Optimization of Tb3+/Gd3+ Molar Ratio for Rapid Detection of Naja Atra Cobra Venom by Immunoglobulin G-Conjugated GdPO4·nH2O : Tb3+ Nanorods

Lien, Pham Thi; Huong, Nguyen Thanh; Huong, Tran Thu; Khuyen, Hoang Thi; Anh, Nguyen Thi Ngoc; Van, Nguyen Duc; Tuan, Nguyen Ngoc; Nghia, Vu Xuan; Minh, Le Quoc

doi:https://doi.org/10.1155/2019/3858439

Journal of Nanomaterials

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Abstract Introduction Materials and Methods Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

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Hydrothermal Synthesis of Nanomaterials

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Research Article | Open Access

Volume 2019 | Article ID 3858439 | https://doi.org/10.1155/2019/3858439

Optimization of Tb³⁺/Gd³⁺ Molar Ratio for Rapid Detection of Naja Atra Cobra Venom by Immunoglobulin G-Conjugated GdPO₄·nH₂O : Tb³⁺ Nanorods

Pham Thi Lien,^1,2Nguyen Thanh Huong ,^1,2Tran Thu Huong,^1,2Hoang Thi Khuyen,^1,2Nguyen Thi Ngoc Anh,^1,2Nguyen Duc Van,¹Nguyen Ngoc Tuan,³Vu Xuan Nghia,³and Le Quoc Minh^1,2,4

Guest Editor: Zhen Yu

Received01 Feb 2019

Accepted30 Apr 2019

Published16 May 2019

Abstract

In this report, GdPO₄·nH₂O and Tb³⁺-doped GdPO₄·nH₂O nanorods@silica-NH₂ conjugated with IgG antibody were synthesized by applying hydrothermal, sol-gel, and coprecipitation methods successively. The effects of Tb³⁺/Gd³⁺ molar ratios of reactants on the size, morphology, and luminescence of the synthesized samples were also investigated. For the optimized GdPO₄·nH₂O : Tb³⁺ sample, uniform nanorods sizing from 10 to 30 nm in diameter and from 200 to 300 nm in length were obtained with the strongest luminescence in green color with narrow bands under the UV excitation (325 nm). The results revealed that, after being coated with silica-NH₂ and conjugated with IgG antibody, all luminescence characteristic peaks of GdPO₄·nH₂O : Tb³⁺ corresponding to the process of energy transfer from Gd³⁺ to Tb³⁺ and then the emission from ⁵D₄ → ⁷F_J () of Tb³⁺ were still clearly observed. The initial results of using the optimized Tb³⁺-doped GdPO₄·nH₂O nanorods@silica-NH₂ conjugated with IgG antibody for rapid selective detection of Naja atra cobra venom were also reported.

1. Introduction

Rare earth-containing luminescent nanomaterials have drawn a special interest for telecommunication, imaging, lightning, fluorescent security labelling, and biomedical applications due to their attractive physical and optical properties, biocompatibility, environmentally friendly characteristics, and nontoxicity and especially due to their high efficiency [1–18]. These materials exhibited outstanding performances such as strong, stable luminescent intensity with a large Stock shift, narrow peak width, and long luminescent lifetime [6]. This luminescent lifetime of these materials is significantly longer, up to milliseconds, in comparison to that of quantum dots or organic luminescent materials. That enables to minimize intrinsic luminescent background emitted from biological samples by employing the time-resolved signal recording process. Many targeted applications such as fluorescent labelling [19], drug delivery [20], and imaging for detecting biological species like virus, bacteria, cell, DNA, RNA molecules, or proteins [15, 18, 19] of new hybrid nanophosphors containing rare-earth elements (Eu, Tb, and Er) with various host materials (GdPO₄, Gd₂O₃, YVO₄, and NaYF₄) have been carried out so far [20–25]. For the synthesis of these materials, numerous chemical methods of luminescent nanomaterials containing rare earth elements have been used such as coprecipitation [5], sol-gel Pechini [6], and hydrothermal/solvothermal method [26–29]. Among these hybrid nanophosphors, Tb³⁺-doped GdPO₄·nH₂O nanomaterials are found to be one of the most promising candidates for these abovementioned applications due to these nanomaterials that exhibit strong luminescent intensity, paramagnetic behavior, no toxicity, and ability to minimize photobleaching and photochemical decomposition [22, 23, 30–33]. It was reported in literature that Tb³⁺-doped GdPO₄·nH₂O nanomaterials were usually synthesized by the hydrothermal method and the effects of the doping concentration on their luminescent properties were already performed [27, 31–33]. However, it was indicated that, to obtain the highest luminescence intensity of Tb³⁺-doped GdPO₄·nH₂O, the doping Tb³⁺ concentration depended strongly on the hydrothermal synthesis parameters and no optimized procedures was provided. Furthermore, these materials have not been applied in biomedical applications to date. In details, the silica coating of Tb³⁺-doped GdPO₄·nH₂O followed by functionalization and conjugation with antibody have not been investigated.

