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Sensors and Actuators B 202 (2014) 674–682

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

jo u r nal homep age: www.elsev ier .com/ locate /snb

eneral

luorescent chemosensors for Zn2+ ions based on flavonol derivatives

inod Kumar Gupta ∗, Naveen Mergu, Ashok Kumar Singhepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India

r t i c l e i n f o

rticle history:eceived 7 May 2014eceived in revised form 28 May 2014ccepted 29 May 2014

a b s t r a c t

New fluorescence chemosensors (CS1 and CS2) based on flavonol derivatives were successfully synthe-sized and characterized. Complexation behaviour of sensors towards zinc and other tested metals havebeen studied using UV–vis and fluorescence spectrometric methods. These reveal selective detectiontowards Zn2+ ion, along with fluorometric response. Also, those serve as a highly selective chemod-

vailable online 6 June 2014

eywords:luorescent chemosensorlavonol moietyinc ionaked-eye detection.

osimeter for Zn2+ at neutral pH with naked-eye detection and successfully examined the reversibility ofchemosensor–Zn(II) complexation.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Zinc is the second most abundant transition metal ion after ironn the human body, and essential with concentration ranging fromub-nM to 0.3 mM [1,2]. It is a very important ion species in manyiological activities such as cellular metabolism, gene expression,eural signal transmission, DNA binding or recognition, pathology,ell apoptosis and mammalian reproduction [3–9]. The disorder ofinc metabolism in biological systems is associated with diabetes,pilepsy and Alzheimer’s diseases [10–16].

Therefore, there is a large demand for exploring novel devel-pment of Zn2+ chemosensors over other techniques [17–27]. Theevelopment of chemosensors for metal ions with high selectivitynd sensitivity is an active field in analytical chemistry. Fluorescenthemosensors for metal ions have attracted particular attentionue to their advantages such as low cost, good sensitivity, simplic-

ty, capability of real-time detection and non-destructive emissionignals [28–32].

Till date, numerous fluorescent chemosensors for zinc haveeen developed using indole [33], coumarin [34,35], quinoline36,37], BODIPY [38–40], bipyridine [41,42], nanoparticles [43,44]nd other fluorophores [45–48], which exhibited excellent selec-

ivity and sensitivity towards zinc and some of them could be usedor biological imaging in a physiological environment. However,

ost of them need complicated synthesis process, work in toxic

∗ Corresponding author. Tel.: +91 1332285801; fax: +91 1332273560.E-mail addresses: vinodfcy@iitr.ac.in, vinodfcy@gmail.com (V.K. Gupta).

ttp://dx.doi.org/10.1016/j.snb.2014.05.133925-4005/© 2014 Elsevier B.V. All rights reserved.

organic-containing solution such as acetonitrile. Moreover, manyreported fluorescent chemosensors for Zn2+ encountered difficultyin distinguishing zinc from other transition metal ions, especiallyCd2+, because Cd2+ is in the same group of the periodic table andshows similar properties to Zn2+ [49–52]. Flavonol derivatives arealso detected as a fluorescent chemosensor for some ions [53].

Herein, we describe an elaborately designed Zn2+ chemosensorwith functionalized flavonol derivatives (CS1 and CS2). Upon theaddition of Zn2+ to methanol solution of chemosensor, enhance-ment of fluorescence emission accompanied by a blue shift wasobserved, enabling fluorescence “turn-on” detection of Zn2+ bynaked-eye under a UV lamp. Both UV–vis and fluorescence spectro-scopic studies show that the prepared chemosensors (CS1 and CS2)are highly sensitive and selective towards zinc over other metal ionsin methanol. Thus compounds CS1 and CS2 are suitable for selectivedetection of Zn2+ as fluorescence “turn-on” sensors.

2. Experimental

2.1. UV–vis and fluorescent studies of chemosensor with variousmetal ions

UV–vis absorption and fluorescence emission spectra were mea-sured in 1.0 cm path length quartz cuvettes in alcoholic medium(MeOH) using a Shimadzu UV-2450 spectrophotometer and a

Shimadzu RF-5301PC spectrofluorophotometer. Absorption andemission spectra of the chemosensors in the presence of variousmetal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cs+, Cu2+, Fe2+, Fe3+,Hg2+, K+, Li+, Mg2+, Mn2+, Na+, Nd3+, Ni2+, Pb2+, Sr2+ and Zn2+) were

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V.K. Gupta et al. / Sensors an

ecorded in the concentration of 5 �M (for CS1 and CS2, absorp-ion spectra), 5 �M (for CS1, emission spectra) and 2 �M (for CS2,mission spectra).

