- Email: [email protected]
Electrogenerated chemiluminescence of Ag2Te quantum dots and its application in sensitive detection of catechol
Journal of Luminescence 190 (2017) 221–227
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Electrogenerated chemiluminescence of Ag2Te quantum dots and its application in sensitive detection of catechol ⁎
Ying Penga, YongPing Donga, , MiMi Aia, HouCheng Dingb, a b
MARK
⁎
School of chemistry and chemical engineering, Anhui University of Technology, Maanshan 243002, China School of Construction Engineering, Anhui University of Technology, Maanshan 243002, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Electrogenerated chemiluminescence Ag2Te quantum dots Catechol Resonance energy transfer
Ag2Te quantum dots (QDs) were synthesized through ion-exchange method with CdTe QDs as precursors. The same size of Ag2Te QDs can be obtained from the different sizes of precursors, which results in the similar fluorescent behaviors. The maximum FL peak of Ag2Te QDs is red-shifted from 510 nm to 950 nm with the increase of ion-exchange time. Strong cathodic ECL of Ag2Te QDs can be observed in neutral condition with K2S2O8 as coreactant, which is much stronger than that of CdTe QDs. The ECL signals exhibit close relationship with the reaction time, the modified amount of QDs, and the K2S2O8 concentration. Resonance energy transfer can occur between Ag2Te QDs ECL and catechol resulting in the decreased ECL signals, which can be used in the sensitively detection of catechol. Under the optimal conditions, the decreased ECL signals varied linearly with the concentrations of catechol in the range of 1.0 × 10−9−1.0 × 10−5 mol L−1 with a detection limit of 0.31 nM (3σ). The ECL sensor exhibited satisfied stability, repeatability and selectivity in the detection of catechol.
1. Introduction Electrogenerated chemiluminescence (ECL) is the optical signal triggered by electrochemical reactions. As an important analytical method, ECL has been widely used due to its outstanding advantages such as simplicity, high sensitivity, and low background signal [1,2]. Among numerous ECL emitter materials, semiconductor quantum dots (QDs), including CdS, CdSe, CdTe and their composites, have been widely investigated during the past few decades because of their unique advantages including high quantum yields of fluorescence, size controlled luminescence, and good stability [3–6]. The biosensing application of QDs ECL has become the most interesting area and many exciting results were obtained [7–11]. However, a serious disadvantage with these popular QDs is that they contain heavy metals, such as cadmium, whose significant toxicity and environmental hazard are well-documented [12–14]. Therefore, the search for benign nanomaterials with excellent optical properties is urgent. Silver chalcogenide semiconductor nanocrystals are ideal materials in bioimaging for its low-toxicity [15]. As one of silver chalcogenide materials, various nanostructures of Ag2Te, including nanowires, nanotubes, nanorods, and nanoparticles, have been reported [16–21]. But there have few studies on the luminescent behaviors of Ag2Te QDs due to the difficulty in the synthesis. Recently, simple cation exchange
⁎
Corresponding authors. E-mail addresses: [email protected] (Y. Dong), [email protected] (H. Ding).
http://dx.doi.org/10.1016/j.jlumin.2017.05.051 Received 7 December 2016; Received in revised form 14 April 2017; Accepted 17 May 2017 Available online 23 May 2017 0022-2313/ © 2017 Elsevier B.V. All rights reserved.
method has been successfully used in the synthesis of Ag2Te QDs, which make it possible for the luminescent applications of Ag2Te QDs [22–26]. For example, Son et al. revealed that cation exchange between cadmium-based nanocrystals (e.g. CdS, CdSe and CdTe QDs) and Ag+ ions can be used to form silver-based nanocrystals in organic phase [22]. Soon afterwards, Ma et al. reported that near-infrared Ag2Te QDs and Ag2Te/ZnS core/shell QDs can be synthesized by facile aqueous cation exchange process between CdTe QDs and Ag+, which is ideal for optical bioimaging in the second biological window [23]. Pang et al. reported for the first time that water-dispersed Ag2Se QDs can generate strong cathodic ECL in aqueous solution, which can be used in the sensitive detection of dopamine [27]. The above work revealed that silver chalcogenide QDs are the potential alternative for cadmiumbased QDs in ECL investigation. However, as far as we know, ECL behavior of Ag2Te QDs has never been reported. Herein, water-dispersed Ag2Te QDs were synthesized through cation exchange between CdTe QDs and Ag+. Strong and stable cathodic ECL of Ag2Te QDs was obtained in neutral condition with K2S2O8 as coreactant. Catechol exhibited apparent inhibiting effect on cathodic ECL signal due to the resonance energy transfer and could be sensitively detected.
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 1. ECL of bare GCE, CdTe/GCE and Ag2Te/GCE (A), EDX spectra of CdTe QDs and Ag2Te QDs (B), Fluorescence spectra of Ag2Te QDs incubating in AgNO3 solution for 5 min (C) and 30 min (D), UV–vis absorption spectra of Ag2Te QDs, CdTe QDs, and AgNO3 (E), Cyclic voltammograms of the bare GCE and the Ag2Te/GCE in PBS with and without K2S2O8 (F). PBS, 0.1 mol L−1; pH, 7.4; K2S2O8, 0. 1 mol L−1; potential scan rate, 100 mV s−1.
2. Experimental sections
Ltd., China) at room temperature. All electrochemical experiments were carried out with a conventional three-electrode system, including a modified GCE as the working electrode, a platinum wire as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode, respectively. A homemade 5 mL cylindroid glass cell was used as ECL cell and was placed directly in front of the photomultiplier tube (PMT), and the voltage of the PMT was set at −800 V in all detections. The UV–vis absorption spectra were obtained on a Shimadzu UV-3600 spectrophotometer (Shimadzu, Japan). The fluorescence (FL) measurements were carried out on a RF-5301PC FL spectrophotometer (Shimadzu, Japan) and Fluorolog-3-tau spectrophotometer (Jobin Yvon, France). The ECL spectrum was obtained by collecting the ECL data during cyclic potential sweep with 8 pieces of filter at 425, 450, 475, 500, 525, 550, 575, and 600 nm, respectively. Transmission electron microscopy (TEM) images and energy diffraction X-ray (EDX) spectra were obtained with a FEI Talos F200X TEM operating at 120 kV of acceleration voltage.
