Colorimetric chemosensor and test kit for detection copper(II) cations in aqueous solution with specific selectivity and high sensitivity

Article abstract of DOI:10.1016/j.dyepig.2013.01.024

The specific colorimetric detection of Cu²⁺ in the context of interference from coexisting metal ions in aqueous solution is a challenge. Therefore, a series of Cu²⁺ colorimetric chemosensors CS1～CS3, bearing acylthiosemicarbazide moiety as binding site and nitrophenyl moiety as signal group, were designed and synthesized. Among these sensors, CS3 showed excellent colorimetric specific selectivity and high sensitivity for Cu ²⁺in DMSO/H₂O binary solutions. When Cu²⁺ was added to the solution of CS3, a dramatic color change from brown to green was observed, while the cations Fe³⁺, Hg²⁺, Ag, Ca ²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ni2 , Co ²⁺, Cr³⁺ and Mg²⁺ did not interfere with the recognition process for Cu²⁺. The detection limits were 5.0 × 10^-6 and 1.0 × 10^-7 M of Cu²⁺ using the visual color changes and UVevis changes respectively. Test strips based on CS3 were fabricated, which could act as a convenient and efficient Cu²⁺ test kit.

Full text of DOI:10.1016/j.dyepig.2013.01.024

Dyes and Pigments 98 (2013) 100e105
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Colorimetric chemosensor and test kit for detection copper(II) cations
in aqueous solution with specific selectivity and high sensitivity
,
a
b
a
a
a,
Qi Lin a , Pei Chen , Juan Liu , Yong-Peng Fu , You-Ming Zhang , Tai-Bao Wei
*
*
a Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Polymer Materials of Gansu Province,
College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, PR China
b College of Chemical Engineering, Northwest University of Nationality, Lanzhou, Gansu 730030, PR China
a r t i c l e i n f o
a b s t r a c t
The specific colorimetric detection of Cu2þ in the context of interference from coexisting metal ions in
aqueous solution is a challenge. Therefore, a series of Cu2þ colorimetric chemosensors CS1wCS3, bearing
acylthiosemicarbazide moiety as binding site and nitrophenyl moiety as signal group, were designed and
synthesized. Among these sensors, CS3 showed excellent colorimetric specific selectivity and high
sensitivity for Cu2þ in DMSO/H2O binary solutions. When Cu2þ was added to the solution of CS3, a
Article history:
Received 24 September 2012
Received in revised form
5 January 2013
Accepted 30 January 2013
Available online 16 February 2013
dramatic color change from brown to green was observed, while the cations Fe3þ, Hg2þ, Agþ, Ca2þ, Zn2þ
,
Pb2þ, Cd2þ, Ni2þ, Co2þ, Cr3þ and Mg2þ did not interfere with the recognition process for Cu2þ. The
detection limits were 5.0 ꢀ 10ꢁ6 and 1.0 ꢀ 10ꢁ7 M of Cu2þ using the visual color changes and UVevis
changes respectively. Test strips based on CS3 were fabricated, which could act as a convenient and
efficient Cu2þ test kit.
Keywords:
Copper(II) cations
Colorimetric sensor
Test strips
Ó 2013 Elsevier Ltd. All rights reserved.
Specific selectivity
High sensitivity
Acylthiosemicarbazide
1. Introduction
carried out only by trained professionals, which significantly
restricting the practical application of these Cu2þ sensors. For
Copper is an essential trace element, the third most abundant in
humans, which is fundamental in many metabolic processes [1e5].
Excess copper, however, can cause various intoxications. For
example, the increasing concentration of copper cations in body
causes imbalance in cellular processes resulting in pathogenesis
such as Wilson’s disease [1,6,7], amyotrophic lateral sclerosis [8],
Menkes syndrome [9,10], Alzheimer’s disease [11] and Parkinson’s
disease [12]. According to the U.S. Environmental Protection Agency
(EPA), the maximum acceptable level of Cu2þ in drinking water is
w2 ꢀ 10ꢁ5 M [13]. Therefore, the rational design and synthesis of
efficient sensors to selectively recognize copper cations is an
important topic in supramolecular chemistry [14e19]. Although
previous work has involved the development of a wide variety of
chemical [20e52] and physical [53e55] sensors for the detection of
Cu2þ, so far, improving the detection selectivity in the context of
interference from coexisting metal ions has been challenging.
