Enhanced Electrochemiluminescence Behavior of GoldâSilver

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Enhanced Electrochemiluminescence Behavior of Au-Ag Bimetallic Nanoclusters and its Sensing Application for Hg(II) Qingfeng Zhai, Huanhuan Xing, Xiaowei Zhang, Jing Li, and Erkang Wang Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 22 Jun 2017 Downloaded from http://pubs.acs.org on June 22, 2017

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Analytical Chemistry

Enhanced Electrochemiluminescence Behavior of Au-Ag Bimetallic Nanoclusters and its Sensing Application for Hg(II) Qingfeng Zhai, †‡ Huanhuan Xing, †‡ Xiaowei Zhang, †‡ Jing Li,*,† Erkang Wang*,† †

State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of

Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, China. ‡

University of Chinese Academy of Sciences, Beijing, 100039, China.

*Corresponding Author E-mail: [email protected] (J. Li);[email protected] (E. Wang) Tel: +86-431-85262003. Fax: +86-431-85689711.

ABSTRACT Bimetallic nanoclusters (NCs) with super performance than monometallic nanoclusters have attracted extensive research interest due to the synergetic effect of two atoms. Inspired from the silver effect on enhanced the fluorescence intensity of Au NCs, a series of BSA-protected Au-Ag bimetallic NCs were prepared by regulating the molar ratios of HAuCl4/AgNO3 and their ECL property was investigated using triethylamine as co-reactant. Notably, multifolds higher efficiency was achieved with Au-Ag bimetallic NCs in reference to the monometallic

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nanoclusters. Moreover, the doping of Ag atoms not only made the ECL emission of the Au NCs blue shift, but also decreased the peak potential and onset potential, which provided an efficient and facile way to improve the ECL behavior. Based on the ECL quenching effect of Hg2+ towards Au-Ag bimetallic NCs via the formation of metallophilic bond, an ECL sensor for Hg2+ detection was proposed with good stability, high selectivity and sensitivity. These results indicated that the as-prepared Au-Ag bimetallic NCs with enhanced ECL properties can be served as an ideal luminescent material in sensing application.

INTRODUCTION In recent years, electrochemiluminescence (ECL) as a powerful technique has been widely used in immunoassays and environmental monitoring1,2. Because the ECL emission is generated from electrochemical high-energy electron transfer reaction rather than the excitation of light source, therefore it not only avoids the light scattering but also has its unique advantages, such as lower background signal, easy operation, and high sensitivity3-5. Apart from the traditional chemiluminescent reagents (e,g, ruthenium complexes6,7, luminol8,9), some novel nanomaterials with excellent luminescent properties were developed and used in ECL system along with the development of nanoscience and nanotechnology since the first ECL emitter of silica nanoparticles was reported in 200210, such as semiconductor nanocrystals11,12, carbon nanodots13,14. Recently, metal nanoclusters (NCs) with special optical, electronic and chemical properties have gained a great of attention in ECL system due

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to their molecule-like properties and low toxicity15,16, including Au NCs17,18, Ag NCs19,20, Cu NCs21, etc. Among these, Au NCs with enhanced super catalytic activity, good water solubility, excellent stability and ease of synthesis have attracted wide interest in ECL from the fundamental to the analytical field, including different molecular composition of Au NCs (Au822, Au2523,24, Au3825, Au14426). However, the short lifetime in annihilation reaction made the Au NCs have the weak ECL emission signal that restricted its further application, and many efforts have been made to improve its ECL efficiency27. The common method adopted is to attach the effective group acting as co-reactant onto ECL emitter for providing a self-enhanced ECL emission through the efficient, intramolecular electron transfer28-31. For example, Wang’s group32 designed a smart strategy of covalent attachment of co-reactant N,N-diethylethylenediamine onto lipoic acid stabilized Au NCs for enhancing the ECL signal. This strategy achieved multifolds higher ECL efficiency than the standard Ru(bpy)32+/tri-n-propylamine system by the intracluster reactions without the additional high excess co-reactant. In addition, other effective methods were also developed, for instance, layer-by-layer assembly process was used to locate Au NCs on layered double hydroxides nanosheets to enhance its ECL performance. Although the proposed methods have greatly enhanced the ECL intensity of Au NCs, other effective strategies are also highly desired, especially in enhancing the ECL performances of ECL emitter itself.