.2. Fluorescence titration

Stock solutions of CS1 (10 �M), CS2 (4 �M) and Zn(OAc)210 �M and 4 �M) were prepared in methanol solvent. 0.0–1.0quiv. of zinc metal ion added to both receptors while using aboverepared solutions. After mixing them for a few seconds, Fluores-ence spectra were taken at room temperature.

.3. Job’s plot measurement

The binding stoichiometry of sensor–metal complex was deter-ined by continuous variation (job’s) method. From a stock

olutions of CS1 (10 �M) and CS2 (4 �M), 4.5, 4.0, 3.5, 3.0, 2.5, 2.0,.5, 1.0 and 0.5 mL taken and transfer to vials. 0.5, 1.0, 1.5, 2.0, 2.5,.0, 3.5, 4.0 and 4.5 mL of stock solution of metal ion (10 �M, for CS1nd 4 �M, for CS2) were added to each compound (CS1 and CS2)olution. Each vial had a total volume of 5.0 mL. After shaking theials for a few seconds, fluorescence spectra were taken at roomemperature.

.4. Calculations of dissociation and association constants

From the fluorescence titration, association and dissociationonstants were calculated by using Benesi−Hildebrand equation54]:

og(

I − IoIMax − I

)= n × log[M] − log Kd

where I, IO and IMAX are the corrected fluorescence emissionntensity (at � = 476 nm, for CS1 and � = 478 nm, for CS2) of the com-lex at initial, interval t, and the final state at which the complexas fully formed upon addition of metal ion, respectively. [M] is the

oncentration of metal ion, n is the slop (from Hill plot), Kd is theissociation constant. Association constant (Ka) was determinedy:

a = 1Kd

.5. Quantum yield calculations

Quantum yield is determined by using optically matching solu-ion of Coumarin 1 (Фr = 0.99 in ethyl acetate) as standard at anxcitation wavelength of 362 nm and quantum yield is calculatedy fluorometrically using the equation:

s = ˚r × 1 − 10−Ar Lr

1 − 10−AsLs× �2

s

�2r

× Ds

Dr

Фs and Фr are the quantum yields of sample and the referenceespectively, As and Ar are the respective absorbance of the samplend the reference, Ds and Dr are the areas of emission for samplend reference respectively, Ls and Lr are the lengths of the absorp-ion cells of sample and reference respectively. �s and �r are theefractive indexes of the sample and reference solutions.

.6. Reagents and apparatus

All the commercially available chemicals were purchased from

erck and Aldrich and used without further purification. The IR

pectra were recorded on a Nexus FT-IR (Illinois, USA) spectrome-er in the range 4000–400 cm−1 with KBr. The NMR spectra wereecorded on a Bruker 500 MHz (USA), TMS as an internal standard,

ators B 202 (2014) 674–682 675

CDCl3 taken as solvent. The UV–vis absorption spectra were mea-sured on a Shimadzu UV-2450 spectrophotometer (Japan) and theFluorescent spectra were recorded on a Shimadzu RF-5301PC spec-trofluorophotometer (Japan). The pH was measured by use of aEutech CyberScan pH 510 (Singapore).

2.7. Synthesis and characterization

The chemosensors (CS1 and CS2) were prepared by the reportedmethod [55–66] with some modifications (Scheme 1). NaOH(4 equiv.) was added to a solution of 2′-hydroxyacetophenone(10 mmol) and aldehyde (10 mmol) in methanol and the mixturewas stirred for 18 h at room temperature. The reaction mixture wasacidified with HCl (30%) and the 2′-hydroxychalcone was isolatedby filtration. The 2′-hydroxychalcone (5 mmol) was suspended inmethanol, and NaOH (4 equiv.) and H2O2 (30%, 10 equiv.) wereadded at 0–4 ◦C. The mixture was stirred for 2–3 h at room tem-perature, then acidified with HCl (30%) and poured into water(400 mL). Collected the precipitate by filtration and the pure prod-uct was obtained by recrystallization from methanol. The structuresof chemosensors were characterized by IR, 1H NMR, 13C NMR spec-tra (Figs. 1–3).

3-Hydroxy-2-phenyl-4H-chromen-4-one (CS1): Yield: 0.94 g(79%); colour: yellow-white solid; m.p. 168–170 ◦C; FT-IR (KBr), �,cm−1: 3236 (O−H), 1611 (C=O), 1480, 1415 (C=C), 1287, 1214, 1129(C−O); 1H NMR (CDCl3), ı, ppm (J, Hz): 7.42 (t, J = 7.5, 1H), 7.48 (t,J = 7.5, 1H), 7.55 (t, J = 7.5, 2H), 7.60 (d, J = 8.5, 1H), 7.71 (dt, J = 1.5,7.5, 1H), 8.26 (d, J = 7.5, 3H); 13C NMR (CDCl3), ı, ppm: 118.3, 120.7,124.6, 125.5, 127.8, 128.6, 130.2, 131.1, 133.7, 138.5, 144.9, 155.5,173.5.