Moreover, most of these methods require expensive equipment and
involve time-consuming and laborious procedures that can be
simplicity, convenience and low cost, easily-prepared Cu2þ colori-
metric sensors [27e33] are needed. On the other hand, in biological
and environmental systems, copperesensor interactions commonly
occur in aqueous solution [15,16,28,29,34e44], therefore, much
attention has been paid to developing copper sensors that work in
the aqueous phase [34e44].
In view of this requirement and as part of our research effort
devoted to ion recognition [56e60], an attempt was made to obtain
efficient colorimetric sensors which could sense Cu2þ with specific
selectivity and high sensitivity in aqueous solutions. This paper
details the design and synthesis of a series of Cu2þ colorimetric
sensors CS1wCS3 bearing acylthiosemicarbazide and nitrophenyl
groups (Scheme 1). The strategies for the design of these sensors
were as follows. Firstly, a acylthiosemicarbazide group was intro-
duced as the binding site. The C]S and C]O moiety on the
acylthiosemicarbazide group possesses a high affinity with Cu2þ
.
Secondly, in order to achieve “naked-eye” colorimetric recognition,
we introduced nitrophenyl group as the signal group. Finally, the
sensor was designed to be easy to synthesize. In order to establish
the signal group’s contribution to the sensor’s colorimetric sensing
abilities for Cu2þ, compound CS1 which without containing the
nitro-group was also synthesized.
* Corresponding authors.
E-mail addresses: linqi2004@126.com (Q. Lin), weitaibao@126.com (T.-B. Wei).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.01.024

Q. Lin et al. / Dyes and Pigments 98 (2013) 100e105
101
Scheme 1. Synthetic procedures for sensors CS1wCS3.
2. Experimental section
precipitate was filtered, washed with 75% ethanol three times, and
recrystallized with ethanol to get white crystal of CS1. The other
compounds CS2 and CS3 were prepared by similar procedures.
CS1: yield: 81%; m.p. 256e259 ꢂC; 1H NMR (DMSO-d6, 400 MHz)
2.1. Materials and physical methods
1H NMR spectra were recorded with a Mercury-400BB spec-
trometer at 400 MHz. 1H chemical shifts are reported in ppm
d
11.36 (s, 1H, NH), 8.64 (s, 2H, NH, ArH), 8.37 (s, 1H, ArH), 7.83e7.30
(m, 9H, ArH); 13C NMR (DMSO-d6, 100 MHz)
d
162.40, 158.89,
downfield from tetramethylsilane (TMS,
d
scale with the solvent
153.95, 147.57, 143.10, 134.50, 133.20, 130.21, 129.35, 128.94, 125.21,
124.96, 124.32, 118.84, 118.01, 116.37, 116.25; IR (KBr, cmꢁ1) v: 3215
(NeH), 1717, 1668 (C]O), 1152 (C]S); Anal. Calcd. for C17H13N3O3S:
C, 60.17; H, 3.86; N, 12.38; Found: C, 60.15; H, 3.84; N, 12.41.
CS2: yield: 85%; m.p. 265e268 ꢂC; 1H NMR (DMSO-d6, 400 MHz)
resonances as internal standards). Ultravioletevisible (UVevis)
spectra were recorded on a Shimadzu UV-2550 spectrometer.
Melting points were measured on an X-4 digital melting-point
apparatus (uncorrected). The infrared spectra were performed on
a Digilab FTS-3000 Fourier transform-infrared spectrophotometer.
