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ARTICLE 

Cite this: DOI: 10.1039/x0xx00000x

A metal (Co)-organic framework-based chemiluminescence system for selective detection of Lcysteine  Na Yang, Hongjie Song, Xiangyu Wan, Xiaoqing Fan, Yingying Su and Yi Lv*

Received 00th January 2012, Accepted 00th January 2012 DOI: 10.1039/x0xx00000x www.rsc.org/

Metal (Co)-Organic Framework (Co-MOF) was first found to catalyze the chemiluminescence (CL) of luminol. On the basis of X-Ray photoelectron spectroscopy, Powder X-Ray diffraction, CL spectral, UV-visible absorption spectral, and electron spin resonance (ESR) spectral studies, as well as the research of the influence of various free radical scavengers, a possible CL mechanism was proposed. The enhanced CL might be attributed to the formation of peroxide analogous complex between the oxygen-related radicals and the active metal site of Co-MOF material. The established Co-MOF-luminol CL system was successfully applied to determine Lcsyteine (CySH) based on selective and sensitive enhancing effect of CySH on this CL system. Under the optimized conditions, CySH was selectively detected in the range of 0.1 ~ 10 μM with a detection limit of 18 nM. This novel CL system obviously gives impetus to the new research field of metal-organic frameworks (MOFs) in chemiluminescence.

Introduction Since the beginning of this century, metal-organic frameworks (MOFs), consisting of metal ions and organic linkers with bridging organic ligands, have been one of the most rapidly developing areas in chemistry and materials due to their fascinating structures and intrinsic properties1. Because of uniform nanoscale cavities, tailorable molecular structures and the variability of both their metal-containing secondary building and organic linkers, MOFs have been of considerable interest as functional nanoporous materials and possess greatly potential for a wide spectrum of promising applications, such as gas storage2, separation3, drug delivery4, chemical sensing5 and catalysis6,7. In addition, they have also been widely used in preconcentration8, chromatographic separation9, as well as fresh established applications in the aspect of biomedical imaging4, membranes and thin film technologies10,11. With the advantages of extraordinarily large surface areas, controlled pore sizes and accessible active sites, MOFs have high catalytic capability in far-ranging reactions, and preferable selectivity in specific molecular adsorption. Chemiluminescence (CL), with the advantages12 of high sensitivity, wide linear range, no excitation light source, facility and economy, has been an attractive topic of extensive research and considered as a powerful tool in analytical fields for chemical assays13, clinical diagnoses14, food inspection15 and environmental monitoring16. Additionally, the present CL systems generally needed to further increase efficiency, due to the poor efficiency of the classical CL systems for transforming Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of chemistry, Sichuan University, Chengdu, Sichuan 610064, P. R. China. E-mail: [email protected] Fax: +86 28 8541 2798; Tel: +86 28 8541 2798

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the chemical energy into light17, these CL systems generally needed to further increase efficiency. In order to obtain strong emission intensity for quantitative analysis, a large amount of approaches have been explored to enhance the efficiency via using diversified catalysts18,19. Furthermore, selectivity is also always a key problem to be resolved in chemiluminescence. Considering the outstanding catalytic efficiency and special adsorption characteristics, we believe that MOFs might help obtain not only highly sensitive but also selective performance in chemiluminescence analysis. However, up to now, to the best of our knowledge, the study in this field has not been reported. Biological thiols, as we all known, consistently play important roles in human physiology, pharmacy and clinic medicine20,21. Generally, the alterative in the level of the concentration of thiols directly is concerned with a great deal of pathemas including psoriasis, leucocyte loss, lever damage and cancer22. For example, CySH, which is a nonessential amino acid, is involved in all sorts of important cellular functions, such as protein synthesis, detoxification metabolic process23. Consequently, measurement of the change of R-SH compounds concentration in plasma, urine, and pharmaceutical in real time consistently attracts a great deal of attention. As so far, many analytical methods based on different principles for the detection of CySH, such as fluorimetry24, spectrophotometry25, electrochemical methods26, have been developed. In spite of their usefulness, these methods suffer from their respective drawbacks, such as photobleaching, poor excitation light penetration, scattering light, instrument-expensive. As a result, it is indispensable to develop a sensitive and selective CL platform for CySH detection. In our work, we found that the injection of Co-MOF into luminol solution can generate enhanced CL intensity. Nevertheless, the CL enhancement behaviour was not obvious