2.1. Chemicals and apparatus All reagents used in the experiments were of analytical grade. Double distilled water was used throughout. 0.1 mol L−1 pH 7.4 phosphate buffer solution (PBS) was prepared by mixing the stock solution of K2HPO4 and KHPO4, and then adjusting the pH with NaOH and H3PO4. Electrochemical measurements were recorded with CHI 760D electrochemical workstation (CH Instruments Co., China). Electrochemical impedance spectroscopy (EIS) was carried out at open circuit potential in 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution containing 0.1 mol L−1 KCl as the supporting electrolyte. The frequency range located 0.01 Hz–100 kHz, and the potential amplitude was set as 5 mV. ECL measurements were conducted on a model MPI-M electrochemiluminescence analyzer (Xi’An Remax Electronic Science & Technology Co. 222
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
are superior to their precursors. The energy diffraction X-ray (EDX) spectra of CdTe QDs and Ag2Te QDs were recorded and shown in Fig. 1B. The EDX results prove the existence of Ag and Te elements in Ag2Te QDs. The atomic ratio of the elements of Ag and Te is nearly 2 : 1, which is close to the appropriate stoichiometry of Ag2Te. Almost no Cd component is retained in the EDX spectrum of Ag2Te QDs, suggesting that the ion-exchange process is completed. Previous work reported that Ag2Te QDs could emit infrared light, which can be used to fabricate bioimaging in the second biological window [23]. In the present work, two kinds of Ag2Te QDs were obtained by incubating CdTe QDs in AgNO3 for different time. It can be found from Fig. 1C and D that the short incubating time leading visible light emission (510 nm) while long incubating time leading infrared light emission (950 nm). It was reported that the FL emission of Ag2S QDs shifted from visible range to infrared range with the increase of incubating time in AgNO3 solution [30]. Therefore, the obtained different FL emission Ag2Te QDs should be due to the different incubating time in AgNO3 solution. Because of the same size, the FL peaks of four Ag2Te QDs are located at the same position either at the visible or at the infrared range only with the difference in FL intensity, which should be due to the difference in surface state during the formation of Ag2Te QDs from CdTe QDs. UV–vis absorption spectra of Ag2Te QDs and CdTe QDs were comparatively studied and shown in Fig. 1E. It can be found that CdTe QDs exhibited apparent absorption in the range of 400–600 nm range. The peak absorption at 530 nm should be result from the existence of Cd2+ because this peak can be found in other cadmium containing QDs, such as CdSe and CdS QDs. AgNO3 has no absorption in this wavelength range, while Ag2Te QDs exhibited wide absorption band from 400 nm to 800 nm, which is in accordance with the reported result [23]. The disappearance of the peak absorption at 530 nm can also be used to confirm the transformation of CdTe QDs to Ag2Te QDs. Electrochemical behaviors of Ag2Te QDs modified electrode were comparatively studied in PBS and K2S2O8/PBS as shown in Fig. 1F. At the bare GCE, no apparent cyclic voltammetric (CV) peak was obtained in PBS while one broad CV peak was obtained around −1.48 V in K2S2O8/PBS, suggesting that the electrochemical reduction of K2S2O8 can occur at this potential. One pair of reduction-oxidation peaks at −1.00 and −0.80 V at the Ag2Te/GCE in PBS can be assigned to the electrochemical reactions of Ag2Te QDs. The electrochemical reduction of K2S2O8 at the Ag2Te/GCE can be found at −1.18 V, which is positively shifted compared with the bare GCE. The increase of reduction current and the decrease of overpotential revealed that Ag2Te QDs can catalyze the electrochemical reduction of K2S2O8.
2.2. Synthesis of CdTe QDs and Ag2Te QDs Mercaptopropionic acid (MPA)-capped CdTe QDs were synthesis referred to the literature with minor revision [28]. 45 μL of 6 mM MPA was first added into 60 mL of 2 mM CdCl2 solution. After adjusted the pH to 11.9 using 1.0 mol L−1 NaOH solution, the resulting clear solution was bubbled with highly pure N2 for 30 min, and 0.50 mL of 0.0625 mol L−1 NaHTe solution was slowly injected and 60 mg NaBH4 was fast added into the vigorously stirred and oxygen-free solution to obtain a yellow brown solution. The obtained QDs solution was refluxed for 40, 80, 120, and 160 min to produce different sizes of QDs (denoted as CdTe-1, CdTe-2, CdTe-3, and CdTe-4). The samples were then dialyzed against doubly distilled water for 5 h to remove excessive MPA. The final QDs solutions were kept in a refrigerator at 4 °C. Ag2Te QDs were synthesized by facile ion-exchange method according to the literature method with minor modification [23]. 12.5 μL of 0.2 mol L−1 AgNO3 and 1 mL of different sizes CdTe QDs were added into a 1.5 mL Eppendorf tube to promote the cation exchange process. Four kinds of Ag2Te QDs were obtained and denoted as Ag2Te-1, Ag2Te2, Ag2Te-3, and Ag2Te-4. The obtained Ag2Te QDs were characterized by TEM, FL, and UV–vis absorption spectroscopy. 2.3. Fabrication of QDs modified electrodes A glassy carbon electrode (GCE, 3 mm in diameter) was mechanically polished to a mirror with alumina pastes of 1.0, 0.3 and 0.05 µm respectively, and then cleaned thoroughly in an ultrasonic cleaner with alcohol and water sequentially. The electrode was rinsed with redistilled water and was dried with blowing N2. Then, 10 μL of QDs was spread on the working area and dried at the room temperature to fabricate QDs modified GCE (denoted as CdTe/GCE and Ag2Te/GCE). 3. Results and discussion 3.1. Synthesis of Ag2Te QDs from CdTe QDs It has already been proven that luminescent CdTe QDs can be widely used in analytical chemistry [29]. In the present work, different sizes of CdTe QDs were obtained by adjusting the refluxing time during the synthesis, and the size distribution of CdTe QDs were shown in Fig. S1. It can be found that the size of CdTe QDs increases with the increase of refluxing time. The FL results confirmed that the maximum FL emission of CdTe QDs is red-shifted with the increase of QDs size (Fig. S2). Fig. 1A revealed that cathodic ECL of CdTe QDs can be obtained in neutral condition with K2S2O8 as coreactant, and the ECL intensity increased with the increase of QDs size. Although CdSe QDs ECL can be obtained in neutral condition, the weak ECL intensities as well as the high-toxic cadmium ions containing in the QDs severely limit its application in ECL biosensor. Therefore, it is necessary to replace cadmium ions with other low-toxic ions. Herein, low-toxic silver ions were used to replace cadmium ions through ion-exchange, and the morphology of synthesized Ag2Te QDs was characterized by TEM. It can be found from Fig. S3 that the Ag2Te QDs synthesized from different sizes of CdTe QDs exhibited almost the same size and morphology. The size distribution analysis revealed that the average sizes of four Ag2Te QDs were all around 6.7 nm, which is consistence with the TEM results (Fig. S4). The possible reason is that the growth process is superior to the nucleation process during the cation exchange process, which results in the formation of same size Ag2Te QDs. ECL behaviors of Ag2Te QDs were investigated in neutral condition, and strong cathodic ECL signals were obtained in the presence of K2S2O8. It can be found from Fig. 1A that the ECL intensities increased in the following order: Ag2Te-1 < Ag2Te-2 < Ag2Te-3 < Ag2Te-4. The ECL intensities of Ag2Te-3 and Ag2Te-4 increased nearly 8-times compared with CdTe QDs, revealing that ECL behaviors of Ag2Te QDs
3.2. Impacting factors of ECL The modified amount of Ag2Te QDs, the concentration of K2S2O8, and the pH values can affect ECL emission. It can be found from Fig. 2A that the ECL intensity increased with the increase of QDs amount. However, large amount of QDs will overflow the working area of the electrode during the electrode modification, which will influence ECL measurement. Therefore, 10 μL of QDs was adopted to modify electrode. Electrochemical impedance spectroscopy (EIS) of different amount of QDs modified electrode was obtained and shown in Fig. 2B. It can be found that the diameter of the semicircle increased with the increase of modified QDs, suggesting the increase of charge transfer resistance between the negatively charged Ag2Te QDs and [Fe (CN)6]3-/4- probe. The EIS results can be used to monitor the successful fabrication of Ag2Te QDs on the GCE. It can be found from Fig. 2C that ECL intensity increased with the increase of K2S2O8 concentration, revealing that K2S2O8 participate the ECL reactions. Because the ECL intensity obtained in 0.1 mol L−1 K2S2O8 solution is strong enough for the ECL detection, 0.1 mol L−1 K2S2O8 solution was chosen in the following study. Fig. 2D displays the effect of pH value on the cathodic ECL. The most intense ECL signal can 223
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 2. (A) Effect of QDs amount; (B) EIS of different amount of QDs modified electrodes; (C) Effect of K2S2O8 concentration; (D) Effect of pH value.