The inorganic salts Ca(ClO4)2$6H2O, Mg(ClO4)2$6H2O,
Cd(ClO4)2$6H2O, Fe(ClO4)3$6H2O, Co(ClO4)2$6H2O, Ni(ClO4)2$6H2O,
Cu(ClO4)2$6H2O, Zn(ClO4)2$6H2O, Pb(ClO4)2$3H2O, AgClO4$H2O
and Cr(ClO4)3$6H2O were purchased from Alfa Aesar Chemical
Reagent Co. (Tianjin, China). All solvents and other reagents were of
analytical grade.
d
10.41 (s, 1H, NH), 9.34 (s, 1H, NH), 8.82 (s, 2H, NH, ArH), 8.12e8.09
(d, J ¼ 12, 1H, ArH), 8.00e7.97 (d, J ¼ 12, 1H, ArH), 7.81e7.76 (m, 1H,
ArH), 7.56e7.44 (m, 2H, ArH), 6.92e6.88 (m, 2H, ArH); 13C NMR
(DMSO-d6, 100 MHz) d 162.06, 159.32, 154.41, 153.98, 147.46, 138.44,
134.35, 130.25, 125.87, 125.26, 119.44, 118.27, 116.30, 111.01; IR (KBr,
cmꢁ1) v: 3227 (NeH),1719,1681 (C]O),1154 (C]S); Anal. Calcd. for
C17H12N4O5S: C, 53.12; H, 3.15; N, 14.58; Found: C, 53.09; H, 3.17; N,
14.56.
CS3: yield: 80%; m.p. 273e276 ꢂC; 1H NMR (DMSO-d6, 400 MHz)
2.2. General procedure for UVevis spectroscopy
d
10.79 (s,1H, NH),10.33(s,1H, NH), 8.91 (s, 2H, NH, ArH), 8.36e8.32
(d, J ¼ 16, 1H, ArH), 8.05e8.03 (d, J ¼ 8, 1H, ArH), 7.83e7.79 (m, 1H,
All the UVevis experiments were carried out in DMSO solution
on a Shimadzu UV-2550 spectrometer. Any changes in the UVevis
spectra of the synthesized compound were recorded on the addi-
tion of perchlorate metal salts while the ligand concentration was
kept constant in all experiments.
ArH), 7.58e7.35 (m, 4H, ArH); 13C NMR (DMSO-d6, 100 MHz)
d
161.64,159.34,154.07,148.24,148.11,137.04,134.64,130.43,130.00,
125.34, 123.09, 118.69, 118.21, 116.32, 115.89; IR (KBr, cmꢁ1) v: 3235
(NeH), 1708,1617 (C]O), 1159 (C]S); Anal. Calcd. for C17H11N5O7S:
C, 47.55; H, 2.58; N, 16.31; Found: C, 47.58; H, 2.56; N, 16.33.
2.3. General procedure for 1H NMR
3. Results and discussion
For 1H NMR titrations, two stock solutions were prepared in
DMSO-d6: one of them contained the host only and the second one
contained an appropriate concentration of guest. Aliquots of the
two solutions were mixed directly in NMR tubes.
