 4:Dy3+a are shown in excitation spectra (Figure 4A), the excitation band at 300–350 nm monitored with 571emission nm emission 3+ ions. It is 4 spectra of Fe 3O4@SiO2@GdVO4:Dy3+ composites with different doped concentrations of Dy Figure 4B. The main emission peaks at 481 nm and 571 nm are results of the –6H15/2 transition and of 4 F9/2 –6 H13/2 electronic transition of Dy3+ can be attributed to a chargeF9/2 transfer through the V–O 3+ ions in the Fe3O4@SiO2@GdVO4:Dy3+ 4F9/2–6H13/2 shown that the optimum concentration of 4 Dy transition of Dy3+ doped ions. Moreover, Figure shows the excitation spectra and emission 3+ bond overlay of the Dy–O charge transfer band. The emission spectra of GdVO4 :Dy 3+ are shown in composites is 1 mol %. spectra of Fe3O4@SiO2@GdVO4:Dy3+ composites with different doped concentrations of Dy ions. It is Figure 4B.To The main emission peaks at 481 nm and nm are results ofnanocomposites, the 4 F9/2 –6 H15/2 transition investigate the porous structure of the Fe571 3of O4@SiO the N3+2 shown that the optimum doped concentration Dy3+ 2@GdVO ions in 4:Dy the 3+ Fe 3O4@SiO2@GdVO 4:Dy 6H 3+ ions. Moreover, Figure 4 shows the excitation spectra and emission and 4 Fadsorption‐desorption isotherms were investigated and are shown in Figure 5. This isotherm profile – transition of Dy 9/2 13/2 composites is 1 mol %. 3+ composites with different doped 3+ spectra of To Fe3investigate O4 @SiO2 @GdVO Dy can be categorized as type IV, with a small hysteresis loop observed at a relative pressure of 0.05–1.0, 4 :Dy the porous structure of the Fe3O4@SiO2@GdVO4:Dy3+ concentrations nanocomposites, of the N2 ions. 3+ indicating the mesoporous features. The inset in Figure 5 is the pore size distribution. As calculated It is shown that the optimum doped concentration of Dy ions in the Fe3 O4 @SiO2 @GdVO4 :Dy3+ adsorption‐desorption isotherms were investigated and are shown in Figure 5. This isotherm profile by the Brunauer‐Emmett‐Teller (BET) method, Fe 3O4@SiO2@GdVO4:Dy3+ nanocomposites’ core‐shell can be categorized as type IV, with a small hysteresis loop observed at a relative pressure of 0.05–1.0, composites is 1 mol %. 2 −1 3∙g−1, structure gives rise to a BET area of 30.21 m ∙g Fe , with a relatively high pore volume of 0.212 cm 3+ nanocomposites, indicating the mesoporous features. The inset in Figure 5 is the pore size distribution. As calculated To investigate the porous structure of the the N2 3 O4 @SiO2 @GdVO4 :Dy and the average pore diameter is 17.46 nm. The BET indicated the potential of such nanostructures by the Brunauer‐Emmett‐Teller (BET) method, Fe3O4@SiO2@GdVO4:Dy3+ nanocomposites’ core‐shell adsorption-desorption isotherms were investigated and are shown in Figure 5. This isotherm profile for drug delivery applications. structure gives rise to a BET area of 30.21 m2∙g−1, with a relatively high pore volume of 0.212 cm3∙g−1, can be categorized as type IV, with a small hysteresis loop observed at a relative pressure of 0.05–1.0, To evaluate the cytotoxicity of the Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles, in vitro cytotoxicity tests and the average pore diameter is 17.46 nm. The BET indicated the potential of such nanostructures indicating the mesoporous features. The inset in Figure 5 is the pore size distribution. As calculated by against HeLa cells were carried out. From the 3‐[4,5‐dimethylthiazol‐2‐y1]‐2,5‐diphenyltetrazolium for drug delivery applications. 3+ nanocomposites’ core-shell the Brunauer-Emmett-Teller (BET) method, Fe3 O2@GdVO @GdVO 3+ nanoparticles, in vitro cytotoxicity tests 4 @SiO24:Dy 4 :Dy To evaluate the cytotoxicity of the Fe 3O4@SiO 2 ´ 1 structure gives rise to a BET area of 30.21 m ¨ g , with a relatively high pore volume of 0.212 cm3 ¨ g´1 , against HeLa cells were carried out. From the 3‐[4,5‐dimethylthiazol‐2‐y1]‐2,5‐diphenyltetrazolium