one electrode to monitor the ECL responses, which was shown in Fig. 4A. The relative standard deviation was 2.5% for successive measurements (n = 18) at 1 nM catechol, suggesting a good stability of the proposed sensor for catechol detection. The reproducibility of the sensor for catechol was estimated by determining 1 nM catechol with six sensors as shown in Fig. 4B. Six sensors exhibited similar ECL responses and the relative standard deviation was 1.2%, indicating that the reproducibility of the proposed sensor for catechol detection is acceptable. The long-term stability of the ECL sensor was evaluated by detecting ECL intensity after the Ag2Te/GCE was stored at 4 °C. The ECL intensity decreased to about 92% of its initial response after three weeks of storage, demonstrating that the sensor possesses good longterm stability. Many ECL systems were used in the detection of catechol [33–37]. The comparison between the proposed method and the previous reported methods was shown in Table 1. As can be seen, the present ECL sensor displays a wide linear detection range and lower detection limit which is lower than that of most previous reported sensors. In order to assess the possible practical applications of the ECL sensor in the determination of catechol, the content of catechol was determined by the standard addition method in human blood serum samples (The sample was obtained from Nanjing Gulou Hospital). The serum 1:5 diluted with PBS (pH 7.4) was spiked with catechol at different concentrations. The results in Table S1 show the acceptable relative standard deviation (RSD) and good recoveries. Therefore, this new method is reliable and effective for the determination of catechol.
be obtained in neutral condition, revealing that the present ECL system is suitable for biosensor application. 3.3. Analytical performance of ECL sensor It was reported that luminescent technique can be used in the sensitive detection of phenolic compounds based on their enhancing or inhibiting effects [31,32]. However, similar structure phenolic compounds often exhibited similar effects on ECL signal during the measurement. As a result, these compounds can't be selectively detected. In the present study, benzenediol, including hydroquinone, catechol, and resorcinol, was selected as the model analyte to evaluate the analytical performance of the present ECL system. It can be found from Fig. 3A that resorcinol and hydroquinone can slightly influence ECL signal, while catechol can significantly inhibit ECL signal, revealing that the proposed ECL system can be used in selectively detection of catechol. In order to further evaluate the selectivity of the ECL sensor, the effects of some other analytes, such as glucose, cytochrome c, ascorbic acid, and dopamine, on ECL signals were also investigated. The results found that the most of analytes exhibited negligible effect on ECL signal except dopamine due to its similar structure as that of catechol. The ECL intensity in the presence of 1 mM catechol decreased to the level of background emission and was only 10% of that in the absence of catechol as shown in Fig. 3B, revealing that catechol can be detected based on its significant inhibiting effect towards the cathodic ECL of Ag2Te QDs. In the range of 1.0 × 10−9 − 1.0 × 10−5 mol L−1, the ECL intensities decreased linearly with the concentration of catechol (Fig. 3C). The linear regression equation was determined as I = −313.6logC + 444, with the regression coefficient as 0.9991 (Fig. 3D). The detection limit of catechol was determined as 3.1 × 10−10 mol L−1 (3σ). The stability is an important factor to evaluate the capability of the sensor. The stability of the present ECL sensor was evaluated by using
3.4. ECL mechanism It was reported in the previous work that all QDs/K2S2O8 ECL systems could emit light according to the following pathway: QDs were reduced to radicals by charge injection, while the coreactant S2O82could be reduced to the strong oxidant SO4-•; QDs radicals could react 224
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 3. (A) Effects of 1 mM hydroquinone, catechol, and resorcinol on ECL signal; (B) Comparison between ECL signals of Ag2Te/GCE in the absence and presence of 1 mM catechol; (C) Effects of different concentrations of catechol on ECL signal; (D) Linear relationship between ECL intensity and catechol concentration.
Fig. 4. Stability (A) and repeatability (B) of the ECL sensor in 1 nM catechol solution.
with SO4-• to produce an excited state of QDs (QDs*) which could emit light in the aqueous solution [24,38,39]. In order to elucidate ECL mechanism of Ag2Te QDs, the FL and ECL spectra as well as the electrochemical behaviors of the present ECL system were recorded and shown in Fig. 5. It can be found from Fig. 5A that the ECL spectrum of the present system is the same as the FL spectrum of Ag2Te QDs, revealing that the light emitter is the excited state of Ag2Te QDs. Fig. 5B displays that the maximum FL emission of Ag2Te QDs located at 510 nm, while catechol and K2S2O8 had no light emission. When catechol and K2S2O8 was added into Ag2Te QDs solution, the FL intensity decreased greatly while the peak position didn’t change, revealing that catechol and K2S2O8 could react with the excited state of QDs. Fig. 5C reveals that the absorption spectrum of catechol overlapped with the FL spectrum of Ag2Te QDs, suggesting that resonance energy transfer can occur between catechol and Ag2Te QDs. Electrochemical results (Fig. 5D) reveals that catechol could not apparent change the reduction current and the reduction potential of
Table 1 Comparison of ECL methods for determination of catechol. Sensor
Linear range
Detection limit
References
Oil film-covered carbon paste electrode CdS nanotube/indium thin oxide electrode Graphene/MWNT/gold nanocluster/glassy carbon electrode AuNPs@C60/glassy carbon electrode CdTe/gold electrode Ag2Te/glassy carbon electrode
4 nM–400 nM
0.2 nM
[33]
2.0 μM–10 μM
0.058 μM
[34]
1.0 μM–80 μM
0.3 μM
[35]
62 nM–120 μM
21 nM
[36]
5 nM–1000 nM 1 nM–1000 nM
2 nM 0.31 nM
[37] This work
225
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 5. (A) FL and ECL spectra of Ag2Te QDs; (B) FL spectra of Ag2Te, catechol, K2S2O8, and their complexes; (C) UV–vis absorption spectrum of catechol and FL spectrum of Ag2Te QDs; (D) CV curves of K2S2O8 and K2S2O8/catechol at the bare GCE and the Ag2Te/GCE.
friendly Ag+ in quantum dots makes its low-toxicity and can become a promising candidate material of ECL biosensors in the future.
K2S2O8 at the bare GCE and the Ag2Te/GCE, revealing that catechol could not react with K2S2O8. According to the experimental and the reference results, the mechanism of the cathodic ECL can be proposed as follows: S2O82- + e- → S2O8•3-
(1)
S2O8•3-
(2)
Acknowledgments
Ag2Te + e- → Ag2Te•-
(3)
This work is financially supported by National Natural Science Foundation of China (No. 21575002), Natural Science Foundation from the Bureau of Education of Anhui Province (No. KJ2015A075), Innovation and Entrepreneurship Program for College Students in Anhui Province (201610360020).
Ag2Te•- + SO4•- → Ag2Te* + SO42-
(4)
Appendix A. Supporting information
Ag2Te* → Ag2Te + hv
(5)
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jlumin.2017.05.051.