In order to investigate the Cu2þ recognition abilities of the
sensors CS1w3 in aqueous solution, we carried out a series of
HosteGuest recognition experiments in DMSO/H2O (9:1/v:v)
HEPES buffered solution at pH 7.0. The colorimetric sensing abilities
were primarily investigated by adding various cations (Ca2þ, Mg2þ
,
2.4. Synthesis and characterization of sensors CS1wCS3
Cd2þ, Fe3þ, Co2þ, Ni2þ, Cu2þ, Hg2þ, Zn2þ, Pb2þ, Agþ and Cr3þ) to the
DMSO/H2O (9:1/v:v, pH 7.0) solutions of sensor CS3. When 5
equivalent (equiv.) of Cu2þ was added to the solution of CS3
Coumarin-3-carboxylic acid (3 mmol) and bis(trichlormethyl)
carbonate (BTC, 1.5 mmol) were added into dry dichloromethane
(15 mL). Then the reaction mixture was stirred at 40 ꢂC for 3 h under
reflux. In this process, the coumarin-3-carboxylic acid has been
converted to the coumarin-3-carbonyl chloride, which did not need
separating. Then, dry and powdered KSCN (4 mmol) and PEG-400
(0.1 mL, as phase transfer catalyst) were added to the reaction so-
lution and stirred it at room temperature for 2 h, and the inorganic
salts were filtered out. The filtrate was a solution of the corre-
sponding coumarin-3-carbonyl isothiocyanate, which did not need
separating also. Then 2.8 mmol of phenylhydrazine was added tothe
filtrate solution and stirred at room temperature for 3 h, yielding the
precipitate of CS1. After evaporating the solvent in a vacuum, the
Fig. 1. Color changes observed upon the addition of various cations (5 equiv.) to the
solutions of sensor CS3 (2 ꢀ 10ꢁ5 M) in DMSO/H2O (9:1, v:v; HEPES buffered, pH 7.0)
solutions. Left to right: free CS3, Fe3þ, Hg2þ, Agþ Ca2þ, Cu2þ, Mg2þ, Cd2þ, Co2þ, Ni2þ
,
Zn2þ, Pb2þ, and Cr3þ. (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article.)

102
Q. Lin et al. / Dyes and Pigments 98 (2013) 100e105
Hg2+
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.9
0.8
0.7
Cu2+
Fe3+
Cu2+
Sensor CS3, other cations
Fe3+
are Ag+, Ca2+, Zn2+, Cd2+,
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
Pb2+
Co2+, and Mg2+
host CS1, other cations
2+ 2+
Ni2+
+
2+
are Ag , Ca , Cu , Zn
,
Pb2+
2+ 2+
2+
3+
Cd , Ni , Co , Cr
2+
Cr3+
and Mg
Cu2+blank
Hg2+
250
300
350
400
450
500
250
300
350
400
450
500
550
600
650
700
750
Wavelength/nm
Wavelength/nm
Fig. 4. UVevis absorption spectra of CS1 in the presence of 5 equiv. of various cations
in DMSO/H2O (9:1, v:v; HEPES buffered, pH 7.0) solution at room temperature.
Fig. 2. UVevis absorption spectra of CS3 in the presence of 5 equiv. of various cations
in DMSO/H2O (9:1, v:v; HEPES buffered, pH 7.0) solution at room temperature.
(2.0 ꢀ 10ꢁ5 M), the sensor responded with dramatic color changes
from brown to green (Fig. 1). In the corresponding UVevis spec-
trum (Fig. 2), the absorption peak at 475 nm took place a 25 nm
blue shift to 450 nm. Meanwhile, a new peak appeared at 650 nm,
which attributed to the color change from brown to green. How-
0.30
0.25
0.20
0.15
0.10
0.05
0.00
ever, when adding 5 equiv. of other cations Ca2þ, Mg2þ, Cd2þ, Fe3þ
,
Co2þ, Ni2þ, Hg2þ, Zn2þ, Pb2þ, Agþ and Cr3þ into the DMSO/H2O (9:1/
v:v, pH 7.0) solution of sensor CS3 respectively, no significant color
changes were observed. Meanwhile, in the corresponding UVevis
spectra (Fig. 2), only a slight absorption changes were induced by
adding Fe3þ, Ni2þ, Hg2þ, Pb2þ, and Cr3þ. Other cations couldn’t
induce any UVevis changes. Therefore, in DMSO/H2O solution, CS3
showed specific colorimetric selectivity to Cu2þ
.
In order to exclude the possibility of these results being due to
Cu2þ self absorption, a blank test were carried out via adding the
same amount of Cu2þ to blank DMSO/H2O solution (without con-
taining CS3), as a result, no color change was observed. In corre-
sponding UVevis spectra, there is no absorption peak appeared at
0.0
0.2
0.4
0.6
0.8
1.0
2+
[CS3]/[Cu ]+[CS3]
Fig. 5. (a) A Job plot of CS3 and Cu2þ, which indicated that the stoichiometry of CS3-
Cu2þ complex was 2:1.