Analyst, 2013, 00, 1‐3 | 1 

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enough because the active coordination sites of Co-MOF did not expose adequately. Interestingly, it was found that the addition of CySH to Co-MOF-luminol system could obviously enhance CL intensity. Based on this phenomenon, a sensitive and selective CL method for the determination of CySH in actual sample was developed. Moreover, the possible enhancement mechanism of the novel CL system was investigated.

Analyst 

Experimental Section

transform infrared spectra (FT-IR) were measured in the 4004000 cm -1 range using a Nicolet IS10 FT-IR spectrometer View Article Online (Thermo Inc., America) with the KBr pellet technique. X-Ray DOI: 10.1039/C5AN00022J photoelectron spectroscopy (XPS) was obtained with a XSAM 800 electron spectrometer (Kratos) FT-IR spectrometer (Thermo Inc., America) with the KBr pellet technique. X-Ray photoelectron spectroscopy (XPS) was obtained with a XSAM 800 electron spectrometer (Kratos) using monochromatic Al Kα radiation for analysis of the chemical states of the product.

Reagents

Preparation of Co-MOF

All reagents used were of analytical grade and used as the received. Cobalt chloride tetrahydrate (CoCl2·4H2O), NaOH, NaHCO3, Na2CO3 and cysteine were purchased from Chengdu Kelong Chemical Reagent Co. Ltd. (Chengdu, China). Benzenetricarboxylic acid (H3BTC) was purchased from Aladdin Chemistry Co. Ltd. (Shanghai, China). Ethanol (CH3CH2OH) was purchased from Chengdu Changlian Chemical Reagent Co. Ltd. (Chengdu, China). A 0.01 M stock solution of luminol was prepared by dissolving 0.8852 g luminol in 500 mL of 0.10 M NaOH solution and storing it in a dark place at least seven days. The working solutions of luminol were by diluting the stock solution with 0.1 M NaHCO3-Na2CO3 buffer solution. Ultra-pure water (18.24 MΩ cm) obtained from a water purification system (ULUOURE, Chengdu, China) was used throughout this work.

Co-MOF was prepared according to the method described in the literature27 with some modifications. To synthesis of CoMOF, 4 mL of ethanol solution of H3BTC (0.210 g, 1 mM) was added into 10 mL aqueous solution of CoCl2·4H2O (0.4134 g, 1.66 mM) in a 20 mL test tube, and then the test tube was shaken up quickly before ultrasonic irradiation at a frequence of 40 KHz for ten minutes at ambient temperature and atmospheric pressure. Ten minutes later, the products were isolated by filtering the precipitation from reaction mixture, and the precipitation washed with water (4×20 mL) and ethanol (4×20 mL), after that dried at 70oC in vacuum. CL Measurements

Fig. 1 (a) XRD image of the Co-MOF. (b) FT-IR spectra of the Co-MOF. (c) SEM image of MOF. (d) SEM image of MOF after dispersing in water.

Scheme 1. Schematic representation of the sensing strategy of the CoMOF-Luminol CL system to detect CySH

Instrumentations Batch CL experiments were carried out with an Ultra-Weak Luminescence Analyzer (Institute of Biophysics, Chinese Academy of Sciences, Beijing, PRC), the high potential of the photomultiplier tube was set as -800 V. Powder X-ray diffraction (XRD) measurements were performed using a XPto Pro X-ray diffractometer (Philips) with Cu Kα radiation ( = 1.5406 Å). The 2θ angle of the diffractometer was stepped from 5° to 65°at a scan rate of 4°/min. The scanning electron microscope (SEM) images were recorded on a JEOL JSM7500F scanning electron microscope at 30.0 KV to investigate the surface morphology of the materials. Absorption spectra in the region of 200-800nm were collected on a U-2910 UV-vis spectrophotometer (Hitachi Co., Tokyo, Japan). Fourier