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and the average pore diameter is 17.46 nm. The BET indicated the potential of such nanostructures for drug delivery applications. To evaluate the cytotoxicity of the Fe3 O4 @SiO2 @GdVO4 :Dy3+ nanoparticles, in vitro cytotoxicity Materials 2016, 9, 149 4 of 7 tests against HeLa cells were carried out. From the 3-[4,5-dimethylthiazol-2-y1]-2,5-diphenyltetrazolium bromide (MTT) viability histogram, shown in Figure 6, we can find that the Fe3 O4 @SiO2 @GdVO4 :Dy3+ 3+ bromide (MTT) viability histogram, shown in Figure 6, we can find that the Fe3O4@SiO2@GdVO4:Dy causesMaterials 2016, 9, 149 insignificant damage to the HeLa cells when the sample concentration increases to 200 4 of 7 µg¨ mL´1 causes insignificant damage to the HeLa cells when the sample concentration increases to for 24 bromide (MTT) viability histogram, shown in Figure 6, we can find that the Fe h, and the cell viability remains at 90.38% even at the highest concentration, which indicates that O4@SiO 2concentration, @GdVO 4:Dy3+ 200 μg∙mL−1 for 24 h, and the cell viability remains at 90.38% even at the 3highest 3+ Fe3 O4 @SiO nanoparticles are biocompatible. Materials 2016, 9, 149 4 of 7 2 @GdVO 4 :Dy damage causes insignificant the HeLa cells when the sample concentration increases to which indicates that Fe 3O4@SiOto 2@GdVO 4:Dy3+ nanoparticles are biocompatible. 200 μg∙mL−1 for 24 h, and the cell viability remains at 90.38% even at the highest concentration, bromide (MTT) viability histogram, shown in Figure 6, we can find that the Fe 3O4@SiO2@GdVO4:Dy3+ which indicates that Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles are biocompatible. causes insignificant damage to the HeLa cells when the sample concentration increases to 200 μg∙mL−1 for 24 h, and the cell viability remains at 90.38% even at the highest concentration, which indicates that Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles are biocompatible.

Figure 4. Excitation spectra (A) and emission spectra (B) of Fe3O4@SiO2@GdVO4:Dy3+ with different Figure 4. Excitation spectra (A)3+and emission spectra (B) of Fe3 O4 @SiO2 @GdVO4 :Dy3+ with different doped concentrations of Dy (a: 0.5%, b: 1%, c: 2%, d: 3% and e: 4%). dopedFigure 4. Excitation spectra (A) and emission spectra (B) of Fe concentrations of Dy3+ (a: 0.5%, b: 1%, c: 2%, d: 3% and3Oe:4@SiO 4%).2@GdVO4:Dy3+ with different doped concentrations of Dy3+ (a: 0.5%, b: 1%, c: 2%, d: 3% and e: 4%).

Figure 4. Excitation spectra (A) and emission spectra (B) of Fe3O4@SiO2@GdVO4:Dy3+ with different doped concentrations of Dy3+ (a: 0.5%, b: 1%, c: 2%, d: 3% and e: 4%).

Figure 5. The N2 adsorption/desorption isotherms and pore size distribution (inset) of Fe3O4@SiO2@GdVO4:Dy3+.

Figure 5. The N2 adsorption/desorption isotherms and pore size distribution (inset) of Fe3O4@SiO2@GdVO4:Dy3+.

Figure 5. The N2 adsorption/desorption isotherms and pore size distribution (inset) of Fe3 O4 @SiO2 @GdVO4 :Dy3+ . Figure 5. The N2 adsorption/desorption isotherms and pore size distribution (inset) of Fe3O4@SiO2@GdVO4:Dy3+.