Recently, bimetallic NCs have attracted special research interest than the monometallic nanoclusters, because it combined the synergetic effects of two atoms 3



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and exhibited more super performances in electronic, optical, and catalytic aspects33-37. Relevant studies have been reported and revealed that the obtained Au-Pd bimetallic NCs through doping platinum atom into Au NCs have the enhanced stability and super catalytic activity than the monometallic ones38. In addition, based on the “silver effect” in gold catalysis, many researches are focusing on doping Au NCs with Ag atoms to shift the optical spectra and enhance the fluorescence intensity for sensing application39-43. For example, Wang44 and Tang45 successfully prepared bovine serum albumin (BSA)-protected Au-Ag bimetallic NCs with enhanced fluorescent intensity for metal ions and pyrophosphatase activity detection, respectively. Yu46 obtained glutathione-capped Au-Ag bimetallic NCs with strong photoluminescent performance for metal ions, anions, and small molecule detection. However, the ECL performance of bimetallic NCs has not been reported.

Inspired by the excellent fluorescence property of bimetallic NCs, the ECL property of Au-Ag bimetallic NCs was investigated for the first time using different molar ratios Au/Ag precursors in the presence of triethylamine (TEA) as a co-reactant. As expected, the doping of Ag into Au NCs led to the higher ECL emission induced by the synergetic effect of two atoms. The ECL activity is about 5 times higher for the bimetallic NCs compared to the individual Au NCs with the molar ratios of 6:1 (Au:Ag). The trend was consistent with the experimental results of fluorescence, indicating the introduction of Ag atom can be served as an effective method for enhancing the ECL property. ECL spectra were used for characterizing the obtained Au-Ag bimetallic NCs, and the enhanced ECL mechanism was proposed. Moreover, 4


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in order to verify the application of the ECL sensor based on Au-Ag bimetallic NCs, Hg2+ was chosen as the model target because of the irreversible damage to the health of body through accumulating in organisms47. Hg2+ can quench the ECL signal of Au-Ag bimetallic NCs through the formation of metallophilic bonding between Hg2+ ions and Au or Ag atom of Au-Ag bimetallic NCs

48-50

, as shown in Scheme 1. The

high selectivity of the ECL sensor for Hg2+ detection can be achieved through addition of ethylenediaminetetraacetic acid (EDTA).

EXPERIMENTAL SECTION Chemicals and Reagents. HAuCl4·4H2O was purchased from Sigma-Aldrich (Beijing, China). BSA, AgNO3 and chitosan were purchased from Sinopharm Chemical Reagent Co. (Shanghai, China). NaClO4, TEA, EDTA, NaOH, acetic acid, chitosan (CS), mercury, copper and other metal salts were purchased from Beijing Chemical Reagent Co. (Beijing, China). All of the chemicals were of at least analytical grade and the water used throughout all experiments was purified by a Milli-Q system (Millipore, Bedford, MA, USA). The Preparation of BSA-stabilized Au-Ag Bimetallic NCs. Before the experiment, all the glassware and magneton used in this experiment were completely immersed in aqua regia (HNO3/HCl = 1:3, v/v) (Caution!!) for 1 h, and then rinsed thoroughly with ultrapure water. BSA-stabilized Au-Ag bimetallic NCs were synthesized according to the reported method44,45 with a slight modification. Briefly, 4.0 mL HAuCl4 (10 mM) aqueous solution and 1.0 mL AgNO3 aqueous solution with 5



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different concentrations were introduced into 5.0 mL BSA (50 mg/mL, 37 °C) aqueous solution under vigorous stirring for 5 min. Then 1.0 mL NaOH (1.0 M) aqueous solution was injected immediately into the mixture, and BSA-stabilized Au-Ag bimetallic NCs were obtained after reaction for 12 h. Finally, the as-prepared Au-Ag bimetallic NCs were filtered with a dialysis membrane in water for 48 h and stored in the dark at 4 °C before use. For characterization, the obtained Au-Ag bimetallic NCs were concentrated through rotary evaporation and vacuum dried at 70° C. Characterization. The fluorescence spectra were collected from 550 nm to 900 nm on an Agilent Cary Eclipse fluorescence spectrophotometer with excitation wavelength of 270 nm, both the excitation and emission slit widths were 5 nm. The electrochemical and ECL measurements were carried out on a model MPI-A capillary electrophoresis ECL system (Xi’an Remex Electronics Co. Ltd.) with the typical three-electrode system in 0.1 M NaClO4 containing 70 mM TEA, and the working electrode, counter electrode and reference electrode were glassy carbon electrode (GCE), platinum wire electrode and Ag/AgCl electrode, respectively. ECL spectra were recorded in Guizheng Zou’s group (Shandong University) with a homemade ECL spectrum system consisting of a monochromator and an electrochemical analyzer. High resolution transmission electron microscopy (HR-TEM) was performed using a JEM-2010 (HR) microscope operated at 200 kV. X-ray photoelectron spectroscopy (XPS) spectra were collected by using a Thermo ESCALAB 250 instrument equipped with Al Ká radiation. Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) 6