3-Hydroxy-2-(2-furyl)-4H-chromen-4-one (CS2): Yield: 0.82 g(72%); colour: pale yellow solid; m.p. 179–181 ◦C; FT-IR (KBr), �,cm−1: 3258 (O−H), 1617 (C=O), 1482, 1418 (C=C), 1280, 1213, 1130(C−O); 1H NMR (CDCl3), ı, ppm (J, Hz): 6.65 (q, J = 1.5, 1H), 7.36 (d,J = 3.5, 1H), 7.41 (t, J = 7.5, 1H), 7.60 (d, J = 8.5, 1H), 7.69 (t, J = 8.5,2H), 8.24 (d, J = 8.0, 1H); 13C NMR (CDCl3), ı, ppm: 112.7, 115.8,118.3, 121.2, 124.7, 125.4, 133.6, 136.4, 138.9, 144.4, 144.8, 155.0,172.4.

3. Results and discussion

The binding ability and mode of sensors (CS1 and CS2) towardsZn2+ and other metal ions was measured through UV–vis, fluores-cent spectrometry and naked-eye observation.

3.1. UV–vis spectral studies

The chemosensors (CS1 and CS2) were investigated by UV–visabsorption spectral behaviour in the presence of various metals inthe 50 �M concentration of each component in methanol solvent.The free ligands CS1 and CS2 exhibited a main absorption bandcentered at 343 nm and 356 nm, respectively. On the addition ofmetal ions to sensors, the absorption band of free receptors CS1and CS2 is shifted to low intensity, while a new broad absorptionband (mainly for Cu2+, Ni2+, Zn2+, Pb2+, Al3+, Co2+, Cd2+, Mn2+ andMg2+ ions) was observed at about 350–480 nm region. As shown inFig. 4, both sensors are responding to the above mentioned metalions and there is no significant changes were observed when mixedwith other metal ions such as Ba2+, Ca2+, Cr3+, Cs+, Fe2+, Fe3+, Hg2+,K+, Li+, Na+, Nd3+ and Sr2+.

3.2. Fluorescence emission studies

The fluorescence response of sensors CS1 (5 �M) and CS2(2 �M) upon addition of various metal ions 5 �M (for CS1) and2 �M (for CS2) have been investigated in methanol. Chemosensors

676 V.K. Gupta et al. / Sensors and Actuators B 202 (2014) 674–682

OH

O

CHO

O

CHO

OH

O

OH

O

O

a

a

a, b

a, b

O

O

OH

O

O

OH

O

CS1

CS2

Scheme 1. Synthetic routes to chemosensors (CS1 and CS2): (a) NaOH; (b) H2O2.

Fig. 1. FT-IR spectrum of CS1 and CS2.

1 ectrum

Cs5tHc(

Fig. 2. H NMR sp

S1 and CS2 alone displayed a weak single fluorescence emis-ion band at 530 nm and a couple of emission bands at 425 and30 nm, respectively, with an excitation of 340 nm. Upon addi-

ion of various metals (Ba2+, Ca2+, Co2+, Cr3+, Cs+, Cu2+, Fe2+, Fe3+,g2+, K+, Li+, Mn2+, Na+, Nd3+, Ni2+, Pb2+ and Sr2+) no signifi-ant changes (except Zn2+, Al3+, Cd2+ and Mg2+) were observedFig. 5). On addition of Zn2+, receptors CS1 and CS2 exhibited a

of CS1 and CS2.

prominent fluorescence enhancement accompanied by a blue shiftof 54 nm from 530 to 476 nm and 52 nm from 530 to 478 nm,respectively. Results are indicating that the sensors CS1 and CS2

exhibit “off–on” mode with high sensitivity towards Zn2+ overother metal ions. Under a UV lamp, the chemosensors CS1 andCS2 in the presence of Zn2+ showed a dramatic colour changesfrom yellow-orange to bright green, which could easily be detected

V.K. Gupta et al. / Sensors and Actuators B 202 (2014) 674–682 677

Fig. 3. 13C NMR spectrum of CS1 and CS2.

Fig. 4. UV–vis absorbance spectra of (a) CS1 (50 �M) and (b) CS2 (50 �M) in the presence of 1 equiv. of various metal ions in methanol.

