Design and application of Fe3+ probe for “naked-eye” colorimetric detection in fully aqueous system

Sensors and Actuators B 160 (2011) 1316–1321

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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Design and application of Fe3+ probe for “naked-eye” colorimetric detection in fully aqueous system Dongbin Wei a,1 , Yanling Sun a,b,1 , Junxia Yin a , Guohua Wei a,∗ , Yuguo Du a,∗ a b

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China Department of Chemistry, Zhengzhou University, Henan Province 450052, China

a r t i c l e

i n f o

Article history: Received 19 July 2011 Received in revised form 20 September 2011 Accepted 21 September 2011 Available online 29 September 2011

a b s t r a c t A novel colorimetric sensor for the detection of Fe3+ by “naked-eye” has been developed. The sensor shows excellent selectivity for Fe3+ over other metal ions in aqueous media, as well as a significant color change visible to the naked-eye at the concentration of 0.3 mg/L, the WHO recommended value in drinking water. The sensor can be directly applied to environmental Fe3+ detection in 100% water medium, and the results are comparable to those obtained from instrumental measurements. © 2011 Elsevier B.V. All rights reserved.

Keywords: Chemosensor Ferric ion Colorimetry Visible detection

1. Introduction The iron element is ubiquitous in the environment, and also an essential element in living cells. Fe3+ performs crucial roles in the function of hemoglobin and various enzymes, and cellular metabolism [1–3]. The current determination of Fe3+ mainly depends on expensive instruments, such as CE (capillary electrophoresis) [4], ICP-AES (inductively coupled plasma-atomic emission spectrometry) [5], and FAAS (flame atomic absorption spectroscopy) [6]. Thus, it is necessary to design simple, highly sensitive and selective chemosensors for Fe3+ detection and establish a method for the determination of trace Fe3+ ions. Considerable efforts have been devoted to Fe3+ sensor development over the last decades by taking advantages of sensitivity, selectivity, response time, and local observation of fluorescent chemosensors. However, the present chromophoric probes are either limited with respect to their low sensitivity and selectivity, or incompatible with aqueous environments [7,8], and only a few of them can be used as practical probes for Fe3+ analysis in fully aqueous media [9–11]. Recently, Rao’s group [12] reported a sugar-containing water soluble chemosensor, 1-(d-glucopyranosyl-2 -deoxy-2 iminomethyl)-2-hydroxynaphthalene (G1, Scheme 1), which could detect Fe3+ in HEPES buffer by producing visual color changes to the

∗ Corresponding authors. Tel.: +86 10 6284 9126; fax: +86 10 6292 3563. E-mail addresses: [email protected] (D. Wei), [email protected] (G. Wei), [email protected] (Y. Du). 1 These authors contributed equally. 0925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.09.068

naked eye. However, this sensor could not easily distinguish Fe3+ from Fe2+ , and thus greatly limited its practical application. Herein we report a design and application of sugar-functionalized chemosensors G2 and G3 for “naked-eye” colorimetric detection of Fe3+ over Fe2+ and other metal ions in 100% water samples in real-time. The improvement in the color response, rapid and accurate recognition of Fe3+ from other cation ions with naked-eye will make this approach a very promising one for detection of Fe3+ in 100% water medium by naked-eye. 2. Experimental 2.1. Reagents and apparatus All chemicals were of reagent grade and used without further purification. Ultrapure water with a Millipore Purification System (Milli-Q water) was used throughout the analytical experiments. The 1 H and 13 C NMR spectra were recorded on ARX 400 spectrometers for solutions in CDCl3 or CD3 OD. Chemical shifts are given in ppm downfield from internal Me4 Si. Mass spectrometry was conducted using ESI-source. Thin layer chromatography (TLC) was performed on silica gel HF254 with detection by charring with 30% (v/v) H2 SO4 in MeOH or in some cases by a UV detector. 2.2. Sample preparation Stock solutions of sensor G2 and G3 (50 mmol/L) were prepared in Milli-Q ultrapure water without using any organic co-solvent,

