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Tm3+
Materials Research Bulletin 111 (2019) 146–153
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In-situ synthesis and enhanced upconversion luminescence of Y2O3/ Y2O2S:Yb3+,Er3+/Tm3+ nanocomposites by reduction of Y2O3:Yb3+,Er3+/ Tm3+ ⁎
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Linna Xua, Lijuan Liua, , Kai Pana, Naiying Fana, , Guofeng Wanga, , Weiping Qinb,
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a Key Laboratory of Functional Inorganic Materials Chemistry Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, 150080, China b College of Electronic Science and Engineering, Jilin University, 120012, China
A R T I C LE I N FO
A B S T R A C T
Keywords: A. Y2O3/Y2O2S:Yb3+Er3+ B. Upconversion luminescence D. Glucose detection
Y2O3/Y2O2S:Ln3+ (Ln = Yb,Er and Yb,Tm) nanocomposites with enhanced upconversion luminescence were successfully prepared by combining hydrothermal with in-situ synthesis method. Under 980 nm excitation, the upconversion luminescence intensity of Y2O3/Y2O2S:Ln3+ increased, and then declined with the rising amount of sulfur powder. Especially, the Y2O3/Y2O2S:Ln3+ nanocomposites can emit brighter upconversion luminescence than those of Y2O3:Ln3+ and Y2O2S:Ln3+. In terms of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites which were prepared with 0.025g sulfur powder, an unusual 4G11/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ could be observed. Besides, we have constructed a simple upconversion Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposite, which can be used for rapid sensing of glucose. The limit of detection of glucose level which based on Y2O3/ Y2O2S:Yb3+,Er3+@Au was only 0.066 μmol/L. The proposed approach, which we have mentioned above, holds a great practical value for diabetes mellitus detection and clinical diagnosis.
1. Introduction Glucose is a major source of energy in the cells, and plays an essential role for monitoring blood glucose levels in the human body [1–3]. Glucose levels in blood are related closely with diabetes or hypoglycemia. Diabetes mellitus is a familiar chronic disease, which can cause many serious complications including heart disease, stroke, damage to the kidneys and nerves, limb amputation, and blindness and so on [4–7]. Accordingly, it is of utmost vital to regular monitor and tightly control the change of blood sugar concentration for effective diagnosis and management of diabetes nowadays [8–11]. And the development of highly sensitive and reliable glucose detection means has been the subject of concern for decades. To date, traditional approaches for detection of blood glucose levels are primarily based on colorimetric chemiluminescence, electrochemistry and fluorescence methods [12–16]. Nevertheless, most of these methods exist some imperfections, including complex instrumentation, complicated processes, and insensitive detection. Enzyme-based H2O2 sensors exhibit obvious advantages (such as high sensitivity and high selectivity), and thus, glucose detection technique based on glucose oxidase (GOx) has become a popular
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strategy [17–22]. Luminescence from lanthanide ions has gained remarkable attention due to its potential applications in optoelectronics, cellular bioimaging, and bioanalytical fields [23–28]. Especially, upconversion (UC) luminescence technology based on luminescence resonance energy transfer (LRET) has received extensive attention in recent years [29–36]. In contrast to traditional luminescence materials, UC nanocrystals possess remarkable advantages, such as large anti Stokes shifts, long luminescence lifetimes, and narrow emission bands, negligible light scattering background, high resistance to photobleaching and non-auto luminescence from biosamples [37–43]. To date, only a few UC LRET-based glucose assays have been designed [44–47]. For example, Yuan’s group discovered that the fluorescence of NaYF4:Yb,Tm@NaYF4 nanoparticles can be quenched by MnO2 nanosheets and the MnO2-mediated quenching can be turned on by adding H2O2, the detection limit of the glucose was estimated to be 3.7 μM [48]. Wu’s group design DNAtemplated Ag nanoparticles and NaYF4:Yb/Tm@NaYF4 core-shell UC nanoparticles, and DNA-Ag nanoparticles serve as efficient quenchers. Ag nanoparticles were etched and transformed into Ag+, when H2O2 exists. The detection limit of glucose was calculated to be 1.41 μM [49]. Liu’s group report an UC nanoparticles-polydopamine nanosystem for
Corresponding authors. E-mail addresses: [email protected] (L. Liu), [email protected] (N. Fan), [email protected] (G. Wang), [email protected] (W. Qin).
https://doi.org/10.1016/j.materresbull.2018.11.019 Received 2 October 2018; Received in revised form 14 November 2018; Accepted 14 November 2018 Available online 15 November 2018 0025-5408/ © 2018 Elsevier Ltd. All rights reserved.
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Scheme 1. Synthesis of Y2O3 /Y2O2S:Yb3+,Er3+@Au nanocomposites together with the design and principle for glucose detection.
Fig. 1. (a) XRD patterns of Y2O3:Yb3+,Er3+, Y2O3/Y2O2S:Yb3+, Er3+ and /Y2O2S:Yb3+, Er3+. (b) Raman spectrum of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites prepared with 0.025 g sulfur powder.
doped with lanthanide ions. [51,52] However, the UC luminescence efficiencies of lanthanide ion doped Y2O3 is much lower than those of sulfides and fluoride, which can be attributable to higher phonon energy of oxides [53,54]. Y2O2S is also a promising UC host material for lanthanide ions, which has outstanding performances, such as nontoxicity, remarkable thermal and chemical stability, low phonon energy and high UC efficiency. We suggested that novel luminescent properties could be obtained by combining Y2O3:Yb3+,Er3+ and Y2O2S:Yb3+,Er3+ [55,56]. Herein, we combined hydrothermal with in situ-synthesis method to synthesize Y2O3/Y2O2S:Ln3+ nanocomposites, which had enhanced UC luminescence. The UC luminescence intensity of Y2O3/Y2O2S:Ln3+ was much stronger than those of Y2O3:Ln3+ and Y2O2S:Ln3+. In addition, we report an UC luminescence detection method based on Y2O3/ Y2O2S:Yb3+,Er3+@Au for rapid sensing of glucose. The limit of detection of glucose level which based on Y2O3/Y2O2S:Yb3+,Er3+@Au was only 0.066 μmol/L, which was smaller than those based on other reported nanosystems [48–50]. Fig. 2. Dynamic light scattering (DLS) spectra of Y2O3/Y2O2S:Yb3+,Er3+ and Y2O3/Y2O2S:Yb3+,Tm3+ nanocomposites in ethanol.