→
SO42-
+
SO4•-
Previous work revealed that o-benzoquinone residues can efficiently quench the fluorescence emission of QDs by energy transfer [40]. ECL energy transfer (ET) can occur between the excited CdTe QDs and the oxidation product of catechol, leading the quenching effect on the anodic ECL of QDs [25]. Therefore, the possible inhibiting mechanism of catechol is proposed as follows: the strong oxidant SO4-• could oxidize catechol to o-benzoquinone which can accept energy from the excited state of Ag2Te QDs. As a result, the cathodic ECL was inhibited in the presence of catechol.
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
4. Conclusions Water dispersible Ag2Te quantum dots were synthesized through facile ion exchange method with CdTe QDs as precursors. The asprepared Ag2Te QDs exhibited strong cathodic ECL in neutral aqueous solution with K2S2O8 as coreactant. Catechol could significantly inhibit the ECL emission due to the energy transfer between the excited state of Ag2Te QDs and the oxidation product of catechol, based on which catechol can be sensitively detected in the range of 1 nM to 10 μM with the detection limit of 0.31 nM. The substitute of toxic Cd2+ with eco-
[10] [11] [12] [13] [14] [15] [16]
226
M.M. Richter, Chem. Rev. 104 (2004) 3003–3036. W.J. Miao, Chem. Rev. 108 (2008) 2506–2553. J.P. Lei, H.X. Ju, Trac-Trends Anal. Chem. 30 (2011) 1351–1359. W.W. Zhao, X.Y. Dong, J. Wang, F.Y. Kong, J.J. Xu, H.Y. Chen, Chem. Commun. 48 (2012) 5253–5255. W.W. Zhao, Z.Y. Ma, P.P. Yu, X.Y. Dong, J.J. Xu, H.Y. Chen, Anal. Chem. 84 (2012) 917–923. F.A. Esteve-Turrillas, A. Abad-Fuentes, Biosens. Bioelectron. 41 (2013) 12–29. G.F. Jie, B. Liu, H.C. Pan, J.J. Zhu, H.Y. Chen, Anal. Chem. 79 (2007) 5574–5581. X. Liu, H.X. Ju, Anal. Chem. 80 (2008) 5377–5382. S.Y. Deng, L.X. Cheng, J.P. Lei, Y. Cheng, Y. Huang, H.X. Ju, Nanoscale 5 (2013) 5435–5441. H.Y. Liu, S.M. Xu, Z.M. He, A.P. Deng, J.J. Zhu, Anal. Chem. 85 (2013) 3385–3392. S.Y. Deng, H.X. Ju, Analyst 138 (2013) 43–61. X. Michalet, F.F. Pinaud, L.A. Bentolila, J.M. Tsay, S. Doose, J.J. Li, G. Sundaresan, A.M. Wu, S.S. Gambhir, S. Weiss, Science 307 (2005) 538–544. A.M. Derfus, W.C.W. Chan, S.N. Bhatia, Nano Lett. 4 (2004) 11–18. C. Kirchner, T. Liedl, S. Kudera, T. Pellegrino, A.M. Javier, H.E. Gaub, S. Stolzle, N. Fertig, W.J. Parak, Nano Lett. 5 (2005) 331–338. R.J. Gui, H. Jin, Z.H. Wang, L.J. Tan, Coord. Chem. Rev. 296 (2015) 91–124. R.Z. Chen, D.S. Xu, G.L. Guo, L.L. Gui, J. Mater. Chem. 12 (2002) 2435–2438.
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
[28] X. Liu, H. Jiang, J.P. Lei, H.X. Ju, Anal. Chem. 79 (2007) 8055–8060. [29] C. Frigerio, D.S.M. Ribeiro, S.S.M. Rodrigues, V.L.R.G. Abreu, J.A.C. Barbosa, J.A.V. Prior, K.L. Marques, J.L.M. Santos, Anal. Chim. Acta 735 (2012) 9–22. [30] P. Jiang, C.N. Zhu, Z.L. Zhang, Z.Q. Tian, D.W. Pang, Biomaterials 33 (2012) 5130–5135. [31] Q.L. Zhang, H. Cui, A. Myint, L. Mei, L.J. Liu, J. Chromatogr. A 1095 (2005) 94–101. [32] Y.G. Sun, H. Cui, X.Q. Lin, Y.H. Li, H.Z. Zhao, Anal. Chim. Acta 423 (2000) 247–253. [33] X.Y. Chen, R.J. Zheng, S.F. Qin, J.J. Sun, Talanta 101 (2012) 362–367. [34] Y. Wen, F. Luo, Y. Yang, L. Lin, J. Du, Y. Guo, D. Xiao, M.M.F. Choi, Anal. Methods 4 (2012) 053–1059. [35] D. Yuan, S. Chen, R. Yuan, J. Zhang, W. Zhang, Analyst 138 (2013) 6001–6006. [36] Q.Y. Lu, H.X. Hu, Y.Y. Wu, S.H. Chen, D.H. Yuan, R. Yuan, Biosens. Bioelectron. 60 (2014) 325–331. [37] Y.P. Dong, Y. Zhou, J. Wang, Y.Q. Dong, C.M. Wang, Talanta 146 (2016) 266–271. [38] G.F. Jie, B. Liu, H.C. Pan, J.J. Zhu, H.Y. Chen, Anal. Chem. 79 (2007) 5574–5581. [39] G.F. Jie, H.P. Huang, X.L. Sun, J.J. Zhu, Biosens. Bioelectron. 23 (2008) 1896–1899. [40] R. Gill, R. Freeman, J.P. Xu, I. Willner, S. Winograd, I. Shweky, U. Banin, J. Am. Chem. Soc. 128 (2006) 15376–15377.
[17] A.M. Qin, Y.P. Fang, P.F. Tao, J.Y. Zhang, C.Y. Su, Inorg. Chem. 46 (2007) 7403–7409. [18] P.F. Zuo, S.Y. Zhang, B.K. Jin, Y.P. Tian, J.X. Yang, J. Phys. Chem. C 112 (2008) 14825–14829. [19] A. Sahu, L. Qi, M.S. Kang, D. Deng, D.J. Norris, J. Am. Chem. Soc. 133 (2011) 6509–6512. [20] M. Yarema, S. Pichler, M. Sytnyk, R. Seyrkammer, R.T. Lechner, G. Fritz-Popovski, D. Jarzab, K. Szendrei, R. Resel, O. Korovyanko, M.A. Loi, O. Paris, G. Hesser, W. Heiss, ACS Nano 5 (2011) 3758–3765. [21] Y. Du, B. Xu, T. Fu, M. Cai, F. Li, Y. Zhang, Q. Wang, J. Am. Chem. Soc. 132 (2010) 1470–1471. [22] D.H. Son, S.M. Hughes, Y. Yin, A.P. Alivisatos, Science 306 (2004) 1009–1012. [23] C. Chen, X.W. He, L. Gao, N. Ma, ACS Appl. Mater. Interfaces 5 (2013) 1149–1155. [24] M. Yang, R.J. Gui, H. Jin, Z.H. Wang, F.F. Zhang, J.F. Xia, S. Bi, Y.Z. Xia, Colloids Surf. B: Biointerfaces 126 (2015) 115–120. [25] H. Jin, R.J. Gui, J. Sun, Y.F. Wang, Colloids Surf. B: Biointerfaces 143 (2016) 118–123. [26] R.J. Gui, J. Sun, D.X. Liu, Y.F. Wang, H. Jin, Dalton Trans. 43 (2014) 16690–16697. [27] R. Cui, Y.P. Gu, L. Bao, J.Y. Zhao, B.P. Qi, Z.L. Zhang, Z.X. Xie, D.W. Pang, Anal. Chem. 84 (2012) 8932–8935.
