A colorimetric squaraine-based probe and test paper for rapid naked eyes detection of copper ion (II)

Article abstract of DOI:10.1016/j.tetlet.2018.09.042

A colorimetric probe N,N’-bis(2-methoxy-ethyl)-2,3,3-trimethyl-3H-squaraine (MOESQ) with H₂O solubility was synthesized to detect Cu²⁺. MOESQ exhibits good selectivity, high sensitivity and fast UV-Vis response toward Cu²⁺ over other competing ions in CH₃CN. The detection limit of MOESQ for Cu²⁺ in CH₃CN can reach 1.88 × 10^?7 molL^?1. By adsorbing MOESQ on the chromatography paper, a colorimetric test paper for Cu²⁺ was prepared, which could detect Cu²⁺ with the color change from blue to faint yellow even in the limit of detection concentration of 10^?6 molL^?1.

Full text of DOI:10.1016/j.tetlet.2018.09.042

Accepted Manuscript
A colorimetric squaraine-based probe and test paper for rapid naked eyes de-
tection of copper ion (II)
Yang Liu, Liqiu Wang, Chenxiao Guo, Yajuan Hou
PII:
S0040-4039(18)31132-8
https://doi.org/10.1016/j.tetlet.2018.09.042
TETL 50281
DOI:
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
4 July 2018
11 September 2018
17 September 2018
Please cite this article as: Liu, Y., Wang, L., Guo, C., Hou, Y., A colorimetric squaraine-based probe and test paper
for rapid naked eyes detection of copper ion (II), Tetrahedron Letters (2018), doi: https://doi.org/10.1016/j.tetlet.
2
018.09.042
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Graphical Abstract
A colorimetric sensor MOESQ based on squaraine was
A colorimetric squaraine-based
probe and test paper for rapid naked
eyes detection of copper ion (II)
2
+
synthesized to detect Cu in CH CN with the detection
3
-
7
-1
limit of 1.88×10 molL . By adsorbing MOESQ on
the chromatography paper, a colorimetric test paper for
2+
2+
Cu was prepared, which could detect Cu with the
color change from blue to faint yellow in the limit of
Yang Liu, Liqiu Wang, Chenxiao Guo, Yajuan Hou
-
6
-1
detection concentration of 10 molL .

1
Tetrahedron Letters
A colorimetric squaraine-based probe and test paper for rapid naked eyes detection
of copper ion (II)
Yang Liu, Liqiu Wang, Chenxiao Guo, Yajuan Hou
College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, 066004, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A colorimetric probe N,N’-bis(2-methoxy-ethyl)-2,3,3-trimethyl-3H-squaraine (MOESQ) with
2+
H O solubility was synthesized to detect Cu . MOESQ exhibits good selectivity, high
2
2+
sensitivity and fast UV-Vis response toward Cu over other competing ions in CH
3
CN. The
2
+
-7
-1
detection limit of MOESQ for Cu in CH CN can reach 1.88×10 molL . By adsorbing
MOESQ on the chromatography paper, a colorimetric test paper for Cu was prepared, which
could detect Cu with the color change from blue to faint yellow even in the limit of detection
3
2
+
Available online
2
+
-6
-1
concentration of 10 molL .
Keywords:
Squaraine
Colorimetric sensor
Copper ion
2
018 Elsevier Ltd. All rights reserved.
Test paper
Naked eye detection
Introduction
Colorimetric sensors based on the changes of their optical
11-12
properties are considerable to solve these problems.
A
Copper is a key element for life activity of animal and plant.
But excessive copper ion enriched into the organism can
interact with nucleic acids, enzymes, and proteins in the
process of metabolism, resulting in biological dysfunction or
2+
variety of sensors for Cu have been developed based on
13-18
colorimetric
fluorophore,
such
as
rhodamine,
naphthalimide, BODIPY and so on, but most of them generally
need fluorometer for the fluorescence variation detection and
could not be used for naked eye detection because the maxima
wavelengths of fluorescence and UV-Vis absorption could not
generate remarkable color change for ions detection.
1
even death. However, copper ion has been produced in large
quantities and used in various processes including industrial
production, agricultural pesticide irrigation, and mineral
2
exploitation. Copper ion pollution is one of the most serious
environmental problems threatening global sustainability and
human health. Thus, there is considerable interest in the
Squaraine is an ideal functional dye used in numerous areas,
such as solar cells, biological detection and luminescent
1
9-20
development of
determination in biomass and environmental samples.
a
detection method for copper ion
materials.
It might solve this problem as a colorimetric
3
-4
sensor because of its unique molecular structure and excellent
optical properties. Containing oxygen and nitrogen heteroatom,
squaraine could be probably sensitive to metal ions because of
coordination effect, and this effect could easily change the
color of squaraine. Larger extinction coefficient makes
squaraine perform deeper color, which can make the color
change more obvious. Besides, multiple functional groups can
be introduced onto squaraine, which makes modification of its
molecular structure more diversified.
In the last few decades, a number of detection strategies for
2
+
Cu such as atomic absorption spectrometry, ultraviolet visible
absorption spectrometry, electrochemical analysis and
inductively coupled plasma mass spectrometry have been
5
-8
developed. But most of them require complex preprocessing,
expensive equipment and special operators, and consume a
large amount of time. Therefore, there is an urgent and
2
+
increasing demand for detecting Cu with a real-time and
9
-10
convenient method.