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characterization were carried out by using a spectrum GX FT-IR spectroscopy system (Perkin Elmer) and a X-ray powder diffractometer (Bruker D8 Advance) with the Cu Ká radiation (λ =1.5418 Å), respectively. Metal ion detection. Prior to each fabrication, the GCE (d=3mm) was successively polished with 0.3 µm and 0.05 µm alumina slurry and then washed ultrasonically in water for a few seconds. Then 5.0 µL of the mixture solution (Au-Ag bimetallic NCs/CS solution (0.01 g/mL, 1% acetic acid) = 2:1, v/v) was dropped onto the pretreated GCE surface and dried at room temperature. In addition, for Hg2+ detection, different concentrations of Hg2+ were added into Au-Ag NCs solution with the final concentration was from 0 to 30 µM, and after the mixture was incubated at room temperature for 10 min, then dropped on the surface of GCE. And the scan voltage is from 0 V to 1.5 V with the scan rate of 0.2 V/s. In order to achieve the highest ECL stability and the sampling rate was set at 10 T/s.

RESULTS AND DISCUSSION Synthesis and Characterization of Au-Ag Bimetallic NCs. It has been demonstrated that BSA-protected Au NCs have strong fluorescence signal51 excited by light, and enhanced fluorescence signal was observed with Au-Ag bimetallic NCs44. In this work, fluorescence spectrum was first used for characterizing the obtained different molar ratios of BSA-protected Au-Ag bimetallic NCs that synthesized by adding different amount of HAuCl4 and AgNO3. And as shown in Figure 1A, the fluorescence intensity of the as-prepared Au-Ag bimetallic NCs was much higher than

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individual Au and Ag NCs due to the synergistic effect of Au and Ag NCs45,46. In addition, the fluorescent emission peak of pure Au NCs was at about 680 nm, and the blue shift of as-prepared Au-Ag bimetallic NCs was observed with the emission peak at about 640 nm, which was consistent with the reported literatures45. Through comparing the experimental results and the histogram of the relative fluorescent intensity of Au-Ag bimetallic NCs with different molar ratio (Figure 1B), we can clearly find that Au-Ag bimetallic NCs with the molar ratio of 6:1 could exhibit the maximum fluorescent emission intensity. HR-TEM was then applied to evaluate size distribution and morphology of the obtained Au-Ag bimetallic NCs (6:1). As shown in Figure 1C, the obtained Au-Ag bimetallic NCs were monodispersed with the mean diameter of 2.3 nm, which indicated the formation of the NCs. Fourier transform infrared (FT-IR) spectroscopy as a powerful tool was also used for monitoring the protein conformational change and the formation of secondary structure52 of BSA-protected Au-Ag bimetallic NCs. As shown in Figure 1D, the characteristic amide I band in 1600-1700 cm−1 (primarily CO stretch) wavenumber region and amide II (near 1545 cm−1) regions are the typical vibrational profiles of BSA. It can be found that the peak shape was noticeably broadened with a little shift in center-of-gravity, indicating the formed Au-Ag bimetallic NCs induced the secondary structure change of BSA. The results were in accordance with the published literatures52. The crystal structure of the obtained Au-Ag bimetallic NCs were characterized through XRD, as shown in Figure S2A, the obtained results exhibited an obvious deviation from that of the normalized Au (JCPDS 04-1784) and Ag 8


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(JCPDS 04-0783) fcc structure (38.2° and 44.4°) and two sharp peaks were shifted at 31.7° and 45.5°, which could correspond to the lattice planes (111) and (200) of bimetallic Au-Ag NCs, respectively. The XRD analysis results were in agreement with many reported literatures44,46. XPS was further used to verify the exact valence state of elements in BSA-protected Au-Ag bimetallic NCs, and the survey spectrum (Figure S2B) was confirmed that the elements including C, O, N, Au, S and Ag were presented. Moreover, the oxidation states of Au and Ag in bimetallic NCs can be determined through the binding energies, Au 4f7/2 and Au 4f5/2 can be indexed to 83.7 eV and 87.2 eV, respectively, indicating the existence of Au(0). Meanwhile, the binding energies of Ag 3d5/2 (367.2 eV) and Ag 3d3/2 (374.2 eV) in Ag 3d spectrum can be assigned to Ag (I) and Ag (0) metallic state in bimetallic NCs, respectively45. Furthermore, the S 2p3/2 and S 2p1/2 components of the S element at 162.4 and 167.5 eV were agreement with the typical values for chemisorbed thiolated forms46. All the above characterization results were indicating the formation of alloying Au-Ag bimetallic NCs. Electrochemical and ECL Behaviors of Au-Ag Bimetallic NCs. In order to investigate the electrochemical and ECL behaviors, the bare GCE, GCE modified with CS solution, GCE modified with the mixture containing the obtained Au-Ag bimetallic NCs and CS solution are compared in electrolyte (0.1 M NaClO4, 70 mM TEA) for electrochemical experiment. The cyclic voltammetry and ECL-potential curves were shown in Figure 2 A and B. It can be clearly found that the bare GCE (curve a) has a much higher oxidation current of TEA than CS modified GCE (curve 9



