mater.scichina.com  link.springer.com Published online 13 December 2016 | doi: 10.1007/s40843-016-5145-1Sci China Mater  2017, 60(1): 68–74

Down-shifting luminescence of water solubleNaYF4:Eu3+@Ag core-shell nanocrystals forfluorescence turn-on detection of glucoseDi Wang1, Ruihong Wang1, Lijuan Liu1, Yang Qu1, Guofeng Wang1* and Yadong Li2

ABSTRACT  Techniques for detecting glucose are developingat a breathtaking speed because diabetes mellitus can causemany serious complications, such as blindness, high bloodpressure heart disease and kidney failure. Herein, water sol-uble NaYF4:Eu3+@Ag core-shell nanocrystals for glucose de-tection with lower detection limit have been successfully de-veloped, using NaYF4:Eu3+ cores as the energy donors andAg shells as the efficient quenchers through energy transfer.After immobilization of glucose oxidase (GOx) on the sur-face of NaYF4:Eu3+@Ag core-shell nanocrystals, the Ag shellscan be decomposed in the presence of glucose, accompaniedby down-shifting luminescence recovery. The limit of detec-tion of NaYF4:Eu3+@Ag was 0.12 μmol L−1. Therefore, theNaYF4:Eu3+@Ag can be easily extended to the detection of avariety of H2O2-involved analytes.

Keywords:  NaYF4:Eu3+@Ag, nanocrystals, luminescence, glu-cose

INTRODUCTIONRecently, luminescence-based techniques have continuedto attract considerable attention because of their wide po-tential in the fields of optical devices and biomedicine, suchas displays, immunoassays, and anticounterfeiting [1–4].In particular, luminescent inorganic nanomaterials have at-tracted considerable interest owing to their tremendous po-tential applications and for fundamental science researchin many fields [5–10]. In terms of the mechanism of lu-minescence, rare earth (RE) luminescence can be dividedinto down-shifting and up-conversion emission processes.The down-shifting process is the conversion of higher-en-ergy photons into lower-energy photons, which often re-quires two main components, an inorganic matrix (known

as the host) and activated Ln3+ doping ions (activators) [11].Many types of inorganic compounds, such as oxides, flu-orides, phosphates, and vanadates, have been widely usedas host materials [12–15]. Among these materials, fluo-rides doped with RE ions have low photon energies andhigh quantum efficiencies, giving them potential for wide-spread applications in optical communication, display de-vices, and solid-state lasers. Especially, NaYF4 is acknowl-edged as the most efficient host material at present [16].

As a common metabolic disease, diabetes mellitus cancause many serious complications, such as blindness, highblood pressure heart disease and kidney failure [17,18].And thus, the burgeoning field of the glucose detection isdeveloping at a breathtaking speed in recent years. The de-tection of glucose at low concentration solution with highsensitivity and specificity has been of great interest. Upuntil now, conventional methods for assay of glucose aregenerally based on electrochemical, colorimetric, chemilu-minescence and fluorescence methods [19–24]. However,most of these approaches suffer from some shortcomings,such as sophisticated instrumentation, complicated oper-ation, and time-consuming immobilizing processes. TheRE luminescence can offer the opportunity to decreasethe limit of detection as well as improve the sensitivityand specificity for assay of glucose. In comparison toorganic dyes and semiconductor quantum dots, RE-dopednanocrystals show superior chemical and optical prop-erties, including low toxicity, large effective Stokes shifts,sharp emissions, long fluorescence lifetimes, and highresistance to photobleaching [25–29]. To the best of ourknowledge, there have been no reports on the glucose

1 Key Laboratory of Functional Inorganic Materials Chemistry (Ministry of Education), School of Chemistry and Materials Science, Heilongjiang Uni-versity, Harbin 150080, China

2 Department of Chemistry, Tsinghua University, Beijing 100084, China*Corresponding author (email: wanggf_w@163.com)

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assays based on down-shifting of NaYF4:Eu3+@Ag to date.Herein, we reported a down-shifting fluorescence

detection method based on NaYF4:Eu3+@Ag core-shellnanocrystals for rapid detection of glucose, which is reliedon the RE fluorescence release effect. After immobilizationof glucose oxidase (GOx) on the surface of NaYF4:Eu3+@Agcore-shell nanocrystals, the fluorescence of NaYF4:Eu3+ canbe recovered by the addition of glucose, which can oxidizethe Ag shells to Ag+ ions due to the enzymatic conversionof glucose by GOx to generate H2O2 [30–33]. The limit ofdetection of NaYF4:Eu3+@Ag is 0.12 μmol L−1.

