Functionalized YVO4:Eu3þ nanophosphors with desirable properties for biomedical applications

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Original Article

Functionalized YVO

₄

:Eu

3

ỵ

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}
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:

YVO4:Eu3ỵ

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:Eu3ỵNPs 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:Eu3ỵNPs with Biotin via a direct reaction between
the functional groups or an intermediate linker. Under UVIS excitation, YVO4:Eu3ỵNPs exhibited strong
red luminescence with narrow bands corresponding to the intra 4f transitions of5_D

0e7Fj(jẳ 1, 2, 3, 4)
Eu3ỵ. The peaks were found at 594 nm (5_D

0e7F1), 619 nm (5D0e7F2), 652 nm (5D0e7F3) and 702 nm
(5_D

0e7F4) with the strongest emission at 619 nm. Theuorescence intensity and stability of the
func-tionalized YVO4:Eu3ỵNPs 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 ( />

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:Eu3ỵnanoparticles[8e13], LnPO4$H2O: Eu,

Tb nanomaterials[14e19]and ZrO2:Yb3ỵ, Er3ỵnanoparticles[20],

which have been developed for molecular biology, agrobiological
and medical applications.

In previous studies, there has been success in synthesizing
nanorods of Tb3ỵ, Eu3ỵions[21,22]and nanoparticles of YVO4:Eu3ỵ

[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:

Eu3ỵNPs. Then, the compatibility of YVO4:Eu3ỵnanomaterials with

a biological system is investigated. The structure, morphology and

* Corresponding author.

E-mail addresses:,(T.T. Huong).
Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices

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luminescence properties of the functionalized YVO4:Eu3ỵNPs 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:Eu3ỵnanophosphors are about 10e25 nm.

The functionalized YVO4:Eu3ỵNPs exhibit red luminescence with

narrow bands corresponding to the intra 4f transitions of5_D
0e7Fj

(j¼ 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
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:Eu3ỵ can be potentially

applied in a variety ofelds of application, especially in fluorescent
labeling for biochemical and biomedical application.

2. Experimental

2.1. Synthesis of YVO4:Eu3ỵnanophosphors

The YVO4:Eu3ỵ 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:Eu3ỵ solution was mixed by

magnetic stirring at room temperature for 24 h. The pH of this
solution was adjusted to the range of 11_{e12 by adding NH}4OH. 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:Eu3ỵnanophosphors 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 reux.
Then, 5 ml of the YVO4:Eu3ỵwith 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:Eu3ỵnanomaterials 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:Eu3ỵSCN products were stored in closing box at 4C

in a refrigerator.

3. Characterization methods

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

l

¼ 1.5406 Å in the range of 15_{ 2}

_q

_{ 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:Eu3ỵNPs 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:Eu3ỵNPs heated at 200C for 6 h in

Fig. 1(a) is about 8e20 nm. When the YVO4:Eu3ỵNPs were

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

increased to about 10e25 nm.

Some YVO4: Eu3ỵsamples were imaged by TEM with higher

resolution. Fig. 2 shows TEM images of the YVO4:Eu3ỵ

nano-phosphors (a) and YVO4:Eu3ỵ @ silica nanophosphors (b). From

these images, we can suppose that the synthesized materials with
YVO4:Eu3ỵNPs at 200C for 6 h (Fig 2(a)) were formed in a

nano-particle shape. The mean sizes of the YVO4:Eu3ỵnano particles are

about 8e20 nm in the diameter.Fig. 2(b) shows the silica-coated
YVO4:Eu3ỵnanoparticles have a clear core/shell structure. When

YVO4:Eu3ỵ were coated with silica using TEOS, the sizes of

YVO4:Eu3ỵnanophosphors 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:Eu3ỵ NPs are investigated. Fig. 3 shows X-ray diffraction

pattern of the YVO4:Eu3ỵNPs prepared at 200C for 6 h. It can be

seen that all of the diffraction peaks (2

q

): 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:Eu3ỵNPs have been measured.Fig. 4shows the FTIR

spec-trum of YVO4:Eu3ỵheated at 200C for 6 h (curve 1); TESCN (curve

2); YVO4:Eu3ỵ@ silica-SCN (curve 3); YVO4:Eu3ỵ@ silica

eSCN-Biotin (curve 4); APS (curve 5); and YVO4:Eu3ỵ @ silica-NH2

(curve 6).

