Research article Received: 11 February 2014,

Revised: 4 April 2014,

Accepted: 22 May 2014

Published online in Wiley Online Library 10 July 2014

(wileyonlinelibrary.com) DOI 10.1002/bio.2729

Highly sensitive fluorescence and SERS detection of azide through a simple click reaction of 8-chloroquinoline and phenylacetylene Qing Zeng,† Lingling Ye,† Lu Ma, Wenqing Yin, Tingsheng Li, Aihui Liang* and Zhiliang Jiang* ABSTRACT: In 0.19 mol/L acetic acid (HAc), a click reaction of 8-chloroquinoline/azide/phenylacetylene take places in aqueous solution without Cu(I) as a catalyst. 8-Chloroquinoline (CQN) exhibited a strong fluorescence peak at 430 nm that was quenched linearly as the concentration of azide increased from 20 to 1000 ng/mL. This quenching was due to consumption of CQN in the click reaction and a decrease in the number of efficiently excited photons due to the presence of triazole–quinoline ramification molecules with strong hydrophobicity. Using blue nanosilver sol as the substrate, CQN absorbed onto the surface of nanosilver particles, showing a strong surface-enhanced Raman scattering (SERS) peak at 1585 cm-1 that decreased linearly as the azide concentration increased from 8 to 500 ng/mL; the detection limit was 4 ng/mL. Thus, two new, simple and sensitive fluorescence and SERS methods have been developed for the determination of azide via the click reaction. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: N3-; click reaction; fluorescence; SERS; blue nanosilver sol

Introduction

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Experimental Instruments and reagents A F-7000 fluorescence spectrophotometer (Hitachi Company, Tokyo, Japan), DXR smart Raman spectrophotometer (Thermo * Correspondence to: Aihui Liang and Zhiliang Jiang, Key Laboratory of Ecology of Rare and Endangered Species and Environmental Conservation of Education Ministry, Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, Guangxi Normal University, Guilin 541004, China. E-mail: [email protected]; [email protected]

L. Ye and Q. Zeng contributed equally to this work. Key Laboratory of Ecology of Rare and Endangered Species and Environmental Conservation of Education Ministry, Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, Guangxi Normal University, Guilin 541004, China

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Azide is a highly poisonous substance whose toxicity is inferior only to cyanide. It strongly inhibits the activity of some enzymes such as cytochrome oxidase (1,2). However, it is widely used in explosives, fireworks, medicine and car airbags (3). Because of its toxicity, the emission of wastewater containing azide should be severely limited, and the detection of azide is very important. Several methods, including spectrophotometry (4), high-performance liquid chromatography (5), ion chromatography (6), mass spectrometry (7) and fluorescence methods (8,9), have been reported for the determination of azide. Although spectrophotometry is simple and low cost, the sensitivity is not high and the detection limit for azide can be measured in μmol/L. Between 0.001 and 20 mg/L azide can be determined by ion chromatography on an IonPac AS18 ion-exchange column and an eluent generator that automatically generates potassium hydroxide as the mobile phase and suppresses conductivity detection, but the operation is complicated and the cost is high. Recently, click chemistry has been of interest to chemists because it is high yielding, wide in scope, creates only byproducts that can be removed without chromatography, is stereospecific, simple to perform and can be conducted in easily removable or benign solvents (10–12). Several click reactions have been reported for the analysis of trace copper, fluoride, flumioxazin, protein and nucleic acid by fluorescence, spectrophotometry and electrochemistry (13–20). Using a click reaction, a liquid chromatography–mass spectrometry method has been developed for the sensitive detection of azide at levels as low as 21 ppb (21), although the method has the disadvantage of high cost. Zhou et al. presented an approach to aqueous hydrazoic acid

detection through the synthesis and evaluation of an alkynebased fluorescent probe (22). To our knowledge, there has been no report of the fluorescence and surface-enhanced Raman scattering (SERS) study of a 8-chloroquinoline–phenylacetylene–azide click reaction without Cu(I) catalyst and its application in the detection of azide using the two sensitive techniques. Here, a click reaction using the easily obtained reagents 8-chloroquinoline (CQN) and phenylacetylene (PhA) is reported using fluorescence and SERS with highly active blue nanosilver sol substrate, and two new fluorescence and SERS methods are developed for the determination of trace amounts of azide.