EXPERIMENTAL SECTION

Synthesis of water soluble NaYF4:Ln3+

All the RE nitrates used for synthesis were of 99.999% pu-rity. GOx was purchased from Aladdin Industrial Corpo-ration (Shanghai, China). The other chemicals were of an-alytical grade and used directly without further purifica-tion. Trisodium citrate (1.176 g), 0.6 mL of Eu(NO3)3 (0.5mol L−1) aqueous solution and 3 g NaNO3 were dissolvedinto ultrapure water (5 mL) under stirring for 20 min, then0.252 g NaF was added into the above mixture and thor-oughly stirred. The colloidal solution was transferred intoa 30-mL Teflon-lined autoclave and heated at 180°C for 12h. The systems were then allowed to cool to room temper-ature. The final products were collected by means of cen-trifugation and washed with diluted trisodium citrate solu-tion for several times.

Preparation of NaYF4:Eu3+@AgThe obtained NaYF4:Eu3+ powders were dispersed intrisodium citrate solution and some AgNO3 (0.05 mol L−1)solution was added into the solution. And then the mixturesolution was stirred and heated to 99°C slowly. Finally,the obtained products were centrifugally precipitated andwashed several times with ultrapure water.

Immobilization of GOx on NaYF4:Eu3+@AgThe NaYF4:Eu3+@Ag core-shell nanocrystals were trans-ferred to 20 mL of 2 wt.% glutaraldehyde solution. Aftervigorous stirring, the solution was dried at room tem-perature. Then GOx was immobilized on the surface ofNaYF4:Eu3+@Ag for 30 h with 40 mL of GOx solution(100 U mL−1) at 4°C. The product was collected by cen-trifugation and washed several times with ultrapure water,and ultrasonic dispersed in 20 mL ultrapure water. Theresulting NaYF4:Eu3+@Ag-GOx was saved at 4°C for lateruse.

Glucose detectionOne mililiter of the NaYF4:Eu3+@Ag-GOx was further dis-persed in ultrapure water, and different amounts of glucosesolution were added into the solution. Then the mixturesolution was diluted to 3 mL with ultrapure water beforemixing the solution thoroughly. Finally, the fluorescencespectra of the mixture solution were measured after incu-bation at room temperature for 1 min.

Materials characterizationThe crystal structure was analyzed by X-ray powderdiffraction (XRD) patterns using a Bruker D8 Advancediffractometer and Cu Kα radiation (λ = 1.5406 Å, 40 kV,40 mA).

The size and morphology of the final products wereinvestigated by scanning electron microscopy (SEM,Hitachi, S-4800) and transmission electron microscopy(TEM, JEOL, JEM-2100). Nitrogen adsorption-desorptionisothermswere collected using a Tristar II 3020 surface areaand porosity analyzer (micromeritics). UV-vis absorptionspectra were determined by a UV-vis spectrophotometer(Shimadzu UV-2550, Tokyo, Japan). The laser beam wasfocused with a 50× objective lens to a ca. 1 μm spot on thesurface of the sample.

The photoluminescence spectra were recorded with aHitachi F-4600 fluorescence spectrophotometer at roomtemperature. For comparison of the luminescence prop-erties of different samples, the luminescence spectra ofNaYF4:Eu3+@Ag (powder) were measured with the sameinstrument parameters (2.5 nm for spectral resolution(full-width-half-maximum, FWHM) of the spectropho-tometer and 700 V for photon multiple tube voltage). Forglucose detection, the instrument parameter was 5.0 nmfor spectral resolution (FWHM) of the spectrophotometer.