2. Experimental section
the accurate detection of glucose, the detection limit of glucose was calculated to be 1.2 μM [50]. It is well known that the Y2O3 crystals possess high thermal conductivity, desired chemical durability, excellent photochemical stability and wide bandgaps. More importantly, the Y2O3 crystals can be easily
2.1. Materials 2.1.1. Synthesis of Y2O3/Y2O2S:Yb3+,Er3+ and Y2O3/Y2O2S:Yb3+,Tm3+ As noted by literature [53], the Y(OH)3:Yb3+,Er3+ and Y (OH)3:Yb3+,Tm3+ were synthesized first. And then, 0.1 g of the 147
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Fig. 3. SEM images of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites prepared with (a) 0.05 g and (b) 0.2 g sulfur powder.
Fig. 4. SEM images of Y2O3/Y2O2S:Yb3+,Tm3+ nanocomposites prepared with (a) 0.05 g and (b) 0.2 g sulfur powder.
Fig. 5. (a) TEM image of Y2O3/Y2O2S:Yb3+,Tm3+ nanocomposites prepared with 0.2 g sulfur powder. (b) TEM image of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites prepared with 0.025 g sulfur powder. (c–e) TEM and HRTEM images of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites prepared with 0.025 g sulfur powder.
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different volume of the above liquid and collected by centrifugation. 2.1.3. Immobilization of GOx on Y2O3/Y2O2S:Yb3+,Er3+@Au According to the method described by previous work18, the GOx was immobilized on the surface of the Y2O3/Y2O2S:Yb3+,Er3+@Au. 2.1.4. Glucose detection The Y2O3/Y2O2S:Yb3+,Er3+@Au-GOx (1 mL) was dispersed in ultrapure water, and various amounts of glucose solution were added into the solution. The obtained mixtures were diluted to 3 ml with ultrapure water before detection. Then, the fluorescence spectra of the obtained solutions were recorded after incubation at 4 °C. The design scheme of glucose detection was shown in Scheme 1. 2.2. Characterizations
Fig. 6. The survey XPS spectrum of Yb3+/Er3+ codoped Y2O3/Y2O2S@Au nanocomposites.
The crystal structure was characterized by X-ray powder Diffraction (XRD) equipped with a Bruker D8 Advance Diffractometer and CuKα radiation (λ = 1.5406 Å, 40 kV, 40 mA). The morphology of the samples was observed by scanning electron microscopy (SEM, Hitachi S4800 with operating voltage of 15 kV) and transmission electron microscopy (TEM, JEM 2010 with operating voltage of 200KV). The Hitachi F-4600 fluorescence spectrophotometer was used to investigate UC luminescence spectra. X-ray photoelectron spectroscopy (XPS) analysis was executed by a VGESCALABMK II with a Mg KR (1253.6 eV) achromatic X-ray source. Fourier transform infrared (FTIR) spectra of the samples were recorded with a Perkin-Elmer Spectrum one FTIR spectrometer using the KBr pellet method. Raman measurements were executed at 458 nm with a Jobin Yvon HR 800 micro-Raman
prepared products and some sulfur powder (0.005, 0.008, 0.0125, 0.025, 0.05, 0.1 and 2 g) were put into a porcelain boat, then sintered at 800 °C for 2 h in N2 atmosphere. When the sulfur powder content was 2.0 g, the product was Y2O2S:Ln3+. 2.1.2. Preparation of Y2O3/Y2O2S:Yb3+,Er3+@Au 50 ml of 1 mmol/L HAuCl4 solution was heated to boiling in an oil bath and 5 ml of trisodium citrate (38.8 mmol/L) was added, then stirred vigorously for 10 min. The stirring was stopped for 15 min, then stirring was continuing for 15 min. The remaining liquid is diluted to 50 ml. The Y2O3/Y2O2S:Yb3+,Er3+ samples were stirred for 3 h with
Fig. 7. High resolution XPS spectra of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites. 149
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Fig. 8. (a) FTIR spectra of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites and Y2O3/Y2O2S: Yb3+, Er3+ @Au nanocomposites. (b) EDS spectrum of Y2O3/ Y2O2S:Yb3+,Er3+@Au nanocrystals.
Fig. 9. (a) UC luminescence spectra of Y2O3/Y2O2S:Yb3+,Er3+ prepared with different amounts of sulfur powder. Inset shows the UC luminescence spectra of Y2O3/ Y2O2S:Yb3+,Er3+ with 350–430 nm. (b) UC luminescence spectra of Y2O3/Y2O2S:Yb3+,Er3+ prepared with 0.025 g sulfur powder under different excitation power.
The SEM images in Figs. 3 and 4 indicated that the Y2O3/ Y2O2S:Yb3+,Er3+ and Y2O3/Y2O2S:Yb3+,Tm3+ nanoparticles are in spherical shape. The TEM image of Y2O3/Y2O2S:Yb3+,Tm3+ is shown in Fig. 5. Fig. 5(b) shows TEM image of the Y2O3/Y2O2S:Yb3+,Er3+ nanoparticle prepared with 0.025 g sulfur powder. The concentration of S has no significant effect on the morphology of the samples, because the nanoparticles are a little reunited and the morphology is irregular. Further detailed component analysis on the Y2O3/ Y2O2S:Yb3+,Er3+@Au nanoparticle was carried out by the high-resolution transmission electron microscope (HRTEM), as shown in Fig. 5(c–e). Typical HRTEM photographs indicate three interplanar spacings of 0.433, 0.293 and 0.235 nm corresponding to the < 211 > plane of Y2O2S:Yb3+,Er3+, < 101 > plane of Y2O3:Yb3+,Er3+ and < 111 > plane of Au, respectively. The results indicated that Au exists on the surface of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites. The elemental analysis of Y2O3/Y2O2S:Yb3+,Er3+@Au nanoparticles was performed by XPS, as shown in Fig. 6. The O 1 s peaks are observed at 528.7 eV. The values of 394.02, 301.88, 158.4 eV and 20.18 eV are assigned for Y 3 s, Y 3p, Y 3d, and Y 4 P speaks, respectively. The S 2p peak is observed at 170 eV. It was observed at 87.3 eV peak indicates the presence of the Au 4f. Fig. 7 shows the high resolution XPS spectra of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites. The O 1 s spectrum exhibits at 526.82, 528.67 and 530.65 eV, as displayed in Fig. 7(a). The Y 3d3/2 spectral peaks were at 155.4 eV, and the