Fig. 5. Fluorescence emission spectra (�ex = 340 nm) of (a) CS1 (5 �M) and (b) CS2 (2 �M) in the presence of 1 equiv. of various metal ions in methanol.

678 V.K. Gupta et al. / Sensors and Actuators B 202 (2014) 674–682

Fig. 6. The variation in fluorescence emission spectra of (a) CS1 (5 �M) and (b) CS2 (2 �M) with increasing amounts of Zn2+ ion (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9,1.0, 2.0, 5.0 and 10.0 equiv.) in methanol. Inset, left: the fluorescence changes excited by UV lamp of (a) CS1 (5 �M) and (b) CS2 (2 �M) with 1 equiv. of Zn2+. Right: thefl moun

btc

iicarZtwf

uorescence change at 476 nm (for CS1) and 478 nm (for CS2) as a function of the a

y the naked-eye (Fig. 6, inset). At the same time, the addi-ion of other metal ions did not show any significant colourhange.

In addition, the fluorescence response of CS1 and CS2 to var-ous concentrations of Zn2+ (0–1.0, 2.0, 5.0 and 10 equiv.) wasnvestigated. Upon addition of Zn2+, the fluorescence intensityentred at 476 nm (CS1) and 478 nm (CS2) gradually increasednd remained steady when 1 equiv. Zn2+ was added. The satu-ation behaviour of the fluorescence intensity after 1 equiv. of

n2+ reveals that the chemosensor–Zn2+ has a 1:1 stoichiome-ry (Fig. 6). These results were further confirmed by Job’s plot,hich indicates that a binding stoichiometry of the complex

ormed between chemosensors and Zn2+ is 1:1 (Fig. 7). From the

t of Zn2+ ions.

fluorescence titration profiles (Fig. 6), the association constant forchemosensor–Zn2+ in MeOH was determined as 1.2 × 109 M−1 (forCS1) and 3.8 × 1010 M−1 (for CS2) by a Hill plot (Fig. 8). Whenexcited at � = 362 nm, receptor exhibited low fluorescence quan-tum yield, Ф = 0.0144 (CS1), 0.0498 (CS2) (standard: Coumarin 1 inethyl acetate; Ф = 0.99). On the other hand, receptor–Zn2+ exhibitedstrong fluorescence quantum yield, Ф = 0.0302 (CS1–Zn2+), 0.1158(CS2–Zn2+). These data ensured that an enhancement in quantumyield can be achieved during the Zn2+ sensing process by using

chemosensor.

The selectivity of CS1 (5 �M) and CS2 (2 �M) for Zn2+ over othermetal ions (1.0 equiv.) were examined by the competition exper-iments. As shown in Fig. 9, the fluorescence response of CS1 and

V.K. Gupta et al. / Sensors and Actu

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0a

I/Io

[Host]/ ([Host]+[Zn2+])

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5b

I/Io

[Host]/ ([Host] +[Z n2+])

Fig. 7. Job’s plot for the binding of CS1 (a) and CS2 (b) with Zn2+. Fluorescenceintensity at 476 nm (for CS1) and 478 nm (for CS2) was plotted as a function of themolar ratio.

-6.4 -6.2 -6.0 -5.8 -5.6 -5.4 -5.2

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0a

y = 1.5728x + 9.078 6

R² = 0.975 6

Kd= 8.34 × 10-10 M

Ka= 1.2 × 109 M-1

log(

(I-Io

)/(Im

ax-I)

)

log[Zn2+]

Fig. 8. Hill plot of CS1 (a, fluorescence intensity at 476 n

ators B 202 (2014) 674–682 679

CS2 towards Zn2+ in the presence of various metal ions was inves-tigated, and the results show that Cu2+ and Ni2+ could interfere inthe interaction between receptor (CS1 and CS2) and Zn2+ that Indi-cates the binding ability of chemosensors towards Cu2+ and Ni2+ isstronger than Zn2+. Upon addition of 1.0 equiv. of Zn2+ in the pres-ence of other metal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cs+, Fe2+,Fe3+, Hg2+, K+, Li+, Mg2+, Mn2+, Na+, Nd3+, Pb2+ and Sr2+), 4-foldenhancement of the fluorescence intensity was observed, which islarge enough to determine Zn2+ from other metal ions. By addi-tion of other metal ions (Cu2+ and Ni2+) quenches the fluorescenceof the receptor–Zn2+ complex (Fig. 10), due to the more bindingability towards Cu2+ and Ni2+ ions. It means, the reported sen-sors provide simultaneous detection of Zn2+ and other metal ions(Cu2+ and Ni2+).