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To investigate the effect of the Co-MOF activity on the luminol CL system, CL kinetic curves were obtained by the static injection CL analysis, which was carried out in a 2 mL quartz cuvette. One hundred microliters of Co-MOF (2 μg mL-1) was quickly injected into the 200 μL luminol (5 μM) solution by a microliter syringe from the upper injection port. Another 50 μL Co-MOF (4 μg mL-1) and 50 μL cysteine (1 μM) mixed solution was added into 200 μL luminol (5 μM) solution. The CL profiles were displayed and integrated at intervals of 0.1 s. The flow injection analysis (FIA) system for detection of CySH concentration consisted of two flow lines. The CySH solution was injected through a six-valve injector and mixed with Co-MOF and luminol within the mixing coil in front of the PMT. The flow rates for the Co-MOF, luminol were 1.8 and 2.4 mL min-1, separately. The signals were monitored and recorded with the BPCL luminescence analyzer.

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Analyst Accepted Manuscript

ARTICLE 

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Journal Name  Analysis of Real Sample Human plasma samples were collected from three volunteers. After centrifugation at 4500 rpm for 10 min at room temperature, 0.5 mL of supernatant was subjected to 100-fold dilution with Ultra-pure water for use.

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DOI: 10.1039/C5AN00022J

Results and Discussion Characterization of Co-MOF The XRD pattern of the prepared Co-BTC, as shown in Fig. 1a, demonstrated two characteristic diffraction peaks at 17.5° and 18.7°, which indicated the modular arrangement of the CoBTC cubic lattice were consistent with the previous reports28. The infrared spectra of Co-BTC compound appeared at 1523 and 1430 cm-1 corresponded to the absorption bands of the asymmetric and symmetric vibration of carboxylic groups in benzenetricarboxylate (BTC), as shown in Fig. 1b. The broad bands at 3450 cm-1 and the sharp band at 1622 cm-1 were indicative of the presence of water in the metal-organic framework. Some bands were found in the region of 1300 cm-1 and 600 cm-1, which were ascribed to the out-of-plane vibrations of BTC29. The size and morphology of the synthesized MOF were characterized by SEM. Fig. 1c made clear that Co-BTC were well-shaped rectangular bar in the range of 7-15 μm in length. Furthermore, after dispersing in water by ultrasonic stripping, the morphology of the Co-BTC did not change, keeping integrated structure, as seen in Fig. 1d.

Fig. 2 The CL diagram obtained when (a) Co-MOF was added into the luminol solution (the inset), (b) L-Cysteine injected in the Co-MOFluminol system

Enhancement of luminol CL An obvious CL emission was observed after addition of CoBTC to luminol solution without the usual co reagent of H2O2 (Fig. 2). The maximum CL intensity was about 20 times enhancement compared with the pure luminol solution under similar experimental conditions. Furthermore, when CySH was injected into the Co-BTC-luminol solution, the CL response further indicated a sharp enhancement. No CL emission phenomenon was observed for the Co-BTC, CySH or Co-BTC and CySH solution, indicating that the luminophor in the CL system was not the MOF material. To establish the optimal conditions for the CL system, the influences of pH value, buffer medium, concentration, flow rate were investigated. Firstly, the extensive pH range from 2.1 to 10.2 was tested, and the CL intensity increased in the region of alkali. Meanwhile, experiments in different buffer medium with the pH from 9.0 to 11.2 were further performed, which were obtained from NaHCO3-Na2CO3, NaHCO3-NaOH, NaH2PO4NaOH, H3BO3-NaOH (0.1 M) buffer medium. Fig. 3a indicated that higher CL signals and better precision were collected from N a H C O 3 - N a 2 C O 3 b u f fe r s y s te m in t h e C L r e a c t io n , demonstrated the general opinion that carbonate was an important role in radical reactions involving O 2 and favourable for the CL of luminol solution29. The CL intensity was increased with increasing pH value, reaching a maximum at pH 10.13. With the increasing pH, the system possessed more OH-, the Co-BTC surface was more negatively charged and beneficial to some peroxide complex formation. Furthermore, the O2 species was more stable in high pH solution, which was conducive to the CL emission and gave rise to the increasing CL intensity. However, too many anions loaded on the surface of Co-BTC, when the pH value was higher than 10.13, which hindered the approach of O2 to the. Co-BTC surface, and leaded to the decrease of CL intensity.