D. Wei et al. / Sensors and Actuators B 160 (2011) 1316–1321 OH O

HO HO

OH

N OH HO

O

OH

O

HO HO

N

O

OH O

HO HO

N OH

O

O

HO

O

HO

G1

G2

G3

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for 3 steps). 1 HNMR (CD3 OD, 400 MHz) ı (TMS, ppm): 3.14–3.26 (m, 3H), 3.32–3.35 (m, 1H), 3.60–3.67 (m, 8H), 3.75–3.85 (m, 6H), 4.21 (d, 1H, J = 7.3 Hz), 6.77 (d, 1H, J = 9.3 Hz), 7.20 (t, 1H, J = 7.5 Hz), 7.44 (t, 1H, J = 7.7 Hz), 7.59 (d, 1H, J = 7.8 Hz), 7.73 (d, 1H, J = 9.4 Hz), 7.99 (d, 1H, J = 8.5 Hz), 8.98 (s, 1H, ArCH = N). 13 CNMR (CD3 OD, 125 MHz) ı (TMS, ppm): 45.89, 50.42, 51.39, 61.67, 68.66, 69.92, 70.25, 70.51, 73.49, 75.93, 76.53, 103.06, 106.26, 117.98, 122.65, 125.57, 125.85, 128.16, 129.16, 134.10, 138.08, 159.02, 178.38. ESI(-)-MS (m/z): calcd. for C23 H31 NO9 : 465.2, found 464.2 [M−H]− .

Scheme 1. The structures of Fe3+ chemo-sensors.

respectively. The stock solutions of Fe3+ , Fe2+ , and other cation ions were prepared by dissolving 1 molar of corresponding chloride salts into Milli-Q ultrapure water. 2.3. Visible detection A 0.1 mL of sensor G2 or G3 stock solution (50 mmol/L) was blended with 0.5 mL of Fe3+ or testing cation ions solution with different concentration in a 10 mL colorimetric tube, the Milli-Q water was added to scale of 10.00 mL. After mixing the sensor and the sample, detection of optical change can be carried out immediately due to the rapid reaction and inevitable color formation. 3. Results and discussion 3.1. Designation and synthesis of sensors for Fe3+ detection In our initial attempt to distinguish Fe3+ from Fe2+ , we designed the G2 sensor according to the orientation of the proposed binding atoms. We expected that introduction of a longer linker trienthylene glycol in G2 could enhance the detection selectivity for Fe3+ . In addition, based on the electron-intensity, we envisaged that replacement of 2-hydroxy-1-naphthaldehyde in G1 with the electron-poor 8-formyl-7-hydroxy-4-methylcoumarin in G3 could improve the selectivity and sensitivity for Fe3+ . The synthetic route to sensor G2 is shown in Scheme 2. Removal of the acetyl groups in 1 [13] followed by hydrogenation afforded 2, which was condensed with 2-hydroxy-1-naphthalene carboxaldehyde to give sensor G2 in a total yield of 90%. The synthetic route to sensor G3 is shown in Scheme 3. Treatment of 7-hydroxy-4-methylcoumarin with hexamethylenetetramine in the presence of TFA gave compound 3 [14] in 57% yield. Condensation of 3 with d-glucosamine hydrochloride afforded sensor G3 in 97% yield.