Figure 6. The viability histograms of HeLa cells incubated with different concentrations of measured Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles for 24 h by a 3‐(4,5‐dimethylthiazol‐2‐y1)‐2,5‐diphenyltetrazolium bromide (MTT) assay. Figure 6. The viability histograms of HeLa cells incubated with different concentrations of Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles for 24 h measured by a 3. Materials and Methods 3‐(4,5‐dimethylthiazol‐2‐y1)‐2,5‐diphenyltetrazolium bromide (MTT) assay. Figure 6. The viability histograms of HeLa cells incubated with different concentrations of Figure The viability histograms of HeLa cells different concentrations of Fe6. 3O4@SiO2@GdVO4:Dy3+ nanoparticles for incubated 24 h with measured by a 3.1. Materials 3. Materials and Methods 3+ Fe3 O43‐(4,5‐dimethylthiazol‐2‐y1)‐2,5‐diphenyltetrazolium bromide (MTT) assay. @SiO2 @GdVO4 :Dy nanoparticles for 24 h measured by a 3-(4,5-dimethylthiazol-2-y1)-2,5-

All reagents are of analytical reagent grade and used without further purification. Gd2O3 diphenyltetrazolium bromide (MTT) assay. 3.1. Materials (99.9%) and Eu 2O3 (99.9%) were purchased from Jinan Camolai Trading Company, Ferrous chloride 3. Materials and Methods All reagents are of analytical reagent grade and used without further purification. Gd2O3 (99.9%) and Eu 3.1. Materials 2O3 (99.9%) were purchased from Jinan Camolai Trading Company, Ferrous chloride All reagents are of analytical reagent grade and used without further purification. Gd2O3 (99.9%) and Eu2O3 (99.9%) were purchased from Jinan Camolai Trading Company, Ferrous chloride


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3. Materials and Methods 3.1. Materials All reagents are of analytical reagent grade and used without further purification. Gd2 O3 (99.9%) and Eu2 O3 (99.9%) were purchased from Jinan Camolai Trading Company, Ferrous chloride hexahydrate (FeCl3 ¨ 6H2 O) (99%), tetraethyl orthosilicate (TEOS, 99.0%), sodium acetate (NaAc), Citrate acid monohydrate were purchased from Beijing Chemicals Corporation. Nitric acid, ethanol, ethylene glycol (EG), and ammonia aqueous (25%) were purchased from Tianjin Chemicals Corporation. Deionized water obtained from the Milli-Q system (Millipore, Bedford, MA, USA) was used in all experiments. The magnetic Fe3 O4 nanoparticles were prepared using a modified solvothermal reaction. Materials 2016, 9, 149 5 of 7 3.2. Synthesis of Fe3 O4(FeCl3∙6H2O) (99%), tetraethyl orthosilicate (TEOS, 99.0%), sodium acetate (NaAc), hexahydrate Citrate acid monohydrate were purchased from Beijing Chemicals Corporation. Nitric acid, ethanol,

The magnetic Fe3 O(EG), were prepared to a from previously 4 nanoparticles ethylene glycol and ammonia aqueous (25%) according were purchased Tianjin reported Chemicals synthetic process [19]. Typically, FeCl3 ¨water 6H2 Oobtained (1.3495from g) and NaAcsystem (7.1926 g) wereBedford, dissolved EG solution Corporation. Deionized the Milli‐Q (Millipore, MA, in USA) was used in all experiments. 3O4 nanoparticles were prepared a modified (40 mL). Then PEG-10000 (1.0015 g)The wasmagnetic added Fe with vigorous stirring and theusing mixture was stirred for solvothermal reaction. 30 min to form a homogeneous russet solution. The obtained solution was transferred to a Teflon-lined ˝ stainless-steel autoclave 3(50 3.2. Synthesis of Fe O4 mL capacity) and heated at 200 C for 10 h. Subsequent cooling to room temperature yielded black magnetite particles, which were washed with ethanol and deionized water The magnetic Fe 3O4 nanoparticles were prepared according to a previously reported synthetic ˝ C for 12 h. three times, respectively, and dried at2O 60(1.3495 process [19]. Typically, FeCl3∙6H g) and NaAc (7.1926 g) were dissolved in EG solution (40 mL). Then PEG‐10000 (1.0015 g) was added with vigorous stirring and the mixture was stirred for 30 min form 2a homogeneous russet solution. The obtained solution was transferred to a 3.3. Synthesis of Fe 3 Oto 4 @SiO Teflon‐lined stainless‐steel autoclave (50 mL capacity) and heated at 200 °C for 10 h. Subsequent