In this paper, GdPO₄·nH₂O : Tb³⁺ nanorods were synthesized by controlling hydrothermal process and the effects of the Tb³⁺/Gd³⁺ molar ratio on the nanorod size, morphology, and luminescence of the as-prepared products were also investigated systematically. Moreover, GdPO₄·nH₂O : Tb³⁺ nanorods have been covered by silica as a shell, functionalized with NH₂ and conjugated with a specific antibody (IgG) to enable to set up a fluorescent immunoassay procedure for rapid detection and microscopic bioimaging Naja atra cobra venom in vitro.

2. Materials and Methods

All used chemicals were of analytical grade, including Gd(NO₃)₃·6H₂O (Sigma-Aldrich, 99.9%), Tb(NO₃)₃·6H₂O (Sigma-Aldrich, 99.9%), NH₄H₂PO₄ (Merck), and NH₄OH 28% (Merck). The deionized (DI) water was used through all the preparation steps of nanomaterials. Naja atra cobra venom antigen was supplied by the Immunology Department of Vietnam Military Medical University.

2.1. Synthesis of GdPO₄·nH₂O : Tb³⁺ Materials

For the synthesis of GdPO₄·nH₂O : Tb³⁺ nanorods, 20 ml of 0.1 M NH₄H₂PO₄ solution was added into a 100 ml round-bottom flask containing 0.05 M Gd(NO₃)₃ and 0.05 M Tb(NO₃)₃ with molar ratios of Tb⁺³/Gd³⁺ are 1%, 3%, 5%, 7%, and 9% during stirring. The pH value of the obtained solution was adjusted to 2 by using 1 M NH₄OH solution. After being stirred for 1 h, the mixture was transferred into a 100 ml teflon-lined stainless-steel autoclave. The autoclave was sealed and heated at 200°C for 24 hours. The white precipitate was centrifuged, washed with DI water and ethanol, and dried at 70°C for 24 hours.

2.2. GdPO₄·nH₂O : Tb³⁺ Materials Coated with Silica Layer via the Sol-Gel Process

Briefly, 0.1 g GdPO₄·nH₂O : Tb³⁺ nanorods were dispersed in 20 ml of ethanol (EtOH) by using a Vortex mixing equipment to obtain mixture A. Subsequently, 60 μl of deionized water and 60 μl of CH₃COOH were added into a 250 ml round-bottom flask containing 50 ml of EtOH and 30 μl TEOS during stirring for 15 minutes to receive mixture B. Mixture A was then dropped into mixture B, and the final mixture was stirred for 24 hours. Finally, the resulting precipitate was centrifuged and washed with distilled water and ethanol several times. The white precipitate was dispersed in 30 ml EtOH solution for the next functionalization process.