0.9
Pb2+
0.8
0.7
host CS2, other cations
Fe3+
are Ag+, Ca2+, Zn2+, Pb2+,
Cd2+, Ni2+, Co2+, Cr3+
and Mg2+
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Hg2+
Cu2+
250
300
350
400
450
500
550
600
650
Wavelength/nm
Fig. 3. UVevis absorption spectra of CS2 in the presence of 5 equiv. of various cations
in DMSO/H2O (9:1, v:v; HEPES buffered, pH 7.0) solution at room temperature.
Fig. 6. UVevis spectral titration of sensor CS3 with Cu2þ in DMSO solution.

Q. Lin et al. / Dyes and Pigments 98 (2013) 100e105
103
Fig. 7. The proposed reaction mechanism of the sensor CS3 with Cu2þ
.
the visible region (Fig. 2). Which confirmed that CS3 could colori-
metrically detect Cu2þ in DMSO/H2O binary solution.
absorption peaks at ultraviolet region took place slight shifts,
however, at the visible region of these spectra, there is no ab-
sorption peak appeared. Which indicated that CS2 or CS1 couldn’t
colorimetric sense any cations under these conditions.
The same tests were applied to CS2 and CS1. In this case, when
various cations were added to the DMSO/H2O (9:1/v:v, pH 7.0) so-
lutions of CS2 or CS1 respectively, no obvious color changes were
observed. In corresponding UVevis spectra of CS2 or CS1 (Figs. 3
Therefore, according to these results we can find that the
nitrophenyl moiety acted as a signal group and played a crucial role
in the process of colorimetric recognition. The sensor CS3 employ
2,4-dinitrophenyl as signal groups, which possess colorimetric
response abilities for Cu2þ cations. Because the CS1 doesn’t employ
nitrophenyl as signal group, it could not colorimetric sense any
cations. Although CS2 employ a nitrophenyl as single group, owing
to CS2 only has one nitrophenyl group, the chromogenic capability
of CS2 is too weak to colorimetric recognize any cations also.
As CS3 showed specific selectivity for Cu2þ, a series of experi-
ments was carried out to investigate the Cu2þ recognition capa-
bility and mechanism of CS3. To gain an insight into the
stoichiometry of the CS3-Cu2þ complex, the method of continuous
variations (Job’s method) was used (Fig. 5). When the molar frac-
tion of sensor CS3 was 0.67, the absorbance value approached a
maximum, which demonstrated the formation of a 2:1 complex
between the sensor CS3 and Cu2þ [61].
and 4), although Cu2þ
, ,
Hg2þ Pb2þ and Fe3þ induced the
The binding properties of sensor CS3 with Cu2þ were further
studied by UVevis titration experiments (Fig. 6). It turned out that
in DMSO solution of CS3, with an increasing amount of Cu2þ, the
absorption peak at 480 nm gradually shifted to 454 nm. Meanwhile,
at 650 nm, a new peak gradually appeared. Three clear isosbestic
points were observed at 311, 387 and 530 nm, which indicated the
formation of an CS3-Cu2þ complex. The binding constant Ks of the
metal complex was determined by Equation (1) [61], assuming that
the concentration of free metal is about equal to its total concen-
tration ([M] z [M]t), where A0, Ae, and Am are the corrected UVeVis
absorbances of the complex at initial, interval, and the final states at
which the complex was fully formed upon addition of metal ion,
Fig. 8. (a) UVevis absorption spectra sensor CS3 (2.0 ꢀ 10ꢁ5 M) in DMSO/H2O solu-
tions in the presence of Cu2þ (5 equiv.) and the miscellaneous cations Ca2þ, Mg2þ
,
Fig. 9. Color changes observed upon the addition of varying quantities of Cu2þ (from
left to right: free CS3, 1 ꢀ 10ꢁ4 M, 1 ꢀ 10ꢁ5 M, 1 ꢀ 10ꢁ6 M, 1 ꢀ 10ꢁ7 M) to the solutions
of sensor CS3 (1 ꢀ 10ꢁ5 M; DMSO/H2O, 9:1, v:v; HEPES buffered, pH 7.0). (For inter-
pretation of the references to color in this figure legend, the reader is referred to the
web version of this article.)