RESULTS AND DISCUSSION

Design principle of NaYF4:Eu3+@Ag for glucose detectionThe design strategy for glucose detection was based on thedown-shifting luminescence recovery of NaYF4:Eu3+@Agcore-shell nanocrystals in the presence of H2O2 (Scheme1). First, the Ag nanoparticles were formed and assem-bled on the surface of NaYF4:Eu3+ to form NaYF4:Eu3+@Agcore-shell nanocrystals. The fluorescence quenching willoccur accompanied by the energy transfer (ET) betweenNaYF4:Eu3+ and Ag. It is well known that glucose can beoxidized by oxygen (O2) to produce H2O2 in the presence ofGOx and Ag nanocrystals can be etched and transformedinto Ag+ by adding a small amount of H2O2. And thus, the

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Scheme 1   Design and principle for glucose detection using the NaYF4:Eu3+@Ag core-shell nanocrystals.

Ag quenching effect can be reversed in the presence ofGOx, leading to decomposition of the Ag nanocrystals ac-companied by down-shifting luminescence recovery. Thereaction of Ag to Ag+ in the presence of a small amount ofH2O2 can be represented as Equation (1):

-D-C H O O H O D-C H O COOH H O

H O Ag Ag H O

6 12 6 2 2

GOx

5 11 5 2 2

2 20 H

2

+ + +

+ +++

(1)So, a sensitive and cost effective down-shifting fluo-

rescent assay can be achieved for monitoring the glucosethrough the detection of enzymatically generated H2O2.

Sample crystal strutures and morphologiesThe XRD patterns of pure NaYF4:Eu3+ and NaYF4:Eu3+@Agcore-shell nanocrystals are shown in Fig. 1a. It can be seenfrom the XRD pattern of the bareNaYF4:Eu3+ (red line) thatthey are well crystallized and all the diffraction peaks agreewell with those of the pure hexagonal phase NaYF4 (JPCDS16-0334). No other impurity peaks were detected. In theXRD pattern of the NaYF4:Eu3+@Ag core-shell nanocrys-tals (black line), the diffraction peaks of Ag appear besides

the peaks of hexagonal phase NaYF4:Eu3+, which indicatesthe formation of NaYF4:Eu3+@Ag composite structure.Moreover, to further prove the coexistence of NaYF4:Eu3+

and Ag in the nanocrystals, the NaYF4:Eu3+@Ag core-shellnanocrystals were confirmed by energy-dispersive X-rayspectroscopy (EDX), as shown in Fig. 1b. The resultsindicate that the elemental components are O, Na, F, Y, Eu,and Ag.

The TEM image of the NaYF4:Eu3+ in Fig. 2a shows thatthe as-prepared NaYF4:Eu3+ hexagonal plates with an aver-age size of 150 nm are monodisperse. Figs 2b and c showtheTEM image of theNaYF4:Eu3+@Ag core-shell nanocrys-tals. Obviously, the NaYF4:Eu3+@Ag with hexagonal geom-etry is very similar to the NaYF4:Eu3+ parents. The cen-tral part of the hexagonal plates is dark grey and the edgesare light grey, suggesting the formation of core-shell nanos-tructures. Typical high-resolution TEM (HRTEM) imageof the NaYF4:Eu3+@Ag core-shell nanocrystals shows twointerplanar spacings of 0.282 and 0.303 nm correspondingto the ⟨104⟩ plane of Ag and ⟨311⟩ plane of NaYF4:Eu3+, re-spectively.

Figure 1    (a) XRD patterns and (b) EDX analysis of NaYF4:Eu3+ and NaYF4:Eu3+@Ag (Ln3+:Ag+ = 1:0.02) core-shell nanocrystals .

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Figure 2   TEM and HRTEM images of (a) NaYF4:Eu3+ and (b,c) NaYF4:Eu3+@Ag (Ln3+:Ag+ = 1:0.02) core-shell nanocrystals.