spectrometer. Dynamic light scattering (DLS) experiments were performed by a Malvern Zetasizer (Nano-ZS, USA). 3. Results and discussion 3.1. Crystal structures and morphologies The XRD patterns of the Y2O3:Yb3+,Er3+ and Y2O3/ Y2O2S:Yb3+,Er3+ nanocomposites as demonstrated in Fig. 1(a). The diffraction peaks of Y2O3:Yb3+,Er3+ can be indexed to the cubic phase Y2O3 (JCPDS 43-1036), and the diffraction peaks of Y2O2S:Yb3+,Er3+ can be indexed to the hexagonal phase Y2O2S (JCPDS 24-1424). It is noted that the pure Y2O2S:Ln3+ was obtained, the corresponding sulfur powder was set as 2.0 g. The Raman spectrum of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites was displayed in Fig. 1(b). The results show that Y2O3:Yb3+,Er3+ and Y2O2S:Yb3+,Er3+ coexists in Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites. The Raman active modes of Y2O3:Yb3+,Er3+ are characterized by three bands at approximately 300∼450 cm−1, which can be induced by the Fg + Eg and Fg + Ag modes. The Raman active modes of Y2O2S:Yb3+,Er3+ detected at 460 cm−1 were identified to the Eg modes. Fig. 2 indicates the dynamic light scattering spectra of Y2O3/ Y2O2S:Ln3+ in ethanol. The results indicated that the mean particle size of Y2O3/Y2O2S:Ln3+ is about 200 nm. 150
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Fig. 10. (a) UC luminescence spectra of Y2O3/ Y2O2S:Yb3+,Tm3+ prepared with different amounts of sulfur powder. Inset shows the enlarged view that the UC luminescence spectra of Y2O3/Y2O2S:Yb3+,Tm3+ with 400–750 nm. (b,c) UC luminescence spectra of Y2O3/ Y2O2S:Yb3+,Tm3+ prepared with 0.025 g sulfur powder under different excitation power. Inset shows the photographs of samples lighting by 980 nm excitation. (d) The CIE 1931 chromaticity diagram of Y2O3/Y2O2S:Yb3+,Tm3+ prepared with 0.025 g sulfur powder.
Fig. 11. (a) Plots (log-log) of emission intensity versus pump power density of Y2O3/Y2O2S:20%Yb3+,2%Er3+ prepared with 0.025 g sulfur powder.
Fig. 12. Plots (log-log) of emission intensity versus pump power density of Y2O3/Y2O2S:20%Yb3+,1%Tm3+ prepared with 0.025 g sulfur powder.
Y 3d5/2 spectral peaks were at 157.5 and 158.65 eV, as presented in Fig. 7(b). The S 2p2/3 spectral peaks were at 166.5 and 170.23 eV, as illustrated in Fig. 7(c). In addition, Fig. 7(d) shows the Au 4f spectral peaks were at 83.7and 87.3 eV. Fig. 8(a) shows the IR spectra of Y2O3/Y2O2S:Yb3+,Er3+ and Y2O3/ Y2O2S:Yb3+,Er3+@Au nanocomposites, the peak at 580 cm−1 can be attributed to YeO lattice vibrations, the peak at 1580 cm−1and 1420 cm−1 were attributed to the νOH and νCO stretching vibrations, respectively. The peak at 3450 cm−1 corresponds to eOH vibration. It is noted that the vibration peak moved to a higher wavenumber with increasing the present of gold particles, suggesting the formation of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites. Since the sodium citrate
was used when the Au nanoparticle was synthesized, the carboxyl vibration peak of the material was significantly enhanced. It is also due to the presence of trisodium citrate that makes the material hydrophilic. Moreover, to further prove the coexistence of Y2O3/Y2O2S:Yb3+,Er3+ and Au in the nanocrystals, the Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites were confirmed by energy-dispersive X-ray spectroscopy (EDS), as shown in Fig. 8(b).The results indicate that the elemental components are O, Y, S and Au. 3.2. UC luminescence Fig. 9(a) shows the UC luminescence spectra of the as-produced 151
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Fig. 13. (a) Absorption spectrum of Au nanocrystals (red line) exhibits significant spectral overlap with the UC emission spectrum (blacked line) of Y2O3/ Y2O2S:Yb3+,Er3+ nanocrystals. (b) UC fluorescence response of Y2O3/Y2O2S:Yb3+,Er3+@Au UCNPs after incubation with glucose solution of different concentrations (0–1.67 μM). (c) Plot of the fluorescence intensity of Y2O3/Y2O2S:Yb3+,Er3+@Au at 980 nm excitation against the glucose concentration. (d) The fluorescence intensity changes of complex upon addition of different analytes. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Y2O3/Y2O2S:18%Yb3+,2%Er3+ prepared with different amounts of sulfur powder under 980 nm excitation. The weak emission peaks centered at 385 and 410 nm can be attributed to the 4G11/2 → 4I15/2 and 4 F9/2 → 4I15/2 transitions, respectively. The emission bands in the green region centered at 525 and 550 nm are separately ascribed to the transitions from the 2H11/2 and 4S3/2 excited states to the 4I15/2 ground state. The emission band in the red region centered at 660 nm is ascribed to the transitions from the 4F9/2 excited state to the ground state. The CIE chromaticity coordinates of Y2O3/Y2O2S:18%Yb3+,2%Er3+ prepared with 0.025 g sulfur powder were calculated to be (0.346, 0.537). Fig. 9(b) reveals the UC luminescence spectra of the Y2O3/ Y2O2S:Yb3+,Er3+ nanoparticles (prepared with 0.025 g sulfur powder) under different excitation power. As can be seen, with the increase in power, luminescence intensity is increasing. It is well known that sulfide has lower phonon energy, while oxide has higher phonon energy. The low phonon energy of the matrix material helps to reduce the nonradiative transition probability and improve the efficiency of UC luminescence. However, phonon assisted energy transfer is an important process for UC luminescence. And thus, enhanced UC luminescence of Y2O3/Y2O2S:Yb3+,Er3+/ nanocomposites were obtained. Fig. 10(a) shows the UC luminescence spectra of Y2O3/Y2O2S:18% Yb3+,2%Tm3+ prepared with different amounts of sulfur powder under 980 nm excitation. The 1G4 → 3H6, 3F2/3 → 3H6 and 3H4 → 3H6 transitions were observed. Fig. 10(b,c) shows the UC luminescence spectra of the Y2O3/Y2O2S:18%Yb3+,2%Tm3+ nanoparticles (prepared with 0.025 g sulfur powder) under different excitation power. Inset of Fig. 10(c) shows the photographs of samples lighting by 980 nm excitation. The CIE chromaticity coordinates of Y2O3/Y2O2S:18% Yb3+,2%Tm3+ (prepared with 0.025 g sulfur powder) was calculated to be (0.306, 0.309), as shown in Fig. 10(d). To research the fundamental UC mechanisms of Y2O3/ Y2O2S:Yb3+,Er3+, the pumping power dependence of the fluorescent