3.1.2. 8-Formyl-7-hydroxy-4-methylcoumarin (3) To a pre-cooled TFA (20 mL) was added 7-hydroxy-4methylcoumarin (1.21 g, 8.90 mmol) and hexamethylenetetramine (1.93 g, 13.8 mmol) under N2 atmosphere at 0 ◦ C. The solution was stirred at reflux conditions for 8 h, at the end of which time TLC showed all starting materials consumed (petroleum ether: ethyl acetate = 2:1). The excess TFA was removed under diminished pressure, water (50 mL) was then added to the remaining solution. The solid from the mixture was collected by filtration and washed several times with water to give compound 3 (brown solid, 0.80 g, 57%). 1 HNMR (CDCl3 , 400 MHz) ı (TMS, ppm): 2.43 (s, 3H, CH3 ), 6.21 (s, 1H), 6.92 (d, 1H, J = 9.0 Hz), 7.74 (d, 1H, J = 9.0 Hz), 10.63 (s, 1H, HC = O), 12.22 (s, 1H, HO). 13 CNMR (DMSO, 125 MHz) ı (TMS, ppm): 18.76, 109.06, 111.53, 112.23, 113.92, 133.70, 154.00, 155.46, 159.21, 164.10, 192.12. GC/MS-QP2010 (m/z): calcd. for C11 H8 O4 : 204, found 204. 3.1.3. Synthesis of sensor G3 To a thoroughly blended mixture of d-glucosamine hydrochloride (0.79 g, 1.66 mmol) and NaOH (0.07 g, 1.66 mmol) in water (5 mL) was added compound 3 (0.35 g, 1.66 mmol) in ethanol (5 mL) in one portion at room temperature. The mixture was stirred at these conditions for 1 h, and a yellowish precipitated was collected by filtration. Recrystallization of the solid from hot ethanol afforded compound G3 (pale yellow solid, 0.59 g, 97%). 1 HNMR (CD3 OD, 400 MHz) ı (TMS, ppm): 2.38 (s, 3H, CH3 ), 3.43–3.48 (m, 1H), 3.64 (dd, 1H, J = 3.1, 9.9 Hz), 3.76 (dd, 1H, J = 3.8, 10.8 Hz), 3.81–3.86 (m, 2H), 3.87–3.92 (m, 1H), 5.36 (d, 1H, J = 3.1 Hz), 5.99 (s, 1H), 6.58 (d, 1H, J = 9.4 Hz), 7.65 (d, 1H, J = 9.4 Hz), 8.92 (s, 1H, ArHC = N). 13 CNMR (DMSO, 125 MHz) ı (TMS, ppm): 18.54, 60.76, 65.86, 70.08, 71.04, 72.48, 90.12, 103.18, 105.29, 106.75, 120.27, 131.47, 154.86, 156.39, 159.76, 160.17, 178.00. ESI(+)-MS(m/z): calcd. for C17 H19 NO8 : 365.1, found 366.0 [M+H]+ , 388.1 [M+Na]+ . 3.2. Characterization of sensor for Fe3+ detection

3.1.1. Synthesis of sensor G2 To a solution of compound 1 (1.50 g, 2.97 mmol) in CH3 OH (20 mL) was added 1 M NaOCH3 by drops until the pH of the solution reached 9–10. The reaction mixture was allowed to stir at room temperature for 2 h. The thin layer chromatography (TLC) showed no starting material and a spot (Rf = 0.5, ethyl acetate: methanol = 4:1), then neutralized with Amberlite IR-120 (H+ ). The mixture was filtered, and methanol of the filtrate was removed at 50 ◦ C under reduced pressure to give the resulting residue. The residue was re-dissolved in 20 mL ethanol, 20% Pd/C (0.08 g) was added. H2 was bubbled into the solution under normal pressure for 1 h. The TLC plate showed no starting material and a spot (Rf = 0.3, ethyl acetate: methanol = 2:1). The solids ware filtered out and to give resulting solution of compound 2. To the solution of compound 2 was added 2-hydroxy-1-naphthalene carboxaldehyde (0.51 g, 2.97 mmol) and stirred for 3 h. The TLC plate showed no starting material and a spot (Rf = 0.4, ethyl acetate: methanol = 4:1). The solution was concentrated at 50 ◦ C under reduced pressure. The resulting residue purified by silica gel column chromatography to afford sensor G2 (yellow solid, 1.20 g, 90%

Unlike other Fe3+ ion sensors [7,8], G2 has very good solubility in pure water without adding any toxic organic co-solvent, which facilitates the detection processes and makes it suitable for applications in detecting real environmental samples. The selectivity of sensor G2 for Fe3+ against other individual cation ions was explored by adding Ag+ , Ca2+ , Cu2+ , Ni2+ , Mg2+ , Fe2+ , Fe3+ , Hg2+ , Pb2+ , Co2+ , Mn2+ , Cd2+ , and Zn2+ to an aqueous solution of G2 (0.5 mmol/L), respectively. As shown in Fig. 1, only Fe3+ induced a significant color change in the test solution from slight yellow color (sensor G2 as Blank) to dark red color. Addition of other cation ions, including Fe2+ ion at a concentration as high as 0.5 mmol/L, cause no detectable color changes to the naked eye. Furthermore, all of eleven noniron cation ions mixed up and divided into two vials, Fe2+ and Fe3+ ions were respectively added into two vials, and marked as MIX 1 (containing Fe2+ ) and MIX 2 (containing Fe3+ ). It was also found that the obvious color change occurred in the vial of MIX 2. It is highly attractive that only Fe3+ ion from the testing list triggered the significant “naked-eye” color change, while other cation ions including Fe2+ ion did not interfere the Fe3+ detection.

