Functionalized YVO4:Eu3þ nanophosphors with desirable properties for biomedical applications

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 bi[r]

Original Article

for biomedical applications

Tran Thu Huonga,*, Ha Thi Phuonga,b, Le Thi Vinha,c, Hoang Thi Khuyena,

a Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay Distr., Hanoi, Viet Nam

b Department of Chemistry, Hanoi Medical University, Viet Nam

c Department of Chemistry, Hanoi University of Mining and Geology, Viet Nam

d Duy Tan University, K7/25 Quang Trung, Da Nang, Viet Nam

a r t i c l e i n f o

Article history:

Received 19 July 2016

Received in revised form

28 July 2016

Accepted 28 July 2016

Available online 5 August 2016

Keywords:

YVO 4 :Eu3þ

Nanophosphors

Fluorescent label

Functionalization

Conjugation

a b s t r a c t

Highly luminescent nanophosphors (NPs) containing rare earth (RE) ions were successfully prepared by careful control of nanosynthesis The YVO4:Eu3þNPs formed core/shell structures with sizes from 10 nm

to 25 nm The NPs were functionalized with biocompatible groups such as OH, NH2and SCN A chemical coupling reaction connected the functionalized YVO4:Eu3þNPs with Biotin via a direct reaction between the functional groups or an intermediate linker Under UVIS excitation, YVO4:Eu3þNPs exhibited strong red luminescence with narrow bands corresponding to the intra 4f transitions of5D0e7Fj(j¼ 1, 2, 3, 4)

Eu3þ The peaks were found at 594 nm (5D0e7F1), 619 nm (5D0e7F2), 652 nm (5D0e7F3) and 702 nm (5D0e7F4) with the strongest emission at 619 nm Thefluorescence intensity and stability of the func-tionalized YVO4:Eu3þNPs have been increased This is a promising result in sense of using the conjugates

of YVO4:Eu3þ 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/)

1 Introduction

Detection analysis of biomolecules is crucial for many

applica-tions in biochemistry, molecular biology and medicine Typical

analytical methods such asfluorescent 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

devel-opment of new probes, either for biomolecule labeling or detection

of an intracellular signaling species

Among the newly developedfluorecent 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

earth ions with high luminescent efficiency up to several tens of percent such as YVO4:Eu3þnanoparticles[8e13], LnPO4$H2O: Eu,

Tb nanomaterials[14e19]and ZrO2:Yb3þ, Er3þnanoparticles[20], which have been developed for molecular biology, agrobiological and medical applications

In previous studies, there has been success in synthesizing nanorods of Tb3þ, Eu3þions[21,22]and nanoparticles of YVO4:Eu3þ

[23,24] The nanoscale and high-emission characteristics of these nanomaterials are more effective for ultrahigh sensitivefluorescent label for biomolecules, cell and tissue

For the biological applications, surface functionalization of the nanomaterials is an important step The objective isfirst 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 prop-erties of functionalized nanomaterials should not be lost Therefore,

in this report, focus is paid on the surface functionalization of YVO4:

Eu3þNPs Then, the compatibility of YVO4:Eu3þnanomaterials with

a biological system is investigated The structure, morphology and

* Corresponding author.

E-mail addresses: tthuongims@gmail.com , huongtt@ims.vast.vn (T.T Huong).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

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

Journal of Science: Advanced Materials and Devices 1 (2016) 295e300

luminescence properties of the functionalized YVO4:Eu3þNPs 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:Eu3þnanophosphors are about 10e25 nm

The functionalized YVO4:Eu3þNPs exhibit red luminescence with

narrow bands corresponding to the intra 4f transitions of5D0e7Fj

(j¼ 1, 2, 3, 4) Eu3 þ.

