Journal of Science: Advanced Materials and Devices (2016) 295e300 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Functionalized YVO4:Eu3ỵ nanophosphors with desirable properties for biomedical applications Tran Thu Huong a, *, Ha Thi Phuong a, b, Le Thi Vinh a, c, Hoang Thi Khuyen a, Tran Kim Anh d, Le Quoc Minh a, d a Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay Distr., Hanoi, Viet Nam Department of Chemistry, Hanoi Medical University, Viet Nam Department of Chemistry, Hanoi University of Mining and Geology, Viet Nam d Duy Tan University, K7/25 Quang Trung, Da Nang, Viet Nam b c a r t i c l e i n f o a b s t r a c t Article history: Received 19 July 2016 Received in revised form 28 July 2016 Accepted 28 July 2016 Available online August 2016 Highly luminescent nanophosphors (NPs) containing rare earth (RE) ions were successfully prepared by careful control of nanosynthesis The YVO4:Eu3ỵ NPs formed core/shell structures with sizes from 10 nm to 25 nm The NPs were functionalized with biocompatible groups such as OH, NH2 and SCN A chemical coupling reaction connected the functionalized YVO4:Eu3ỵ NPs with Biotin via a direct reaction between the functional groups or an intermediate linker Under UVIS excitation, YVO4:Eu3ỵ NPs exhibited strong red luminescence with narrow bands corresponding to the intra 4f transitions of D0 e7 Fj (j ẳ 1, 2, 3, 4) Eu3ỵ The peaks were found at 594 nm (5 D0 e7 F1 ), 619 nm (5 D0 e7 F2 ), 652 nm (5 D0 e7 F3 ) and 702 nm (5 D0 e7 F4 ) with the strongest emission at 619 nm The fluorescence intensity and stability of the functionalized YVO4:Eu3ỵ NPs have been increased This is a promising result in sense of using the conjugates of YVO4:Eu3ỵ and a bioactive molecule, Biotin for the development of a fluorescent label tool in biomedical analysis © 2016 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: YVO4:Eu3ỵ Nanophosphors Fluorescent label Functionalization Conjugation Introduction Detection analysis of biomolecules is crucial for many applications in biochemistry, molecular biology and medicine Typical analytical methods such as fluorescent immunoassay (FIA) along with other, labeling and imaging techniques have thus been developed for decades These detection techniques, however, are often limited by the optical (fluorescent) properties of the available probes This has been one of the main motivations for the development of new probes, either for biomolecule labeling or detection of an intracellular signaling species Among the newly developed fluorecent probes, nanophosphors (NPs) containing rare earths have become of great interest in biochemistry, molecular biology and biomedicine applications because of their non-toxicity and strong luminescence properties [1e7] There are several kinds of nanophosphors containing rare * Corresponding author E-mail addresses: tthuongims@gmail.com, huongtt@ims.vast.vn (T.T Huong) Peer review under responsibility of Vietnam National University, Hanoi earth ions with high luminescent efficiency up to several tens of percent such as YVO4:Eu3ỵ nanoparticles [8e13], LnPO4$H2O: Eu, Tb nanomaterials [14e19] and ZrO2:Yb3ỵ, Er3ỵ nanoparticles [20], which have been developed for molecular biology, agrobiological and medical applications In previous studies, there has been success in synthesizing nanorods of Tb3ỵ, Eu3ỵ ions [21,22] and nanoparticles of YVO4:Eu3ỵ [23,24] The nanoscale and high-emission characteristics of these nanomaterials are more effective for ultrahigh sensitive fluorescent label for biomolecules, cell and tissue For the biological applications, surface functionalization of the nanomaterials is an important step The objective is first to ensure good dispersion of the nanomaterials in biological media, that is, in water at neutral pH and at high ionic strength Next, nanomaterials should contain specific organic or bioorganic groups which aim at targeting specific receptor sites, and/or ensuring innocuity in the case of in vivo experiments In addition, the luminescence properties of functionalized nanomaterials should not be lost Therefore, in this report, focus is paid on the surface functionalization of YVO4: Eu3ỵ NPs Then, the