Fe3 O4cooling @SiO2to nanoparticles were prepared to the modified bywashed the Stöber room temperature yielded black according magnetite particles, which were with method. ethanol In brief, 1.0 g of Fe3and deionized water three times, respectively, and dried at 60 °C for 12 h. O4 nanoparticles were homogeneously dispersed in a mixture of 160 mL of ethanol, 40 mL of deionized water, and 3.0 mL of 28 wt % concentrated ammonia aqueous solution, followed by 3.3. Synthesis of Fe3O4@SiO2 the addition of 3.0 mL of tetraethyl orthosilicate (TEOS). After vigorous stirring at 40 ˝ C for 6 h, Fe3O4@SiO2 nanoparticles were prepared according to the modified by the Stöber method. In the obtained Fe3 O4 @SiO2 microspheres were separated with a magnet and washed repeatedly with brief, 1.0 g of Fe3O4 nanoparticles were homogeneously dispersed in a mixture of 160 mL of ethanol, ethanol and deionized water to remove nonmagnetic by products. 40 mL of deionized water, and 3.0 mL of 28 wt % concentrated ammonia aqueous solution, followed by the addition of 3.0 mL of tetraethyl orthosilicate (TEOS). After vigorous stirring at 40 °C for 6 h,

3+ Nanoparticles the obtained Fe 3O4@SiO 2 microspheres were separated with a magnet and washed repeatedly with 3.4. Synthesis of Fe3 O4 @SiO 2 @GdVO 4 :Dy

ethanol and deionized water to remove nonmagnetic by products.

Functionalization of GdVO4 :Dy3+ on the template Fe3 O4 @SiO2 was achieved according to the 3.4. Synthesis of Fe 4@SiO2@GdVO 4:Dy3+ Nanoparticles reported process with a3Odoping concentration of Dy3+ of 0.5–4 mol % to Dy3+ in GdVO4 :Dy3+ . 3+ on the template Functionalization of GdVOis4:Dy Fe3O4stoichiometric @SiO2 was achieved according The typical procedure for synthesis described as follows: amounts of to Gdthe 2 O3 , Dy2 O3 3+ of 0.5–4 mol % to Dy3+ in GdVO4:Dy3+. The reported process with a doping concentration of Dy and citric acid were dissolved in dilute nitric acid with heating followed by the addition of NH4 VO3 typical procedure for synthesis is described as follows: stoichiometric amounts of Gd2O3, Dy2O3 and in distilled water. Then PEG-10000 was added with a concentration of 0.05 g¨ mL´1 . After stirring citric acid were dissolved in dilute nitric acid with heating followed by the addition of NH4VO3 in for 0.5 h, adistilled homogenous sol PEG‐10000 was formed. Then with the desired amount of Fe nanoparticles was 3 O4−1@SiO water. Then was added a concentration of 0.05 g∙mL . After 2stirring for ˝ h, gel, a homogenous sol was formed. the desired amount of Fe3O 4@SiO2 nanoparticles added into0.5 the after further stirring forThen another 3 h, the resulting material was driedwas at 120 C for added into the gel, after further stirring for another 3 h, the resulting material was dried at 120 °C for 12 h to obtain the precursors. Then the precursors were calcined at 700 ˝ C for another 4 h. The obtained 12 h to obtain the precursors. Then the precursors were calcined at 700 °C for another 4 h. nanoparticles were denoted as Fe3 O4 @SiO2 @GdVO4 :Dy3+ (Scheme 1). 3+ The obtained nanoparticles were denoted as Fe3O4@SiO2@GdVO4:Dy (Scheme 1).