2.3. The Surface Functionalization with –NH₂ (GdPO₄·nH₂O : Tb³⁺@Silica-NH₂)

For the surface functionalization of GdPO₄·nH₂O : Tb³⁺ by the NH₂ group, 20 μl APTES (3-aminopropyltriethoxysilane) and 40 μl CH₃COOH was added into a 250 ml round-bottom flask containing 50 ml of EtOH. The solution was stirred by magnetic stirring at room temperature for 2 hours. The mixture of 0.3 g GdPO₄·nH₂O : Tb³⁺ and 30 ml EtOH was then dropped into the above solution, and the stirring was remained for 2 hours. The resulting products were collected, centrifuged, and washed with ethanol and distilled water several times. The white precipitate was kept in 30 ml deionized water for the binding process with biological elements.

2.4. Conjugation between GdPO₄·nH₂O : Tb³⁺@Silica-NH₂ with Specific IgG Antibody to Detect Naja Atra Cobra Venom

Glutaraldehyde (GDA) was used to form a complex between GdPO₄·nH₂O : Tb³⁺@silica-NH₂ with IgG antibody due to the fact that it is a homobifunctional cross-linker to bridge both homogenous aldehyde groups, resulting in conjugation.

The specific IgG antibody conjugation process is as follows: The GdPO₄·nH₂O : Tb³⁺@silica-NH₂ solution obtained above (in 2.3.) was centrifuged and cleaned three times with 25 mM sodium phosphate (pH 7.0). The resulting products were dissolved in 5 ml of sodium phosphate solution. Then, 10 ml of glutaraldehyde 0.5% was added and mixed by a vortex mixer for 1 hour at room temperature to form an uniform suspension. 10 μl of anti-venom rabbit antibody was mixed with 100 μl of the solution obtained above in a ratio of 1 : 10 then mixed well and kept at room temperature for 2 to 4 hours.

Excess glutaraldehyde linkers were blocked by adding 1.5 M ethanolamine in phosphate-buffered saline (PBS) reacting with 10% volume of GdPO₄·nH₂O : Tb³⁺@silica-NH₂-IgG solution for 2 hours at room temperature. The residual ethanolamine was then removed by washing and centrifugation three times with 0.1 mM PBS solution. The resulting products were dissolved in 5 ml of 25 mM sodium phosphate (pH 7.0) and stored at 4°C for the next steps. The final obtained product was GdPO₄·nH₂O : Tb³⁺@silica-NH₂-IgG solution.

2.5. Detection of Cobra Venom by the Nanorods-Antibodies (GdPO₄·nH₂O : Tb³⁺@Silica-NH₂-IgG)

Cobra venom for detection was conducted as follows: six-well plates (polystyrene plate) were coated with 50 μl/well of Naja atra venom (20 μg/ml) then diluted in 0.05 M carbonate buffer at . After incubation at 4°C for 12 h, the plates were washed three times with 0.15 M PBS–0.05% Tween-20 (PT) and blocked with 50 μl/well PBS, 1% BSA, 0.05% Tween-20, and 0.02% sodium azide (PBTN) for 1 hour at room temperature. After three times of washing cycle in PT, 50 μl antibody nanorods diluted in PBTN were added into each well and incubated at room temperature for 2 hours. Specific antibody-bound GdPO₄·nH₂O : Tb³⁺@silica-NH₂ nanorods were used to bind cobra venom antigens. After the plates were washed four times with PT to remove the nonsticking components, the emission color of the nanorods was used to detect the presence of specific expressed venom found under excitation UV light.

2.6. Measurements

The morphology of these nanomaterials was observed by field emission scanning electron microscopy (FESEM, Hitachi S4800). The structure of the materials was determined with the X-ray diffraction system (Siemens D5000). The fluorescence emission and excitation spectra of the materials were measured with a high-resolution microscope (FL 3-22 HORIBA). The ability to detect venom of the nanoparticles is indicated by emitting a green color under a fluorescence microscope (ZEISS Primo Star iLED).

3. Results and Discussion

3.1. The Morphology of Synthesized Samples

The FESEM images of GdPO₄·nH₂O : Tb³⁺ with different molar ratios of Tb³⁺/Gd³⁺ from 1 to 9 mol % are given in Figure 1. FESEM images of GdPO₄·nH₂O : Tb³⁺ show no significant change in the shape and size of the nanorods with different molar ratios.