compatibility of YVO4:Eu3ỵ nanomaterials with a biological system is investigated The structure, morphology and http://dx.doi.org/10.1016/j.jsamd.2016.07.010 2468-2179/© 2016 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 296 T.T Huong et al / Journal of Science: Advanced Materials and Devices (2016) 295e300 luminescence properties of the functionalized YVO4:Eu3ỵ NPs have been studied by powder X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and photoluminescence spectroscopy The average size of the functionalized YVO4:Eu3ỵ nanophosphors are about 10e25 nm The functionalized YVO4:Eu3ỵ NPs exhibit red luminescence with narrow bands corresponding to the intra 4f transitions of D0 e7 Fj (j ẳ 1, 2, 3, 4) Eu3ỵ To develop a new conjugate suitable for labeling we focused on some strong bioaffinity molecules and organisms such as biotin, protein IgG or bovine serum albumin (BSA) Based on the immunereactions between antibody of the conjugate and antigen of virus/ vaccine one can be detected by a fluorescence microscope and imaged by a digital camera These results indicate that, the bioactive molecule linked nanoparicles YVO4:Eu3ỵ can be potentially applied in a variety of fields of application, especially in fluorescent labeling for biochemical and biomedical application Experimental 2.1 Synthesis of YVO4:Eu3ỵ nanophosphors The YVO4:Eu3ỵ NPs were prepared by the controlling nanosynthesis method In a typical synthesis, 0.55 g sodium orthovanadate Na3VO4 90% (SigmaeAldrich) were completely dissolved in 50 ml H2O Subsequently, 0.91 g Yttrium (III) nitrate hexahydrate Y(NO3)3$6H2O 99,8% (SigmaeAldrich) and 0.13 g Europium (III) nitrate pentahydrate Eu(NO3)3$5H2O, 99,9% (Aldrich) were added to the solution in a 100 ml round-bottomed flask This was followed by magnetic stirring for 60 Various pH values of the reaction solution were made in the range of 10e12 by using NaOH After that, the reaction solution was transferred into an autoclave and heated at 200 C for 1e24 h, and then cooled down slowly to room temperature The resulting products were collected and centrifuged at 5900 rpm The precipitate was washed several times in water and then dried in air at 60 C for he24 h 2.2 The primary silica shell as protecting layer 10 ml of Tetraethylorthosilicate (TEOS) (1/2) in absolute ethanol and 10 ml of as-synthesized YVO4:Eu3ỵ solution was mixed by magnetic stirring at room temperature for 24 h The pH of this solution was adjusted to the range of 11e12 by adding NH4OH The resulting products were collected, centrifuged and cleaned several times with ethanol and distilled water The final products were dried at 60 C in 6he24 h on air The results experimented several times, showed good reproducibility 2.3 The surface functionalization Surface functionalization of materials with functional groups on their surfaces can be designed from substrates with standard bulk material properties It is well-known that, the functionalization of the materials is a key step toward the aforementioned applications, since it determines the control of the coupling between the materials and the biological species of interest Functional silane compounds containing an organo-functional or organo-reactive arm can be used to conjugate biomolecules to inorganic substrates The appropriate selection of the functional or reactive group for a particular application can allow the attachment of proteins, oligonucleotides, whole cells, organelles, or even tissue sections to substrates The organosilanes used for these applications include functional or reactive groups such as hydroxyl, amino, aldehyde, epoxy, carboxylate, thiol, and even alkyl groups to bind molecules through hydrophobic interactions as discussed by [25] 3-Aminopropyltrimethoxysilane is among the most popular choices for creating a functional group on an inorganic surface or particle This reagent contains a short organic 3-amino propyl group, which terminates in a primary amine The 3Aminopropyltrimethoxysilane reactive portion contains a trimethoxy group Thus, the trimethoxy compound is more reactive and can be deposited on a substrate using 100 percent organic solvent without the presence