Photoluminescence of NaYF4:Eu3+ and NaYF4:Eu3+@AgFig. S1 in Supplementary information shows the emissionspectra of NaYF4:Eu3+ nanocrystals doped with differentconcentrations of Eu3+ under 396 nm excitation. The spec-tral peaks correspond to the following transitions: 5D0→7F1

(~595 nm), 5D0→7F2 (~619 nm), 5D0→7F3 (~657 nm), and5D0→7F4 (~698 nm). It is obvious that the 5D0→7F2 transi-tion has the strongest intensity. As expected, the lumines-cence for the NaYF4:Eu3+ cores is obviously quenched byAg shells via ET from the NaYF4:Eu3+ to Ag. The samplewith a dopant concentration of 20 mol.% shows the high-est emission intensity. The corresponding excitation spec-tra of NaYF4:Eu3+ with different Eu3+ concentrations mon-itored at 619 nm are shown in Fig. S2. Fig. S3 showsthe emission spectra of NaYF4:Eu3+ (20 mol.%) nanocrys-tals excited at different wavelengths. The intensity ratio ofthe 5D0→7F2 to the 5D0→7F1 transition remains unchangedwith excitation wavelength. The emission intensities werethe strongest when the excitation was performed at 396nm. Fig. S4 shows the excitation spectra of NaYF4:Eu3+ (20

mol.%) nanocrystals monitored at different wavelengths.Fig. 3a shows the emission spectra of NaYF4:Eu3+@Ag

with different Ag contents. With the increase of the Agcontent, the luminescence intensities of NaYF4:Eu3+@Agare weakened gradually, which can be attributed to the ETfrom NaYF4:Eu3+ (core) to Ag (shell), which will be dis-cussed later. Fig. S5 shows the excitation spectra of theNaYF4:Eu3+@Ag core-shell nanocrystals with different Agcontents. The influence of the Ag content on the quench-ing efficiency of NaYF4:Eu3+@Ag at 619 nm is shown in Fig.3b. The quenching efficiency is presented as (F0 − F)/F0,where F0 and F represent the fluorescence intensity at 619nm without and with Ag modification, respectively.

Fig. S6 shows the emission spectra of NaYF4:Eu3+@Ag(Eu3+:Ag+ = 1:0.002) excited at different wavelengths. Itis noted that a broad emission band centered at ~420 nmis observed, which corresponds to the plasmon resonancepeak from Ag shells. Fig. S7 shows the excitation spectra ofNaYF4:Eu3+@Ag (Eu3+:Ag+= 1:0.002) monitored at differentwavelengths.

Figure 3    (a) Emission spectra of NaYF4:Eu3+@Ag with different Ag contents. (b) Relationship between the fluorescence quenching efficiency ofNaYF4:Eu3+@Ag at 619 nm and the Ag content.

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In order to investigate the ET from NaYF4:Eu3+ to Ag, theUV-vis absorption spectrum of the Ag nanocrystals wasrecorded, as shown in Fig. 4a. The results indicate that theplasmon band of Ag overlaps well with the excitation spec-tra of NaYF4:Eu3+ nanocrystals, indicating high probabilityof ET between NaYF4:Eu3+ nanocrystals and Ag. And thus,fluorescence quenching will occur accompanied by the res-onance ET. Fig. 4b shows the plasmon resonance peak fromAg in NaYF4:Eu3+@Ag with different Ag contents. The in-tensity of the plasmon resonance peak increased with in-creasing Ag content first, and then decreased drastically.

The possible ET mechanism from NaYF4:Eu3+ to Ag isillustrated on the basis of energy matching conditions,as shown in Fig. S8. In the proposed ET system, theNaYF4:Eu3+ serves as the energy donor and Ag is the energyreceptor. The NaYF4:Eu3+ exhibits four emission lines at595, 619, 654 and 700 nm, which could be assigned to5D0→7F1, 5D0→7F2, 5D0→7F3, and 5D0→7F4 transitions. TheET from the 5D1,2,3 and 5L7 levels of Eu3+ ions to Ag shouldoccur in the NaYF4:Eu3+@Ag core@shell nanocrystals,which leads to the decrease of the luminescence intensityof NaYF4:Eu3+.