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OAc

OH O

AcO AcO

O

OAc

O

O

i, ii

N3

O

HO HO

OH

1

O

O

O

NH2

2

OH HO HO

O

O

OH

O

O

iii

N

HO

HO

CHO

G2 Scheme 2. Synthesis of sensor G2. Reagents and conditions: (i) NaOCH3 , pH 9–10, CH3 OH; (ii) Pd/C, H2 , CH3 CH2 OH; (iii) CH3 CH2 OH.

OH HO

O

O

i

HO

CHO

O

O

ii

O

HO HO

N OH HO

O

O

3 G3 Scheme 3. Synthesis of sensor G3. Reagents and conditions: (i) hexamethylene-tetramine, TFA, reflux; (ii) d-glucosamine hydrochloride, NaOH, H2 O, CH3 CH2 OH.

Fig. 1. “Naked-eye” color changes after addition of individual and complex cation ions (0.5 mmol/L) to sensor G2 (0.5 mmol/L). Blank is only sensor G2, MIX 1 is eleven cation ions and Fe2+ ion, and MIX 2 is eleven cation ions and Fe3+ ion.

Subsequently, the sensitivity of sensor G2 was checked. A series of Fe3+ solutions with different concentration was prepared, and the sensor G2 was added respectively. As shown in Fig. 2, the red color can be narrowly distinguished at 3.5 mg/L of Fe3+ by naked eye, and it can be clearly recognized up to 7 mg/L of Fe3+ .

However, the high detection limit would heavily limit the application of sensor G2 in practices. Compared to sensor G2, the sensor G3 also has high solubility in pure water with a slight yellow color, and has good selectivity for Fe3+ . As shown in Fig. 3, the color of G3 solution changed from

Fig. 2. The color changes of sensor G2 with the increasing concentration of Fe3+ . The concentrations of Fe3+ varied from 0.28 mg/L (0.005 mmol/L) to 28 mg/L (0.5 mmol/L), and the concentration of sensor G2 was added as 1:1 molar equivalent to Fe3+ concentration.

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Fig. 3. The various colors of sensor G3 as adding of Fe2+ , Fe3+ and other cation ions individually and complexly. All cation ions were prepared at a concentration of 0.5 mmol/L, and the sensor was added into all of vials as 0.5 mmol/L, respectively. Blank is only sensor G3, MIX 1 is eleven cation ions and Fe2+ , and MIX 2 is eleven cation ions and Fe3+ .

Fig. 4. “Naked-eye” color changes of sensor G3 upon addition of different concentration of Fe3+ . (The ratio of Fe3+ concentration to sensor G3 was added as 1:1 molar equivalent). Blank 1 is only Fe3+ , and Blank 2 is only sensor G3.

slight yellow to red, and continuously thickened as the increasing of Fe3+ , while Fe2+ and other cations (Mg2+ , Ca2+ , Cu2+ , Zn2+ , Ni2+ , Co2+ , Mn2+ , Cd2+ , Pb2+ , Hg2+ , and Ag+ ) did not induce color changes. Similarly, the mixture of eleven cation ions with Fe2+ (MIX 1) did not occur color change after adding sensor G3, while MIX 2 (containing Fe3+ ) appeared significant red color. Apparently, under naked eye conditions, the red color of solution is of correlation with the concentration of Fe3+ ion. Fig. 4 shows the color variation of sensor G3 solution in terms of different Fe3+ concentration. It can be seen that the color changes could be exclusively confirmed with naked-eye when the Fe3+ concentration increased to 0.3 mg/L, the recommended standard value for Fe3+ in drinking water by WHO, USEPA, SEPA [15–17]. This result suggested that sensor G3 could be conveniently applied to a naked-eye observation, to see if the Fe3+ concentration in water sample meets the drinking water quality requirement, and thus greatly simplified the traditional detection process and reduce the corresponding costs.