of water to promote hydrolysis of the alkoxy groups prior to coupling In this case, the organic solvent deposition processes described in the previous section can be used to covalently bond a layer of aminosilane to substrates The advantage of this process is that a thinner, more controlled deposition of the silane can be made to create a monolayer of aminopropyl groups on the surface Isocyanate groups are extremely reactive toward nucleophiles and will hydrolyze rapidly in aqueous solution [25] They are especially useful for covalent coupling to hydroxyl groups under non-aqueous conditions, which is appropriate for conjugation to many carbohydrate ligands 3-(Triethoxysilyl) propylthiocyanate (TESCN) contains an isocyanate group at the end of a short propyl spacer, which is connected to the triethoxysilane group useful for attachment to inorganic substrates Silanation can be accomplished in dry organic solvent to form reactive surfaces while preserving the activity of the isocyanates An isocyanate reacts with amines to form isourea linkages and with hydroxyls to form carbamate (urethane) bonds Both reactions can take place in organic solvent to conjugate molecules to inorganic substrates The solvent used for this reaction must be of high purity and should be dried using molecular sieves prior to adding the silane compound The functionalization of YVO4:Eu3ỵ nanophosphors with NH2/ SCN was performed by using 3-aminopropyltrimetoxysilane (APS) with -NH2 group and 3-(Triethoxysilyl) propylthiocyanate (TESCN) with e SCN group, respectively In these typical syntheses, 22.5 ml of absolute ethanol and ml of APTMS (TESCN) were put in a 100 ml three-necked flask under magnetic stirring at room temperature for 30 The solution is heated up to 60 C under reflux Then, ml of the YVO4:Eu3ỵ with silica shell nanomaterial solution at pH is added drop wise The reaction time is about h The solution is next gently stirred for 20 h The resulting products were collected by three centrifugation/dispersion steps in a water/ ethanol mixture (2:5, v/v) The final products were again washed with deionized water and then dried at 60 C for 24 h in air 2.4 Biotin binding with solegel functionalized nanophosphors Coupling of the protein immunoglobulin to the -NH2/-SCN groups functionalized nanomaterial, was achieved using the amine reactive linker glutaraldehyde by forming a thioure linker The APS/ TESCN treated YVO4:Eu3ỵ nanomaterials solution and glutaraldehyde were dispersed in vanadate buffered saline (PBS, 0.1 M, pH 5) with concentration of glÀ1 The above solution is added to different concentrations of Biotin (Aldrich) These reaction mixtures were incubated at 30 C for h The resulting products were collected, centrifuged at 5900 rpm, and washed several times by using ethanol/water and distilled water The Biotin linked silica coated YVO4:Eu3ỵ SCN products were stored in closing box at C in a refrigerator Characterization methods The morphology of the as-synthesized samples was observed by using field emission scanning electron microscopy (FE-SEM, Hitachi, S-4800) and transmission electron microscopy (TEM, JEM1010) X-ray diffraction (XRD) measurements of the products T.T Huong et al / Journal of Science: Advanced Materials and Devices (2016) 295e300 were performed on an X-ray diffractometer (Siemens D5000 with l ¼ 1.5406 Å in the range of 15 2q 75 ) Infrared spectra were also investigated with FTIR spectroscopy by an IMPACT 410-Nicolet instrument The luminescent properties of studied samples were measured at high-resolution on a steady-state photoluminescent setup based on a luminescence spectrum photometer system by Horiba Jobin Yvon IHR 320 (USA) Results and discussion 297 There are three regions that can be defined in the spectrum, one from 2800 cmÀ1 to 3400 cmÀ1, the second in the range of 1300e1650 cmÀ1, and the third in the longer wavelength range from 400 cmÀ1 to 900 cmÀ1 In the first region, a peak at 2960 cmÀ1 can be assigned to the CeH stretching vibrational mode Two other peaks are found at 3300 cmÀ1 and 2854 cmÀ1 (indicating the NH2, eCeNH2 stretching vibrational mode) The vibration of the OeH group was found at a higher wavenumber