227
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Electrogenerated chemiluminescence of Ag2Te quantum dots and its application in sensitive detection of catechol ⁎
Ying Penga, YongPing Donga, , MiMi Aia, HouCheng Dingb, a b
MARK
⁎
School of chemistry and chemical engineering, Anhui University of Technology, Maanshan 243002, China School of Construction Engineering, Anhui University of Technology, Maanshan 243002, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Electrogenerated chemiluminescence Ag2Te quantum dots Catechol Resonance energy transfer
Ag2Te quantum dots (QDs) were synthesized through ion-exchange method with CdTe QDs as precursors. The same size of Ag2Te QDs can be obtained from the different sizes of precursors, which results in the similar fluorescent behaviors. The maximum FL peak of Ag2Te QDs is red-shifted from 510 nm to 950 nm with the increase of ion-exchange time. Strong cathodic ECL of Ag2Te QDs can be observed in neutral condition with K2S2O8 as coreactant, which is much stronger than that of CdTe QDs. The ECL signals exhibit close relationship with the reaction time, the modified amount of QDs, and the K2S2O8 concentration. Resonance energy transfer can occur between Ag2Te QDs ECL and catechol resulting in the decreased ECL signals, which can be used in the sensitively detection of catechol. Under the optimal conditions, the decreased ECL signals varied linearly with the concentrations of catechol in the range of 1.0 × 10−9−1.0 × 10−5 mol L−1 with a detection limit of 0.31 nM (3σ). The ECL sensor exhibited satisfied stability, repeatability and selectivity in the detection of catechol.
1. Introduction Electrogenerated chemiluminescence (ECL) is the optical signal triggered by electrochemical reactions. As an important analytical method, ECL has been widely used due to its outstanding advantages such as simplicity, high sensitivity, and low background signal [1,2]. Among numerous ECL emitter materials, semiconductor quantum dots (QDs), including CdS, CdSe, CdTe and their composites, have been widely investigated during the past few decades because of their unique advantages including high quantum yields of fluorescence, size controlled luminescence, and good stability [3–6]. The biosensing application of QDs ECL has become the most interesting area and many exciting results were obtained [7–11]. However, a serious disadvantage with these popular QDs is that they contain heavy metals, such as cadmium, whose significant toxicity and environmental hazard are well-documented [12–14]. Therefore, the search for benign nanomaterials with excellent optical properties is urgent. Silver chalcogenide semiconductor nanocrystals are ideal materials in bioimaging for its low-toxicity [15]. As one of silver chalcogenide materials, various nanostructures of Ag2Te, including nanowires, nanotubes, nanorods, and nanoparticles, have been reported [16–21]. But there have few studies on the luminescent behaviors of Ag2Te QDs due to the difficulty in the synthesis. Recently, simple cation exchange
⁎
Corresponding authors. E-mail addresses: [email protected] (Y. Dong), [email protected] (H. Ding).
http://dx.doi.org/10.1016/j.jlumin.2017.05.051 Received 7 December 2016; Received in revised form 14 April 2017; Accepted 17 May 2017 Available online 23 May 2017 0022-2313/ © 2017 Elsevier B.V. All rights reserved.
method has been successfully used in the synthesis of Ag2Te QDs, which make it possible for the luminescent applications of Ag2Te QDs [22–26]. For example, Son et al. revealed that cation exchange between cadmium-based nanocrystals (e.g. CdS, CdSe and CdTe QDs) and Ag+ ions can be used to form silver-based nanocrystals in organic phase [22]. Soon afterwards, Ma et al. reported that near-infrared Ag2Te QDs and Ag2Te/ZnS core/shell QDs can be synthesized by facile aqueous cation exchange process between CdTe QDs and Ag+, which is ideal for optical bioimaging in the second biological window [23]. Pang et al. reported for the first time that water-dispersed Ag2Se QDs can generate strong cathodic ECL in aqueous solution, which can be used in the sensitive detection of dopamine [27]. The above work revealed that silver chalcogenide QDs are the potential alternative for cadmiumbased QDs in ECL investigation. However, as far as we know, ECL behavior of Ag2Te QDs has never been reported. Herein, water-dispersed Ag2Te QDs were synthesized through cation exchange between CdTe QDs and Ag+. Strong and stable cathodic ECL of Ag2Te QDs was obtained in neutral condition with K2S2O8 as coreactant. Catechol exhibited apparent inhibiting effect on cathodic ECL signal due to the resonance energy transfer and could be sensitively detected.
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 1. ECL of bare GCE, CdTe/GCE and Ag2Te/GCE (A), EDX spectra of CdTe QDs and Ag2Te QDs (B), Fluorescence spectra of Ag2Te QDs incubating in AgNO3 solution for 5 min (C) and 30 min (D), UV–vis absorption spectra of Ag2Te QDs, CdTe QDs, and AgNO3 (E), Cyclic voltammograms of the bare GCE and the Ag2Te/GCE in PBS with and without K2S2O8 (F). PBS, 0.1 mol L−1; pH, 7.4; K2S2O8, 0. 1 mol L−1; potential scan rate, 100 mV s−1.
2. Experimental sections
Ltd., China) at room temperature. All electrochemical experiments were carried out with a conventional three-electrode system, including a modified GCE as the working electrode, a platinum wire as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode, respectively. A homemade 5 mL cylindroid glass cell was used as ECL cell and was placed directly in front of the photomultiplier tube (PMT), and the voltage of the PMT was set at −800 V in all detections. The UV–vis absorption spectra were obtained on a Shimadzu UV-3600 spectrophotometer (Shimadzu, Japan). The fluorescence (FL) measurements were carried out on a RF-5301PC FL spectrophotometer (Shimadzu, Japan) and Fluorolog-3-tau spectrophotometer (Jobin Yvon, France). The ECL spectrum was obtained by collecting the ECL data during cyclic potential sweep with 8 pieces of filter at 425, 450, 475, 500, 525, 550, 575, and 600 nm, respectively. Transmission electron microscopy (TEM) images and energy diffraction X-ray (EDX) spectra were obtained with a FEI Talos F200X TEM operating at 120 kV of acceleration voltage.