Scheme 1. Illustration for the synthesis process of the spherical Fe3O4@SiO2@GdVO4:Dy3+ nanocomposite. 1. Illustration for the synthesis process of the spherical Fe3 O4 @SiO2 @GdVO4 :

Scheme Dy3+ nanocomposite. 3.5. Cytotoxicity Study of Fe3O4@SiO2@GdVO4:Dy3+ Nanoparticle

Cell viabilities of Fe3O4@SiO2@GdVO4:Dy3+ nanoparticles at different concentrations were tested by MTT assay on HeLa (human cervical cancer cells). In the experiment, the corresponding 3+ Nanoparticle 3.5. Cytotoxicity Study Fe3 O untreated cells ofwere used as control. First, the HeLa cells were pre‐incubated in a 96‐well plate 4 @SiO 2 @GdVO 4 :Dy (about 3000 cells per well) for 24 h. Second, 2 mg of the Fe 3O4@SiO2@GdVO4:Dy3+ nanoparticles were 3+ nanoparticles at different concentrations were tested Cell viabilities 3O 4 @SiO 2 @GdVO 4 :Dy added into of 10 Fe mL of 0.01 M phosphate buffered saline (PBS, pH = 7.4) to form a stable orange by MTT assay on HeLa (human cancer cells). In theor corresponding solution. Third, the above cervical solution at concentrations of the 6.25, experiment, 12.5, 25, 50, 100 200 μg∙mL−1 was untreated added to the cells. Six parallel‐group experiments were simultaneously conducted for each concentration. After 24 h, the viability of HeLa cells was examined by a MTT assay.


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cells were used as control. First, the HeLa cells were pre-incubated in a 96-well plate (about 3000 cells per well) for 24 h. Second, 2 mg of the Fe3 O4 @SiO2 @GdVO4 :Dy3+ nanoparticles were added into 10 mL of 0.01 M phosphate buffered saline (PBS, pH = 7.4) to form a stable orange solution. Third, the above solution at concentrations of 6.25, 12.5, 25, 50, 100 or 200 µg¨ mL´1 was added to the cells. Six parallel-group experiments were simultaneously conducted for each concentration. After 24 h, the viability of HeLa cells was examined by a MTT assay. 3.6. Characterization The purities of all the nanoparticles were checked by X-ray diffraction (XRD) measurements at room temperature using Cu Kα radiation (Kα = 1.54059 Å). The morphology and microscope structure of all the nanocomposites were characterized by a scanning electronic microscope (SEM, NoVa™ Nano SEM 430, FEI Co., Ltd., Hillsboro, OR, USA) and transmission electron microscopy (TEM, JEOL JEM-2010F, JEOL Co., Ltd., Tokyo, Japan). The room temperature magnetic hysteresis (M-H) loops were measured using a superconducting quantum interference device vibrating sample magnetometry (SQUID-VSM, Quantum Design Co., Ltd., San Diego, CA, USA). Luminescence spectra were recorded on a FluoroMax-4 spectrophotometer (HORIBA Jobin Yvon Co., Ltd., Paris, France). The specific surface area was determined by the Brunauer-Emmett-Teller (BET) method. The HeLa cells were assayed for viability by using a microplate reader (Bio-Rad 680, Bio-Rad Co., Ltd., Hercules, CA, USA). 4. Conclusions In summary, we report a novel magnetic/luminescence multifunctional nanocomposite, Fe3 O4 @SiO2 @GdVO4 :Dy3+ , with a core-shell structure from a combination of hydrothermal reaction and the sol-gel process. The as-prepared nanocomposites, combining the merits of the good magnetic response of the assembled Fe3 O4 @SiO2 microspheres and the fluorescence property of GdVO4 :Dy3+ , displayed high surface area and biocompatibility. Therefore, our study may provide new insight and useful information for the design of diverse, functional nanocomposites as drug carriers. Acknowledgments: This work is supported by the National Natural Science Foundation of China (Nos. 21401112, 21301100). Author Contributions: Huitao Fan, and Bo Li were involved in designing the aim of this manuscript, performed the experiments and prepared the manuscript. Qiang Zhao performed the room temperature magnetic hysteresis (M-H) loops measurements and analyzed the data. Congcong Wang helped with several analyses. Each contributor was essential to the production of this work. Conflicts of Interest: The authors declare no conflict of interest.

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