in the region of 3448 cmÀ1 The stretching vibrational mode of e NH2 group can be found in the second region of 1300e1650 cmÀ1 4.1 Morphological and structural properties 4.2 Photoluminescence (PL) properties 4.1.1 Morphology Fig show FESEM images of the YVO4:Eu3ỵ NPs prepared by the controlling nanosynthesis method The mean diameter of a nanoparticle corresponds to the diameter of a spherical volume of the NPs The diameter of the YVO4:Eu3ỵ NPs heated at 200 C for h in Fig (a) is about 8e20 nm When the YVO4:Eu3ỵ NPs were functionalized with NH2 in (b), with SCN in (c), the average size increased to about 10e25 nm Some YVO4: Eu3ỵ samples were imaged by TEM with higher resolution Fig shows TEM images of the YVO4:Eu3ỵ nanophosphors (a) and YVO4:Eu3ỵ @ silica nanophosphors (b) From these images, we can suppose that the synthesized materials with YVO4:Eu3ỵ NPs at 200 C for h (Fig 2(a)) were formed in a nanoparticle shape The mean sizes of the YVO4:Eu3ỵ nano particles are about 8e20 nm in the diameter Fig 2(b) shows the silica-coated YVO4:Eu3ỵ nanoparticles have a clear core/shell structure When YVO4:Eu3ỵ were coated with silica using TEOS, the sizes of YVO4:Eu3ỵ nanophosphors became much larger, increasing diameter up to around 25 nm 4.1.2 Phase and structure The X-ray diffraction (XRD) pattern of the as prepared YVO4:Eu3ỵ NPs are investigated Fig shows X-ray diffraction pattern of the YVO4:Eu3ỵ NPs prepared at 200 C for h It can be seen that all of the diffraction peaks (2q): 18.8 , 25 , 33.5 , 49.8 , 57.9 , 62.8 , 64.8 , 70.3 and 74.2 are all a Wakefieldite e (Y) tetragonal phase of YVO4 and no other phases were detected The reference No.17-0341 was used for comparison 4.1.3 The FTIR spectra The FTIR spectra of the as synthesized and functionalized YVO4:Eu3ỵ NPs have been measured Fig shows the FTIR spectrum of YVO4:Eu3ỵ heated at 200 C for h (curve 1); TESCN (curve 2); YVO4:Eu3ỵ @ silica-SCN (curve 3); YVO4:Eu3ỵ @ silica eSCNBiotin (curve 4); APS (curve 5); and YVO4:Eu3ỵ @ silica-NH2 (curve 6) The room temperature, PL spectra of YVO4:Eu3ỵ, YVO4:Eu3ỵ @ silica, YVO4:Eu3ỵ @ silica-NH2 and YVO4:Eu3ỵ@ silica - SCN NPs were measured under 325 nm excitation (Fig 5) Under UV excitation, the as synthesized and functionalized YVO4:Eu3ỵ NPs both exhibit strong red luminescence with narrow bands corresponding to the intra-4f transitions of D0 e7 Fj (j ¼ 1, 2, 3, 4) Eu3ỵ The most intense peak at 619 nm corresponds to the D /7 F forced electric dipole transitions While the weak peaks at j 594, 652 and 702 nm correspond to the transitions of Do /7 F1 , D /7 F and D /7 F , respectively The D /7 F electric-dipole transitions is a hypersensitive transition, which is allowed only on the condition that the europium ion occupy a site without an inversion center and thus is very sensitive to the local environment It is deduced then that the Eu3ỵ ions in the YVO4:Eu3ỵ NPs occupy the sites without inversion symmetry, resulting in the high luminescence intensity at 619 nm The consider able fluorescence enhancement of 1.80 times was observed for silica-coated YVO4:Eu3ỵ NPs, indicating that the core/shell structures can play a double role; one for enhancing luminescence efficiency and the other for providing nanophosphors with better stability in water media, which ultimately facilitates the penetration of the NPs core into a biomedical environment As it is well known, for rare earth-doped materials, hydroxyl groups play an important role in fluorescence quenching When the NPs are dispersed in aqueous solutions or a water soluble nanosuspension, the surface of the NPs greatly adsorbs hydroxyl species After the YVO4:Eu3ỵ NPs cores were coated by an outer shell of silica, the emission intensity increased significantly This could be mainly due to the silica layer protecting the NPs core from water, which would effectively isolate the Eu3ỵ ions from water and therefore reduce the quenching effects of the hydroxyl group on luminescence yield In addition, surface defects play important roles in quenching the luminescence of nanophosphors due to the large surface-to-volume ratio Based on experimental and theoretical studies, many reports have