The interaction between receptor (CS1 and CS2) and Zn2+ ionwas investigated at a pH range from 2.0 to 10.0. This experimentwas carried out at a fixed concentration of receptor–Zn2+ is 5 �M(for CS1) and 2 �M (for CS2) in methanol. As shown in Fig. 11, thefluorescence intensity changes were observed at 476 nm (for CS1)and 478 nm (for CS2) with the pH value at acidic and basic condi-tions (pH <7.0>). The chemosensors CS1 and CS2 in the presenceof Zn2+ showed a dramatic colour changes in different pH media,which could easily be detected by the naked-eye (Fig. 11, inset)under a UV lamp. However, the fluorescence intensity decreased atacidic condition (pH <7.0), due to receptor could be protonated andhence its binding ability reduced. Reduction in fluorescence inten-sity at basic condition (pH >7.0), could be due to the formation ofsalt.

3.3. Reversibility test of CS1 and CS2

The reversibility of the chemosensor is an important aspect inpractical applications. Thus EDTA addition was conducted to exam-ine the reversibility of CS–Zn(II) complexation. The reversibilityof the reaction of CS and Zn(II) was performed by the titra-tion of the mixture of CS and Zn(II) (1:1) with EDTA (Fig. 12).The increase in the fluorescence intensity at 530 nm (Fig. 12a,for CS1) indicates the regeneration of free CS1. The fluorescence

intensity was again quenched at 530 nm on addition of moreZn(II) to the same mixture. Upon addition of EDTA to the mix-ture of CS2 and Zn(II), no significant changes were observed(Fig. 12b).

-6.8 -6.6 -6.4 -6.2 -6.0 -5.8 -5.6

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0b

y = 1.7279x + 10.575

R² = 0.9699

Kd= 2.66 × 10-11 M

Ka= 3.8 × 1010 M-1

log(

(I-Io

)/(Im

ax-I)

)

log[Zn2+]

m) and CS2 (b, fluorescence intensity at 478 nm).

680 V.K. Gupta et al. / Sensors and Actuators B 202 (2014) 674–682

none Al3+ Ba 2+ Ca 2+ Cd2+ Co2+ Cr3+ Cs+ Cu2+ Fe2+ Fe3+ Hg2+ K+ Li+ Mg2+Mn2+ Na+ Nd3+ Ni2+ Pb2+ Sr2+0

1

2

3

4

5

a

I/Io

CS1+Mn+

CS1+Mn++Zn2+

none Al3+ Ba2 + Ca2 + Cd2+ Co2+ Cr3+ Cs+ Cu2+ Fe2 + Fe3 + Hg2+ K+ Li+ Mg2+Mn2+ Na+ Nd3+ Ni2+ Pb2+ Sr2+0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0 bCS2 +Mn+

CS2 +Mn++Zn2+

I/Io

Fig. 9. Competitive selectivity of CS1 (a) and CS2 (b) towards Zn2+ in the presence of other metals (1 equiv.) with an excitation of 340 nm.

Fig. 10. The variation in fluorescence emission spectra (fluorescent colour, inset) ofchemosensor–Zn2+ on addition of other metal ions (Cu2+ and Ni2+).

Fig. 11. The variation in fluorescence intensity as a function of pH at 476 nm (forCS1) and 478 nm (for CS2) in the presence of Zn2+; �ex = 340 nm. Inset, the colourchanges of mixture of chemosensor (CS)–Zn2+ in different pH media under a UVlamp.

400 500 6000

100

200

300

400

500

600 a

Fluo

resc

ence

Inte

nsity

(au)

Waveleng th (nm)

0.0 eq.

1.0 eq.

400 500 6000

100

200

300

400

500

600

700 b

Fluo

resc

ence

Inte

nsity

(au)

Wavel eng th (nm )

0.0 eq.

1.0 eq.

Fig. 12. The variation in fluorescence emission spectra of (a) CS1+ Zn2+ (5 �M) and (b) CS2+ Zn2+ (2 �M) upon the addition of EDTA (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9and 1.0 equiv.) in methanol. Inset shows the fluorescence change at 476 nm (for CS1) and 478 nm (for CS2) as a function of the amount of EDTA.

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R

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V.K. Gupta et al. / Sensors an

. Conclusion

The reported chemosensors (CS1 and CS2) show fluorometricesponse for Zn2+ ions, exhibit high selective and sensitive towardsinc over other tested metal ions. Under a UV lamp, the detectionrocess gives rise to a colour change (from yellow-orange to brightreen), which could easily be detected by the naked eye. Thus, theroposed sensors have the ability to serve as a practical sensor foretection of zinc ion in both environment and biological samples.

cknowledgements

One of the authors (Naveen) is thankful to the Ministry of Humanesource and Development (MHRD), New Delhi, India for financialupport.