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b) in the voltage range from 0.4 V to 1.5 V because the modified CS hindered the electronic transfer to the electrode surface and negligible ECL emission was obtained with bare GCE (curve a′ and b′)18. While for the mixture with Au-Ag bimetallic NCs modified GCE (curve c), much higher current than CS modified GCE was observed due to the low compactness of CS caused by doped Au-Ag bimetallic NCs, and a strong ECL emission signal appeared at the maximum potential of 1.12 V with the onset potential at 0.63 V. The strong ECL emission is attributed to the superior catalytic performance of noble metals (Au and Ag) and the synergistic effect of ECL from Au NCs and Ag NCs. Moreover, the ECL intensity of Au-Ag bimetallic NCs was much higher than individual Au NCs and Ag NCs and the enhanced ECL signal from the Au-Ag bimetallic NCs was also dependent on the amount of the doped Ag. When the molar ratio of Au:Ag was 6:1, maximum ECL intensity was obtained with Au-Ag bimetallic NCs (Figure 2 C and D). With the further increase of Ag, the ECL intensity decreased. As a control, the ECL of performance from the BSA capped Ag NCs alone was recorded. In stark contrast, the pure Ag NCs exhibited very weak ECL response relative to the Au NCs due to the lower efficiency, which was consistent with the fluorescent emission. Moreover, the doping of Ag atoms into Au NCs decreased the peak potential and onset potential. For example, ECL generation from Au NCs was observed at an onset potential of 0.73 V (vs. Ag/AgCl) and reaches the strongest intensity at around 1.35 V. While for the Au-Ag bimetallic NCs with the molar ratio of 6:1, the onset potential and peak potential were shift to 0.63 V and 1.12 V, respectively. The more negative reaction may be attributed to their synergistic 10


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effect, which facilitated the oxidation of TEA due to the doping of Ag atoms. To further investigate the ECL performance of Au-Ag bimetallic NCs, the ECL spectra of bare GCE, Au NCs, Ag NCs and Au-Ag bimetallic NCs modified GCE in TEA solution were recorded in Figure 3. It can be clearly found that bare GCE and Ag NCs exhibited a very weak ECL peak at 700 nm and 900 nm, respectively, which is significantly different from the emission peak of Au NCs (794 nm) and Au-Ag bimetallic NCs (756 nm). These results demonstrated that the ECL emission of Au-Ag bimetallic NCs was resulted from the synergistic effect of Au and Ag NCs, not the individual Au or Ag NCs. In addition, doping Ag atom into Au NCs caused the ECL emission of Au NCs blue shift, which is consistent with the fluorescence results. And compared with the fluorescence spectrum (640 nm), the ECL spectrum of Au-Ag bimetallic NCs (756 nm) was red shift, indicating its ECL performance was dependent on the surface-state, and the same result was also observed in carbon-based quantum dots53,54 and other nanocluster-based ECL systems20,21,25. Finally, the ECL mechanism is given and it is belonged to co-reactant pathway, which is the same with the ECL emission of the reported semiconductors12, Au NCs18 and Ag NCs20 in the presence of co-reactant, the possible reaction process of Au-Ag bimetallic NCs/TEA ECL system in the present work is summarized as follows: TEA–e-→ TEA•+

(1)

Au-Ag + TEA•+ → TEA + Au-Ag+

(2)

OH– + TEA•+ → TEA• + H2O

(3)

TEA• + Au-Ag → Et2N+CHCH3 + Au-Ag–

(4)

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Au-Ag+ + Au-Ag

–

→ Au-Ag* + Au-Ag

Au-Ag* →Au-Ag + hv

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(5) (6)