There are three regions that can be de_{fined 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: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:Eu3ỵNPs both exhibit strong red luminescence with narrow

bands corresponding to the intra-4f transitions of5_D

0e7Fj(j¼ 1, 2,

3, 4) Eu3ỵ. The most intense peak at 619 nm corresponds to the

5_D

0/7Fjforced electric dipole transitions. While the weak peaks at

594, 652 and 702 nm correspond to the transitions of5_D
o/7F1,
5_D

0/7F3and5D0/7F4, 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 Eu3ỵ ions in the YVO4:Eu3ỵ 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:Eu3ỵNPs, 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:Eu3ỵ NPs cores were coated by an outer shell of

silica, the emission intensity increased signi_{ficantly. 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
theo-retical studies, many reports have confirmed that surface and
interior environments are different in nanophosphors doped with

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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:Eu3ỵ@ silica-NH2and YVO4:Eu3ỵ@ 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:Eu3ỵnanomaterials 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 YVO4:Eu3ỵ(a) and YVO4:Eu3ỵ@ silica (b).

Fig. 3. XRD pattern of the YVO4:Eu3ỵnanophosphors at 200C for 6 h.

Fig. 4. FTIR spectra of as synthesized YVO4:Eu3ỵ(1); TESCN (2); YVO4:Eu3ỵ@

silica-SCN (3); YVO4:Eu3ỵ@ silica-SCN-Biotin (4); APS (5) YVO4:Eu3ỵ@ silica-NH2(6).

Fig. 5. PL spectra of nanophosphors YVO4: Eu3ỵ, YVO4: Eu3ỵ@ silica, YVO4: Eu3ỵ@

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possible. These nanoscale and higheemission characters
demon-strate that the YVO4:Eu3ỵnanoparticles functionalized by NH2/SCN

have more potential application as afluorescent label for studying
bioactive molecules, cells and tissues. The PL spectra of
YVO4:Eu3ỵ@ silicae SCNeBiotin conjugates are presented inFig. 6.

They exhibit strong red luminescence with narrow bands
corre-sponding to the intrae4f transitions of5_D

0e7Fj(jẳ 1, 2, 3, 4) Eu3ỵ.

These results revealed that the luminescent intensity was
sub-stantially 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 auorescent tool
for biomedical analyses.

5. Conclusions

In summary, YVO4:Eu3ỵnanophosphors were synthesized

suc-cessfully 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.

Further conjugation with Biotin was successful in the synthesis. The
mean size of the functionalized YVO4:Eu3ỵ NPs was about

10_{e25 nm in diameter and the phase of the YVO}4:Eu3ỵNPs were

determined to be a Wakefieldite e (Y) tetragonal phase.

Under UVIS excitation, the functionalized YVO4:Eu3ỵNPs and

nano YVO4:Eu3ỵ@ silica - SCN-Biotin conjugates exhibit strongly

red luminescence with narrow bands corresponding to the intra 4f
transitions of 5_D

0e7Fj (j ẳ 1, 2, 3, 4) Eu3ỵ, with the strongest

emission at 619 nm. Thefluorescence intensity of the as
synthe-sized and functionalized YVO4:Eu3ỵ 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,
Functionalizedfluorescent 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:Eu3ỵ
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:Eu3ỵ 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 YVO4:Eu3ỵnano 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:Eu3ỵphosphor 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 Eu3ỵdoped porous
YVO4nanowires 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 TbPO4hierarchical
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,

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 YVO4:Eu3ỵ @ silica-SCN-Biotin conjugates with

</div>
<span class='text_page_counter'>(6)</span><div class='page_container' data-page=6>

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

properties of nanocrystalline ZrO2:Yb3ỵ, Er3ỵphosphors, 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, />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:Eu3ỵnanomaterials 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:Eu3ỵ 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.

</div>

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