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

immune-reactions 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

bioac-tive molecule linked nanoparicles YVO4:Eu3þ can be potentially

applied in a variety offields of application, especially in fluorescent

labeling for biochemical and biomedical application

2 Experimental

2.1 Synthesis of YVO4:Eu3þnanophosphors

The YVO4:Eu3þ NPs were prepared by the controlling

nano-synthesis method In a typical nano-synthesis, 0.55 g sodium

orthova-nadate Na3VO490% (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-bottomedflask This was followed

by magnetic stirring for 60 min 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 200C 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 60C for 6 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:Eu3þ 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 Thefinal products were

dried at 60C 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

ma-terials 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

applica-tions 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 3-Aminopropyltrimethoxysilane reactive portion contains a trime-thoxy group Thus, the trimetrime-thoxy 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 cova-lently 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:Eu3þnanophosphors with NH2/ SCN was performed by using 3-aminopropyltrimetoxysilane (APS) with -NH2group and 3-(Triethoxysilyl) propylthiocyanate (TESCN) withe SCN group, respectively In these typical syntheses, 22.5 ml

of absolute ethanol and 2 ml of APTMS (TESCN) were put in a

100 ml three-neckedflask under magnetic stirring at room tem-perature for 30 min The solution is heated up to 60C under reflux Then, 5 ml of the YVO4:Eu3þwith silica shell nanomaterial solution

at pH 7 is added drop wise The reaction time is about 5 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) Thefinal products were again washed with deionized water and then dried at 60C 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:Eu3þnanomaterials solution and glutaralde-hyde were dispersed in vanadate buffered saline (PBS, 0.1 M, pH 5) with concentration of 5 gl1 The above solution is added to different concentrations of Biotin (Aldrich) These reaction mix-tures were incubated at 30C for 4 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:Eu3þSCN products were stored in closing box at 4C

in a refrigerator

3 Characterization methods The morphology of the as-synthesized samples was observed by usingfield emission scanning electron microscopy (FE-SEM, Hita-chi, S-4800) and transmission electron microscopy (TEM, JEM-1010) X-ray diffraction (XRD) measurements of the products

T.T Huong et al / Journal of Science: Advanced Materials and Devices 1 (2016) 295e300 296

were performed on an X-ray diffractometer (Siemens D5000 with

l¼ 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)

4 Results and discussion

4.1 Morphological and structural properties

4.1.1 Morphology

Fig 1show FESEM images of the YVO4:Eu3þNPs prepared by the

controlling nanosynthesis method The mean diameter of a

nano-particle corresponds to the diameter of a spherical volume of the

NPs The diameter of the YVO4:Eu3þNPs heated at 200C for 6 h in

Fig 1(a) is about 8e20 nm When the YVO4:Eu3þNPs were

func-tionalized with NH2 in (b), with SCN in (c), the average size

increased to about 10e25 nm

Some YVO4: Eu3þsamples were imaged by TEM with higher

resolution Fig 2 shows TEM images of the YVO4:Eu3þ

nano-phosphors (a) and YVO4:Eu3þ @ silica nanophosphors (b) From

these images, we can suppose that the synthesized materials with

YVO4:Eu3þNPs at 200C for 6 h (Fig 2(a)) were formed in a

nano-particle shape The mean sizes of the YVO4:Eu3þnano particles are

about 8e20 nm in the diameter.Fig 2(b) shows the silica-coated

YVO4:Eu3þnanoparticles have a clear core/shell structure When

YVO4:Eu3þ were coated with silica using TEOS, the sizes of

YVO4:Eu3þnanophosphors became much larger, increasing

diam-eter up to around 25 nm

4.1.2 Phase and structure

The X-ray diffraction (XRD) pattern of the as prepared

YVO4:Eu3þ NPs are investigated Fig 3 shows X-ray diffraction

pattern of the YVO4:Eu3þNPs prepared at 200C for 6 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 YVO4and 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:Eu3þNPs have been measured.Fig 4shows the FTIR

spec-trum of YVO4:Eu3þheated at 200C for 6 h (curve 1); TESCN (curve

2); YVO4:Eu3þ@ silica-SCN (curve 3); YVO4:Eu3þ@ silica

eSCN-Biotin (curve 4); APS (curve 5); and YVO4:Eu3þ @ silica-NH2

(curve 6)

There are three regions that can be defined in the spectrum, one from 2800 cm1 to 3400 cm1, the second in the range of