(a) GdPO4

(b) GdTb1%

(c) GdTb3%

(d) GdTb5%

(e) GdTb7%

(f) GdTb9%

It can be seen that GdPO₄·nH₂O : Tb³⁺ nanorods with the molar ratio of 7% are the most uniform rods (average length of 300–500 nm and width of 10-30 nm).

3.2. X-Ray Diffraction Investigation of GdPO₄·nH₂O : Tb³⁺

Figure 2 shows that the all diffraction peaks of GdPO₄·nH₂O and GdPO₄·nH₂O : Tb³⁺ have high intensity, narrow width at 2θ angles of 15.24, 20.61, 25.81, 30.00, 32.19, 38.71, 43.09, 48.1, 49.86, and 53.15 and can be distinctly indexed to a standard pattern coded 98-004-3396 of gadolinium orthophosphate hydrate.

3.3. Photoluminescence Properties

In order to investigate the luminescence intensity and determine the radiative transfer between the energy levels of the electrons in these materials, the excitation and fluorescence spectra of these samples were measured under 543 nm and 272 nm excitations, respectively (Figure 3).

(a)

(b)

In the excitation spectra of GdPO₄·nH₂O : Tb³⁺ (Figure 3(a)), the characteristic transition peaks exist around 310 nm and 272 nm which belong to ⁶P_J → ⁸S_7/2 and ⁸S_7/2 → ⁶I_J of Gd³⁺, respectively [34]. The energy level between ⁶P_J and ⁸S_7/2 of Gd³⁺ is similar to Tb³⁺, so that the excitation energy of Gd³⁺ can be transferred to Tb³⁺. Under the 272 nm excitation, the photoluminescence spectra of the GdPO₄·nH₂O : Tb³⁺ (1-9%) samples emitted in the green light region with the characteristic transitions of Tb³⁺ : ⁵D₄ → ⁷F_n (, 5, 4, 3) (shown in Figure 3(b)). The transition of ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅, ⁵D₄ → ⁷F₄, and ⁵D₄ → ⁷F₃ of Tb³⁺ can be observed at 488, 543, 586, and 620 nm, respectively, and the strongest emission peak was found at 543 nm. The results showed that GdPO₄·nH₂O : Tb³⁺ nanorods with 7% exhibit the strongest green luminescence. It can be seen that the fluorescence of GdPO₄·nH₂O doped with Tb³⁺ was greatly enhanced due to the energy transfer process from Gd³⁺ to Tb³⁺ [34, 35]. The uniform nanorods were obtained by changing the ratios of Gd³⁺ and Tb³⁺ which were functionalized and dispersed in the water and ready for biological applications.

Figure 4 presents the photoluminescence spectra of nanorod solutions: GdPO₄·nH₂O : Tb³⁺ (1); GdPO₄·nH₂O : Tb³⁺@silica (2), GdPO₄·nH₂O : Tb³⁺@silica-NH₂ (3), and GdPO₄·nH₂O : Tb³⁺@silica-NH₂-IgG (4) under 355 nm excitation. The green emission at 491, 544, 588, and 620 nm corresponding to ⁵D₄ → ⁷F₆, ⁵D₄ → ⁷F₅, ⁵D₄ → ⁷F₄, and ⁵D₄ → ⁷F₃ of Tb³⁺ transitions of Tb³⁺ ions, respectively. The emission intensity of these samples decreases with the functional steps of GdPO₄·nH₂O : Tb³⁺ nanorods. However, luminescent intensity is not much changed after conjugating with IgG and the maximum emission peak is found at 543 nm. This is the good condition for labelling the cobra venom antigen identification in the next steps.

3.4. IR Properties

The functionalized nanorods were analyzed by IR spectra using the Nexus 670 infrared spectrometer (Nicolet).