intensity was analyzed, as presented in Fig. 11. Obviously, the population of the 4F9/2/4F9/2/2H11/2 comes from two-photon process. The pumping power dependence of the fluorescent intensity for Y2O3/ Y2O2S:Yb3+,Tm3+ was shown in Fig. 12. The population of the 3H4 and 3 F3/2 comes from two-photon process. It is well known that white light can be obtained by co-doping of Er3+ and Tm3+ in samples. Due to the doping amount of Er3+ and Tm3+ needs further adjusting, the experimental results will be reported separately in another article. 3.3. Detection of glucose As mentioned above, strict determination of the amount of glucose in the blood has an important effect on physical health. The main goal of our work is to develop a method based on Y2O3/ Y2O2S:Yb3+,Er3+@Au for rapid monitoring of blood glucose levels. Fig. 13(a) illuminates the UC luminescence spectrum of the as-produced Y2O3/Y2O2S:Yb3+,Er3+ under 980 nm excitation and the UV–vis absorption spectrum of the Au nanocrystals. The results indicated that the plasmon band of Au overlaps well with the UC emission spectra of Y2O3/Y2O2S:Yb3+,Er3+ nanocrystals, indicating high probability of LRET between Y2O3/Y2O2S:Yb3+,Er3+ nanocrystals and Au. As we expected, the UC luminescence intensity increased with increasing glucose concentration, varying from 0 to 1.25 μM (Fig. 13(b)), and the fluorescence intensity at 525 nm was linearly related to the glucose concentration in the ranges of 0–0.835 μM. The calibration function of I = 19.233C+1.49 with a good linearity (R2 = 0.998) for the detection of glucose was acquired, where I is the relative UC luminescence intensity and C is the concentration of glucose presumably, the addition of glucose can result in a relatively significant UC luminescence recovery. As the amount of glucose increases, significant UC luminescence recovery occurs. Therefore, the fluorescence intensity at 525 nm was linearly correlated with the glucose concentration in 152
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ranges. The detection limit of the glucose was calculated to be 0.066 μM according to the 3σ rule (LOD = 3σ/K)16. Of course, the amount of Au in nanocomposites affects the detection limit. If the amount of Au is too small, it is impossible to detect glucose because the effect of fluorescence quenching is not obvious. Furthermore, if the amount of Au is too high, the fluorescence recovery effect was not obvious. Therefore, the appropriate content of Au is beneficial to the optimization of the limit of glucose detection. In addition, when the amount of glucose added from 0.835 to 1.25 umol/L, the fluorescence intensity almost leveled, which is a normal phenomenon. As mentioned above, the Au quenching effect can be reversed in the presence of GOx, leading to decomposition of the Au nanocrystals accompanied by UC luminescence recovery. When the
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H+
chemical reaction (H2 O2 +Au0⟶Au+ + H2 O) reaches the balance, the fluorescence intensity remains constant. To further assess the selectivity of the sensor, the luminescence response of other possible interfering substances including some metal ions was studied in aqueous solutions. The experimental results were presented in Fig. 13(d). Therefore, our experiments are started from a general test of 8 metal ions, including M = Zn2+, Sr2+, Fe3+, Ca2+, Cu2+, Co2+, Mg2+, EDTA and SO42− with a concentration of 10-2 M. Obviously, only glucose can be effectively detected. It is possible to detect glucose selectively from a mixture of analytes when the metal concentration is low. It is noted that we have done a lot of experiments including the detection of glucose based on Y2O3:Yb3+,Er3+@Au. However, the UC luminescence of Y2O3:Yb3+,Er3+ was too weak. And thus, the detection of glucose based on Y2O3:Yb3+,Er3+@Au cannot be carried out at all. 4. Conclusions In conclusion, Y2O3/Y2O2S:Ln3+ (Ln = Yb/Er and Yb/Tm) nanocomposites have been prepared by combining hydrothermal with insitu synthesis method. With the rising amount of sulfur powder, under 980 nm excitation, the upconversion luminescence intensity of Y2O3/ Y2O2S:Ln3+ increased, and then declined. When the mass of sulfur powder is 0.025 g, the UC luminescence intensity of Y2O3/Y2O2S:Ln3+ was the strongest. It is surprised that the UC luminescence intensity of Y2O3/Y2O2S:Ln3+ was much stronger than either Y2O3:Ln3+ or Y2O2S:Ln3+. We also developed a method based on Au modified Y2O3/ Y2O2S:Yb3+,Er3+ for rapid monitoring of blood glucose levels in this paper. The limit of detection of glucose level which based on Y2O3/ Y2O2S:Yb3+,Er3+@Au was only 0.066 μmol/L. This nanosystem is also generalizable and can be easily extended to the detection of various H2O2-involved analytes. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21471050 and 21871079) and the Innovative Project of Postgraduate of Heilongjiang University (YJSCX2018180HLJU). References [1] E. Vezouviou, C.R. Lowe, Biosens. Bioelectron. 68 (2015) 371–381. [2] K. Sun, Y.K. Yang, H. Zhou, S.Y. Yin, W.P. Qin, J.B. Yu, D.T. Chiu, Z. Yuan, X.J. Zhang, C.F. Wu, ACS Nano (2018), https://doi.org/10.1021/acsnano.8b02188. [3] K. Sun, Y. Tang, Q. Li, S.Y. Yin, W.P. Qin, J.B. Yu, D.T. Chiu, Y.B. Liu, Z. Yuan, X.J. Zhang, C.F. Wu, ACS Nano 10 (2016) 6769–6781. [4] S. Liu, B. Yu, F. Li, Y. Ji, T. Zhang, Electrochim. Acta 141 (2014) 161–166. [5] Y.H. Song, J.Y. Chen, H.Y. Liu, Y.G. Song, F.G. Xu, H.L. Tan, L. Wang, Electrochim. Acta 158 (2015) 56–63. [6] A.A. Ibrahim, R. Ahmad, A. Umar, M.S. Al-Assiri, A.E. Al-Salami, R. Kumar, S.G. Ansari, S. Baskoutas, Biosens. Bioelectron. 98 (2017) 254–260. [7] M.S. Steiner, A. Duerkop, O.S. Wolfbeis, Chem. Soc. Rev. 40 (2011) 4805–4839.