Q. Zeng et al. Fisher Co., Georgia, USA) with a laser of 633 nm wavelength, a collection time of 5 s and a power of 2 5 mW, TU-1901 doublebeam UV/vis spectrophotometer (Beijing Purkinje General Instrument Co., Ltd., Beijing, China), FEI Quanta 200 FEG scanning electron microscope (FEI Co., Amsterdam, The Netherlands), 79-1 magnetic stirrer with heating (Zhongda Instrumental Plant, Jiangsu, China) and NaNo-ZS90 nanoparticle and zeta potentiometric analyzer (Malvern Co., Worcestershire, UK) were used. A solution of 75 mmol/L CQN was prepared by dissolving 12.3 mg CQN (100 μL) in 7 mL ethanol and diluting to 10 mL with water. A solution of 91 mmol/L PhA was prepared by dissolving 9.3 mg PhA (100 μL) in 7 mL ethanol and diluting to 10 mL with water. A 10 g/L poly(ethylene glycol) 10000 (PEG) solution was prepared by dissolving 1.0 g PEG in 100 mL water. An aliquot of 2.6 mL of 17.5 mol/L acetic acid (HAc) was diluted to 6 mL with water to obtain 7.6 mol/L HAc. A 1.00 mg/mL N3- standard stock solution was prepared by accurately weighing 0.155 g of NaN3 and dissolving it in water. The solution was transferred to a 100 mL volume flask and diluted to the mark with water. The blue nanosilver (AgNPB) sol preparation (23) was prepared as follows: into a 100 mL round-bottom flask containing 45 mL of water on a magnetic stirrer, were added 500 μL of 10 mmol/L AgNO3, 1.5 mL of 60 mmol/L trisodium citrate, and 120 μL of 30% H2O2; the mixture was colorless. After addition of 200 μL of 0.1 mol/L NaBH4 solution, the color quickly changed from pale yellow to orange and then blue and a lot of bubbles were produced. After standing for 12 h, the mixture was stored in a refrigerator at 4ºC, the concentration of Ag calculated as 0.10 mmol/L. All reagents were of analytical grade and all water used was doubly distilled. Procedure Into a 5 mL marked test tube were added 50 μL of 75 mmol/L CQN, a known amount of 0.10 mg/mL N3-, 30 μL of 91 mmol/L PhA, 100 μL of 10 g/L PEG and 50 μL of 7.6 mol/L HAc; the mixture was diluted to 2 mL with water. The tube was mixed well and placed at room temperature for 20 min. Part of the mixture was then transferred to a 1 cm quartz cell. The fluorescence spectrum was recorded on a spectrometer at a detector voltage of 500 V, slit of 5.0 nm and excitation wavelength of 350 nm, and the fluorescence intensity at 430 nm (F) was recorded.

Meanwhile, a reagent blank solution F0 without NO2 - was recorded, and the value of ΔF = F0 – F was calculated. Following the addition of 1.0 mL of 0.10 mmol/L Ag to the 2 mL mixture, the SERS peak at 1585 cm-1 (I), a blank without azide (I0) and a value of ΔI = I0 – I were obtained.