2.1. Chemicals and apparatus All reagents used in the experiments were of analytical grade. Double distilled water was used throughout. 0.1 mol L−1 pH 7.4 phosphate buffer solution (PBS) was prepared by mixing the stock solution of K2HPO4 and KHPO4, and then adjusting the pH with NaOH and H3PO4. Electrochemical measurements were recorded with CHI 760D electrochemical workstation (CH Instruments Co., China). Electrochemical impedance spectroscopy (EIS) was carried out at open circuit potential in 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution containing 0.1 mol L−1 KCl as the supporting electrolyte. The frequency range located 0.01 Hz–100 kHz, and the potential amplitude was set as 5 mV. ECL measurements were conducted on a model MPI-M electrochemiluminescence analyzer (Xi’An Remax Electronic Science & Technology Co. 222
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
are superior to their precursors. The energy diffraction X-ray (EDX) spectra of CdTe QDs and Ag2Te QDs were recorded and shown in Fig. 1B. The EDX results prove the existence of Ag and Te elements in Ag2Te QDs. The atomic ratio of the elements of Ag and Te is nearly 2 : 1, which is close to the appropriate stoichiometry of Ag2Te. Almost no Cd component is retained in the EDX spectrum of Ag2Te QDs, suggesting that the ion-exchange process is completed. Previous work reported that Ag2Te QDs could emit infrared light, which can be used to fabricate bioimaging in the second biological window [23]. In the present work, two kinds of Ag2Te QDs were obtained by incubating CdTe QDs in AgNO3 for different time. It can be found from Fig. 1C and D that the short incubating time leading visible light emission (510 nm) while long incubating time leading infrared light emission (950 nm). It was reported that the FL emission of Ag2S QDs shifted from visible range to infrared range with the increase of incubating time in AgNO3 solution [30]. Therefore, the obtained different FL emission Ag2Te QDs should be due to the different incubating time in AgNO3 solution. Because of the same size, the FL peaks of four Ag2Te QDs are located at the same position either at the visible or at the infrared range only with the difference in FL intensity, which should be due to the difference in surface state during the formation of Ag2Te QDs from CdTe QDs. UV–vis absorption spectra of Ag2Te QDs and CdTe QDs were comparatively studied and shown in Fig. 1E. It can be found that CdTe QDs exhibited apparent absorption in the range of 400–600 nm range. The peak absorption at 530 nm should be result from the existence of Cd2+ because this peak can be found in other cadmium containing QDs, such as CdSe and CdS QDs. AgNO3 has no absorption in this wavelength range, while Ag2Te QDs exhibited wide absorption band from 400 nm to 800 nm, which is in accordance with the reported result [23]. The disappearance of the peak absorption at 530 nm can also be used to confirm the transformation of CdTe QDs to Ag2Te QDs. Electrochemical behaviors of Ag2Te QDs modified electrode were comparatively studied in PBS and K2S2O8/PBS as shown in Fig. 1F. At the bare GCE, no apparent cyclic voltammetric (CV) peak was obtained in PBS while one broad CV peak was obtained around −1.48 V in K2S2O8/PBS, suggesting that the electrochemical reduction of K2S2O8 can occur at this potential. One pair of reduction-oxidation peaks at −1.00 and −0.80 V at the Ag2Te/GCE in PBS can be assigned to the electrochemical reactions of Ag2Te QDs. The electrochemical reduction of K2S2O8 at the Ag2Te/GCE can be found at −1.18 V, which is positively shifted compared with the bare GCE. The increase of reduction current and the decrease of overpotential revealed that Ag2Te QDs can catalyze the electrochemical reduction of K2S2O8.
2.2. Synthesis of CdTe QDs and Ag2Te QDs Mercaptopropionic acid (MPA)-capped CdTe QDs were synthesis referred to the literature with minor revision [28]. 45 μL of 6 mM MPA was first added into 60 mL of 2 mM CdCl2 solution. After adjusted the pH to 11.9 using 1.0 mol L−1 NaOH solution, the resulting clear solution was bubbled with highly pure N2 for 30 min, and 0.50 mL of 0.0625 mol L−1 NaHTe solution was slowly injected and 60 mg NaBH4 was fast added into the vigorously stirred and oxygen-free solution to obtain a yellow brown solution. The obtained QDs solution was refluxed for 40, 80, 120, and 160 min to produce different sizes of QDs (denoted as CdTe-1, CdTe-2, CdTe-3, and CdTe-4). The samples were then dialyzed against doubly distilled water for 5 h to remove excessive MPA. The final QDs solutions were kept in a refrigerator at 4 °C. Ag2Te QDs were synthesized by facile ion-exchange method according to the literature method with minor modification [23]. 12.5 μL of 0.2 mol L−1 AgNO3 and 1 mL of different sizes CdTe QDs were added into a 1.5 mL Eppendorf tube to promote the cation exchange process. Four kinds of Ag2Te QDs were obtained and denoted as Ag2Te-1, Ag2Te2, Ag2Te-3, and Ag2Te-4. The obtained Ag2Te QDs were characterized by TEM, FL, and UV–vis absorption spectroscopy. 2.3. Fabrication of QDs modified electrodes A glassy carbon electrode (GCE, 3 mm in diameter) was mechanically polished to a mirror with alumina pastes of 1.0, 0.3 and 0.05 µm respectively, and then cleaned thoroughly in an ultrasonic cleaner with alcohol and water sequentially. The electrode was rinsed with redistilled water and was dried with blowing N2. Then, 10 μL of QDs was spread on the working area and dried at the room temperature to fabricate QDs modified GCE (denoted as CdTe/GCE and Ag2Te/GCE). 3. Results and discussion 3.1. Synthesis of Ag2Te QDs from CdTe QDs It has already been proven that luminescent CdTe QDs can be widely used in analytical chemistry [29]. In the present work, different sizes of CdTe QDs were obtained by adjusting the refluxing time during the synthesis, and the size distribution of CdTe QDs were shown in Fig. S1. It can be found that the size of CdTe QDs increases with the increase of refluxing time. The FL results confirmed that the maximum FL emission of CdTe QDs is red-shifted with the increase of QDs size (Fig. S2). Fig. 1A revealed that cathodic ECL of CdTe QDs can be obtained in neutral condition with K2S2O8 as coreactant, and the ECL intensity increased with the increase of QDs size. Although CdSe QDs ECL can be obtained in neutral condition, the weak ECL intensities as well as the high-toxic cadmium ions containing in the QDs severely limit its application in ECL biosensor. Therefore, it is necessary to replace cadmium ions with other low-toxic ions. Herein, low-toxic silver ions were used to replace cadmium ions through ion-exchange, and the morphology of synthesized Ag2Te QDs was characterized by TEM. It can be found from Fig. S3 that the Ag2Te QDs synthesized from different sizes of CdTe QDs exhibited almost the same size and morphology. The size distribution analysis revealed that the average sizes of four Ag2Te QDs were all around 6.7 nm, which is consistence with the TEM results (Fig. S4). The possible reason is that the growth process is superior to the nucleation process during the cation exchange process, which results in the formation of same size Ag2Te QDs. ECL behaviors of Ag2Te QDs were investigated in neutral condition, and strong cathodic ECL signals were obtained in the presence of K2S2O8. It can be found from Fig. 1A that the ECL intensities increased in the following order: Ag2Te-1 < Ag2Te-2 < Ag2Te-3 < Ag2Te-4. The ECL intensities of Ag2Te-3 and Ag2Te-4 increased nearly 8-times compared with CdTe QDs, revealing that ECL behaviors of Ag2Te QDs
3.2. Impacting factors of ECL The modified amount of Ag2Te QDs, the concentration of K2S2O8, and the pH values can affect ECL emission. It can be found from Fig. 2A that the ECL intensity increased with the increase of QDs amount. However, large amount of QDs will overflow the working area of the electrode during the electrode modification, which will influence ECL measurement. Therefore, 10 μL of QDs was adopted to modify electrode. Electrochemical impedance spectroscopy (EIS) of different amount of QDs modified electrode was obtained and shown in Fig. 2B. It can be found that the diameter of the semicircle increased with the increase of modified QDs, suggesting the increase of charge transfer resistance between the negatively charged Ag2Te QDs and [Fe (CN)6]3-/4- probe. The EIS results can be used to monitor the successful fabrication of Ag2Te QDs on the GCE. It can be found from Fig. 2C that ECL intensity increased with the increase of K2S2O8 concentration, revealing that K2S2O8 participate the ECL reactions. Because the ECL intensity obtained in 0.1 mol L−1 K2S2O8 solution is strong enough for the ECL detection, 0.1 mol L−1 K2S2O8 solution was chosen in the following study. Fig. 2D displays the effect of pH value on the cathodic ECL. The most intense ECL signal can 223
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 2. (A) Effect of QDs amount; (B) EIS of different amount of QDs modified electrodes; (C) Effect of K2S2O8 concentration; (D) Effect of pH value.