The ECL mechanism is relyed on the electrochemical oxidation of amine (Scheme 1), briefly, Au-Ag bimetallic NCs are oxidized to form Au-Ag+ by the electrochemical oxidization product of TEA•+. The strong reductant TPrA• is formed by losing proton and Au-Ag bimetallic NCs was reduced to form Au-Ag–. Finally, the obtained Au-Ag+ and Au-Ag–are reacting with each other to form excited states (Au-Ag*) and produce ECL emission. It is worthy to notice that the synergistic effect of doped Ag atom in Au NCs playing an important role in electron transfer and catalytic reaction for enhanced ECL emission. Sensing Application. To investigate the potential application of the as-prepared Au-Ag bimetallic NCs, the typical environmental pollutant-Hg2+, was chosen as the model target for analysis as demonstrated in many literatures that Hg2+ can quench the fluorescence of Au NCs and Au-Ag bimetallic NCs through the formation of strong metallophilic bonding (Au-Hg2+/Ag-Hg2+)48-50. And the ECL results for Hg2+ detection were shown in Figure 4. It can be clearly found that the quenched ECL signal was observed with the increase of Hg2+ concentration and reached a platform value after 5 µM. And a linear relationship between the concentrations of Hg2+ and quenched ECL signal ranging from 10 nM to 5 µM was shown in Figure 4B and it can be represented as RECL=1.13-0.27lgCHg2+, where RECL was the normalized ECL intensity and CHg2+ was the concentration of Hg2+. The detection limit of Hg2+ was 5 nM (S/N=3), which is lower than the standard of World Health Organization (WHO) 12


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for Hg2+ in drinkable water (30 nM)55. Selectivity is the key factor for target detection, in order to investigate the selectivity of the proposed ECL sensor for Hg2+ detection based on the as-prepared Au-Ag bimetallic NCs, a series of environmental relevant metal ions with the concentration of 10 µM were chosen as interferences, including K+, Na+, Pb2+, Mn2+, Co2+, Ca2+, Ag+, Cu2+, Ba2+, Fe2+, Fe3+, Ni2+, Mg2+, Zn2+ and Cr3+. And the corresponding ECL experimental results were shown in Figure 5A. It can be found that most of the metal ions have no inference on the ECL signal of the Au-Ag bimetallic NCs apart from Cu2+. This experimental result was not surprised for us, because the same results have been reported in the fluorescence analysis44. The inference caused by Cu2+ was mostly attributed to the interaction between Cu2+ and histidyl or carboxyl groups from the capping ligand of Au-Ag bimetallic NCs, which led to the aggregation of the protein and formation of a protein-Cu2+ complex56,44 and thus induced the quenching of ECL signal. While for Hg2+, the ECL quenching effect mainly results from the formation of metallophilic bonding between Hg2+ ions and Au or Ag atom of Au-Ag bimetallic NCs. Based on the different quenching mechanisms between Cu2+ and Hg2+ towards the ECL signal of Au-Ag bimetallic NCs, a smart method has to propose to eliminate the inference from Cu2+ and to enhance the veracity for Hg2+ detection. Luckily, EDTA as the strong chelating agent has a higher affinity towards Cu2+ than the BSA-Cu2+ complex with the ratio at 1:1 (EDTA/Cu2+)57, and the quenched ECL signal by Cu2+ can be recovered through the dissolution from the BSA-Cu2+ complex based on the competitive reaction. On the contrary, the 13



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addition of EDTA cannot restore the decreased ECL signal caused by Hg2+ because the formation of metallophilic Au-Hg2+ bonding was much stronger than Hg2+-EDTA chelation58. Therefore, the introduction of EDTA to the proposed Au-Ag bimetallic NCs-based ECL detection system endowed the sensor good selectivity for Hg2+. In addition, operational stability as one of the major concerns for practical application of the ECL sensor based on Au-Ag bimetallic NCs is also investigated, and the results were shown in Figure 5B. The strong and stable ECL emission of Au-Ag bimetallic NCs modified GCE were observed with a relative standard deviation of 3.39% under nine cycles of continuous potential scans. After 500 nM Hg2+ was added, the ECL emission signal was dramatically decreased. And mostly, the decreased ECL signal was very stable with a relative standard deviation of 0.73%, indicating its satisfying reliability as a sensing signal. In order to further demonstrate the practical applications of the proposed ECL platform based on Au-Ag bimetallic NCs, different concentrations of Hg2+ were spiked into tap water and lake water (Nanhu Lake in Changchun) with 10-fold dilution for the detection; specifically, the lake water sample was filtered firstly through filter membrane to remove larger particles. The recovery analyses of the spiked samples were shown in Table S1 and the recoveries were obtained with a satisfied result from 94% to 108%, indicating the proposed ECL sensor was applicable for Hg2+ detection in real sample.