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In-situ synthesis and enhanced upconversion luminescence of Y2O3/ Y2O2S:Yb3+,Er3+/Tm3+ nanocomposites by reduction of Y2O3:Yb3+,Er3+/ Tm3+ ⁎
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Linna Xua, Lijuan Liua, , Kai Pana, Naiying Fana, , Guofeng Wanga, , Weiping Qinb,
T
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a Key Laboratory of Functional Inorganic Materials Chemistry Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, 150080, China b College of Electronic Science and Engineering, Jilin University, 120012, China
A R T I C LE I N FO
A B S T R A C T
Keywords: A. Y2O3/Y2O2S:Yb3+Er3+ B. Upconversion luminescence D. Glucose detection
Y2O3/Y2O2S:Ln3+ (Ln = Yb,Er and Yb,Tm) nanocomposites with enhanced upconversion luminescence were successfully prepared by combining hydrothermal with in-situ synthesis method. Under 980 nm excitation, the upconversion luminescence intensity of Y2O3/Y2O2S:Ln3+ increased, and then declined with the rising amount of sulfur powder. Especially, the Y2O3/Y2O2S:Ln3+ nanocomposites can emit brighter upconversion luminescence than those of Y2O3:Ln3+ and Y2O2S:Ln3+. In terms of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites which were prepared with 0.025g sulfur powder, an unusual 4G11/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ could be observed. Besides, we have constructed a simple upconversion Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposite, which can be used for rapid sensing of glucose. The limit of detection of glucose level which based on Y2O3/ Y2O2S:Yb3+,Er3+@Au was only 0.066 μmol/L. The proposed approach, which we have mentioned above, holds a great practical value for diabetes mellitus detection and clinical diagnosis.
1. Introduction Glucose is a major source of energy in the cells, and plays an essential role for monitoring blood glucose levels in the human body [1–3]. Glucose levels in blood are related closely with diabetes or hypoglycemia. Diabetes mellitus is a familiar chronic disease, which can cause many serious complications including heart disease, stroke, damage to the kidneys and nerves, limb amputation, and blindness and so on [4–7]. Accordingly, it is of utmost vital to regular monitor and tightly control the change of blood sugar concentration for effective diagnosis and management of diabetes nowadays [8–11]. And the development of highly sensitive and reliable glucose detection means has been the subject of concern for decades. To date, traditional approaches for detection of blood glucose levels are primarily based on colorimetric chemiluminescence, electrochemistry and fluorescence methods [12–16]. Nevertheless, most of these methods exist some imperfections, including complex instrumentation, complicated processes, and insensitive detection. Enzyme-based H2O2 sensors exhibit obvious advantages (such as high sensitivity and high selectivity), and thus, glucose detection technique based on glucose oxidase (GOx) has become a popular
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strategy [17–22]. Luminescence from lanthanide ions has gained remarkable attention due to its potential applications in optoelectronics, cellular bioimaging, and bioanalytical fields [23–28]. Especially, upconversion (UC) luminescence technology based on luminescence resonance energy transfer (LRET) has received extensive attention in recent years [29–36]. In contrast to traditional luminescence materials, UC nanocrystals possess remarkable advantages, such as large anti Stokes shifts, long luminescence lifetimes, and narrow emission bands, negligible light scattering background, high resistance to photobleaching and non-auto luminescence from biosamples [37–43]. To date, only a few UC LRET-based glucose assays have been designed [44–47]. For example, Yuan’s group discovered that the fluorescence of NaYF4:Yb,Tm@NaYF4 nanoparticles can be quenched by MnO2 nanosheets and the MnO2-mediated quenching can be turned on by adding H2O2, the detection limit of the glucose was estimated to be 3.7 μM [48]. Wu’s group design DNAtemplated Ag nanoparticles and NaYF4:Yb/Tm@NaYF4 core-shell UC nanoparticles, and DNA-Ag nanoparticles serve as efficient quenchers. Ag nanoparticles were etched and transformed into Ag+, when H2O2 exists. The detection limit of glucose was calculated to be 1.41 μM [49]. Liu’s group report an UC nanoparticles-polydopamine nanosystem for
Corresponding authors. E-mail addresses: [email protected] (L. Liu), [email protected] (N. Fan), [email protected] (G. Wang), [email protected] (W. Qin).
https://doi.org/10.1016/j.materresbull.2018.11.019 Received 2 October 2018; Received in revised form 14 November 2018; Accepted 14 November 2018 Available online 15 November 2018 0025-5408/ © 2018 Elsevier Ltd. All rights reserved.
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Scheme 1. Synthesis of Y2O3 /Y2O2S:Yb3+,Er3+@Au nanocomposites together with the design and principle for glucose detection.
Fig. 1. (a) XRD patterns of Y2O3:Yb3+,Er3+, Y2O3/Y2O2S:Yb3+, Er3+ and /Y2O2S:Yb3+, Er3+. (b) Raman spectrum of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites prepared with 0.025 g sulfur powder.
doped with lanthanide ions. [51,52] However, the UC luminescence efficiencies of lanthanide ion doped Y2O3 is much lower than those of sulfides and fluoride, which can be attributable to higher phonon energy of oxides [53,54]. Y2O2S is also a promising UC host material for lanthanide ions, which has outstanding performances, such as nontoxicity, remarkable thermal and chemical stability, low phonon energy and high UC efficiency. We suggested that novel luminescent properties could be obtained by combining Y2O3:Yb3+,Er3+ and Y2O2S:Yb3+,Er3+ [55,56]. Herein, we combined hydrothermal with in situ-synthesis method to synthesize Y2O3/Y2O2S:Ln3+ nanocomposites, which had enhanced UC luminescence. The UC luminescence intensity of Y2O3/Y2O2S:Ln3+ was much stronger than those of Y2O3:Ln3+ and Y2O2S:Ln3+. In addition, we report an UC luminescence detection method based on Y2O3/ Y2O2S:Yb3+,Er3+@Au for rapid sensing of glucose. The limit of detection of glucose level which based on Y2O3/Y2O2S:Yb3+,Er3+@Au was only 0.066 μmol/L, which was smaller than those based on other reported nanosystems [48–50]. Fig. 2. Dynamic light scattering (DLS) spectra of Y2O3/Y2O2S:Yb3+,Er3+ and Y2O3/Y2O2S:Yb3+,Tm3+ nanocomposites in ethanol.