The infrared spectra of GdPO₄·nH₂O : Tb³⁺ (a), GdPO₄·nH₂O : Tb³⁺@silica (b), GdPO₄·nH₂O : Tb³⁺@silica-NH₂ (c), and GdPO₄·nH₂O : Tb³⁺@silica-NH₂-IgG (d) samples are presented in Figure 5. It can be observed that oscillations of the O-H bond were found at around 1600 cm^-1 and near 3500 cm^-1 in lines (a) and (b). Oscillations at 545 and 622 cm^-1 are assigned to the stretching vibrations of (PO₄)^3– [36]. The stretching vibrations of the C-H bond were observed at 2898 cm^-1, 2976 cm^-1 and 2884 cm^-1, 2941 cm^-1 corresponding to GdPO₄·nH₂O : Tb³⁺@silica-NH₂ (c) and GdPO₄·nH₂O : Tb³⁺@silica-NH₂-IgG (d) samples. In these samples, the stretching vibrations of (PO₄)^3– are still observed at 622 and 880 cm^-1. The peaks in the range of 3300-3500 cm^-1 and 1590-1620 cm^-1 appear as stretching and bending vibrations of the N-H bond. These results show that the fabricated samples were successfully surface-functionalized with the NH₂ groups as a binding agent.

3.5. Application of Nanorods Conjugated with Rabbit Antibody to Detect Naja Atra Cobra Venom Antigen

3.5.1. Evaluating the Results of Binding Nanorods with Rabbit Antibody by Infrared Spectra

The infrared spectra of the synthesized samples were used to elucidate the difference between anti-venom antibody before and after conjugating with luminescence nanorods.

In Figure 6(a), the strong and wide peak at 3460 cm^-1 corresponds to the O-H bond. The peak at 2079 cm^-1 belongs to the N-H bond. The wavelengths from 1640 cm^-1 to 1443 cm^-1 are the oscillating peaks of the C=O and N-H bonds in the first amine group, respectively.

Figure 6(b) shows that the peak at 1389 cm^-1 indicates the forming the C-N bond through reaction of the aldehyde group (O=C-H) of the GDA linker with NH₂ of IgG. Thus, it can be suggested that the conjugation (linkage) between luminescence nanorods with anti-venom antibodies was formed.

3.5.2. Evaluation the Ability of the GdPO₄·nH₂O : Tb³⁺@Silica-NH₂-IgG (Nanorods-Antibodies) to Detect the Naja Atra Cobra Venom

As the experimental steps described above (in Section 2.5), in order to evaluate the ability of detection of Naja atra cobra venom of nanorods, two kinds of well groups were organized. The wells coated with Naja atra cobra venom antigens were incubated with nanorods (1) and nanorods-antibodies (2). The image of Naja atra cobra venom antigens after coating on the plate under visible light of a 40x microscope is illustrated in Figure 7(a) while Figures 7(b) and 7(c) present the images of Naja atra cobra venom antigens conjugated with nanorods-antibodies observed without and with UV light of 40x fluorescence microscope, respectively.

(a)

(b)

(c)

The results showed that the wells incubated with nanorods-antibodies provided a green image and nanoparticles distributed uniformly throughout the field green light under a 40x fluorescence microscope (Figure 7(c)). This result shows that these wells have a specific association between the nanorods-antibodies and the Naja atra cobra antigen so that when it was washed, it does not wash away. Meanwhile, other emissions were not green due to the absence of a combination of antibody-coated nanoparticles and Naja atra cobra venom antigens so they were washed away during washing. Based on these results, it could be concluded that this Naja atra venom detection procedure can shorten the time needed for early diagnosis and improve the efficacy of treatment and thus could facilitate early treatment of snake bite and save lives. Thus, with respect to other green-emitting luminescent materials like Yb,Er-codoped NaYF₄ or TbPO₄·H₂O-based nanomaterials [19, 20], our synthesized immunoglobulin G-conjugated GdPO₄·nH₂O : Tb³⁺ nanorods are compatible for detection of antigen-antibody reaction.

4. Conclusions

GdPO₄·nH₂O and GdPO₄·nH₂O : Tb³⁺ nanorods with a tetragonal phase were synthesized by the hydrothermal method. Optical properties of nanorod materials were optimized by varying the concentration ratio of Tb³⁺/Gd³⁺. At 7 mol % of Tb³⁺, the nanorods exhibited the strongest luminescence because of the energy transfer from gadolinium to terbium. The most uniform nanorods have dimensions of 300-500 nm in length and 10-30 nm in width. The surface functionalization of luminescent nanorods conjugated with rabbit IgG antibodies can be used for early and rapid detecting Naja atra cobra venom antigen.