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22] N.S. Gadhari, B.J. Sanghavi, A.K. Srivastava, Potentiometric stripping analysis ofantimony based on carbon paste electrode modified with hexathia crown etherand rice husk, Anal. Chim. Acta 703 (2011) 31–40.

23] V.K. Gupta, A.K. Jain, S.K. Shoora, Multiwall carbon nanotube modified glassy

carbon electrode as voltammetric sensor for the simultaneous determinationof ascorbic acid and caffeine, Electrochim. Acta 93 (2013) 248–253.

24] V.K. Gupta, S. Kumar, R. Singh, L.P. Singh, S.K. Shoora, B. Sethi, Cadmium (II)ion sensing through p-tert-butyl calix[6] arene based potentiometric sensor, J.Mol. Liq. 195 (2014) 65–68.

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25] V.K. Gupta, A.K. Singh, L.K. Kumawat, A novel gadolinium ion-selective mem-brane electrode based on 2-(4-phenyl-1, 3-thiazol-2-yliminomethyl) phenol,Electrochim. Acta 95 (2013) 132–138.

26] V.K. Gupta, A.K. Singh, N. Mergu, A new beryllium ion-selective membrane elec-trode based on dibenzo(perhydrotriazino)aza-14-crown-4 ether, Anal. Chim.Acta 749 (2012) 44–50.

27] V.K. Gupta, A.K. Singh, M.R. Ganjali, P. Norouzi, F. Faridbod, N. Mergu, Compar-ative study of colorimetric sensors based on newly synthesized schiff bases,Sens. Actuators B 182 (2013) 642–651.

28] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy, J.T.Rademacher, T.E. Rice, Signaling recognition events with fluorescent sensorsand switches, Chem. Rev. 97 (1997) 1515–1566.

29] V. Amendola, L. Fabbrizzi, F. Foti, M. Licchelli, C. Mangano, P. Pallavicini, A. Poggi,D. Sacchi, A. Taglietti, Light-emitting molecular devices based on transitionmetals, Coord. Chem. Rev. 250 (2006) 273–299.

30] J.S. Kim, D.T. Quang, Calixarene-derived fluorescent probes, Chem. Rev. 107(2007) 3780–3799.

31] V.K. Gupta, A.K. Singh, L.K. Kumawat, Thiazole schiff base turn-on fluorescentchemosensor for Al3+ ion, Sens. Actuators B 195 (2014) 98–108.

32] V.K. Gupta, A.K. Singh, N. Mergu, Antipyrine based schiff bases as turn-on flu-orescent sensors for Al(III) ion, Electrochim. Acta 117 (2014) 405–412.

33] M. Taki, Y. Watanabe, Y. Yamamoto, Development of ratiometric fluorescentprobe for zinc ion based on indole fluorophore, Tetrahedron Lett. 50 (2009)1345–1347.

34] H.Y. Li, S. Gao, Z. Xi, A colorimetric and “turn-on” fluorescent chemosensorfor Zn(II) based on coumarin Shiff-base derivative, Inorg. Chem. Commun. 12(2009) 300–303.

35] Z.C. Xu, X. Liu, J. Pan, D.R. Spring, Coumarin-derived transformable fluorescentsensor for Zn2+, Chem. Commun. 48 (2012) 4764–4766.

36] J.J. Du, J.L. Fan, X.J. Peng, H.L. Li, S.G. Sun, The quinoline derivative of ratiometricand sensitive fluorescent zinc probe based on deprotonation, Sens. ActuatorsB 144 (2010) 337–341.

37] P.G. Sutariya, N.R. Modi, A. Pandya, B.K. Joshi, K.V. Joshi, S.K. Menon, An ICTbased “turn on/off” quinoline armed calix[4]arene fluoroionophore: its sensingefficiency towards fluoride from waste water and Zn2+ from blood serum, Ana-lyst 137 (2012) 5491–5494.

38] J. Cao, C.C. Zhao, X.Z. Wang, Y.F. Zhang, W.H. Zhu, Target-triggered deprotona-tion of 6-hydroxyindole-based BODIPY: specially switch on NIR fluorescenceupon selectively binding to Zn2+, Chem. Commun. 48 (2012) 9897–9899.

39] A.N. Kursunlu, E. Guler, H.I. Ucan, R.W. Boyle, A novel bodipy-dipyrrin fluo-rescent probe: synthesis and recognition behaviour towards Fe (II) and Zn (II),Dyes Pigm. 94 (2012) 496–502.