Results and discussions Many click reactions take place in organic solvents and the chemicals used are not easy to obtain, making it difficult to use click reactions in analysis. In this study, two easily obtained reagents, CQN and PhA, were used to form the click reaction in a water–ethanol solution. According to the reported click reactions (24–26), the product is the hydrophobic triazole–quinoline ramifications (TQ) that aggregated into TQ particles. CQN has strong fluorescence, whereas PhA and TQ are weak. When the amount of azide increased, the fluorescence and SERS decreased linearly due decreasing amounts of CQN. Thus, two methods can be developed for the determination of azide via the click reaction (Fig. 1). Fluorescence spectra In 0.19 mol/L HAc medium, the CQN system exhibited a strong fluorescence peak at 430 nm and a weak Rayleigh scattering peak at 350 nm when the excitation wavelength was at 350 nm. When the azide concentration increased, the fluorescence peak decreased linearly due to a decrease in the amount of CQN via the click reaction (Fig. 2). Furthermore, the formed TQ ramification molecules aggregated to form hydrophobic TQ particles that scatter the excited photons at 350 nm and decrease the fluorescence efficiency. A fluorescence wavelength of 430 nm was chosen for use. The excited spectrum was also examined. When the excitation wavelength was 350 nm, the fluorescence was strongest, and therefore this excitation wavelength was selected. In general, Cu(I) is commonly used as a catalyst in the click reaction. However, the azide–CQN–PhA reactions take place in HAc at room temperature without the need for Cu(I). Other acids including HCl and H2SO4 were tested but are inferior to the HAc. If HAc was replaced by ethanol, the fluorescence peak decreased greatly. The ethanol system can also be utilized to determine azide, but the sensitivity is low.

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Figure 1. Principles of the two methods for the detection of azide.

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Fluorescence and SERS detection of azide

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Figure 2. Fluorescence spectra of the azide–CQN–PhA–HAc system. (a) 1.88 mmol/L CQN–1.37 mmol/L PhA–0.5 g/L PEG–0.19 mol/L HAc; (b) a–0.3 μg/mL N3 ; (c) a–0.7 μg/mL N3 ; (d) a–1.0 μg/mL N3 .

-5

-5

Figure 3. SPR absorption spectra (left) and SEM (right) of the AgNPB. (a) 2.5 × 10 mol/L AgNPB; (b) 5.0 × 10 mol/L AgNPB.

Figure 4. SERS spectra of the system of azide–CQN–PhA–Hac–blue nanosilver. (a) 1.26 mmol/L CQN–0.92 mmol/L PhA–0.34 g/L PEG–0.13 mol/L Hac–33 μmol/L AgNPB; (b) a–0.50 μg/mL N3 .

SERS spectra

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Figure 5. SERS spectra of the CQN–azide–PhA–Hac–AgNPB system. (a) 1.26 mmol/L CQN–0.92 mmol/L PhA–0.34 g/L PEG–0.12 mol/L Hac–33 μmol/L AgNPB; (b) a–0.12 μg/mL N3 ; (c) a–0.23 μg/mL N3 ; (d) a–0.30 μg/mL N3 ; (e) a–0.50 μg/mL N3 .

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Orange–red nanogold, yellow nanosilver and blue nanosilver (AgNPB) sol substrates were examined, AgNPB shows high SERS activity and good stability, and was chosen for the SERS study. The AgNPB sol preparation conditions were examined, and those that gave stable nanosol and a reproducible and sensitive

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Figure 6. Laser scattering of the CQN–azide–PhA–HAc system. 1.88 mmol/L CQN–1.37 mmol/L PhA–0.5 g/L PEG–0.19 mol/L Hac–0.4 μg/mL N3 .

SERS signal were chosen for use. The selected conditions were: 0.10 mmol/L AgNO3–1.8 mmol/L trisodium citrate–0.072% H2O2, giving good stability, the highest sensitivity and the best accuracy for the preparation of AgNPB sol that exhibited a outsurface quadrupole surface plasmon resonance (SPR) absorption peak at 330 nm (Fig. 3), an out-surface dipole SPR absorption peak at 390 nm and a wide in-surface dipole SPR absorption peak at 590 nm (27,28). The silver nanoparticles were observed by scanning electron microscopy (SEM), and ranged in size from 5 to 20 nm, with an average of 10 nm (Fig. 3). CQN has hydrophobicity, can adsorb onto the surface of AgNPB and showed four strong SERS peaks at 990, 1190, 1585 and 1986 cm-1 in the nanosol substrate (Fig. 4). The peak at 990 cm-1 is ascribed to out-of-plane benzene, and the three peaks at 1190, 1585 and

Figure 7. RRS spectra of the CQN–azide–PhA–HAc system. (a) 1.88 mmol/L CQN– 1.37 mmol/L PhA–0.5 g/L PEG–0.19 mol/L HAc;(b) a–0.4 μg/mL N3 ; (c) a–0.8 μg/mL N3 .