one electrode to monitor the ECL responses, which was shown in Fig. 4A. The relative standard deviation was 2.5% for successive measurements (n = 18) at 1 nM catechol, suggesting a good stability of the proposed sensor for catechol detection. The reproducibility of the sensor for catechol was estimated by determining 1 nM catechol with six sensors as shown in Fig. 4B. Six sensors exhibited similar ECL responses and the relative standard deviation was 1.2%, indicating that the reproducibility of the proposed sensor for catechol detection is acceptable. The long-term stability of the ECL sensor was evaluated by detecting ECL intensity after the Ag2Te/GCE was stored at 4 °C. The ECL intensity decreased to about 92% of its initial response after three weeks of storage, demonstrating that the sensor possesses good longterm stability. Many ECL systems were used in the detection of catechol [33–37]. The comparison between the proposed method and the previous reported methods was shown in Table 1. As can be seen, the present ECL sensor displays a wide linear detection range and lower detection limit which is lower than that of most previous reported sensors. In order to assess the possible practical applications of the ECL sensor in the determination of catechol, the content of catechol was determined by the standard addition method in human blood serum samples (The sample was obtained from Nanjing Gulou Hospital). The serum 1:5 diluted with PBS (pH 7.4) was spiked with catechol at different concentrations. The results in Table S1 show the acceptable relative standard deviation (RSD) and good recoveries. Therefore, this new method is reliable and effective for the determination of catechol.
be obtained in neutral condition, revealing that the present ECL system is suitable for biosensor application. 3.3. Analytical performance of ECL sensor It was reported that luminescent technique can be used in the sensitive detection of phenolic compounds based on their enhancing or inhibiting effects [31,32]. However, similar structure phenolic compounds often exhibited similar effects on ECL signal during the measurement. As a result, these compounds can't be selectively detected. In the present study, benzenediol, including hydroquinone, catechol, and resorcinol, was selected as the model analyte to evaluate the analytical performance of the present ECL system. It can be found from Fig. 3A that resorcinol and hydroquinone can slightly influence ECL signal, while catechol can significantly inhibit ECL signal, revealing that the proposed ECL system can be used in selectively detection of catechol. In order to further evaluate the selectivity of the ECL sensor, the effects of some other analytes, such as glucose, cytochrome c, ascorbic acid, and dopamine, on ECL signals were also investigated. The results found that the most of analytes exhibited negligible effect on ECL signal except dopamine due to its similar structure as that of catechol. The ECL intensity in the presence of 1 mM catechol decreased to the level of background emission and was only 10% of that in the absence of catechol as shown in Fig. 3B, revealing that catechol can be detected based on its significant inhibiting effect towards the cathodic ECL of Ag2Te QDs. In the range of 1.0 × 10−9 − 1.0 × 10−5 mol L−1, the ECL intensities decreased linearly with the concentration of catechol (Fig. 3C). The linear regression equation was determined as I = −313.6logC + 444, with the regression coefficient as 0.9991 (Fig. 3D). The detection limit of catechol was determined as 3.1 × 10−10 mol L−1 (3σ). The stability is an important factor to evaluate the capability of the sensor. The stability of the present ECL sensor was evaluated by using
3.4. ECL mechanism It was reported in the previous work that all QDs/K2S2O8 ECL systems could emit light according to the following pathway: QDs were reduced to radicals by charge injection, while the coreactant S2O82could be reduced to the strong oxidant SO4-•; QDs radicals could react 224
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 3. (A) Effects of 1 mM hydroquinone, catechol, and resorcinol on ECL signal; (B) Comparison between ECL signals of Ag2Te/GCE in the absence and presence of 1 mM catechol; (C) Effects of different concentrations of catechol on ECL signal; (D) Linear relationship between ECL intensity and catechol concentration.
Fig. 4. Stability (A) and repeatability (B) of the ECL sensor in 1 nM catechol solution.
with SO4-• to produce an excited state of QDs (QDs*) which could emit light in the aqueous solution [24,38,39]. In order to elucidate ECL mechanism of Ag2Te QDs, the FL and ECL spectra as well as the electrochemical behaviors of the present ECL system were recorded and shown in Fig. 5. It can be found from Fig. 5A that the ECL spectrum of the present system is the same as the FL spectrum of Ag2Te QDs, revealing that the light emitter is the excited state of Ag2Te QDs. Fig. 5B displays that the maximum FL emission of Ag2Te QDs located at 510 nm, while catechol and K2S2O8 had no light emission. When catechol and K2S2O8 was added into Ag2Te QDs solution, the FL intensity decreased greatly while the peak position didn’t change, revealing that catechol and K2S2O8 could react with the excited state of QDs. Fig. 5C reveals that the absorption spectrum of catechol overlapped with the FL spectrum of Ag2Te QDs, suggesting that resonance energy transfer can occur between catechol and Ag2Te QDs. Electrochemical results (Fig. 5D) reveals that catechol could not apparent change the reduction current and the reduction potential of
Table 1 Comparison of ECL methods for determination of catechol. Sensor
Linear range
Detection limit
References
Oil film-covered carbon paste electrode CdS nanotube/indium thin oxide electrode Graphene/MWNT/gold nanocluster/glassy carbon electrode AuNPs@C60/glassy carbon electrode CdTe/gold electrode Ag2Te/glassy carbon electrode
4 nM–400 nM
0.2 nM
[33]
2.0 μM–10 μM
0.058 μM
[34]
1.0 μM–80 μM
0.3 μM
[35]
62 nM–120 μM
21 nM
[36]
5 nM–1000 nM 1 nM–1000 nM
2 nM 0.31 nM
[37] This work
225
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
Fig. 5. (A) FL and ECL spectra of Ag2Te QDs; (B) FL spectra of Ag2Te, catechol, K2S2O8, and their complexes; (C) UV–vis absorption spectrum of catechol and FL spectrum of Ag2Te QDs; (D) CV curves of K2S2O8 and K2S2O8/catechol at the bare GCE and the Ag2Te/GCE.
friendly Ag+ in quantum dots makes its low-toxicity and can become a promising candidate material of ECL biosensors in the future.
K2S2O8 at the bare GCE and the Ag2Te/GCE, revealing that catechol could not react with K2S2O8. According to the experimental and the reference results, the mechanism of the cathodic ECL can be proposed as follows: S2O82- + e- → S2O8•3-
(1)
S2O8•3-
(2)
Acknowledgments
Ag2Te + e- → Ag2Te•-
(3)
This work is financially supported by National Natural Science Foundation of China (No. 21575002), Natural Science Foundation from the Bureau of Education of Anhui Province (No. KJ2015A075), Innovation and Entrepreneurship Program for College Students in Anhui Province (201610360020).
Ag2Te•- + SO4•- → Ag2Te* + SO42-
(4)
Appendix A. Supporting information
Ag2Te* → Ag2Te + hv
(5)
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jlumin.2017.05.051.
→
SO42-
+
SO4•-
Previous work revealed that o-benzoquinone residues can efficiently quench the fluorescence emission of QDs by energy transfer [40]. ECL energy transfer (ET) can occur between the excited CdTe QDs and the oxidation product of catechol, leading the quenching effect on the anodic ECL of QDs [25]. Therefore, the possible inhibiting mechanism of catechol is proposed as follows: the strong oxidant SO4-• could oxidize catechol to o-benzoquinone which can accept energy from the excited state of Ag2Te QDs. As a result, the cathodic ECL was inhibited in the presence of catechol.