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Fig. 3 Effects of (a) the pH value, (b) the concentration of Co-MOF, (c) the concentration of luminol, (d) the flow rate. Conditions: (a) 5 μM luminol, 2 μg mL-1 Co-MOF; (b) 5 μM luminol, pH 10.13 in NaHCO3-Na2CO3 buffer; (c) 2 μg mL-1 Co-MOF, pH 10.13 in NaHCO3-Na2CO3 buffer; (d) 5 μM luminol, 2 μg mL-1 Co-MOF, pH 10.13 in NaHCO3-Na2CO3 buffer

Therefore, pH 10.13 was selected in the CL system. Secondly, the concentration of Co-BTC played a vital role in the CL reaction. It was found that the CL intensity for 0.1-10 μM CySH analysis increased with the increasing concentration of Co-BTC in the range of 0.1-2 μg mL-1 (Fig. 3b), and reached a maximum at the concentration of 2 μg mL-1. Higher concentration of Co-BTC was not desirable, since the quenching effect would be enhanced as a result of collision effect of Co-BTC in high concentration. Hence, the optimum Co-BTC concentration of 2 μg mL-1 was selected to offer a strong CL response. The effect of luminol concentration was investigated over the range of 0.1 μM to 500 μM. The CL intensity kept increasing from 0.1-5 μM, and then sharply decreased in intensity when the concentration was above 5 μM (Fig. 3c). So 5 μM was chosen as the best luminol concentration for subsequent study. Besides, the effect of flow rates of the carrier stream was also discussed (Fig. 3d). The slow flow rate generated a broad CL signal, which reduced the

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ARTICLE  CL intensity. Too high flow rates, however, increased the pressure in the flow line as well as decreased the reagent passing time in the helical detection cell, which caused the reduction of the CL response. The most suitable flow rates for Co-BTC and luminol were 2.1 and 1.8 mL min-1, respectively, considering the solution consumption and analytical precision.

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DOI: 10.1039/C5AN00022J

CL Mechanism In this current work, the mechanism of the Co-MOF-luminol CL reaction was investigated. The CL spectra (Fig. 4a) showed that the maximum wavelength of CL emission of luminol in carbonate-bicarbonate buffer solution was about 425 nm, suggesting the luminophor in the course of the CL reaction was still the formation of an excited 3-aminophthalate anion.11 Interestingly, with the injection of Co-MOF into luminol solution, there was a slightly red shift of the maximal emission wavelength and generated intensive luminescence owing to the effect of Co-MOF on luminol molecule. Because of no CL appearance without the existence of luminol, the red-shifted most possibly attributed to the conjugative effect of both luminol and the organic linker30, as well as the coordinative association of active metal center with the amino of luminol. In order to further verify the above ratiocination, we investigated the UV-Vis absorption of the luminol in the presence or absence of Co-MOF. The absorption of luminol at 350 nm disappeared upon the addition of Co-MOF solution and another absorption peak at 365 nm appeared in the UV-vis spectrum, as shown in the Fig. 4b. The conjugation action in between luminol and ligand structure of the MOF was thought to be the cause of the new absorption feature. Because cobalt ions have terrific catalytic activity for luminol-H2O2 CL system, the catalysis of Co-MOF may originate in the cobalt from the residual in the precursor of CoMOF or the decomposition of material in the solution. To confirm this doubt, the same concentration of Co-MOF dispersed in water was renewedly disposed by ultracentrifugation with 8000 rpm for 10 min, and then the supernatant was obtained and added into luminol solution to test the catalytic activity under the same condition. It was found that the influence of the supernatant on luminol was negligible in comparison with Co-MOF. Therefore, the enhancement of CL in this system was not the free ion, but indeed the intrinsic catalytic properities of MOF due to the favourable stability of this material without collapse happened and the ion release in solution. In addition, the major CL-generating mechanism of luminol in aqueous solution generally summarized in three basic steps, oxidation of the luminol to the luminol radical, farther to hydroxyl hydroperoxide and the decomposition of hydroxyl hydroperoxide with the CL emission. The presence of oxygenrelated radicals as oxidants, are usually supposed to generate during the process. Therefore, the effect of the dissolved oxygen in this system was investigated by purging with pure nitrogen gas and oxygen gas. When the dissolved oxygen was removed from the solution, the CL intensity was reduced 49.8%, while was added 46.8% after bubbling the pure oxygen gas into the solution. These results indicated that the dissolved oxygen played a relatively important role in the CL reaction. R o o m - t e m p e r a t u r e e l e c tr o n s p i n re s o n a n c e (E S R ) spectroscopy was utilized to confirm the existence of the free radical intermediates, 2,2,6,6-tetramethyl-4-piperidine-Noxide(TEMPO) was the specific detection reagent for 1O231. Fig. 5a showed the specific signals of TEMPO, which confirmed the