2. Experimental section
the accurate detection of glucose, the detection limit of glucose was calculated to be 1.2 μM [50]. It is well known that the Y2O3 crystals possess high thermal conductivity, desired chemical durability, excellent photochemical stability and wide bandgaps. More importantly, the Y2O3 crystals can be easily
2.1. Materials 2.1.1. Synthesis of Y2O3/Y2O2S:Yb3+,Er3+ and Y2O3/Y2O2S:Yb3+,Tm3+ As noted by literature [53], the Y(OH)3:Yb3+,Er3+ and Y (OH)3:Yb3+,Tm3+ were synthesized first. And then, 0.1 g of the 147
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Fig. 3. SEM images of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites prepared with (a) 0.05 g and (b) 0.2 g sulfur powder.
Fig. 4. SEM images of Y2O3/Y2O2S:Yb3+,Tm3+ nanocomposites prepared with (a) 0.05 g and (b) 0.2 g sulfur powder.
Fig. 5. (a) TEM image of Y2O3/Y2O2S:Yb3+,Tm3+ nanocomposites prepared with 0.2 g sulfur powder. (b) TEM image of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites prepared with 0.025 g sulfur powder. (c–e) TEM and HRTEM images of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites prepared with 0.025 g sulfur powder.
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different volume of the above liquid and collected by centrifugation. 2.1.3. Immobilization of GOx on Y2O3/Y2O2S:Yb3+,Er3+@Au According to the method described by previous work18, the GOx was immobilized on the surface of the Y2O3/Y2O2S:Yb3+,Er3+@Au. 2.1.4. Glucose detection The Y2O3/Y2O2S:Yb3+,Er3+@Au-GOx (1 mL) was dispersed in ultrapure water, and various amounts of glucose solution were added into the solution. The obtained mixtures were diluted to 3 ml with ultrapure water before detection. Then, the fluorescence spectra of the obtained solutions were recorded after incubation at 4 °C. The design scheme of glucose detection was shown in Scheme 1. 2.2. Characterizations
Fig. 6. The survey XPS spectrum of Yb3+/Er3+ codoped Y2O3/Y2O2S@Au nanocomposites.
The crystal structure was characterized by X-ray powder Diffraction (XRD) equipped with a Bruker D8 Advance Diffractometer and CuKα radiation (λ = 1.5406 Å, 40 kV, 40 mA). The morphology of the samples was observed by scanning electron microscopy (SEM, Hitachi S4800 with operating voltage of 15 kV) and transmission electron microscopy (TEM, JEM 2010 with operating voltage of 200KV). The Hitachi F-4600 fluorescence spectrophotometer was used to investigate UC luminescence spectra. X-ray photoelectron spectroscopy (XPS) analysis was executed by a VGESCALABMK II with a Mg KR (1253.6 eV) achromatic X-ray source. Fourier transform infrared (FTIR) spectra of the samples were recorded with a Perkin-Elmer Spectrum one FTIR spectrometer using the KBr pellet method. Raman measurements were executed at 458 nm with a Jobin Yvon HR 800 micro-Raman
prepared products and some sulfur powder (0.005, 0.008, 0.0125, 0.025, 0.05, 0.1 and 2 g) were put into a porcelain boat, then sintered at 800 °C for 2 h in N2 atmosphere. When the sulfur powder content was 2.0 g, the product was Y2O2S:Ln3+. 2.1.2. Preparation of Y2O3/Y2O2S:Yb3+,Er3+@Au 50 ml of 1 mmol/L HAuCl4 solution was heated to boiling in an oil bath and 5 ml of trisodium citrate (38.8 mmol/L) was added, then stirred vigorously for 10 min. The stirring was stopped for 15 min, then stirring was continuing for 15 min. The remaining liquid is diluted to 50 ml. The Y2O3/Y2O2S:Yb3+,Er3+ samples were stirred for 3 h with
Fig. 7. High resolution XPS spectra of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites. 149
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Fig. 8. (a) FTIR spectra of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites and Y2O3/Y2O2S: Yb3+, Er3+ @Au nanocomposites. (b) EDS spectrum of Y2O3/ Y2O2S:Yb3+,Er3+@Au nanocrystals.
Fig. 9. (a) UC luminescence spectra of Y2O3/Y2O2S:Yb3+,Er3+ prepared with different amounts of sulfur powder. Inset shows the UC luminescence spectra of Y2O3/ Y2O2S:Yb3+,Er3+ with 350–430 nm. (b) UC luminescence spectra of Y2O3/Y2O2S:Yb3+,Er3+ prepared with 0.025 g sulfur powder under different excitation power.
The SEM images in Figs. 3 and 4 indicated that the Y2O3/ Y2O2S:Yb3+,Er3+ and Y2O3/Y2O2S:Yb3+,Tm3+ nanoparticles are in spherical shape. The TEM image of Y2O3/Y2O2S:Yb3+,Tm3+ is shown in Fig. 5. Fig. 5(b) shows TEM image of the Y2O3/Y2O2S:Yb3+,Er3+ nanoparticle prepared with 0.025 g sulfur powder. The concentration of S has no significant effect on the morphology of the samples, because the nanoparticles are a little reunited and the morphology is irregular. Further detailed component analysis on the Y2O3/ Y2O2S:Yb3+,Er3+@Au nanoparticle was carried out by the high-resolution transmission electron microscope (HRTEM), as shown in Fig. 5(c–e). Typical HRTEM photographs indicate three interplanar spacings of 0.433, 0.293 and 0.235 nm corresponding to the < 211 > plane of Y2O2S:Yb3+,Er3+, < 101 > plane of Y2O3:Yb3+,Er3+ and < 111 > plane of Au, respectively. The results indicated that Au exists on the surface of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites. The elemental analysis of Y2O3/Y2O2S:Yb3+,Er3+@Au nanoparticles was performed by XPS, as shown in Fig. 6. The O 1 s peaks are observed at 528.7 eV. The values of 394.02, 301.88, 158.4 eV and 20.18 eV are assigned for Y 3 s, Y 3p, Y 3d, and Y 4 P speaks, respectively. The S 2p peak is observed at 170 eV. It was observed at 87.3 eV peak indicates the presence of the Au 4f. Fig. 7 shows the high resolution XPS spectra of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites. The O 1 s spectrum exhibits at 526.82, 528.67 and 530.65 eV, as displayed in Fig. 7(a). The Y 3d3/2 spectral peaks were at 155.4 eV, and the
spectrometer. Dynamic light scattering (DLS) experiments were performed by a Malvern Zetasizer (Nano-ZS, USA). 3. Results and discussion 3.1. Crystal structures and morphologies The XRD patterns of the Y2O3:Yb3+,Er3+ and Y2O3/ Y2O2S:Yb3+,Er3+ nanocomposites as demonstrated in Fig. 1(a). The diffraction peaks of Y2O3:Yb3+,Er3+ can be indexed to the cubic phase Y2O3 (JCPDS 43-1036), and the diffraction peaks of Y2O2S:Yb3+,Er3+ can be indexed to the hexagonal phase Y2O2S (JCPDS 24-1424). It is noted that the pure Y2O2S:Ln3+ was obtained, the corresponding sulfur powder was set as 2.0 g. The Raman spectrum of Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites was displayed in Fig. 1(b). The results show that Y2O3:Yb3+,Er3+ and Y2O2S:Yb3+,Er3+ coexists in Y2O3/Y2O2S:Yb3+,Er3+ nanocomposites. The Raman active modes of Y2O3:Yb3+,Er3+ are characterized by three bands at approximately 300∼450 cm−1, which can be induced by the Fg + Eg and Fg + Ag modes. The Raman active modes of Y2O2S:Yb3+,Er3+ detected at 460 cm−1 were identified to the Eg modes. Fig. 2 indicates the dynamic light scattering spectra of Y2O3/ Y2O2S:Ln3+ in ethanol. The results indicated that the mean particle size of Y2O3/Y2O2S:Ln3+ is about 200 nm. 150
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Fig. 10. (a) UC luminescence spectra of Y2O3/ Y2O2S:Yb3+,Tm3+ prepared with different amounts of sulfur powder. Inset shows the enlarged view that the UC luminescence spectra of Y2O3/Y2O2S:Yb3+,Tm3+ with 400–750 nm. (b,c) UC luminescence spectra of Y2O3/ Y2O2S:Yb3+,Tm3+ prepared with 0.025 g sulfur powder under different excitation power. Inset shows the photographs of samples lighting by 980 nm excitation. (d) The CIE 1931 chromaticity diagram of Y2O3/Y2O2S:Yb3+,Tm3+ prepared with 0.025 g sulfur powder.