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
4. Conclusions Water dispersible Ag2Te quantum dots were synthesized through facile ion exchange method with CdTe QDs as precursors. The asprepared Ag2Te QDs exhibited strong cathodic ECL in neutral aqueous solution with K2S2O8 as coreactant. Catechol could significantly inhibit the ECL emission due to the energy transfer between the excited state of Ag2Te QDs and the oxidation product of catechol, based on which catechol can be sensitively detected in the range of 1 nM to 10 μM with the detection limit of 0.31 nM. The substitute of toxic Cd2+ with eco-
[10] [11] [12] [13] [14] [15] [16]
226
M.M. Richter, Chem. Rev. 104 (2004) 3003–3036. W.J. Miao, Chem. Rev. 108 (2008) 2506–2553. J.P. Lei, H.X. Ju, Trac-Trends Anal. Chem. 30 (2011) 1351–1359. W.W. Zhao, X.Y. Dong, J. Wang, F.Y. Kong, J.J. Xu, H.Y. Chen, Chem. Commun. 48 (2012) 5253–5255. W.W. Zhao, Z.Y. Ma, P.P. Yu, X.Y. Dong, J.J. Xu, H.Y. Chen, Anal. Chem. 84 (2012) 917–923. F.A. Esteve-Turrillas, A. Abad-Fuentes, Biosens. Bioelectron. 41 (2013) 12–29. G.F. Jie, B. Liu, H.C. Pan, J.J. Zhu, H.Y. Chen, Anal. Chem. 79 (2007) 5574–5581. X. Liu, H.X. Ju, Anal. Chem. 80 (2008) 5377–5382. S.Y. Deng, L.X. Cheng, J.P. Lei, Y. Cheng, Y. Huang, H.X. Ju, Nanoscale 5 (2013) 5435–5441. H.Y. Liu, S.M. Xu, Z.M. He, A.P. Deng, J.J. Zhu, Anal. Chem. 85 (2013) 3385–3392. S.Y. Deng, H.X. Ju, Analyst 138 (2013) 43–61. X. Michalet, F.F. Pinaud, L.A. Bentolila, J.M. Tsay, S. Doose, J.J. Li, G. Sundaresan, A.M. Wu, S.S. Gambhir, S. Weiss, Science 307 (2005) 538–544. A.M. Derfus, W.C.W. Chan, S.N. Bhatia, Nano Lett. 4 (2004) 11–18. C. Kirchner, T. Liedl, S. Kudera, T. Pellegrino, A.M. Javier, H.E. Gaub, S. Stolzle, N. Fertig, W.J. Parak, Nano Lett. 5 (2005) 331–338. R.J. Gui, H. Jin, Z.H. Wang, L.J. Tan, Coord. Chem. Rev. 296 (2015) 91–124. R.Z. Chen, D.S. Xu, G.L. Guo, L.L. Gui, J. Mater. Chem. 12 (2002) 2435–2438.
Journal of Luminescence 190 (2017) 221–227
Y. Peng et al.
[28] X. Liu, H. Jiang, J.P. Lei, H.X. Ju, Anal. Chem. 79 (2007) 8055–8060. [29] C. Frigerio, D.S.M. Ribeiro, S.S.M. Rodrigues, V.L.R.G. Abreu, J.A.C. Barbosa, J.A.V. Prior, K.L. Marques, J.L.M. Santos, Anal. Chim. Acta 735 (2012) 9–22. [30] P. Jiang, C.N. Zhu, Z.L. Zhang, Z.Q. Tian, D.W. Pang, Biomaterials 33 (2012) 5130–5135. [31] Q.L. Zhang, H. Cui, A. Myint, L. Mei, L.J. Liu, J. Chromatogr. A 1095 (2005) 94–101. [32] Y.G. Sun, H. Cui, X.Q. Lin, Y.H. Li, H.Z. Zhao, Anal. Chim. Acta 423 (2000) 247–253. [33] X.Y. Chen, R.J. Zheng, S.F. Qin, J.J. Sun, Talanta 101 (2012) 362–367. [34] Y. Wen, F. Luo, Y. Yang, L. Lin, J. Du, Y. Guo, D. Xiao, M.M.F. Choi, Anal. Methods 4 (2012) 053–1059. [35] D. Yuan, S. Chen, R. Yuan, J. Zhang, W. Zhang, Analyst 138 (2013) 6001–6006. [36] Q.Y. Lu, H.X. Hu, Y.Y. Wu, S.H. Chen, D.H. Yuan, R. Yuan, Biosens. Bioelectron. 60 (2014) 325–331. [37] Y.P. Dong, Y. Zhou, J. Wang, Y.Q. Dong, C.M. Wang, Talanta 146 (2016) 266–271. [38] G.F. Jie, B. Liu, H.C. Pan, J.J. Zhu, H.Y. Chen, Anal. Chem. 79 (2007) 5574–5581. [39] G.F. Jie, H.P. Huang, X.L. Sun, J.J. Zhu, Biosens. Bioelectron. 23 (2008) 1896–1899. [40] R. Gill, R. Freeman, J.P. Xu, I. Willner, S. Winograd, I. Shweky, U. Banin, J. Am. Chem. Soc. 128 (2006) 15376–15377.
[17] A.M. Qin, Y.P. Fang, P.F. Tao, J.Y. Zhang, C.Y. Su, Inorg. Chem. 46 (2007) 7403–7409. [18] P.F. Zuo, S.Y. Zhang, B.K. Jin, Y.P. Tian, J.X. Yang, J. Phys. Chem. C 112 (2008) 14825–14829. [19] A. Sahu, L. Qi, M.S. Kang, D. Deng, D.J. Norris, J. Am. Chem. Soc. 133 (2011) 6509–6512. [20] M. Yarema, S. Pichler, M. Sytnyk, R. Seyrkammer, R.T. Lechner, G. Fritz-Popovski, D. Jarzab, K. Szendrei, R. Resel, O. Korovyanko, M.A. Loi, O. Paris, G. Hesser, W. Heiss, ACS Nano 5 (2011) 3758–3765. [21] Y. Du, B. Xu, T. Fu, M. Cai, F. Li, Y. Zhang, Q. Wang, J. Am. Chem. Soc. 132 (2010) 1470–1471. [22] D.H. Son, S.M. Hughes, Y. Yin, A.P. Alivisatos, Science 306 (2004) 1009–1012. [23] C. Chen, X.W. He, L. Gao, N. Ma, ACS Appl. Mater. Interfaces 5 (2013) 1149–1155. [24] M. Yang, R.J. Gui, H. Jin, Z.H. Wang, F.F. Zhang, J.F. Xia, S. Bi, Y.Z. Xia, Colloids Surf. B: Biointerfaces 126 (2015) 115–120. [25] H. Jin, R.J. Gui, J. Sun, Y.F. Wang, Colloids Surf. B: Biointerfaces 143 (2016) 118–123. [26] R.J. Gui, J. Sun, D.X. Liu, Y.F. Wang, H. Jin, Dalton Trans. 43 (2014) 16690–16697. [27] R. Cui, Y.P. Gu, L. Bao, J.Y. Zhao, B.P. Qi, Z.L. Zhang, Z.X. Xie, D.W. Pang, Anal. Chem. 84 (2012) 8932–8935.
227