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Fig. 4 (a) The CL spectrum, (b) UV-vis absorption spectra of Co-BTC, luminol, Co-BTC + luminol. (c) and (b) are the corresponding Co 2p spectra before and after the reaction.

generation of 1O2 in luminol solution. However, the signal intensity decreased when TEMP was added to the mixture solution of Co-MOF and luminol. The result indicated that signal oxygen was consumed in this solution32, which was ascribed to two possible that (1) the change of cobalt states from bivalent to higher or lower valence by superoxide oxidization33 and (2) the formation of the cobalt-peroxide analogous complex between the oxygen-related radical and the exposed active metal sites of the polyporous materials34. XPS is an available tool to characterize the chemical state and composition of materials. Two Co 2p spectra were compared before (Fig. 4c) and after (Fig. 4d) addition of CoMOF to luminol solution, and showed a pairs of spin-orbit doublet of Co2+ as well as its two shake-up satellites, indicating the valence state of centre metal ion of the MOF material was not changed in the catalytic process. As compared to the XPS energy35 at 781.3 eV and 797.1 eV readily assigned to Co 2p3/2 and Co 2p1/2 of the Co-BTC, respectively, while the shift of the corresponding peak of Co-MOF to 781.5 eV and 797.5 eV after the material reacting with luminol. The comparison test result was probably ascribed to the effect of luminol solution on cobalt existence form of the material, resulting in the impaired electron density of Co atoms of Co-MOF36. Therefore, the first possible of the reason of the decreased signals of TEMPO can be ignored, and the interaction of oxygen-related radical and material should be consider as the relatively reasonable cause, as the report34 that the cobalt-peroxide complex formation was the essential for cobalt catalysis of luminol CL. Hence, the reactive oxygen species, such as O2 , OH in correlation with the formation of peroxide complex, were necessary to investigate in this study. As illustrated in Fig. 5b, the CL single was significantly quenched upon addition of superoxide dismutase (SOD), which was frequently used as the specific target molecule of O2 37. For example, only 0.03 mg mL-1 SOD could quench 91.45% of the original intensity. NBT was also widely accepted as an effective radical scavenger of O2 38, as shown in Fig. 5c, the existence of O2 was confirmed with the obvious quenching effect upon the addition of NBT. When 1 mM sodium azide (NaN3) as the specific scavenger reagent for 1O2 was introduced into the proposed system 39 , no obvious inhibition of the CL was observed,

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the relatively low angle region and approximately disappeared with a higher concentration of CySH, indicating a has greatly Online potential as an outstanding catalytic material for View the Article detection DOI: 10.1039/C5AN00022J of CySH in the practical case. Analytical Performance

Fig. 5 (a) EPR spectra of singlet oxygen generated via the raction of TEMPO probe in the luminol and Co-BTC + luminol system. Conditions: concentration of TEMPO, Co-BTC, luminol solution was 0.05 M, 2 μg mL-1, 1×10-5 M, respectively. Effects of different radical scavengers of (b) SOD, (c) NBT and (d) thioruea on the Co-MOFluminol CL system.