Corresponding author. Tel.: +86-0335-8061569; e-mail: liqiuwang@tom.com

2
Tetrahedron Letters
Scheme 1. Synthetic route of MOESQ
Inspiring by this idea, this paper designed and synthesized a
squaraine-based colorimetric sensor MOESQ for naked eye
detection of Cu ion. The synthetic route was shown in
2
+
water
methanol
ethanol
propanol
butyl alcohol
acetonitrile
DMF
a)
1
Scheme 1. MOESQ displayed good selectivity, rapid response,
2
+
and high sensitivity toward Cu in CH CN. Furthermore, a
3
DMSO
colorimetric test paper was prepared by absorbing MOESQ to
chromatography paper, which could be used for the detection
2
+
of Cu quickly and conveniently.
Results and discussion
UV–Vis absorption and fluorescence spectra of MOESQ in
0
5
00
600
700
800
solvents
Wavelength (nm)
The spectra were tested in polar solvents (H O, MeOH,
2
EtOH, n-propanol, n-butyl alcohol, CH CN, DMF and DMSO),
3
water
and the corresponding Normalized UV-Vis absorption and
emission spectra were shown as Fig. 1. The maxima absorption
wavelengths were ranged from 630 nm to 655 nm, and the
maxima fluorescence wavelengths were ranged from 645 nm to
b)
methanol
ethanol
propanol
butyl alcohol
acetonitrile
DMF
1
DMSO
6
69 nm. The spectral data indicated another rule that in the
proton solvents, the maxima absorption and fluorescence
wavelengths took blue shift with increase of the polarity of the
solvents, while in the aprotic solvents, the maxima wavelengths
showed red shift. The explicit spectral data were listed in Table
0
650
700
750
800
1
.
Wavelength (nm)
Selectivity of MOESQ towards ions
Changes in the UV-Vis spectra toward ions (Ag , Al , Ca ,
Fig. 1. Normalized UV–Vis absorption a) and fluorescence b)
spectra of MOESQ in different solvents
+
3+
2+
2+
2+
2
+
3+
3+
3+
+
2+
3+
2+
+
Cd , Ce , Co , Cr , Cu , Cu , Fe , Hg , K , Mg , Mn ,
Table 1. Spectral data of MOESQ in solvents
+
2+
2+
2+
4+
2+
Na , Ni , Pb , Sn , Sn , Zn ) were studied in different
solvents including H O, EtOH, CH CN, DMF and DMSO
Solvent
λabs (nm)
630
λem (nm)
645
Δλ (nm)
15
2
3
because MOESQ dissolved well in these solvents (Fig. S1-S5).
The results showed that MOESQ performed no selectivity in
H O
2
H O, EtOH, DMF and DMSO, there were no remarkable
MeOH
EtOH
638
651
13
2
varication of wavelengths of absorption and fluorescence, but
2
+
640
652
12
as shown in Fig. 2, it performed selectivity toward Cu in
CH CN because of the remarkable change that the absorption
3
n-propanol
n-butyl alcohol
642
654
12
at 643 nm disappeared. Furthermore no significant spectral
+
+
changes in CH CN were observed in the presence of Ag , Cu ,
643
654
11
3
2
+
+
2+
2+
2+
4+
Hg , K , Mg , Ni , Sn , and Sn because of their lower
affinity with MOESQ. However, Al , Ca , Cd , Ce , Co ,
3
+
2+
2+
3+
3+
CH
3
CN
643
653
10
3
+
3+
2+
+
2+
2+
Cr , Fe , Mn , Na , Pb and Zn produced slight changes to
MOESQ absorption spectra, which probably attributed to the
dimerization of MOESQ caused by the combination with these
ions.
DMF
652
665
13
DMSO
655
669
14