40] S.L. Zhu, J.T. Zhang, J. Janjanam, G. Vegesna, F.T. Luo, A. Tiwari, H.Y. Liu,Highly water-soluble BODIPY-based fluorescent probes for sensitive fluores-cent sensing of zinc(II), J. Mater. Chem. B 1 (2013) 1722–1728.

41] J.F. Zhang, S. Bhuniya, Y.H. Lee, C. Bae, J.H. Lee, J.S. Kim, Novel 2,2′-bipyridine-modified calix[4]arenes: ratiometric fluorescent chemosensors for Zn2+ ion,Tetrahedron Lett. 51 (2010) 3719–3723.

42] L. Kong, Y. Chen, W.B. Ye, L. Zhao, B. Song, J.X. Yang, Y.P. Tian, X.T. Tao, Syn-thesis characterization, optical property of a bipyridine derivative and itsapplication to determine trace Zn2+ in water, Sens. Actuators B 177 (2013)218–223.

43] G. Kang, H.J. Son, J.M. Lim, H.S. Kweon, I.S. Lee, D.M. Kang, J.H. Jung, Func-tionalized Fe3O4 nanoparticles for detecting zinc ions in living cells and theircytotoxicity, Chem. Eur. J. 18 (2012) 5843–5847.

44] Y. Li, Z.Y. Yang, Z.C. Liu, B.D. Wang, S.L. Li, Highly selective and sensitive fluo-rescent nanosensor for zinc ions, Sens. Actuators B 160 (2011) 1504–1507.

45] S. Lee, J.H. Lee, T. Pradhan, C.S. Lim, B.R. Cho, S. Bhuniya, S. Kim, J.S. Kim, Fluo-rescent turn-on Zn2+ sensing in aqueous and cellular media, Sens. Actuators B160 (2011) 1489–1493.

46] A. Ciupa, M.F. Mahon, P.A.D. Bank, L. Caggiano, Simple pyrazoline and pyrazoleturn on fluorescent sensors selective for Cd2+ and Zn2+ in MeCN, Org. Biomol.Chem. 10 (2012) 8753–8757.

47] T. Mistri, M. Dolai, D. Chakraborty, A.R. Khuda-Bukhsh, K.K. Das, M. Ali, A highlyselective and sensitive in vivo fluorosensor for zinc(II) without cytotoxicity,Org. Biomol. Chem. 10 (2012) 2380–2384.

48] S.C. Yin, J. Zhang, H.K. Feng, Z.J. Zhao, L.W. Xu, H.Y. Qiu, B.Z. Tang, Zn2+-selective fluorescent turn-on chemosensor based on terpyridine-substitutedsiloles, Dyes Pigm. 95 (2012) 174–179.

49] E.M. Nolan, S.J. Lippard, The zinspy family of fluorescent zinc sensors: synthesesand spectroscopic investigations, Inorg. Chem. 43 (2004) 8310–8317.

50] E.M. Nolan, S.C. Burdette, J.H. Hervey, S.A. Hilderbrand, S.J. Lippard, Synthesisand characterization of zinc sensors based on a monosubstituted fluoresceinplatform, Inorg. Chem. 43 (2004) 2624–2635.

51] S. Aoki, D. Kagata, M. Shiro, K. Takeda, E. Kimura, Metal chelation-controlledtwisted intramolecular charge transfer and its application to fluorescentsensing of metal ions and anions, J. Am. Chem. Soc. 126 (2004) 13377–13390.

52] R. Parkesh, T.C. Lee, T. Gunnlaugsson, Highly selective 4-amino-1,8-naphthalimide based fluorescent photoinduced electron transfer (PET)chemosensors for Zn(II) under physiological pH conditions, Org. Biomol. Chem.5 (2007) 310–317.

53] J.L. Fillaut, J. Andries, R.D. Marwaha, P.H. Lanoe, O. Lohio, L. Toupet, J.A.G.Williams, Flavonol based ruthenium acetylides as fluorescent chemosensorsfor lead ions, J. Organomet. Chem. 693 (2008) 228–234.

54] Y.W. Liu, C.H. Chen, A.T. Wu, A turn-on and reversible fluorescence sensor forAl3+ ion, Analyst 137 (2012) 5201–5203.

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55] A. Kurzwernhart, W. Kandioller, C. Bartel, S. Bachler, R. Trondl, G. Muhlgassner,M.A. Jakupec, V.B. Arion, D. Marko, B.K. Keppler, C.G. Hartinger, Targetingthe DNA topoisomerase complex in a double-strike approach with a topoiso-merase inhibiting moiety and covalent DNA binder, Chem. Commun. 48 (2012)4839–4841.