Cd2þ, Fe3þ, Co2þ, Ni2þ, Hg2þ, Zn2þ, Pb2þ, Agþ and Cr3þ (5 equiv., respectively). (b) UVe
vis absorption at 475 nm of sensor CS3 (2.0 ꢀ 10ꢁ5 M) in DMSO solutions in the
presence of Cu2þ (5 equiv.) and the miscellaneous cations Ca2þ, Mg2þ, Cd2þ, Fe3þ, Co2þ
Ni2þ, Cu2þ, Zn2þ, Pb2þ, Agþ and Cr3þ (5 equiv., respectively).
,

104
Q. Lin et al. / Dyes and Pigments 98 (2013) 100e105
Fig. 10. Photographs of the CS3 based test strips colorimetric detect Cu2þ. (a) Left to right: free test strip, test strip þ DMSO, test strip þ DMSO solution of Cu2þ. (b) After addition the
DMSO solutions of various metal cations respectively and dried them under room temperature. Left to right: free, Cu2þ, Ca2þ, Mg2þ, Cd2þ, Fe3þ, Co2þ, Ni2þ, Hg2þ, Zn2þ, Pb2þ, Agþ
and Cr3þ
.
respectively. The binding constant Ks was determined from the plot
of the linear regression of ln[(A0 ꢁ Ae)/(Ae ꢁ Am)] versus ln[M] in
Equation (1), to obtain the intercept as ln Ks and the slope as n. The
association constant Ks of the chemosensors CS3 toward Cu2þ was
detection limit of the UVevis changes calculated on the basis of 3sB/
S [62] is 1.0 ꢀ 10ꢁ7 M for Cu2þ cation, which pointing to the high
detection sensitivity.
To investigate the practical application of chemosensor CS3, test
strips were prepared by immersing filter papers into a DMSO so-
lution of CS3 (0.1 M) and then drying in air. The test strips con-
taining CS3 were utilized to sense different cations. As shown in
Fig. 10, when different cation solutions were added on the test kits
respectively, the obvious color change was observed only with Cu2þ
solution. Therefore, the test strips could directly detect Cu2þ in
DMSO or DMSO/H2O binary solutions. In addition, the test strips
could detect Cu2þ in pure water also, before adding the pure water
solution of Cu2þ to the test strip, one drop of DMSO has been added
to the test strip and the test strip was moistened by DMSO. Then the
pure water solution of Cu2þ was added to the DMSO moistened test
strip, the test strip carried out similar color changes just like the
DMSO/H2O solution of Cu2þ added to the dry test strip. Therefore,
the DMSO moistened test strip could conveniently detect the Cu2þ
in pure water.
calculated as 1.5 ꢀ 104 Mꢁ1
.
ln½ðA0 ꢁ AeÞ=ðAe ꢁ AmÞꢃ ¼ ln Ks þ nln½Mꢃ
(1)
The recognition mechanism of the sensor CS3 with Cu2þ were
investigated by IR spectra and 1H NMR titration methods. In the IR
spectra (Fig. S-1 in Supplementary data) of CS3, the stretching vi-
bration absorption peaks of coumarin C]O, acyl C]O and thio-
semicarbazide C]S appeared at 1709, 1616 and 1184 cmꢁ1
respectively. However, when CS3 coordinated with Cu2þ, the
stretching vibration absorption peaks of thiosemicarbazide C]S
shifted to 1143 cmꢁ1, while, other absorption peaks such as the
stretching vibration absorption peaks of NeH, coumarin C]O and
acyl C]O didn’t take place any shift, which indicated that CS3
complexed with Cu2þ via Cu2þ-S coordination bond as shown in
Fig. 7.