Fig. 11. (a) Plots (log-log) of emission intensity versus pump power density of Y2O3/Y2O2S:20%Yb3+,2%Er3+ prepared with 0.025 g sulfur powder.
Fig. 12. Plots (log-log) of emission intensity versus pump power density of Y2O3/Y2O2S:20%Yb3+,1%Tm3+ prepared with 0.025 g sulfur powder.
Y 3d5/2 spectral peaks were at 157.5 and 158.65 eV, as presented in Fig. 7(b). The S 2p2/3 spectral peaks were at 166.5 and 170.23 eV, as illustrated in Fig. 7(c). In addition, Fig. 7(d) shows the Au 4f spectral peaks were at 83.7and 87.3 eV. Fig. 8(a) shows the IR spectra of Y2O3/Y2O2S:Yb3+,Er3+ and Y2O3/ Y2O2S:Yb3+,Er3+@Au nanocomposites, the peak at 580 cm−1 can be attributed to YeO lattice vibrations, the peak at 1580 cm−1and 1420 cm−1 were attributed to the νOH and νCO stretching vibrations, respectively. The peak at 3450 cm−1 corresponds to eOH vibration. It is noted that the vibration peak moved to a higher wavenumber with increasing the present of gold particles, suggesting the formation of Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites. Since the sodium citrate
was used when the Au nanoparticle was synthesized, the carboxyl vibration peak of the material was significantly enhanced. It is also due to the presence of trisodium citrate that makes the material hydrophilic. Moreover, to further prove the coexistence of Y2O3/Y2O2S:Yb3+,Er3+ and Au in the nanocrystals, the Y2O3/Y2O2S:Yb3+,Er3+@Au nanocomposites were confirmed by energy-dispersive X-ray spectroscopy (EDS), as shown in Fig. 8(b).The results indicate that the elemental components are O, Y, S and Au. 3.2. UC luminescence Fig. 9(a) shows the UC luminescence spectra of the as-produced 151
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Fig. 13. (a) Absorption spectrum of Au nanocrystals (red line) exhibits significant spectral overlap with the UC emission spectrum (blacked line) of Y2O3/ Y2O2S:Yb3+,Er3+ nanocrystals. (b) UC fluorescence response of Y2O3/Y2O2S:Yb3+,Er3+@Au UCNPs after incubation with glucose solution of different concentrations (0–1.67 μM). (c) Plot of the fluorescence intensity of Y2O3/Y2O2S:Yb3+,Er3+@Au at 980 nm excitation against the glucose concentration. (d) The fluorescence intensity changes of complex upon addition of different analytes. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Y2O3/Y2O2S:18%Yb3+,2%Er3+ prepared with different amounts of sulfur powder under 980 nm excitation. The weak emission peaks centered at 385 and 410 nm can be attributed to the 4G11/2 → 4I15/2 and 4 F9/2 → 4I15/2 transitions, respectively. The emission bands in the green region centered at 525 and 550 nm are separately ascribed to the transitions from the 2H11/2 and 4S3/2 excited states to the 4I15/2 ground state. The emission band in the red region centered at 660 nm is ascribed to the transitions from the 4F9/2 excited state to the ground state. The CIE chromaticity coordinates of Y2O3/Y2O2S:18%Yb3+,2%Er3+ prepared with 0.025 g sulfur powder were calculated to be (0.346, 0.537). Fig. 9(b) reveals the UC luminescence spectra of the Y2O3/ Y2O2S:Yb3+,Er3+ nanoparticles (prepared with 0.025 g sulfur powder) under different excitation power. As can be seen, with the increase in power, luminescence intensity is increasing. It is well known that sulfide has lower phonon energy, while oxide has higher phonon energy. The low phonon energy of the matrix material helps to reduce the nonradiative transition probability and improve the efficiency of UC luminescence. However, phonon assisted energy transfer is an important process for UC luminescence. And thus, enhanced UC luminescence of Y2O3/Y2O2S:Yb3+,Er3+/ nanocomposites were obtained. Fig. 10(a) shows the UC luminescence spectra of Y2O3/Y2O2S:18% Yb3+,2%Tm3+ prepared with different amounts of sulfur powder under 980 nm excitation. The 1G4 → 3H6, 3F2/3 → 3H6 and 3H4 → 3H6 transitions were observed. Fig. 10(b,c) shows the UC luminescence spectra of the Y2O3/Y2O2S:18%Yb3+,2%Tm3+ nanoparticles (prepared with 0.025 g sulfur powder) under different excitation power. Inset of Fig. 10(c) shows the photographs of samples lighting by 980 nm excitation. The CIE chromaticity coordinates of Y2O3/Y2O2S:18% Yb3+,2%Tm3+ (prepared with 0.025 g sulfur powder) was calculated to be (0.306, 0.309), as shown in Fig. 10(d). To research the fundamental UC mechanisms of Y2O3/ Y2O2S:Yb3+,Er3+, the pumping power dependence of the fluorescent