56] M.P. Gharpure, V.N. Ingle, H.D. Juneja, R.G. Choudhary, Microwave assistedsynthesis and biological evaluation of 2-aryl/heteryl-3-aryloxy/heteryloxy-4h-chromones (4-oxo-2-aryl/heteryl-4h-chromen-3-yl-carboxylate), Int. J. Appl.Biol. Pharm. Technol. 3 (2012) 287–296.

57] V.K. Gupta, Alok Mittal, Lisha Krishnan, Jyoti Mittal, Adsorption Treatment andRecovery of the Hazardous Dye, Brilliant Blue FCF, Over Bottom Ash and De-Oiled Soya, J. Colloid Interface Sci 293 (2006) 16–26.

58] V.K. Gupta, T.A. Imran Ali, Saleh, Arunim Nayak, Shilpi Agarwal, Chemical Treat-ment Technologies for Wastewater Recycling –a Review, RSC Adv 2 (2012)6380–6388.

59] V.K. Gupta, A.K. Singh, S. Mehtab, B. Gupta, A Cobalt (II) selective PVC membranebased on a Schiff base complex of N, N’-bis (salicylidene)-3,4-diaminotoluene,Anal. Chim. Acta. 566 (2006) 5–10.

60] R.N. Goyal, V.K. Gupta, S. Chatterjee, Electrochemical oxidation of 2’, 3’-dideoxyadenosine at pyrolytic graphite electrode, Electrochim. Acta. 53 (2008)5354–5360.

61] A.K. Jain, V.K. Gupta, A. Bhatnagar, Suhas, A comparative study of adsorbentsprepared from industrial wastes for removal of dyes, Sep. Sci. Technol. 38 (2003)463–481.

62] V.K. Gupta, A.K. Singh, M. Al Khayat, Barkha Gupta, Neutral carriers based poly-meric membrane electrodes for selective determination of Mercury (II), Anal.Chim. Acta 590 (2007) 81–90.

63] V.K. Gupta, R. Prasad, R. Mangla, P. Kumar, New nickel (II) selective poten-

tiometric sensor based on 5,7,12,14-tetramethyldibenzotetraazaannulene in apoly (vinyl chloride) matrix, Anal. Chim. Acta 420 (2000) 19–27.

64] V.K. Gupta, S. Agarwal, T.A. Saleh, Synthesis and characterization of alumina-coated carbon nanotubes and their application for lead removal, J. HazardousMat. 185 (2011) 17–23.

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65] V.K. Gupta, Alok Mittal, Jyoti Mittal, Removal and Recovery of Chrysoidine Yfrom Aqueous Solutions by Waste Materials, J. Colloid Interface Sci. 344 (2010)497–507.

66] R.N. Goal, V.K. Gupta, S. Chatterjee, Simultaneous determination of adenosineand inosine using single-wall carbon nanotubes modified pyrolytic graphiteelectrode, Talanta 76 (2008) 662–668.

Biographies

Vinod Kumar Gupta obtained his PhD degree in chemistry from the University ofRoorkee (now Indian Institute of Technology Roorkee) Roorkee, India, in 1979. Sincethen he is pursuing research at the same institute and presently holding the posi-tion of Professor, Chemistry Department, at Indian Institute of Technology Roorkee,Roorkee. He worked as a post-doctoral fellow at University of Regensburg, Germany,in 1993 as an EC fellow and was DAAD visiting professor at University of Chemnitzand Freie University of Berlin in 2002. He has published more than 400 researchpapers, many reviews and two books which fetched him more than 25,000 citationswith h-index of 107. He was awarded the Indian Citation Laureate Award in 2004.His research interests include chemical sensors, wastewater treatment, environ-mental and electro analytical chemistry. Dr. Gupta is an elected Fellow of the WorldInnovation Foundation (FIWF) since July 2004 and Fellow of the National Academyof Sciences (FNASc) since 2008.

Naveen Mergu is a PhD student and pursuing research on chemical sensors underthe supervision of V.K. Gupta and A.K. Singh at IIT Roorkee. He did his M.Sc. in 2010in Chemistry at NIT Warangal.

Ashok Kumar Singh completed his Ph.D. in chemistry at Banaras Hindu Univer-

sity in 1977. He worked as lecturer at Banaras Hindu University from 1979-1981.He joined as Lecturer at University of Roorkee (since 2001 it is changed to IndianInstitute of Technology Roorkee) in 1981. Since 2004 he is working as a Professor inthe Department of Chemistry, Indian Institute of Technology, Roorkee. His researchinterests include chemical sensor, ion-selective electrodes, macrocyclic synthesis.