Data Availability

The concerning data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgments

This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.03-2017.53. The authors are also grateful to the Key Laboratory for Electronic and Devices, Institute of Materials Science, Vietnam Academy of Science and Technology.

References

S. Gai, C. Li, P. Yang, and J. Lin, “Recent progress in rare earth micro/nanocrystals: soft chemical synthesis, luminescent properties, and biomedical applications,” Chemical Reviews, vol. 114, no. 4, pp. 2343–2389, 2013.
View at: Publisher Site | Google Scholar
P. Mi, N. Dewi, H. Yanagie et al., “Hybrid calcium phosphate polymeric micelles in corporating gadolinium chelates for imaging-guided gadolinium neutron capture tumor therapy,” ACS Nano, vol. 9, no. 6, pp. 5913–5921, 2015.
View at: Publisher Site | Google Scholar
W. U. Yanli, X. U. Xianzhu, L. I. Qianlan, R. YANG, H. DING, and Q. XIAO, “Synthesis of bifunctional Gd₂O₃:Eu³⁺ nanocrystals and their applications in biomedical imaging,” Journal of Rare Earths, vol. 33, no. 5, pp. 529–534, 2015.
View at: Publisher Site | Google Scholar
V. Kumar, S. Singh, R. K. Kotnala, and S. Chawla, “GdPO4:Eu3+ nanoparticles with intense orange red emission suitable for solar spectrum conversion and their multifunctionality,” Journal of Luminescence, vol. 146, pp. 486–491, 2014.
View at: Publisher Site | Google Scholar
Y. S. Vidya, K. S. Anantharaju, H. Nagabhushana, and S. C. Sharma, “Euphorbia tirucalli mediated green synthesis of rose like morphology of Gd 2 O 3 :Eu 3+ red phosphor: structural, photoluminescence and photocatalytic studies,” Journal of Alloys and Compounds, vol. 619, pp. 760–770, 2015.
View at: Publisher Site | Google Scholar
H. T. Khuyen, P. T. Thu, T. T. Huong et al., “Synthesis and characterization of nanostructured europium(III) complexes containing gold nanoparticles,” Journal of Luminescence, vol. 166, pp. 67–70, 2015.
View at: Publisher Site | Google Scholar
T. Yang, C. Mocofanescu, H. G. Shen, and C. Xiao, “Nanoparticles for biomedical applications,” in Micro and Nano Manipulations for Biomedical Applications, T. C. Yih and I. Talpasanu, Eds., pp. 43–100, Artech House Publishers, Norwood, Mass, USA, 2008.
View at: Google Scholar
D. Yang, P. Ma, Z. Hou, Z. Cheng, C. Li, and J. Lin, “Current advances in lanthanide ion (Ln³⁺)-based upconversion nanomaterials for drug delivery,” Chemical Society Reviews, vol. 44, no. 6, pp. 1416–1448, 2015.
View at: Publisher Site | Google Scholar
O. J. Fakayode, N. Tsolekile, S. P. Songca, and O. S. Oluwafemi, “Applications of functionalized nanomaterials in photodynamic therapy,” Biophysical Reviews, vol. 10, no. 1, pp. 49–67, 2018.
View at: Publisher Site | Google Scholar
W. Xu, Y. Chang, and G. H. Lee, “Biomedical applications of lanthanide oxide nanoparticles,” Journal of Biomaterials and Tissue Engineering, vol. 7, no. 9, pp. 757–769, 2017.
View at: Publisher Site | Google Scholar
D. Kennedy and M. G. Wilkinson, “Application of flow cytometry to the detection of pathogenic bacteria,” Current Issues in Molecular Biology, vol. 23, pp. 21–38, 2017.
View at: Publisher Site | Google Scholar