CONCLUSIONS

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A facile strategy for enhancing ECL efficiency is presented by simple doping different molars of Ag atoms into Au NCs. Using Au-Ag bimetallic NCs with the molar ratio of 6:1, 5-fold enhanced efficiency is achieved. Moreover, the obtained ECL emission from the Au-Ag bimetallic NCs was blue shift due to the synergistic effect of Au NCs and Ag NCs. With this excellent ECL probe, a signal-off ECL sensor for Hg2+ detection was proposed through the metallophilic interaction between Hg2+ and Au or Ag atom. The proposed platform exhibited low detection limit, broad linear range, good sensitivity and stability. Doping Ag atoms into Au NCs for preparing Au-Ag bimetallic NCs opened promising avenues to enhance the ECL performances of Au NCs in sensing assays. ASSOCIATED CONTENT

Additional information about the UV−vis absorption, fluorescence excitation and emission spectra of Au-Ag bimetallic NCs, electrochemical and ECL behaviors of Au-Ag bimetallic NCs in the absence and presence of TEA, the real sample detection results. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION

Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS

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This work was supported by the National Natural Science Foundation of China (Grant No. 21427811), Youth Innovation Promotion Association CAS (No.2016208),

and

MOST

China

(No.

2016YFA0203200

and

2016YFA0201300) and Jilin province science and technology development plan project 20170101194JC. Furthermore, we would like to extend our thanks to Professor Guizheng Zou at Shandong University for his support of the National Natural Science Foundation of China (Grant No. 21427808).

REFERENCES (1) Richter, M. M. Chem. Rev. 2004, 104, 3003-3036. (2) Miao, W. Chem. Rev. 2008, 108, 2506-2553. (3) Hu, L.; Xu, G. Chem. Soc. Rev. 2010, 39, 3275-3304. (4) Liu, Z.; Qi, W.; Xu, G. Chem. Soc. Rev. 2015, 44, 3117-3142. (5) Li, J.; Xu, Y.; Wei, H.; Huo, T.; Wang, E. Anal. Chem. 2007, 79, 5439-5443. (6) Zhai, Q.; Zhang, X.; Han, Y.; Zhai, J.; Li, J.; Wang, E. Anal. Chem. 2016, 88, 945-951. (7) Sun, X. P.; Du, Y.; Dong, S. J.; Wang, E. K. Anal. Chem.2005, 77, 8166-8169. (8) Gu, W.; Deng, X.; Gu, X.; Jia, X.; Lou, B.; Zhang, X.; Li, J.; Wang, E. Anal. Chem. 2015, 87, 1876-1881. (9) Liu, M.; Zhang, H.; Shu, J.; Liu, X.; Li, F.; Cui, H. Anal. Chem. 2014, 86, 2857-2861. (10) Ding, Z. F.; Quinn, B. M.; Haram, S. K.; Pell, L. E.; Korgel, B. A.; Bard, A. J. Science 2002, 296, 1293-1297. (11) Zhang, X.; Zhang, B.; Miao, W.; Zou, G. Anal. Chem. 2016, 88, 5482-5488. (12) Zhang, X.; Tan, X.; Zhang, B.; Miao, W.; Zou, G. Anal. Chem. 2016, 88, 6947-6953. (13) Li, L.-L.; Ji, J.; Fei, R.; Wang, C.-Z.; Lu, Q.; Zhang, J.-R.; Jiang, L.-P.; Zhu, J.-J. Adv. Funct. Mater. 2012, 22, 2971-2979. (14) Zhao, W. W.; Wang, J.; Zhu, Y. C.; Xu, J. J.; Chen, H. Y. Anal. Chem. 2015, 87, 9520-9531. (15) Shang, L.; Dong, S.; Nienhaus, G. U. Nano Today 2011, 6, 401-418. (16) Zhang, L.; Wang, E. Nano Today 2014, 9, 132-157. (17) Li, L.; Liu, H.; Shen, Y.; Zhang, J.; Zhu, J. J. Anal. Chem. 2011, 83, 661-665. (18) Fang, Y. M.; Song, J.; Li, J.; Wang, Y. W.; Yang, H. H.; Sun, J. J.; Chen, G. N. Chem. Commun. 2011, 47, 2369-2371. (19) Diez, I.; Pusa, M.; Kulmala, S.; Jiang, H.; Walther, A.; Goldmann, A. S.; Muller, A. H.; Ikkala, O.; Ras, R. H. Angew. Chem. Int. Ed. 2009, 48, 2122-2125. (20) Chen, A.; Ma, S.; Zhuo, Y.; Chai, Y.; Yuan, R. Anal. Chem. 2016, 88, 3203-3210. (21) Zhao, M.; Chen, A.; Huang, D.; Zhuo, Y.; Chai, Y.; Yuan, R. Anal. Chem. 2016, 88, 11527-11532. (22) Guo, W.; Yuan, J.; Wang, E. Chem. Commun. 2012, 48, 3076-3078. (23) Hesari, M.; Workentin, M. S.; Ding, Z. Chem. Sci. 2014, 5, 3814-3822. (24) Hesari, M.; Workentin, M. S.; Ding, Z. Chem.-Eur. J. 2014, 20, 15116-15121. 16


Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Hesari, M.; Workentin, M. S.; Ding, Z. ACS Nano 2014, 8, 8543-8553. (26) Hesari, M.; Ding, Z.; Workentin, M. S. Organometallics 2014, 33, 4888-4892. (27) Zhai, Q.; Li, J.; Wang, E. ChemElectroChem 2017, DOI: 10.1002/celc.201600898. (28) Carrara, S.; Arcudi, F.; Prato, M.; De Cola, L. Angew. Chem. Int. Ed. 2017, 56, 4757-4761. (29) Wang, H.; Yuan, Y.; Zhuo, Y.; Chai, Y.; Yuan, R. Anal. Chem. 2016, 88, 2258-2265. (30) Zhuo, Y.; Liao, N.; Chai, Y.-Q.; Gui, G.-F.; Zhao, M.; Han, J.; Xiang, Y.; Yuan, R. Anal. Chem. 2014, 86, 1053-1060. (31) Swanick, K. N.; Ladouceur, S.; Zysman-Colman, E.; Ding, Z. Angew. Chem. Int. Ed. 2012, 51, 11079-11082. (32) Wang, T.; Wang, D.; Padelford, J. W.; Jiang, J.; Wang, G. J. Am. Chem. Soc. 2016, 138, 6380-6383. (33) Zhang, H.; Watanabe, T.; Okumura, M.; Haruta, M.; Toshima, N. Nat. Mater. 2012, 11, 49-52. (34) Zugic, B.; Wang, L.; Heine, C.; Zakharov, D. N.; Lechner, B. A. J.; Stach, E. A.; Biener, J.; Salmeron, M.; Madix, R. J.; Friend, C. M. Nat. Mater. 2017, 16, 558-564. (35) Christensen, S. L.; MacDonald, M. A.; Chatt, A.; Zhang, P.; Qian, H.; Jin, R. J. Phys. Chem. C 2012, 116, 26932-26937. (36) Yao, C.; Chen, J.; Li, M. B.; Liu, L.; Yang, J.; Wu, Z. Nano Lett. 2015, 15, 1281-1287. (37) Wang, S.; Song, Y.; Jin, S.; Liu, X.; Zhang, J.; Pei, Y.; Meng, X.; Chen, M.; Li, P.; Zhu, M. J. Am. Chem. Soc. 2015, 137, 4018-4021. (38) Qian, H.; Jiang, D. E.; Li, G.; Gayathri, C.; Das, A.; Gil, R. R.; Jin, R. J. Am. Chem. Soc. 2012, 134, 16159-16162. (39) Guan, G.; Cai, Y.; Liu, S.; Yu, H.; Bai, S.; Cheng, Y.; Tang, T.; Bharathi, M. S.; Zhang, Y. W.; Han, M. Y. Chem.-Eur. J. 2016, 22, 1675-1681. (40) Jia, X.; Li, J.; Zhang, X.; Wang, E. Chem. Commun. 2015, 51, 17417-17419. (41) Le Guével, X.; Hötzer, B.; Jung, G.; Hollemeyer, K.; Trouillet, V.; Schneider, M. J. Phys. Chem. C 2011, 115, 10955-10963. (42) Huang, H.; Li, H.; Feng, J.-J.; Wang, A.-J. Sensor. Actuat. B-Chem. 2016, 223, 550-556. (43) Zheng, B.; Zheng, J.; Yu, T.; Sang, A.; Du, J.; Guo, Y.; Xiao, D.; Choi, M. M. F. Sensor. Actuat. B-Chem. 2015, 221, 386-392. (44) Zhang, N.; Si, Y.; Sun, Z.; Chen, L.; Li, R.; Qiao, Y.; Wang, H. Anal. Chem. 2014, 86, 11714-11721. (45) Zhou, Q.; Lin, Y.; Xu, M.; Gao, Z.; Yang, H.; Tang, D. Anal. Chem. 2016, 88, 8886-8892. (46) Zhang, J.; Yuan, Y.; Wang, Y.; Sun, F.; Liang, G.; Jiang, Z.; Yu, S.-H. Nano Res. 2015, 8, 2329-2339. (47) Zhai, Q.; Zhang, S.; Jiang, H.; Wei, Q.; Wang, E.; Wang, J. J. Mater. Chem. B 2014, 2, 6371-6377. (48) Xie, J.; Zheng, Y.; Ying, J. Y. Chem. Commun. 2010, 46, 961-963. (49) Guo, C.; Irudayaraj, J. Anal. Chem. 2011, 83, 2883-2889. (50) Guo, W.; Yuan, J.; Wang, E. Chem. Commun. 2009, 3395-3397. (51) Xie, J.; Zheng, Y.; Ying, J. Y. J. Am. Chem. Soc. 2009, 131, 888-889. (52) Hofmann, C. M.; Essner, J. B.; Baker, G. A.; Baker, S. N. Nanoscale 2014, 6, 5425-5431. (53) Zhu, H.; Wang, X.; Li, Y.; Wang, Z.; Yang, F.; Yang, X. Chem. Commun. 2009, 5118-5120. (54) Xu, Y.; Wu, M.; Feng, X. Z.; Yin, X. B.; He, X. W.; Zhang, Y. K. Chem.-Eur. J. 2013, 19, 6282-6288. (55) Zhou, W. Y.; Liu, J. Y.; Song, J. Y.; Li, J. J.; Liu, J. H.; Huang, X. J. Anal. Chem. 2017, 89, 3386-3394. (56) Wu, C.; Fan, D.; Zhou, C.; Liu, Y.; Wang, E. Anal. Chem. 2016, 88, 2899-2903. (57) Muhammed, M. A. H.; Verma, P. K.; Pal, S. K.; Retnakumari, A.; Koyakutty, M.; Nair, S.; Pradeep, T. Chem.-Eur. J. 2010, 16, 10103-10112. (58) Ganguly, M.; Mondal, C.; Pal, J.; Pal, A.; Negishi, Y.; Pal, T. Dalton. Trans. 2014, 43, 11557-11565.