Detection of glucose based on NaYF4:Eu3+@AgConsidering the significant importance of the monitoringof glucose levels, we further interrogated the feasibility ofthe NaYF4:Eu3+@Ag core-shell nanocrystals for glucosedetection. It is noted that a slight variation in the mea-surement condition may cause a noted difference. Afteroptimizing the experimental conditions, NaYF4:Eu3+@Ag(Ln3+:Ag+ = 1:0.02) was used to detect glucose. Theinstrument parameter was 5.0 nm for spectral resolu-tion (FWHM) of the spectrophotometer. Fig. 5a shows

the emission spectra of the NaYF4:Eu3+@Ag core-shellnanocrystals in the presence of glucose solution under396 nm excitation. Obviously, the emission intensity at619 nm is found to gradually increase with increasingthe concentrations of glucose in the range of 0.33–6.6μmol L−1. It is noted that the emission intensity exhibitsa linear correlation to the concentration of glucose in therange of 0.33–3.3 μmol L−1. The calibration function of I= 20.493C + 131.58 with a good linearity (R2 = 0.9944) forthe glucose analysis was obtained, where I is the relativefluorescence intensity andC is the concentration of glucose(μmol L−1). Therefore, the glucose concentration over therange of 0.33–3.3 μmol L−1 (Fig. 5b) can be acquired at ameasured fluorescence intensity, with the limit of detection(LOD=3σ/K) being calculated as 0.12 μmol L−1.

CONCLUSIONSIn conclusion, we reported a down-shifting fluorescencedetection system based on Ag shell-modified NaYF4:Eu3+

nanocrystals for rapid detection of glucose. In this strat-egy, NaYF4:Eu3+ nanocrystals were synthesized using afacile hydrothermal method, and then, Ag shells weregrown on the surface of the NaYF4:Eu3+ nanocrystals. Agshells on the surface of NaYF4:Eu3+ nanocrystals serve as aquencher. After immobilization of GOx on the surface ofthe NaYF4:Eu3+@Ag core-shell nanocrystals, the fluores-cence of NaYF4:Eu3+ can be recovered by the addition ofglucose. It is worth mentioning that the GOx enzyme is anoxido-reductase, by which the glucose can be oxidized toform H2O2 and Ag shells can rapidly react with H2O2. Thelimit of detection of NaYF4:Eu3+@Ag was 0.12 μmol L−1.The proposed approach holds great potential for diabetesmellitus research and clinical diagnosis.

Figure 4    (a) Absorption spectrum of Ag nanocrystals (blue line) exhibits significant spectral overlap with the excitation spectrum (red line) and emis-sion spectrum (blacked line) of NaYF4:Eu3+ nanocrystals. (b) The plasmon resonance peaks from Ag in NaYF4:Eu3+@Ag with different Ag contents.

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Figure 5    (a) Emission spectra of NaYF4:Eu3+@Ag as a function of the concentration of glucose in solution. (b) Plot of the fluorescence intensity at 619nm against the glucose concentration.

Received 14 October 2016; accepted 22 November 2016;published online 13 December 2016

1 Wang G, Peng Q, Li Y. Lanthanide-doped nanocrystals: synthe-sis, optical-magnetic properties, and applications. Acc Chem Res,2011, 44: 322–332

2 Wang F, Liu X. Recent advances in the chemistry of lan-thanide-doped upconversion nanocrystals. Chem Soc Rev, 2009,38: 976–989

3 Zhao P, Zhu Y, Yang X, et al. Plasmon-enhanced effi-cient dye-sensitized solar cells using core–shell-structuredβ-NaYF4:Yb,Er@SiO2@Au nanocomposites. J Mater Chem A,2014, 2: 16523–16530

4 Deng M, Tu N, Bai F, et al. Surface functionalization of hydropho-bic nanocrystals with one particle per micelle for bioapplications.Chem Mater, 2012, 24: 2592–2597

5 Wang H, Wang L. One-pot syntheses and cell imaging applicationsof poly(amino acid) coated LaVO4:Eu3+ luminescent nanocrystals.Inorg Chem, 2013, 52: 2439–2445