A. Escudero, A. I. Becerro, C. Carrillo-Carrión et al., “Rare earth based nanostructured materials: synthesis, functionalization, properties and bioimaging and biosensing applications,” Nano, vol. 6, no. 5, pp. 881–921, 2017.
View at: Publisher Site | Google Scholar
Z. Wang, J. G. Li, Q. Zhu et al., “EDTA-assisted phase conversion synthesis of (Gd_0.95RE_0.05)PO₄ nanowires (RE = Eu, Tb) and investigation of photoluminescence,” Science and Technology of Advanced Materials, vol. 18, no. 1, pp. 447–457, 2017.
View at: Publisher Site | Google Scholar
J. Shen, L. D. Sun, and C. H. Yan, “Luminescent rare earth nanomaterials for bioprobe applications,” Dalton Transactions, vol. 42, no. 42, pp. 5687–5697, 2008.
View at: Publisher Site | Google Scholar
T. H. Greg, Bioconjugate Techniques, Pierce Biotechnology, Thermo Fisher Scientific, Rockford, IL, 3rd Edition edition, 2013.
D. Shen, B. Zhao, S. Yang et al., “NaScMo₂O₈:RE³⁺ (RE = Tb, Eu, Tb/Eu, Yb/Er, Yb/Ho) phosphors: hydrothermal synthesis, energy transfer and multicolor tunable luminescence,” Journal of Materials Science, vol. 52, no. 24, pp. 13868–13878, 2017.
View at: Publisher Site | Google Scholar
J. J. H. A. van Hest, G. A. Blab, H. C. Gerritsen, C. de Mello Donega, and A. Meijerink, “Probing the influence of disorder on lanthanide luminescence using Eu-doped LaPO₄ nanoparticles,” The Journal of Physical Chemistry C, vol. 121, no. 35, pp. 19373–19382, 2017.
View at: Publisher Site | Google Scholar
B. M. Anshu, Nanotechnology in Cancer, Elsevier, Houston, TX, USA, 2016.
N. T. Huong, P. T. Lien, N. M. Hung et al., “Conjugation of TbPO₄.H₂O-based nanowires with immunoglobulin G for bioimaging,” Journal of Electronic Materials, vol. 45, no. 5, pp. 2463–2467, 2016.
View at: Publisher Site | Google Scholar
M. Wang, C. C. Mi, W. X. Wang et al., “Immunolabeling and NIR-excited fluorescent imaging of HeLa cells by using NaYF₄:Yb,Er upconversion nanoparticles,” ACS Nano, vol. 3, no. 6, pp. 1580–1586, 2009.
View at: Publisher Site | Google Scholar
Q. Du, Z. Huang, Z. Wu et al., “Facile preparation and bifunctional imaging of Eu-doped GdPO₄ nanorods with MRI and cellular luminescence,” Dalton Transactions, vol. 44, no. 9, pp. 3934–3940, 2015.
View at: Publisher Site | Google Scholar
E. Pavitra and J. Su Yu, “A facile large-scale synthesis and luminescence properties of Gd₂O₃:Eu³⁺ nanoflowers,” Materials Letters, vol. 90, pp. 134–137, 2013.
View at: Publisher Site | Google Scholar
L. Zhang, H. Jiu, Y. Fu et al., “Facile synthesis and luminescence of GdPO₄:Eu hollow microspheres by a sacrificial template route,” Materials Letters, vol. 101, pp. 47–50, 2013.
View at: Publisher Site | Google Scholar
L. K. Bharat, Y. I. Jeon, and J. S. Yu, “Synthesis and luminescent properties of trivalent rare-earth (Eu³⁺, Tb³⁺) ions doped nanocrystalline AgLa(PO₃)₄ polyphosphates,” Journal of Alloys and Compounds, vol. 614, pp. 443–447, 2014.
View at: Publisher Site | Google Scholar
L. I. Fuhai, H. LIU, S. WEI, W. SUN, and Y. U. Lixin, “Photoluminescent properties of Eu³⁺ and Tb³⁺ codoped Gd₂O₃ nanowires and bulk materials,” Journal of Rare Earths, vol. 31, no. 11, pp. 1063–1068, 2013.
View at: Publisher Site | Google Scholar