3
EDTA is a strong complexing agent, which can combine
most ions, thus eliminating the effect of ions by competing
them from their composites on the spectrum of MOESQ. For
response of MOESQ. So the results indicated the strongest
affinity and selectivity for Cu .
2
+
2
+
further study, the reversibility of MOESQ banding Cu was
investigated through EDTA contending the ions from MOESQ
solutions. As shown in Fig. 3, after addition of EDTA, the
absorption spectra of MOESQ in most ions solutions
0
.35
Ion
2+
Ion+Cu
0.30
0.25
0.20
0.15
2
+
recovered respectively, except in Cu
solution, w+ hich
2
indicated that the banding process of MOESQ to Cu was
irreversible. For the corresponding fluorescence spectra, the
results also supported the conclusion (Fig. S6-S7). These
0.10
2
+
specific spectral response of MOESQ to Cu might be the
0
.05
.00
2
+
result of formation of clusters of MOESQ-Cu caused by
0
2
+
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
MOESQ coordinating with Cu (1:2), which EDTA was
2
+
difficult to capture out Cu from the clusters.
Fig. 4. UV–Vis absorption spectra of MOESQ in different ion
2
+
+
3+
blank
solutions after addition of Cu in CH CN (1-20 were Ag , Al ,
3
+
Ag
2+
2+
3+
3+
3+
+
3+
2+
+
2+
2+
+
0
0
0
0
.3
.2
.1
.0
Al3+
Ca , Cd , Ce , Co , Cr , Cu , Fe , Hg , K , Mg , Mn , Na ,
2
2
3
3
+
+
+
+
Ca
Cd
Ce
Co
2+
2+
2+
4+
2+
Ni , Pb , Sn , Sn and Zn in turn).
3
+
Cr
+
2
Cu
Cu
+
2+
3
+
Quantity titration for Cu
Fe
Hg
2
+
+
K
2
+
Mg
Mn2+
2
+
Na
+
Fig. 5 showed the absorption titration experiment result of
MOESQ with Cu in CH CN. With increasing of the quantity
of Cu added to the solution of MOESQ, the intensity of the
absorbance at 642 nm decreased gradually, and the absorbance
ranged from 420 nm to 510 nm increased slightly. The inset
Cu
2+
Ni
2+
2
2
+
+
Pb
3
Sn
Sn4+
Zn2+
2+
4
00
500
600
700
800
Wavelength (nm)
2
+
was the plot of absorption intensity at 643 nm versus Cu
equivalent. On addition of 2 equivalents of Cu to the solution
2
+
Fig. 2. UV–Vis absorption spectra of MOESQ in different ions
CH CN solutions
of MOESQ, the absorbance at 643 nm decreased to its limiting
value, and it indicated that the Cu /MOESQ complex
3
2
+
stoichiometry was 2:1. In CH CN, the UV–Vis absorption
3
2
+
detection limit of MOESQ for Cu was calculated to be 1.88
blank +EDTA
+
Ag +EDTA
-7
-1
0.3
0.2
0.1
0.0
Al3+ +EDTA
×10 molL based on the theory of Martins and Naes (Table
S1). The fluorescence titration experiment was also conducted,
and the results coincided with those of the absorption titration
experiment (Fig. S8).
2
+
Ca +EDTA
2
+
Cd +EDTA
3
+
Ce +EDTA
3
+
Co +EDTA
3
+
Cr +EDTA
+
2
Cu
+EDTA
+
Cu +EDTA
3
+
Fe +EDTA
2
+
Hg +EDTA
+
K
+EDTA
2+
2
+
Mg +EDTA
Mn2+ +EDTA
Cu +EDTA
+
Na +EDTA
2
+
Ni +EDTA
2
+
Pb +EDTA
0.40
2
+
0.35
Sn +EDTA
4
+
0.30
Sn +EDTA
Zn2+ +EDTA
0.35
0
.25
500
600
700
800
0.30
0.20
0
.15
Wavelength (nm)
0
.25
.20
0.10
0 eq
0
0
.05
.00
0
0
.0
0.5
1.0
Cu
1.5
(eq)
2.0
2.5
Fig. 3. UV–Vis absorption spectra of MOESQ in different ions
0.15
0.10
2+
2.5 eq
CH CN solutions after addition of EDTA
3
0.05
Competition experiments were performed by detecting the
0.00
4
00
500
600
700
800
UV–Vis absorption intensity at 643 nm in the presence of 5
Wavelength (nm)
+
3+
2+
2+
3+
3+
3+
+
3+
equivalents of Ag , Al , Ca , Cd , Ce , Co , Cr , Cu , Fe ,
2
+
+
2+
2+
+
2+
2+
2+
4+
2+
Hg , K , Mg , Mn , Na , Ni , Pb , Sn , Sn or Zn , with
the subsequent addition of 5 equivalents of Cu . As shown in
2
+
Fig. 5. Variation of UV–Vis absorption intensity of MOESQ with
Cu concentrations. (Inset: plot of absorption intensity at 643 nm
versus Cu equivalent for the banding of MOESQ to Cu ).
2
+
Fig. 4, MOESQ in each of the ion solutions had stronger
2
+
2+
2+
absorption intensity at 643 nm, while the adding of Cu caused
the absorption at 643 nm significantly decreased which
illustrated that the responses were undisturbed in the presence
2
+
The test paper for Cu ion
2
+
of most of the ions, only Cd slightly limited the turn-off