1986 cm-1 are ascribed to the benzene ring stretch vibration of CQN. However, PhA showed weak SERS peaks. As the NaN3 concentration increased, there was a linear decrease in the SERS peaks (Fig. 5). The peak at 1585 cm-1 is the most sensitive, and was selected for the determination of azide.

Laser scattering The laser scattering technique was used to measure the size distribution of the CQN–azide–PhA–HAc system (Fig. 6), which ranged from 50 to 1000 nm, with an average size of 590 nm. This

Figure 9. Effect of PhA concentration on ΔF. 1.88 mmol/L CQN–0.5 g/L PEG–0.19 mol/L Hac–0.42 μg/mL N3 .

1600 1400 1200

ΔF

1000 800 600 400 200 0

0

0.2

0.4

0.6

0.8

1

1.2

1.4

C(g/L)

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Figure 8. Effect of CQN concentration on ΔF. 1.37 mmol/L PhA–0.5 g/L PEG–0.19 mol/L Hac–0.42 μg/mL N3 .

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Figure 10. Effect of PEG concentration on ΔF. 1.88 mmol/L CQN–1.37 mmol/L PhA–0.19 mol/L Hac–0.42 μg/mL N3 .

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Fluorescence and SERS detection of azide range of 8–500 ng/mL and a detection limit of 4 ng/mL, but the equipment cost is higher than for the fluorescence method. The accuracy of the SERS system was examined. Results showed that the relative standard deviation values for 10, 100 and 400 ng/mL N3 -, determined five times, were 6.9%, 5.2% and 4.1%, respectively. Compared with the reported method, this fluorescence method is sensitive, has a wide linear range and uses easily obtained reagents. Although the sensitivity of the fluorescence method is lower than that of the SERS method, the linear range is wide, the operation is simple, and the reagents used cost much less.

also demonstrated that the formed hydrophobic TQ ramification molecules were aggregated into TQ particles in the system.

Absorption and resonance Rayleigh scattering spectra CQN–PhA has strong molecular absorption at ~ 330 nm. The absorption does not change as the azide concentration increases. The CQN– PhA–azide system has three RRS peaks at 370, 450 and 500 nm (Fig. 7). The peak at 266 nm is due to the free molecular absorption of CQN and PhA. Although the peak at 370 nm increased with the increase in azide concentration, the linear relationship was not strong.

Influence of coexistent substances Optimization of analytical conditions

Following the described procedure, the influence of coexisting substances on the fluorescence determination of 6.0 × 10-6 mol/L N3 was tested, with a relative error of ± 10%. The results indicated that common anions and cations did not interfere with the determination within a certain concentration range (Table 2), showing that this method had good selectivity because of selective click reaction.

The analytical conditions, including CQN, PhA, PEG and HAc concentrations, reaction temperature and time were considered. HAc concentrations in the range 0.1–0.3 mol/L do not affect the ΔF value. PEG is a surfactant that makes the system stabile and was chosen for use. The results showed that 1.88 mmol/L CQN–1.37 mmol/L PhA–0.5 g/L PEG–0.19 mol/L HAc gave high sensitivity (Figs. 8–10), and was selected for use. The reaction took place at room temperature, which was selected because the operation is simple. When the reaction time is longer than 20 min the fluorescence intensity is constant, and so a reaction time of 20 min was chosen.

Sample analysis Two wastewater samples were taken from a chemical factory using two 250 mL glass sampling bottles, and filtered through a 1.0 μm sand core funnel to obtain sample solutions. The azide content of the samplewas then determined using the fluorescence method. The results were in agreement with results obtained using carbon disulfide-cetylpyridinium chloride spectrophotometry (29). A known amount of NaN3 was added to the sample and recoveries of with 99.5–103% were obtained (Table 3).