L. Hernández-Adame, A. Méndez-Blas, J. Ruiz-García, J. R. Vega-Acosta, F. J. Medellín-Rodríguez, and G. Palestino, “Synthesis, characterization, and photoluminescence properties of Gd:Tb oxysulfide colloidal particles,” Chemical Engineering Journal, vol. 258, pp. 136–145, 2014.
View at: Publisher Site | Google Scholar
H. Song, L. Zhou, L. Li, F. Hong, and X. Luo, “Hydrothermal synthesis, characterization and luminescent properties of GdPO₄.H₂O:Tb³⁺ nanorods and nanobundles,” Materials Research Bulletin, vol. 48, no. 12, pp. 5013–5018, 2013.
View at: Publisher Site | Google Scholar
M. Shang, D. Geng, X. Kang, D. Yang, Y. Zhang, and J. Lin, “Hydrothermal derived LaOF:Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) nanocrystals with multicolor-tunable emission properties,” Inorganic Chemistry, vol. 51, no. 20, pp. 11106–11116, 2012.
View at: Publisher Site | Google Scholar
V. Kumar, S. Singh, and S. Chawla, “Fabrication of dual excitation, dual emission nanophosphor with broad UV and IR excitation through simultaneous doping of triple rare earth ions Er³⁺, Yb³⁺, Eu³⁺ in GdPO₄,” Superlattices and Microstructures, vol. 79, pp. 86–95, 2015.
View at: Publisher Site | Google Scholar
N. T. Huong, N. M. Hung, P. T. Lien et al., “Fabrication and characterization of luminescent magnetic bifunctional nanocomposite based on TbPO₄.H₂O nanowires and Fe₃O₄ nanoparticles,” Journal of Electronic Materials, vol. 45, no. 7, pp. 3646–3650, 2016.
View at: Publisher Site | Google Scholar
F. Hu, X. Wei, Y. Qin et al., “Yb³⁺/Tb³⁺ co-doped GdPO₄ transparent magnetic glass-ceramics for spectral conversion,” Journal of Alloys and Compounds, vol. 674, pp. 162–167, 2016.
View at: Publisher Site | Google Scholar
H. Lai, X. Yang, and H. Yang, “Luminescent properties of GdPO₄:Eu nanorods,” Journal of Materials Science: Materials in Electronics, vol. 23, no. 1, pp. 285–289, 2012.
View at: Publisher Site | Google Scholar
X.-y. Kuang, H. Liu, W.-y. Hu, and Y.-z. Shao, “Hydrothermal synthesis of core–shell structured TbPO₄:Ce³⁺@TbPO₄:Gd³⁺ nanocomposites for magnetic resonance and optical imaging,” Dalton Transactions, vol. 43, no. 32, pp. 12321–12328, 2014.
View at: Publisher Site | Google Scholar
L. Li, G. Li, D. Wang, Y. Tao, and X. Zhang, “Energy transfer mechanism of GdPO₄:RE³⁺ (RE= Tb, Tm) under VUV-UV excitation,” Science in China Series E: Technological Sciences, vol. 49, no. 4, pp. 408–413, 2006.
View at: Publisher Site | Google Scholar
C. R. Kesavulu, H. J. Kim, S. W. Lee, J. Kaewkhao, E. Kaewnuam, and N. Wantana, “Luminescence properties and energy transfer from Gd³⁺ to Tb³⁺ ions in gadolinium calcium silicoborate glasses for green laser application,” Journal of Alloys and Compounds, vol. 704, pp. 557–564, 2017.
View at: Publisher Site | Google Scholar
N. Yaiphaba, R. S. Ningthoujam, N. R. Singh, and R. K. Vatsa, “Luminescence properties of redispersible Tb³⁺-doped GdPO₄ nanoparticles prepared by an ethylene glycol route,” European Journal of Inorganic Chemistry, vol. 2010, no. 18, pp. 2682–2687, 2010.
View at: Publisher Site | Google Scholar

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Copyright © 2019 Pham Thi Lien et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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