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FIGURE CAPTIONS

Scheme 1. (A) The preparation process of Au-Ag bimetallic NCs. (B) The ECL mechanisms of Au-Ag bimetallic NCs and the proposed ECL sensor for Hg2+ detection.

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Figure 1. (A) Fluorescence emission spectra of Au-Ag bimetallic NCs with different molar ratios at excitation wavelength of 270 nm. (B) The histogram of the fluorescence emission intensities depended on the silver composition. (C) HR-TEM image of Au-Ag bimetallic NCs (insert: size distributions). (D) FT-IR spectra of BSA and BSA-protected Au-Ag bimetallic NCs.

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Figure 2. (A) Cyclic voltammetry and (B) ECL-potential curves of GCE (a, a′), CS modified GCE (b, b′) and Au-Ag bimetallic NCs/CS modified GCE (c, c′) in 0.1 M NaClO4 containing 70 mM TEA. The inset displays the enlarged view of curve a′ and b′. (C) The ECL intensities of Au-Ag bimetallic NCs with different molar ratios. (D) The histogram of the highest ECL intensities depended on the silver composition.

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Figure 3. Normalized ECL spectrum of bare GCE (A), Ag nanocluster (B), Au nanocluster (C) and Au-Ag bimetallic NCs (D) modified GCE in 70 mM TEA solution under the scan voltage from 0 to 1.5 V with the scan rate of 200 mV/s.

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Figure 4. (A) The normalized ECL emission intensity of Au-Ag bimetallic nanocluster based sensor upon the addition of different concentrations of Hg2+ from 0 to 30µM. (B) Plots of the ECL intensity versus the Hg2+ concentration (the inset shows a linear relationship between the ECL intensity and the logarithm of the Hg2+ concentration).

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Figure 5 (A) Normalized ECL intensity of Au-Ag bimetallic NCs based sensor in the presence of different metal ions with the concentration of 10 µM. And equal amount of EDTA (10 µM) was added to shield the interference of Cu2+. (B) The ECL intensity stabilities of Au-Ag bimetallic NCs based sensor in the absence and presence of 500 nM Hg2+, respectively.

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For TOC only

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Enhanced Electrochemiluminescence Behavior of GoldâSilver

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