3.3. Environmental application of sensor G3 As the synthesized sensor G3 possesses advantages as high solubility in water media, distinguishing Fe3+ from Fe2+ , no interfering from other cations, and clear color changes under naked-eye conditions, it provides application potentials for Fe3+ identification and detection. In a real case, it would be more interesting to know the relative Fe3+ content with respect to the permission limit, rather than its exact concentration since iron is not a high toxic element. Based on the optical variation of sensor G3, a color chart was prepared according to the relationship between the color change and the concentration of Fe3+ ion. As shown in Fig. 5, the concentration range of Fe3+ in water sample could be judged through comparing the color in test vial with that on the color chart under naked eye conditions. In order to test the valid of the synthesized sensor G3 for detecting Fe3+ contents in real ambient water samples, 4 drinking water

Fig. 5. The prepared color chart according to the solution color with different concentrations of Fe3+ ion.

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Fig. 6. “Naked-eye” color changes of 12 real ambient water samples and corresponding samples spiked 0.5 mg/L of Fe3+ . DW-1, DW-2, DW-3, DW-4 are four drinking water samples, and DW-1*, DW-2*, DW-3*, DW-4* are 0.5 mg/L Fe3+ spiked samples. SW-1, SW-2, SW-3, SW-4 are four surface water samples, and SW-1*, SW-2*, SW-3*, SW-4* are 0.5 mg/L Fe3+ spiked samples. WW-1, WW-2, WW-3, WW-4 are four wastewater samples, and WW-1*, WW-2*, WW-3*, WW-4* are 0.5 mg/L Fe3+ spiked samples. The concentration of sensor G3 added into each vial was 0.5 mmol/L.

samples, 4 surface water samples and 4 wastewater samples were collected in northern China. The samples were filtrated through 0.7 ␮m of GF/F glass fiber filter, and then sensor G3 solution was respectively added to detect Fe3+ contents. As shown in Fig. 6, all of water samples, except SW-4, did not show “naked-eye” color change, which implied that the Fe3+ in the water samples were lower than the recommended limit (0.3 mg/L) for drinking water and Class III surface water in China GB 3838-2002 [18]. After spiking 0.5 mg/L of Fe3+ ion into each test vial, the color appeared and located between 0.5 mg/L and 1.0 mg/L comparing to the color chart in Fig. 5. The exception sample SW-4, of which Fe3+ content was higher than 0.5 mg/L judged with naked eye, was collected

from a river in northeast of China. The higher value of Fe3+ might be attributed to the effluent from the iron mine upstream the river. Meanwhile, the exact Fe3+ concentrations in 12 water samples were determined by using standard method of flame atomic absorption spectrometry [19]. As shown in Table 1, the concentrations of Fe3+ in water samples were in tested water samples were well matched to those judged by naked eye according to the color chart.

4. Conclusions Table 1 Fe3+ concentration determined by flame atomic absorption spectrometry. Water sample Drinking water DW-1 DW-2 DW-3 DW-4 Surface water SW-1 SW-2 SW-3 SW-4 Wastewater WW-1 WW-2 WW-3 WW-4

Fe3+ contents (mg/L) 0.11 0.12 0.10 0.15 0.09 0.09 0.11 0.75 0.08 0.07 0.08 0.08

In summary, we have designed, synthesized, and investigated the characteristics of a novel colorimetric sensor G3 for Fe3+ detection in 100% water medium. Sensor G3 exhibits an excellent Fe3+ ion selectivity over other cation ions (including Fe2+ ), as well as a satisfactory naked-eye detection limit at 0.3 mg/L, the standard value recommended by WHO for drinking water. The sensor G3 has been successfully applied to the detection of Fe3+ ion in drinking water, surface water, and wastewater samples with high selectivity and sensitivity, and the results were in accordance with those of instrumental determination. We anticipate that the present work could provide a novel approach to design sugar-functionalized colorimetric chemo-sensors that benefit from high water solubility and high selectivity, which will be developed as a convenient test kit for environmental Fe3+ detection in 100% water medium by naked-eye.