6 Wang G, Peng Q, Li Y. Upconversion luminescence of monodis-perse CaF2:Yb3+/Er3+ nanocrystals. J Am Chem Soc, 2009, 131:14200–14201

7 Xia Z, Liu Q. Progress in discovery and structural design of colorconversion phosphors for LEDs. Prog Mater Sci, 2016, 84: 59–117

8 Yu M, Su J, Wang G, et al. Pt/Y2O3:Eu3+ composite nanotubes: en-hanced photoluminescence and application in dye-sensitized solarcells. Nano Res, 2016, 9: 2338–2346

9 Palanisamy S, Zhang X, He T. Simple colorimetric detection ofdopamine using modified silver nanoparticles. Sci China Chem,2016, 59: 387–393

10 Zhu W, Dong H, Zhen Y, et al. Challenges of organic “cocrystals”.Sci China Mater, 2015, 58: 854–859

11 Luo W, Liu Y, Chen X. Lanthanide-doped semiconductornanocrystals: electronic structures and optical properties. SciChina Mater, 2015, 58: 819–850

12 Xie X, Liu X. Photonics: upconversion goes broadband. Nat Mater,2012, 11: 842–843

13 Wang Y, Nan F, Cheng Z, et al. Strong tunability of cooperativeenergy transfer in Mn2+-doped (Yb3+, Er3+)/NaYF4 nanocrystals bycoupling with silver nanorod array. Nano Res, 2015, 8: 2970–2977

14 Shi F, Wang J, Zhai X, et al. Facile synthesis of β-NaLuF4 : Yb/Tmhexagonal nanoplates with intense ultraviolet upconversion lumi-nescence. CrystEngComm, 2011, 13: 3782–3787

15 Krämer KW, Biner D, Frei G, et al. Hexagonal sodium yttrium fluo-ride based green and blue emitting upconversion phosphors. ChemMater, 2004, 16: 1244–1251

16 Wang M, Li M, Yang M, et al. NIR-induced highly sensitive detec-tion of latent fingermarks by NaYF4:Yb,Er upconversion nanopar-ticles in a dry powder state. Nano Res, 2015, 8: 1800–1810

17 Kong L, Ren Z, ZhengN, et al. Interconnected 1DCo3O4 nanowireson reduced graphene oxide for enzymeless H2O2 detection. NanoRes, 2015, 8: 469–480

18 Guo GM, Wang XD, Zhou TY, et al. Extended detection range foran optical enzymatic glucose sensor coupling with a novel data-processing method. Sci China Chem, 2010, 53: 1385–1390

19 Sanz V, de Marcos S, Castillo JR, et al. Application of molecularabsorption properties of horseradish peroxidase for self-indicatingenzymatic interactions and analytical methods. J Am Chem Soc,2005, 127: 1038–1048

20 Chen S, Hai X, Chen XW, et al. In situ growth of silver nanoparti-cles on graphene quantum dots for ultrasensitive colorimetric de-tection of H2O2 and glucose. Anal Chem, 2014, 86: 6689–6694

21 Chen Q, Liu M, Zhao J, et al. Water-dispersible silicon dots as aperoxidase mimetic for the highly-sensitive colorimetric detectionof glucose. Chem Commun, 2014, 50: 6771–6774

22 Wang J. Electrochemical glucose biosensors. Chem Rev, 2008, 108:814–825

23 Shen P, Xia Y. Synthesis-modification integration: one-step fabri-cation of boronic acid functionalized carbon dots for fluorescentblood sugar sensing. Anal Chem, 2014, 86: 5323–5329

24 Lan D, Li B, Zhang Z. Chemiluminescence flow biosensor for glu-cose based on gold nanoparticle-enhanced activities of glucose ox-idase and horseradish peroxidase. Biosens Bioelectron, 2008, 24:934–938

25 Bostick DT, Hercules DM. Quantitative determination of bloodglucose using enzyme induced chemiluminescence of luminol.Anal Chem, 1975, 47: 447–452