indicating that 1O2 was not the mainly intermediate radical in accordance with the above. Based on the experimental data, it was speculated that O2 was efficiently produced, and then the reaction of O2 with Co-BTC might be responsible for the enhanced CL emission. Besides, thiourea was commonly used for detecting OH radical40. When 1 mM thiourea was added to this system, the CL signal decreased 80% (Fig. 5d), showing that OH was generated in the current solution and greatly contributed to the CL. Nevertheless, there was unobservable the characteristic peak of DMPO- OH adduct when DMPO, the specific spin trap reagent for OH 41, was injected into the investigative CL system. These experimental phenomena demonstrated that OH was indeed existent and involved in a series of relative reaction of this system. It is well known that thiol compound such as cysteine can reduce dissolved oxygen to superoxide ion, as well as take place the auto-oxidation to produce hydrogen peroxide and approaches were poor of selectivity by reason of mostly making use of the common property of the –SH group. In this study, introduction of CySH to the Co-BTC-luminol CL system greatly enhanced the luminescence, compared with the past correlational research42,43. Importantly, the structural feature of the frame Co-BTC material endowed this system with a special selectivity for CySH, which was attributed to the high affinity of material toward reactive lone electron pair and the readily accessible of CySH to the MOF surface with the zigzag chains composed 3-D network construction30 in this CL system. As the catalyst lifetime is usually important for a catalyst, some experiments were performed and found that the catalytic effect was only decreased 7 % in the same condition after two months. Besides, to research the stability of configuration state of MOF material, the XRD measurement before and after these reactions were conducted respectively. Fig. 6 shown that the Co- BTC still maintained single crystallinity structure after the catalytic luminol reaction, which was coincident with the corresponding SEM image, manifesting this material kept their excellent properties. After the injection of CySH to this reaction, however, the XRD patterns of Co-MOF were slightly weaken at

This journal is © The Royal Society of Chemistry 2012 

Under the optimum experimental conditions given above, the calibration plot indicated a good linear relationship between the peak height of the CL intensity and the CySH concentration in the range from 0.1 μM to 10 μM, with a correlation coefficient of 0.9980, as shown in Fig. 7a. The limit of detection (LOD, 3σ) for cysteine was 0.018 μM (S/N = 3). The relative standard deviation (RSD) value for 12 parallel measurements (intra-assay) of 1.0 μM CySH concentration was 2.0 %. The RSD for seven parallel measurements (inter assay) of 1.0 μM CySH using six different batches of Co-BTC was 6.5 %. Besides, the present CL system proposed a lower detection limit for CySH, compared with the other methods, such as dinuclear Cu (Ⅱ)-luminol-H2O244 or Fe(Ⅲ)-luimol45 CL sensor, a Eu-H2O2 complex fluorescent probe46, a colorimetric and fluorescent probe47, an 8-MeS-BODIPY probe48 with detection limits of 0.068 μM, 1.65 μM (or equivalently 0.2 μg mL-1), 100nM, 12nM, 0.8μM, respectively. These results manifested that the presented CL method had nice linearity and relatively high sensitivity. Interference Studies In order to assess the applicability of this CL method before its application in a real sample, except for the requirement of sensitivity, good specificity was also needed. So, the selectivity of this sensing method for CySH was evaluated, interferences from the common molecules present in human blood serum, including methionine (Met), lysine (Lys). Asparagines (Asp), alanine (Ala), glutamic acid (Glu), vingine (Vin), leucine (Leu), tyrosine (Tyr), isoleucine (Iso), cystine, serine(Seri), tryptophan (Try), arginine (Arg), hydroxyl proline (Hyd), asparagine (Asp), phenylalanine (Phe), proline (Pro), glucose, fructose (Fru), lactose (Lac), heparin (Hep), uric acid (Uri), glutathione (GSH), as well as some most probable ions. As shown in Fig. 7b, 100fold amino acids and 1000-fold Mg2+, K+, Ca2+, Na+, CO32-, PO43- had no influence on CL intensity. Apparently, the present sensing system showed lower interference for Cy SH determination than luminol-H2O2 CL system. It turned out that

Fig. 6 (a) The XRD patterns of Co-MOF before and after these reactions. The SEM of Co-MOF after the reaction with luminol (b) and after the detection of CySH (c).