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Acknowledgments This work was supported in partial by NNSF of China (Projects 20872172, 20877090, 21077123, 50938004) and “863 Program” 2007AA06A407. References [1] P. Aisen, M. Wessling-Resnick, E.A. Leibold, Iron metabolism, Curr. Opin. Chem. Biol. 3 (1999) 200–206. [2] R.S. Eisenstein, Iron regulatory proteins and the molecular control of mammalian iron metabolism, Annu. Rev. Nutr. 20 (2000) 627–662. [3] T.A. Rouault, The role of iron regulatory proteins in mammalian iron homeostasis and disease, Nat. Chem. Biol. 2 (2006) 406–414. [4] A.R. Timerbaev, E. Dabek-Zlotorzynska, A.G.T.Marc van den Hoop, Inorganic environmental analysis by capillary electrophoresis, Analyst 124 (1999) 811–826. [5] P. Vanloot, B. Coulomb, C. Brach-Papa, M. Sergent, J.L. Boudenne, Multivariate optimization of solid-phase extraction applied to iron determination in finished waters, Chemosphere 69 (2007) 1351–1360. [6] T. Shamspur, I. Sheikhshoaie, M.H. Mashhadizadeh, Flame atomic absorption spectroscopy (FAAS) determination of iron (III) after pre-concentration onto modified analcime zeolite with 5-((4-nitrophenylazo)-N-(2 ,4 -dimethoxy phenyl)) salicylaldimine by column method, J. Anal. At. Spectrom. 20 (2005) 476–478. [7] Y. Xiang, A.J. Tong, A new rhodamine-based chemosensor exhibiting selective Fe (III)-amplified fluorescence, Org. Lett. 8 (2006) 1549–1552. [8] L. Dong, C. Wu, X. Zeng, L. Mu, S.F. Xue, Z. Tao, J.X. Zhang, The synthesis of a rhodamine B schiff-base chemosensor and recognition properties for Fe3+ in neutral ethanol aqueous solution, Sens. Actuators B 145 (2010) 433–437. [9] Z.Q. Liang, C.X. Wang, J.X. Yang, H.W. Gao, Y.P. Tian, X.T. Tao, M.H. Jiang, A highly selective colorimetric chemosensor for detecting the respective amounts of iron(II) and iron(III) ions in water, New J. Chem. 31 (2007) 906–910. [10] J. Mao, L.N. Wang, W. Dou, X.L. Tang, Y. Yan, W.S. Liu, Tuning the selectivity of two chemosensors to Fe(III) and Cr(III), Org. Lett. 9 (2007) 4567–4570. [11] K.S. Moon, Y.K. Yang, S.H. Ji, J.S. Tae, Aminoxy-linked rhodamine hydroxamate as fluorescent chemosensor for Fe3+ in aqueous media, Tetrahedron Lett. 51 (2010) 3290–3293. [12] A. Mitra, B. Ramanujam, C.P. Rao, 1-(d-Glucopyranosyl-2(-deoxy-2(iminomethyl)))-2-hydroxynaphthalene as chemo-sensor for Fe3+ in aqueous HEPES buffer based on colour changes observable with the naked eye, Tetrahedron Lett. 50 (2009) 776–780. [13] A.K. Sanki, L.K. Mahal, A one-step synthesis od azide-tagged carbohydrates: versatile intermediates for glycotechnology, Synlett 3 (2006) 455–459.

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Biographies Dongbin Wei received his Master degree in analytical chemistry from the Northwest Normal University in 1998. He received his PhD in environmental science from Nanjing University in 2001. He is an associate professor in environmental science at the State Key Laboratory of Environmental Chemistry and Eco-toxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. His current research interests range over the detection of chemical pollutants in environmental media, design and application of chemo-sensor, risk assessment of typical chemical pollutants. Yanling Sun received her Bachelor’s degree from Zhengzhou University in 2008. She is currently a Master student at Zhengzhou University. Her research interests mainly focus on the synthesis of fluorescent chemo-sensors. Junxia Yin received her Master degree in environmental chemistry from Lanzhou Jiaotong University in 2005. She is currently a Doctor student of Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Her major is environmental analytical chemistry. Guohua Wei received his PhD from Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (RCEES, CAS) in 2005, and worked as a postdoctoral at Roswell Park Cancer Institute (2005–2007). He is currently an associate professor at RCEES, CAS. His main research interests include design and synthesis of fluorescent chemo-sensors and their applications in environment and biology. Yuguo Du received his PhD from Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (RCEES, CAS) in 1995. After completing professional experience at the University of Iowa as a postdoctoral, at Wayne State University as a visiting scholar, and at Ohio State University as a visiting scholar, he joined RCEES. He is currently a professor at RCEES, CAS. His main research interests include design and synthesis of carbohydrate-based drug and fluorescent chemo-sensors.