26 Yang D, Li C, Li G, et al. Colloidal synthesis and remarkable en-hancement of the upconversion luminescence of BaGdF5:Yb3+/Er3+

nanoparticles by active-shell modification. J Mater Chem, 2011,21: 5923–5927

27 Mai HX, Zhang YW, Sun LD, et al. Highly efficient multicolorup-conversion emissions and their mechanisms of monodisperseNaYF4:Yb,Er core and core/shell-structured nanocrystals. J PhysChem C, 2007, 111: 13721–13729

28 Yuan J, Cen Y, Kong XJ, et al. MnO2-nanosheet-modified upcon-

 January 2017 | Vol.60 No.1 73 © Science China Press and Springer-Verlag Berlin Heidelberg 2016

SCIENCE CHINA Materials ARTICLES

version nanosystem for sensitive turn-on fluorescence detection ofH2O2 and glucose in blood. ACS Appl Mater Interfaces, 2015, 7:10548–10555

29 Wang F, Liu X. Upconversion multicolor fine-tuning: visible tonear-infrared emission from lanthanide-doped NaYF4 nanoparti-cles. J Am Chem Soc, 2008, 130: 5642–5643

30 Wang G, Peng Q, Li Y. Luminescence tuning of upconversionnanocrystals. Chem - A Eur J, 2010, 16: 4923–4931

31 Lei S, Wang F, Li W, et al. Reversible wettability between super-hydrophobicity and superhydrophilicity of Ag surface. Sci ChinaMater, 2016, 59: 348–354

32 Duan C, Ren B, Liu H, et al. Flexible SERS active detection fromnovel Ag nano-necklaces as highly reproducible and ultrasensitivetips. Sci China Mater, 2016, 59: 435–443

33 Wang M, Meng G, Huang Q, et al. CNTs-anchored egg shellmembrane decorated with Ag-NPs as cheap but effective SERSsubstrates. Sci China Mater, 2015, 58: 198–203

Acknowledgments    This work was supported by the National NaturalScience Foundation of China (21471050 and 21501052), the ChinaPostdoctoral Science Foundation (2015M570304), the PostdoctoralScience Foundation of Heilongjiang Province (LBH-TZ06019), theNatural Science Foundation of Heilongjiang Province (ZD201301d),and the Science Foundation for Excellent Youth of Harbin City of China(2016RQQXJ099).

Author contributions     Wang G designed and engineered the samples;Wang D and Wang R performed the experiments; Qu Y and Liu L wrotethe paper with support from Wang D. All authors contributed to thegeneral discussion.

Conflict of interest     The authors declare that they have no conflict ofinterest.

Supplementary information     Supporting data are available in the on-line version of the paper.

Di Wang is currently a master candidate at Heilongjiang University. She joined Professor Guofeng Wang’s research groupin 2015, mainly working on the synthesis and application of Ln3+-doped nanocrystals.

Guofeng Wang is a professor at the Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education,School of Chemistry and Materials Science, Heilongjiang University. Her current research is focused on the synthesis andapplication of Ln3+-doped nanocrystals.

水溶性NaYF4:Eu3+@Ag 核-壳纳米晶的下转换荧光及其在葡萄糖检测中的应用王迪1, 王瑞红1, 刘丽娟1, 曲阳1, 王国凤1*, 李亚栋2

摘要   糖尿病可引起许多严重的并发症,例如失明,血压心脏病和肾衰竭等. 因此,葡萄糖检测技术正在以惊人的速度发展. 本文合成了水溶性的NaYF4:Eu3+@Ag核-壳纳米晶体,通过能量转移, Ag壳层可以有效吸收NaYF4:Eu3+的能量,导致Eu3+离子荧光淬灭. 在NaYF4:Eu3 +@Ag核-壳纳米晶体的表面上固定葡萄糖氧化酶(GOx)后, 通过加入一定量的葡萄糖, Ag纳米粒子可以分解成Ag+, 并伴随着Eu3+的荧光恢复. 结果表明, 该葡萄糖检测方法具有非常低的检测限(0.12 μmol L−1).

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