1300e1650 cm1, and the third in the longer wavelength range from 400 cm1to 900 cm1 In thefirst region, a peak at 2960 cm1 can be assigned to the CeH stretching vibrational mode Two other peaks are found at 3300 cm1and 2854 cm1(indicating the NH2, eCeNH2stretching vibrational mode) The vibration of the OeH group was found at a higher wavenumber in the region of

3448 cm1 The stretching vibrational mode ofe NH2group can be found in the second region of 1300e1650 cm1

4.2 Photoluminescence (PL) properties The room temperature, PL spectra of YVO4:Eu3þ, YVO4:Eu3þ@ silica, YVO4:Eu3þ@ silica-NH2 and YVO4:Eu3þ@ silica - SCN NPs were measured under 325 nm excitation (Fig 5)

Under UV excitation, the as synthesized and functionalized YVO4:Eu3þNPs both exhibit strong red luminescence with narrow bands corresponding to the intra-4f transitions of5D0e7Fj(j¼ 1, 2,

3, 4) Eu3þ The most intense peak at 619 nm corresponds to the

5D0/7Fjforced electric dipole transitions While the weak peaks at

594, 652 and 702 nm correspond to the transitions of5Do/7F1,

5D0/7F3and5D0/7F4, respectively The5D0/7F2electric-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 Eu3þ ions in the YVO4:Eu3þ NPs occupy the sites without inversion symmetry, resulting in the high luminescence intensity at 619 nm The consider ablefluorescence enhancement of 1.80 times was observed for silica-coated YVO4:Eu3þNPs, 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 influorescence quenching When the NPs are dispersed in aqueous solutions or a water soluble nano-suspension, the surface of the NPs greatly adsorbs hydroxyl species After the YVO4:Eu3þ 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 Eu3þ 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 theo-retical studies, many reports have confirmed that surface and interior environments are different in nanophosphors doped with

T.T Huong et al / Journal of Science: Advanced Materials and Devices 1 (2016) 295e300 297

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 fluorescence

in-tensity of YVO4:Eu3þ@ silica-NH2and YVO4:Eu3þ@ silica-SCN is

similarly observed inFig 5 It should be noted that the functional

groups NH2or 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:Eu3þnanomaterials 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

Fig 2 TEM images of the nanophosphors of YVO 4 :Eu3þ(a) and YVO 4 :Eu3þ@ silica (b).

Fig 3 XRD pattern of the YVO 4 :Eu3þnanophosphors at 200  C for 6 h.

Fig 4 FTIR spectra of as synthesized YVO 4 :Eu3þ(1); TESCN (2); YVO 4 :Eu3þ@

silica-SCN (3); YVO 4 :Eu3þ@ silica-SCN-Biotin (4); APS (5) YVO 4 :Eu3þ@ silica-NH 2 (6).

Fig 5 PL spectra of nanophosphors YVO 4 : Eu3þ, YVO 4 : Eu3þ@ silica, YVO 4 : Eu3þ@ silica-NH 2 and YVO 4 : Eu3þ@ silica eSCN withlexc ¼ 325 nm.

T.T Huong et al / Journal of Science: Advanced Materials and Devices 1 (2016) 295e300 298

possible These nanoscale and higheemission characters

demon-strate that the YVO4:Eu3þnanoparticles functionalized by NH2/SCN

have more potential application as afluorescent label for studying

bioactive molecules, cells and tissues The PL spectra of

YVO4:Eu3þ@ silicae SCNeBiotin conjugates are presented inFig 6

They exhibit strong red luminescence with narrow bands

corre-sponding to the intrae4f transitions of5D0e7Fj(j¼ 1, 2, 3, 4) Eu3þ

These results revealed that the luminescent intensity was

sub-stantially changed when the nanoparticles YVO4:Eu3þcoated with a

shell layer were linked with an organic group thioxyanate (SCN)