confirmed that surface and interior environments are different in nanophosphors doped with Fig FESEM images of the nanophosphors of YVO4:Eu3ỵ (a), YVO4:Eu3ỵ @ silica - NH2 (b) and YVO4:Eu3ỵ @ silica - SCN (c) 298 T.T Huong et al / Journal of Science: Advanced Materials and Devices (2016) 295e300 Fig TEM images of the nanophosphors of YVO4:Eu3ỵ (a) and YVO4:Eu3ỵ @ silica (b) Fig XRD pattern of the YVO4:Eu3ỵ nanophosphors at 200 C for h Fig PL spectra of nanophosphors YVO4: Eu3ỵ, YVO4: Eu3ỵ @ silica, YVO4: Eu3ỵ @ silica-NH2 and YVO4: Eu3ỵ @ silica eSCN with lexc ẳ 325 nm Fig FTIR spectra of as synthesized YVO4:Eu3ỵ (1); TESCN (2); YVO4:Eu3ỵ @ silicaSCN (3); YVO4:Eu3ỵ @ silica-SCN-Biotin (4); APS (5) YVO4:Eu3ỵ @ silica-NH2 (6) rare earth [2,21,26] The situation was substantially changed, when the NPs were coated with a functional group shell such as amine (NH2) and thioxyanate (SCN) The decrease in uorescence intensity of YVO4:Eu3ỵ @ silica-NH2 and YVO4:Eu3ỵ @ silica-SCN is similarly observed in Fig It should be noted that the functional groups NH2 or SCN are strongly dipolar This could be responsible for reducing the luminescence intensity of the functionalized NPs On the other hand, it could be mainly due to the protection effect against water The influences of the shells and organic functionalization on the photoluminescent characterization of YVO4:Eu3ỵ nanomaterials is presented Due to the large surface to volume ratio of NPs their surface plays important roles on their optic properties Therefore the modification of the surface by sol gel coating technology can provide a large change in emission intensity of NPs The conditions used in sol gel deposition were chosen to optimize the fabrication of an outlayer that contained the functional group, with the aim to keep the emission properties as close to the as synthesized state as T.T Huong et al / Journal of Science: Advanced Materials and Devices (2016) 295e300 possible These nanoscale and higheemission characters demonstrate that the YVO4:Eu3ỵ nanoparticles functionalized by NH2/SCN have more potential application as a fluorescent label for studying bioactive molecules, cells and tissues The PL spectra of YVO4:Eu3ỵ@ silicae SCNeBiotin conjugates are presented in Fig They exhibit strong red luminescence with narrow bands corresponding to the intrae4f transitions of D0 e7 Fj (j ẳ 1, 2, 3, 4) Eu3ỵ These results revealed that the luminescent intensity was substantially changed when the nanoparticles YVO4:Eu3ỵcoated with a shell layer were linked with an organic group thioxyanate (SCN) with Biotin This is a promising result in sense of using YVO4:Eu3ỵ @ silica-SCN-Biotin conjugates for development of a fluorescent tool for biomedical analyses Conclusions 299 which indicates the great potential for these Eu nanophosphors as a fluorescence label agent for biological and biomedical systems This is a promising result in sense of using rare earth luminescent nanomaterials for development of fluorescent labeling analysis probes and technical tools in biochemistry, molecular biology and biomedicine Acknowledgements This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number of 103.06 - 2012.72 and partly support of National Key Lab of Electronic Materials and Devices in Institute of Materials Science, Vietnam Academy of Science and Technology References 3ỵ In summary, YVO4:Eu nanophosphors were synthesized successfully by the controlling nanosynthesis method The YVO4:Eu3ỵ NPs were functionalized by attaching a thiocyanate (eSCN) or amine (eNH2) group in conjunction with a silica coating process 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XRD pattern of the YVO4: Eu3ỵ nanophosphors at 200 C for h Fig PL spectra of nanophosphors YVO4: Eu3ỵ, YVO4: Eu3ỵ @ silica, YVO4: ... functionalization of YVO4: Eu3ỵ nanophosphors with NH2/ SCN was performed by using 3-aminopropyltrimetoxysilane (APS) with -NH2 group and 3-(Triethoxysilyl) propylthiocyanate (TESCN) with e SCN group,... volume of the NPs The diameter of the YVO4: Eu3ỵ NPs heated at 200 C for h in Fig (a) is about 8e20 nm When the YVO4: Eu3ỵ NPs were functionalized with NH2 in (b), with SCN in (c), the average size