Working curve Using the selected conditions, the linear range of the fluorescence method is 20–1000 ng/mL, with low costs. The SERS system is more sensitive than the fluorescence system (Table 1), with a linear Table 1. Analytical feature of the fluorescence and SERS systems Detection technique Fluorescence SERS

Regress equation

Linear range (ng/mL)

Coefficient

Detection limit (ng/mL)

ΔF430 = 3.21C + 21.6 ΔI1586 = 0.318C + 12.2

20-1000 8-500

0.9979 0.9533

10 4

Table 2. Influence of coexistence ion Coexistence ion

Limit times

Relative error (%)

Coexistence ion

Limit times

Relative error (%)

50 50 80 50 50 80 100

–2.2 –4.8 1.0 7.2 2.7 –3.1 –0.7

K+ BrFNO2 NO3 SCN SO4 2-

80 20 20 30 100 50 100

–0.8 5.2 3.0 0.2 5.5 8.0 2.1

Fe3+ Mg2+ Ba2+ Cu2+ Cd2+ Ca2+ Co2+

Table 3. Analytical results Sample

Average (mg/L)

RSD (%)

Added (mg/L)

Found (mg/L)

Recovery (%)

Reference results (mg/L)

0.48, 0.49, 0.45, 0.46, 0.49 0.43, 0.41, 0.4, 0.44, 0.46

0.47 0.43

3.7 5.6

0.40 0.40

0.410 0.398

103 99.5

0.486 0.418

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1 2

Single value (mg/L)

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Conclusions CQN exhibited a strong fluorescence peak at 430 nm and the strongest SERS peak at 1585 cm-1 in the highly active SRES substrate of blue nanosilver sol. Using CQN as a probe, the click reaction of CQN–azide–PhA without Cu(I) as a catalyst was studied by fluorescence and SERS. Under the selected analytical conditions, 8–500 and 20–8000 ng/mL azide could be detected using click reaction fluorescence and SERS methods, respectively. Acknowledgements This work supported by the National Natural Science Foundation of China (No. 21165005, 21267004, 21367005), and the Natural Science Foundation of Guangxi (No. 2013GXNSFFA019003).

References 1. Meatherall R, Palatnick W. Convenient headspace gas chromatographic determination of azide in blood and plasma. J Anal Toxicol 2009;33:525–31. 2. Watanabe K, Hirasawa H, Oda S, Shiga H, Matsuda K, Nakamura M, et al. A case of survival following high-dose sodium azide poisoning. Clin Toxicol (Phil) 2007;45:810–11. 3. Chen TL. Treatment and using of azide liquid. Environ Protect Chem Industry 1998;6:379–80. 4. Zhou WC, Wang YB, Cao GP. Research progress of spectrophotometric determination of azide group content. Chem Propell Polym Mater 2006;4:62–5. 5. Jin MC, Yan JL, Fu ZM. Determination of residual sodium azide in binder-azide by high performance liquid chromatography. Anal Instrum 1999;1:39–40. 6. Yao CY. Determination of azide in Sartan by ion chromatography. J Zhejiang Univ 2008;35:305–10. 7. Minakata K, Nozawa H, Yamagishi I, Gonmori K, Hasegawa K, Suzuki M, et al. Determination of azide in gastric fluid and urine by flow-injection electrospray ionization tandem mass spectrometry. Anal Bioanal Chem 2012;403:1793–9. 8. Koushik D, Uday CS, Abhijit D, Sandipan S. A new water-soluble copper(II) complex as a selective fluorescent sensor for azide ion. Chem Commun 2010;46:1754–6. 9. Sahan A, Banerjee A, Guha S, Lohar S, Chattopadhyay A, Mukhopadhyay SK, et al. Highly selective organic fluorescent probe for azide ion: formation of a molecular ring. Analyst 2012;137:1544–6. 10. Liang LY, Astruc D. The copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click reaction and its applications. Coord Chem Rev 2011;255:2933–45. 11. Li FH, Zhang H, Sun Y, Pan YC, Zhou JZ, Wang JY. Expanding the genetic code for photoclick chemistry in E. coli, mammalian cells, and A. thaliana. Angew Chem Int Ed 2013;52:1–6.