with Biotin This is a promising result in sense of using YVO4:Eu3þ@

silica-SCN-Biotin conjugates for development of afluorescent tool

for biomedical analyses

5 Conclusions

In summary, YVO4:Eu3þnanophosphors were synthesized

suc-cessfully by the controlling nanosynthesis method The YVO4:Eu3þ

NPs were functionalized by attaching a thiocyanate (eSCN) or

amine (eNH2) group in conjunction with a silica coating process

Further conjugation with Biotin was successful in the synthesis The

mean size of the functionalized YVO4:Eu3þ NPs was about

10e25 nm in diameter and the phase of the YVO4:Eu3þNPs were

determined to be a Wakefieldite e (Y) tetragonal phase

Under UVIS excitation, the functionalized YVO4:Eu3þNPs and

nano YVO4:Eu3þ@ silica - SCN-Biotin conjugates exhibit strongly

red luminescence with narrow bands corresponding to the intra 4f

transitions of 5D0e7Fj (j ¼ 1, 2, 3, 4) Eu3 þ, with the strongest

emission at 619 nm Thefluorescence intensity of the as

synthe-sized and functionalized YVO4:Eu3þ NPs were nearly identical,

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

[1] C Bouzigues, T Gacoin, A Alexandrou, Biological applications of rare-earth based nanoparticles, ACS Nano 5 (11) (2011) 8488e8505

[2] D Giaume, M Poggi, D Casanova, G Mialon, K Lahlil, A Alexandrou,

T Gacoin, J.-P Boilot, Organic functionalization of luminescent oxide nano-phosphors toward their application as biological probes, Langmuir 24 (2008) 11018e11026

[3] F Wang, W.B Tan, Y Zhang, X Fan, M Wang, Luminescent nanomaterials for biological labeling, Nanotechnology 17 (2006) R1

[4] S.N Misra, M.A Gagnani, I.M Devi, R.S Shukla, Biological and clinical aspects

of lanthanide coordination compounds, Bioinorg Chem Appl 2 (3e4) (2004) 155e192

[5] E Beaurepaire, V Buissette, M.-P Sauviat, D Giaume, K Lahlil, A Mercuri,

D Casanova, A Huignard, J.-L Martin, T Gacoin, J.-P Boilot, A Alexandrou, Functionalized fluorescent oxide nanoparticles: artificial toxins for sodium channel targeting and imaging at the single-molecule level, Nano Lett 4 (2004) 2079e2083

[6] J Feng, G Shan, A Maquieira, M.E Koivunen, B Guo, B.D Hammock, I.M Kennedy, Functionalized europium oxide nanoparticles used as a fluo-rescent label in an immunoassay for atrazine, Anal Chem 75 (2003) 5282e5286

[7] M Luo, T.Y Sun, J.H Wang, P Yang, L Gan, L.L Liang, X.F Yu, X.H Gong, Synthesis of carboxyl-capped and bright YVO4: Eu, Bi nanoparticles and their applications in immunochromatographic test strip assay, Mater Res Bull 48 (2013) 4454e4459

[8] I.S Cho, G.K Choi, J.S An, J Kim, K.S Hong, Microstructure and microwave dielectric properties of rare earth orthophosphates, RePO4 (Re¼La, Ce, Nd, Sm,

Tb, Dy, Y, Yb), Mater Res Bull 44 (2009) 173e178 [9] Y Fu, H Jiu, L Zhang, Y Sun, Y Wang, Template-directed synthesis and luminescence properties of YVO4 :Eu hollow, Mater Lett 91 (2013) 265e267

[10] L Tang, W Gui, K Ding, N Chen, G Du, Ion exchanged YVO4:Eu3þ nano-crystals and their strong luminescence enhanced by energy transfer of the noyltrifluoroacetone ligands, J Alloys Compd 590 (2014) 277e282 [11] Y.S Cho, Y.D Huh, Preparation of transparent red-emitting YVO4: Eu nano-phosphor suspensions, Bull Korean Chem Soc 32 (1) (2011) 335 [12] T Taniguchi, T Watanabe, K Katsumata, K Okada, N Matsushita, Syn-thesis of amphipathic YVO4:Eu3þ nanophosphors by oleate-modified nucleation/hydrothermal-growth process, J Phys Chem C 114 (9) (2010) 3763e3769