4
Tetrahedron Letters
2
+
2+
Motivated by the obvious color changes of MOESQ to Cu
in CH CN, visual test paper was prepared by immersing
detection of Cu with high sensitivity, good selectivity and
rapid response in the CH CN medium.
3
3
-
3
-1
chromatography paper in 10 molL MOESQ EtOH solution
2
+
Acknowledgements
for detecting the Cu simply and directly. An obvious change
in color from blue to unconspicuous yellow was immediately
The authors would like to thank Hebei Natural Science
Foundation (No. B2015203259) for providing the financial
support for this project.
2
+
observed by naked eye on the test paper after addition of Cu
stock solution followed by the addition of drapwise of CH CN.
3+
3
+
3+
2+
2+
3+
3+
However, the other ions (Ag , Al , Ca , Cd , Ce , Co , Cr ,
Supplementary Material
+
3+
2+
+
2+
2+
+
2+
2+
2+
4+
Cu , Fe , Hg , K , Mg , Mn , Na , Ni , Pb , Sn , Sn or
Zn ) did not produce a distinct change in color at the test paper,
as shown in Fig. 6.
2
+
Supplementary data (detailed experimental procedures and
characterization data of MOESQ) associated with this article
can be found in the online version, at http://
To investigate the detection concentration range, test papers
References and notes
2
+
were immersed in CH CN solutions of Cu with varying
3
-
3
-1
-8
-1
1. Breydo L, Uversky VN. Metallomics. 2011, 3(11), 1163-1180.
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2
. Yao Z, Yang Y, Chen X, Hu X, Zhang L, Liu L, Zhao Y, Wu H. Anal.
Chem. 2013, 85(12), 5650-5653.
2
+
3. Li S, Chen X, Ma W, Ding Z, Zhang C, Chen Z, He X, Shang Y, Zou Y.
Sci. Rep. 2016, 6, 36654-36663.
unconspicuous yellow after it met with Cu even in the
-
6
-1
2+
concentration of 10 molL . When the Cu concentration was
-
6
-1
4. Zhang Q, Zhao D, Zhang C, Liu J, An Z. Sensor Actuat. B-chem. 2018,
less than 10 molL , the color of the test paper had no obvious
change. This demonstrated that the test paper could be used to
2
59, 633-641.
2
+
5. Martín-Cameán A, Jos A, Puerto M, Calleja A, Iglesias-Linaresd A,
detect the Cu in real-time, and the limit test concentration was
0 molL , which was less than 1.88×10 molL due to the
-
6
-1
-7
-1
Solano E, Cameán A. J. Trace. Elem. Med. Bio. 2015, 32, 13-20.
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6
. Castro AC, Franca AS, Rojas A, Cavalheiro, ET, Marques EP, Marques
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absorption instrument.
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129(2), 208-215.
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Fig. 6. Color changes of the test paper after adding various ions
14. Dolai B, Bhaumik A, Pramanik N, Ghosh KS, Atta AK. J. Mol. Struct .
2018, 1164, 370-377.
-
3
-1
(
10 molL ).
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1
5. He SJ, Xie YW, Chen QY. Spectrochim. Acta A. 2018, 195, 210-214.
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2
+
Fig. 7. Color changes of the test paper after detecting Cu in
various concentrations (10 molL to 10 molL ).
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-
3
-1
-8
-1
Conclusions
In summary, a colorimetric chemosensor named MOESQ
2
+
2+
for Cu detection in CH CN was developed. Adding Cu into
3
MOESQ CH CN solution could cause fluorescence quench
3
and the absorbance at 643 nm decreased, and the detection
-
7
-1
limit was 1.88×10 molL . After absorbing MOESQ on a
2
+
chromatography paper, a test paper for Cu was prepared,
2
+
which could be used to detect Cu in the limit of detection
-
6
-1
concentration of 10 molL by the naked eye. It exhibited the

5
Highlights
•
•
•
•
N,N’-bis(2-methoxy-ethyl) squaraine with λabs
and λ of 643 nm 653 nm in CH CN.
em
3
A colorimetric squaraine probe for selective
2
+
detection of Cu ion in acetonitrile.
The squaraine-based test paper for rapidly and
2
+
easily detecting Cu by naked eyes.
2
+
-7
-1
Cu detection limit 1.88×10 molL in CH CN
3
-6
-1
and 10 molL for the test paper.