12. Sokolovaa NV, Nenajdenko VG. Recent advances in the CuI-catalyzed alkyne-azide cycloaddition (CuAAC): focus on functionally substituted azides and alkynes. RSC Adv 2013;3:16212–42. 13. Park S, Kim HJ. Highly selective and sensitive fluorescence turn-on probe for a catalytic amount of Cu(I) ions in water through the click reaction. Tetrahedron Lett 2012;53:334473–5. 14. Yao Z, Yang Y, Chen X, Hu X, Zhang L, Liu L, et al. Visual detection of copper(II) ions based on an anionic polythiophene derivative using click chemistry. Anal Chem 2013;85:5650–3. 15. Sui B, Kim B, Zhang Y, Frazer A, Belfield KD. Highly selective fluorescence turn-on sensor for fluoride detection. ACS Appl Mater Interface 2013;5:2920–3. 16. Xie LD, Zheng HY, Ye WM, Qiu SY, Lin ZY, Guo LH, et al. Novel colorimetric molecular switch based on copper(I)-catalyzed azide–alkyne cycloaddition reaction and its application for flumioxazin detection. Analyst 2013;138:688–92. 17. Zhu K, Zhang Y, He S, Chen WW, Shen JZ, Wang Z, et al. Quantification of proteins by functionalized gold nanoparticles using click chemistry. Anal Chem 2012;84:4267 70. 18. Jorgensen AS, Gupta P, Wengel J, Astakhova IK. ‘Clickable’ LNA/DNA probes for fluorescence sensing of nucleic acids and autoimmune antibodies. Chem Commun 2013;49:10751–3. 19. Su J, Xu J, Chen Y, Xiang Y, Yuan R, Chai Y. Sensitive detection of copper(II) by a commercial glucometer using click chemistry. Biosens Bioelectron 2013;45:219–22. 20. Xu X, Daniel WL, Wei W, Mirkin CA. Colorimetric Cu(2+) detection using DNA-modified gold-nanoparticle aggregates as probes and click chemistry. Small 2010;6:623–6. 21. Wang L, Dai C, Chen W, Wang SL, Wang B. Facile derivatization of azide ions using click chemistry for their sensitive detection with LC-MS. Chem Commun 2011;47:10377–9. 22. Zhou Y, Yao YW, Qi Q, Fang Y, Li JY, Yao C. A click-activated fluorescent probe for selective detection of hydrazoic acid and its application in biological imaging. Chem Commun 2013;49:5924–6. 23. Wen GQ, Luo YH, Liang AH, Jiang ZL. Autocatalytic oxidization of nanosilver and its application to spectral analysis. Sci Rep 2014;4:3990. 24. Sasaki T, Eguchi S, Yamada S, Hioki T. Synthesis of adamantane derivatives. Part 53. Simple synthesis of 7-thiaprotoadamantane (7-thiatricyclo(4.3.1.0)decane) and related derivatives via a regiospecific and stereoselective intramolecular Friedel–Crafts reaction. J Chem Soc Perkin Trans 1982;8:1953–8. 25. DuBois GE, Crosby GA, McGarraugh GV, Ng SYW, Stephenson RA, Wang PC, et al. Observations on the chemistry of alpha.-azido ester. Efficient synthesis of a potently sweet homoserine–dihydrochalcone conjugate. J Organ Chem 1982;47:1319–23. 26. Li J, Duan M, Zhang LH, Jiang XH. Click chemistry and its applications, Prog Chem 2007;19:1754–60. 27. Maillard M, Huang P, Brus L. Ag nanodisk growth by surface plasmon enhanced photoreduction of adsorbed [Ag+]. Nano Lett 2003;3:1611–15. 28. Jiang P, Li SY, Xie SS. Machinable long PVP-stabilized silver nanowires. Chem Eur J 2004;10:4817–21. 29. Chen J, Song QZ. Application study on surface active agent in determination of azide ion in wastewater by UV-spectrophotometric method. Acta Armamentarii 1997;18:41–4.

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Luminescence 2015; 30: 303–308

Highly sensitive fluorescence and SERS detection of azide through a simple click reaction of 8-chloroquinoline and phenylacetylene.

In 0.19 mol/L acetic acid (HAc), a click reaction of 8-chloroquinoline/azide/phenylacetylene take places in aqueous solution without Cu(I) as a cataly...
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