[13] B.K Grandhe, V.R Bandi, K Jang, S Ramaprabhu, S.S Yi, Jung-Hyun Jeong, Enhanced red emission from YVO 4 :Eu3þnano phosphors prepared by simple co-precipitation method, Electron Mater Lett 7 (2) (2011) 161e165, http:// dx.doi.org/10.1007/s13391-011-0613-x

[14] C Jang, S.M Lee, K.C Choi, Optical characteristics of YVO4:Eu3þphosphor in close proximity to Ag nanofilm: emitting layer for mirror-type displays, Opt Express 20 (3) (2012) 2143e2148

[15] C Mu, J He, Synthesis and luminescence properties of Eu3þdoped porous YVO4 nanowires by chemical precipitation in nanochannels, Mater Res Bull.

47 (2012) 491e496 [16] M Yang, H You, Y Song, Y Huang, G Jia, K Liu, Y Zheng, L Zhang, H Zhang, Synthesis and luminescence properties of Sheaflike TbPO4 hierarchical ar-chitectures with different phase structures, J Phys Chem C 113 (2009) 20173e20177

[17] L Yu, H Liu, The progress of photoluminescent properties of rare earth ions doped phosphate one dimensional nanocrystals, J Nanomater (2010) 6,

http://dx.doi.org/10.1155/2010/461309 Article ID 461309.

[18] K.L Wong, G.L Law, M.B Murphy, P.A Tanner, W.T Wong, P.K.S Lam, M.H.W Lam, Functionalized europium nanorods for in vitro imaging, Inorg Chem 47 (12) (2008) 5190e5196

[19] J Bao, R Yu, J Zhang, X Yang, D Wang, J Deng, J Chen, X Xing, Controlled synthesis of terbium orthophosphate spindle-like hierarchical nano-structures with improved photoluminescence, Eur J Inorg Chem 16 (2009) 2388e2392

Fig 6 PL spectra of nano YVO 4 :Eu3þ @ silica-SCN-Biotin conjugates with

l ¼ 325 nm.

T.T Huong et al / Journal of Science: Advanced Materials and Devices 1 (2016) 295e300 299

[20] I Hypp€anen, J H€ols€a, J Kankare, M Lastusaari, L Pihlgren, Up conversion

properties of nanocrystalline ZrO2:Yb3þ, Er3þphosphors, J Nanomater 2007

(2007) 8 Article ID 16391

[21] T.T Huong, L.T Vinh, T.K Anh, H.T Khuyen, H.T Phuong, L.Q Minh,

Fabri-cation and Optical characterization of multimorphological nanostructured

materials containing Eu(III) in phosphate matrices for biomedical

applica-tion, New J Chem 38 (2014) 2114e2119, http://dx.doi.org/10.1039/

c3nj01206a

[22] Thu Huong Tran, Kim Anh Tran, Thi Khuyen Hoang, Thu Hien Pham, Quoc

Minh Le, Fabrication and properties of Terbium photphate nanorods, Adv Nat.

Sci Nanosci Nanotechnol 3 (2012) 015010 (4pp)

[23] T.T Huong, V.D Tu, T.K Anh, L.T Vinh, L.Q Minh, Fabrication and charac-terization of YVO4:Eu3þnanomaterials by the microwave technique, J Rare Earths 29 (12) (2011) 1137e1141

[24] T.T Huong, L T.Vinh, H.T Phuong, H.T Khuyen, T.K Anh, V.D Tu, L.Q Minh, Controlled fabrication of the strong emission YVO4:Eu3þ nanoparticles and nanowires by microwave assisted chemical synthesis, J Lumin 173 (2016) 89e93 [25] G.T Hermanson, Bioconjugate Techniques, second ed., Elsevier, New York,

2008 ISBN: 978-0-12-370501-3 [26] J Kang, X.Y Zhang, L.D Sun, X.X Zhang, Bioconjugation of functionalized fluorescent YVO4:Eu nanocrystals with BSA for immunoassay, Talanta 71 (2007) 1186e1191

T.T Huong et al / Journal of Science: Advanced Materials and Devices 1 (2016) 295e300 300