intensity was analyzed, as presented in Fig. 11. Obviously, the population of the 4F9/2/4F9/2/2H11/2 comes from two-photon process. The pumping power dependence of the fluorescent intensity for Y2O3/ Y2O2S:Yb3+,Tm3+ was shown in Fig. 12. The population of the 3H4 and 3 F3/2 comes from two-photon process. It is well known that white light can be obtained by co-doping of Er3+ and Tm3+ in samples. Due to the doping amount of Er3+ and Tm3+ needs further adjusting, the experimental results will be reported separately in another article. 3.3. Detection of glucose As mentioned above, strict determination of the amount of glucose in the blood has an important effect on physical health. The main goal of our work is to develop a method based on Y2O3/ Y2O2S:Yb3+,Er3+@Au for rapid monitoring of blood glucose levels. Fig. 13(a) illuminates the UC luminescence spectrum of the as-produced Y2O3/Y2O2S:Yb3+,Er3+ under 980 nm excitation and the UV–vis absorption spectrum of the Au nanocrystals. The results indicated that the plasmon band of Au overlaps well with the UC emission spectra of Y2O3/Y2O2S:Yb3+,Er3+ nanocrystals, indicating high probability of LRET between Y2O3/Y2O2S:Yb3+,Er3+ nanocrystals and Au. As we expected, the UC luminescence intensity increased with increasing glucose concentration, varying from 0 to 1.25 μM (Fig. 13(b)), and the fluorescence intensity at 525 nm was linearly related to the glucose concentration in the ranges of 0–0.835 μM. The calibration function of I = 19.233C+1.49 with a good linearity (R2 = 0.998) for the detection of glucose was acquired, where I is the relative UC luminescence intensity and C is the concentration of glucose presumably, the addition of glucose can result in a relatively significant UC luminescence recovery. As the amount of glucose increases, significant UC luminescence recovery occurs. Therefore, the fluorescence intensity at 525 nm was linearly correlated with the glucose concentration in 152
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ranges. The detection limit of the glucose was calculated to be 0.066 μM according to the 3σ rule (LOD = 3σ/K)16. Of course, the amount of Au in nanocomposites affects the detection limit. If the amount of Au is too small, it is impossible to detect glucose because the effect of fluorescence quenching is not obvious. Furthermore, if the amount of Au is too high, the fluorescence recovery effect was not obvious. Therefore, the appropriate content of Au is beneficial to the optimization of the limit of glucose detection. In addition, when the amount of glucose added from 0.835 to 1.25 umol/L, the fluorescence intensity almost leveled, which is a normal phenomenon. As mentioned above, the Au quenching effect can be reversed in the presence of GOx, leading to decomposition of the Au nanocrystals accompanied by UC luminescence recovery. When the
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H+
chemical reaction (H2 O2 +Au0⟶Au+ + H2 O) reaches the balance, the fluorescence intensity remains constant. To further assess the selectivity of the sensor, the luminescence response of other possible interfering substances including some metal ions was studied in aqueous solutions. The experimental results were presented in Fig. 13(d). Therefore, our experiments are started from a general test of 8 metal ions, including M = Zn2+, Sr2+, Fe3+, Ca2+, Cu2+, Co2+, Mg2+, EDTA and SO42− with a concentration of 10-2 M. Obviously, only glucose can be effectively detected. It is possible to detect glucose selectively from a mixture of analytes when the metal concentration is low. It is noted that we have done a lot of experiments including the detection of glucose based on Y2O3:Yb3+,Er3+@Au. However, the UC luminescence of Y2O3:Yb3+,Er3+ was too weak. And thus, the detection of glucose based on Y2O3:Yb3+,Er3+@Au cannot be carried out at all. 4. Conclusions In conclusion, Y2O3/Y2O2S:Ln3+ (Ln = Yb/Er and Yb/Tm) nanocomposites have been prepared by combining hydrothermal with insitu synthesis method. With the rising amount of sulfur powder, under 980 nm excitation, the upconversion luminescence intensity of Y2O3/ Y2O2S:Ln3+ increased, and then declined. When the mass of sulfur powder is 0.025 g, the UC luminescence intensity of Y2O3/Y2O2S:Ln3+ was the strongest. It is surprised that the UC luminescence intensity of Y2O3/Y2O2S:Ln3+ was much stronger than either Y2O3:Ln3+ or Y2O2S:Ln3+. We also developed a method based on Au modified Y2O3/ Y2O2S:Yb3+,Er3+ for rapid monitoring of blood glucose levels in this paper. The limit of detection of glucose level which based on Y2O3/ Y2O2S:Yb3+,Er3+@Au was only 0.066 μmol/L. This nanosystem is also generalizable and can be easily extended to the detection of various H2O2-involved analytes. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21471050 and 21871079) and the Innovative Project of Postgraduate of Heilongjiang University (YJSCX2018180HLJU). References [1] E. Vezouviou, C.R. Lowe, Biosens. Bioelectron. 68 (2015) 371–381. [2] K. Sun, Y.K. Yang, H. Zhou, S.Y. Yin, W.P. Qin, J.B. Yu, D.T. Chiu, Z. Yuan, X.J. Zhang, C.F. Wu, ACS Nano (2018), https://doi.org/10.1021/acsnano.8b02188. [3] K. Sun, Y. Tang, Q. Li, S.Y. Yin, W.P. Qin, J.B. Yu, D.T. Chiu, Y.B. Liu, Z. Yuan, X.J. Zhang, C.F. Wu, ACS Nano 10 (2016) 6769–6781. [4] S. Liu, B. Yu, F. Li, Y. Ji, T. Zhang, Electrochim. Acta 141 (2014) 161–166. [5] Y.H. Song, J.Y. Chen, H.Y. Liu, Y.G. Song, F.G. Xu, H.L. Tan, L. Wang, Electrochim. Acta 158 (2015) 56–63. [6] A.A. Ibrahim, R. Ahmad, A. Umar, M.S. Al-Assiri, A.E. Al-Salami, R. Kumar, S.G. Ansari, S. Baskoutas, Biosens. Bioelectron. 98 (2017) 254–260. [7] M.S. Steiner, A. Duerkop, O.S. Wolfbeis, Chem. Soc. Rev. 40 (2011) 4805–4839.
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