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ARTICLE  Acknowledgements

Authors gratefully acknowledge financial support for Online this View Article project from the National Natural ScienceDOI: Foundation of China 10.1039/C5AN00022J (No. 21405107 and 21375089). The authors also thank Analytical & Testing Center and Comprehensive Specialized Laboratory Training Platform of Sichuan University for characterization analysis.

References Fig. 7 (a) Standard curve for the CySH determination in the range from 0.1 to 10 μM. Conditions: Co-MOF with a concentration of 2 μg mL-1, 5 μM luminol. (b) Selectivity of this CL sensor for CySH.

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the developed method offered high selectivity and was suitable for the determination of CySH in real samples.

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Analysis of Real Samples

5

Considering Co-BTC abilities of overcoming interferences from complex matrixes, the presented approach was applied to sensitive and selective determination of CySH in human serum. The recoveries of the CySH in serum were performed to evaluate the accuracy of this method and shown in table 1. It was found that a reasonable (100-fold) dilution of serum was found sufficiently to get a quantitative recovery of spiked CySH about 100% with RSD ranged from 0.8% to 3.7%. The above results confirmed the feasibility and reliability of the proposed method.

6 7

Serum - 1 serum - 2 serum - 3

0.00 2.50 3.50 0.00 2.50 3.50 0.00 2.50 3.50

Measured (μM) (mean ± Standard deviation, n = 3) nd 2.43 ± 0.057 3.54 ± 0.033 nd 2.70 ± 0.094 3.8 ± 0.056 nd 2.63 ± 0.064 3.49 ± 0.027

8 9

S. H. Huo, X. P. Yan, Analyst, 2012, 137, 3445-3451. N. Chang, Z.-Y. Gu, H.-F. Wang and X.-P. Yan, Anal. Chem., 2011, 83, 7094-7101.

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C. R. Wade, M. B. Li, M. Dincă, Angew. Chem. Int. Ed., 2013, 52, 13377-13381. L. E. Kreno, N. G. Greeneltch, O. K. Farha, J. T. Hupp, R. P. Van Duyne, Analyst, 2014, 139, 4073-4080.

12

Z. Lin, H. Chen, J.-M. Lin, Analyst, 2013, 138, 5182-5193.

Recovery (%) ( mean ± Standard deviation, n = 3)

13

97.2 ± 2.2 101.1 ± 0.9

15

M. Liu, Z. Lin, J.-M. Lin, Anal. Chim. Acta., 2010, 670, 1-10.

16

X. Wang, J.-M. Lin, M. L. Liu, X. L. Cheng, TrAC, Trends Anal.

108.0 ± 3.7 108.5 ± 1.6

14

C. Dodeigne, L. Thunus and R. Lejeune, Talanta, 2000, 51, 415-439.

Chem., 2009, 28, 75-87. 17

105.2 ± 2.5 99.7 ± 0.8

In this study, the synthesized Co-BTC by a simple method was first demonstrated to exhibit the catalytic property for enhancing CL intensity of luminol, and a sensitive flowinjection CL method for CySH in serum was developed with excellent selectivity. The preferable selectivity for CySH was attributed to the intrinsic structure of the Co-BT in this system. The possible CL mechanism for the Co-BTC-luminol system was discussed according to the characterization of the materials and most possibly due to the formation of peroxide analogous complex between the oxygen-related radical and the exposed active metal sites. It should be noted that the reactive oxygen species (O2 and OH) existed in the mixing solution could contribute to the peroxide complex and thus enhance the CL emission. This study not only developed a new CL system, but also expanded the analytical application region of metalorganic frameworks.

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Spiked (μM)

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Analyst

Page 8 of 8 View Article Online

DOI: 10.1039/C5AN00022J

Graphic abstract

Metal (Co)-Organic Framework-luminol chemiluminescence system was successfully established for the determination of L-csyteine.

Analyst Accepted Manuscript

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A metal (Co)-organic framework-based chemiluminescence system for selective detection of L-cysteine.

A metal (Co)-Organic Framework (Co-MOF) was first found to catalyze the chemiluminescence (CL) of luminol. On the basis of X-ray photoelectron spectro...
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