The results of 1H NMR titration experiments also support this
presumption. As shown in Fig. 7, before addition of Cu2þ, there were
two intramolecular hydrogen bonds in the molecular structure of
CS3: one was NeHa.O]C, and the other was NeHb.O]C. Owing
to the fact that NeHa.O]C and NeHb.O]C are very strong
intramolecular hydrogen bonds, as shown in Fig. S-2 in Supple-
mentary data, the 1H NMR chemical shift of NeHa and NeHb
4. Conclusion
An easy-to-make Cu2þ colorimetric sensor CS3, bearing thiourea
moiety as the binding site and nitrophenyl moiety as the signal
group, was designed and synthesized. This sensor showed specific
selectivity for Cu2þ in DMSO/H2O binary solutions. Comparison
with sensor CS1 indicated that the nitrophenyl moiety acted as a
signal group and played a crucial role in the process of colorimetric
recognition. Investigation of the recognition mechanism indicated
that the sensor CS3 recognized Cu2þ by forming a stable 2:1 CS3-
Cu2þ complex. The coexistence of other cations did not interfere
with the Cu2þ recognition process. Moreover, the detection limit of
the sensor CS3 toward Cu2þ was 1.0 ꢀ 10ꢁ7 M, which indicated that
the sensor CS3 may be useful as a colorimetric sensor for moni-
toring Cu2þ levels in physiological and environmental systems. In
addition, test strips based on CS3 were fabricated, which also ex-
hibits a good selectivity to Cu2þ as in solution. We believe the test
strips could act as a convenient and efficient Cu2þ test kit.
appeared at the low field of the molecular CS3 at
d 10.79 and
10.33 ppm respectively. The NeHc appeared at 8.91 ppm. After the
addition of 0.2e2.5 equivalent of Cu2þ into the DMSO-d6 solution of
CS3 gradually, the corresponding 1H NMR spectra didn’t take place
any changes. Which indicated that due to the shackle of strong
hydrogen bonds NeHa.O]C and NeHb.O]C, the coumarin C]
O and acyl C]O didn’t coordinate with Cu2þ. Therefore, the CS3
coordinated with Cu2þ only though C]S and form a CS3-Cu2þ
complex.
An important feature of the sensor is its high selectivity toward
the analyte over other competitive species. The variations of UVe
vis spectral and visual color changes of sensor CS3 in DMSO/H2O
binary solutions caused by the metal ions Ca2þ, Mg2þ, Cd2þ, Fe3þ
,
Acknowledgment
Co2þ, Ni2þ, Hg2þ, Zn2þ, Pb2þ, Agþ and Cr3þ were recorded in Fig. 8. It
is noticeable that the miscellaneous competitive metal ions did not
lead to any significant interference. In the presence of these ions,
the Cu2þ still produced similar color and absorption changes
(Fig. 8). These results shown that the selectivity of sensor CS3 to-
ward Cu2þ was not affected by the presence of other cations and
suggested that it could be used as a colorimetric chemosensor for
This work was supported by the National Natural Science
Foundation of china (NSFC) (Nos. 21064006, 21161018 and
21262032), the Natural Science Foundation of Gansu Province
(1010RJZA018) and the Program for Changjian Scholars and Inno-
vative Research Team in University of Ministry of Education of
China (IRT1177).
Cu2þ
.
The colorimetric and UVevis limits of sensor CS3 for Cu2þ cation
were also tested. As presented in Fig. 9, the detection limit using
visual color changes is a concentration of 1.0 ꢀ 10ꢁ6 M of Cu2þ
cation in 1.0 ꢀ 10ꢁ5 M solution of sensor CS3. While, as shown in
Fig. 6, with the gradual addition of Cu2þ, a sharp increase in the
absorbance at 480 nm and an obvious decrease in the absorbance at
344 nm are observed. Simultaneously, the ratio of A480/A344 in-
crease with the increasing in Cu2þ concentrations, which allowing
the Cu2þ concentration to be determined ratiometrically. The
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2013.01.024.
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