A novel dual-function bithiophene-Meldrum's acid based chemosensor for highly sensitive, colorimetric and fluorimetric detection of cyanide and hypochlorite and its applications

Article abstract of DOI:10.1016/j.dyepig.2020.108459

A dual-function bithiophene-Meldrum's acid based chemosensor 2TM was developed, which displayed ultrafast, colorimetric and fluorescence turn-on responses for CN^? and ClO^? with specific selectivity and high sensitivity. The sensor 2TM for CN^? detection in DMSO/H₂O (1/3, V/V) solution was based on the nucleophilic addition of CN^? to sensor, which resulted in remarkable spectral and discernible color changes. Meanwhile, 2TM showed specific selectivity for ClO^? in 100percent aqueous solution based on the sensing mechanism of oxidative cleavage of C[dbnd]C bond. The detection limits were obtained to be 0.96 μM for CN^? and 48 nM for ClO^?. The sensing mechanism of 2TM toward CN^? and ClO^? was investigated by job'plot, FTIR, ¹H NMR, HRMS and optical spectra. The sensor 2TM loaded colorimetric test strips/supported silica measurements demonstrated to be a portable, eco-friendly and ultrafast device for real-time and on-site visual detection of CN^? and ClO^? in water by the naked eye. More importantly, sensor 2TM with excellent photophysical properties and low biotoxicity was successfully applied to detect CN^? and ClO^? in live cells and environmental water samples, as well as capable of monitoring CN^? in the natural food samples, illustrating its practical utility in biological and environmental systems.

Full text of DOI:10.1016/j.dyepig.2020.108459

Journal Pre-proof
A novel dual-function bithiophene-Meldrum's acid based chemosensor for highly
sensitive, colorimetric and fluorimetric detection of cyanide and hypochlorite and its
applications
Chunpeng Li, Qingfen Niu, Tianduo Li, Tao Wei, Tingting Hu, Jianbin Chen, Xuyang
Qin, Lan Yang
PII:
S0143-7208(20)30463-0
DOI:
https://doi.org/10.1016/j.dyepig.2020.108459
DYPI 108459
Reference:
To appear in: Dyes and Pigments
Received Date: 19 February 2020
Revised Date: 1 April 2020
Accepted Date: 19 April 2020
Please cite this article as: Li C, Niu Q, Li T, Wei T, Hu T, Chen J, Qin X, Yang L, A novel dual-function
bithiophene-Meldrum's acid based chemosensor for highly sensitive, colorimetric and fluorimetric
detection of cyanide and hypochlorite and its applications, Dyes and Pigments (2020), doi: https://
doi.org/10.1016/j.dyepig.2020.108459.
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Author contributions
Chunpeng Li: Conceptualization, Data curation, Software, Investigation,
Writing-Original Draft.
Lan Yang: Validation, Formal analysis, Visualization.
Qingfen Niu: Resources, Writing-Review & Editing, Supervision, Data
Curation.
Tianduo Li: Resources, Formal analysis, Review & Editing.
Tao Wei: Formal analysis, Review & Editing.
Tingting Hu: Formal analysis, Review & Editing.
Jianbin Chen: Review & Editing.
Xuyang Qin: Review & Editing.

Graphical Abstract

A novel dual-function bithiophene-Meldrum's acid based chemosensor
for highly sensitive, colorimetric and fluorimetric detection of cyanide
and hypochlorite and its applications
Chunpeng Li, Qingfen Niu*, Tianduo Li, Tao Wei, Tingting Hu, Jianbin Chen, Xuyang
Qin, Lan Yang
Shandong Provincial Key Laboratory of Molecular Engineering, School of Chemistry
and Pharmaceutical Engineering, Qilu University of Technology (Shandong Academy of
Sciences), Jinan 250353, People’s Republic of China
Abstract
A dual-function bithiophene-Meldrum's acid based chemosensor 2TM was developed,
–
which displayed ultrafast, colorimetric and fluorescence turn-on responses for CN and
–
–
ClO with specific selectivity and high sensitivity. The sensor 2TM for CN detection in
–
2
DMSO/H O (1/3, V/V) solution was based on the nucleophilic addition of CN to sensor,
which resulted in remarkable spectral and discernable color changes. Meanwhile, 2TM
–
showed specific selectivity for ClO in 100% aqueous solution based on the sensing
mechanism of oxidative cleavage of C=C bond. The detection limits were obtained to be
–
–
–
0
.96 µM for CN and 48 nM for ClO . The sensing mechanism of 2TM toward CN and
–
1
ClO was investigated by job’plot, FTIR, H NMR, HRMS and optical spectra. The
sensor 2TM loaded colorimetric test strips/supported silica measurements demonstrated
to be a portable, eco-friendly and ultrafast device for real-time and on-site visual
−
−
detection of CN and ClO in water by the naked eye. More importantly, sensor 2TM
with excellent photophysical properties and low biotoxicity was successfully applied to
–
–
detect CN and ClO in live cells and environmental water samples, as well as capable of
−
monitoring CN in the natural food samples, illustrating its practical utility in biological
and environmental systems.
Keywords: Chemosensor; Hypochlorite; cyanide; Bithiophene-Meldrum's acid;
Bioimaging; Test strip.
*
To whom the correspondence should be addressed
E-mail: qf_niu1216@qlu.edu.cn
Telephone: +86(531)89631760
Fax number: +86(531)89631208
1

1
. Introduction
Cyanide (CN ) as a powerful poison is highly toxic to human health
–
even at an extreme low concentration [1-2]. However, cyanide-containing
compounds are widely used in the chemical and industrial processes, such as
synthetic plastic and resin industry, the production of pharmaceuticals and
pesticides, consumption of certain foods, metallurgy, electroplating and
gold/silver mining [3-6]. The extensive exposure of poisonic cyanide anion
to the environment and water source can cause various serious health
problems such as damage to the central nervous system and visual nervous
system, disturbance of metabolism, inhibition of respiration and even death
ascribed to its blocking the electron transport chain and inhibiting cellular
respiration [7,8]. Accordingly, the World Health Organization (WHO)
regulates the specified limit of cyanide in drinking water to be 1.9 µM [9].
–
Therefore, an efficient method to rapidly and precisely detect trace CN in
environmental and biological systems is of great significance to human
health and environment protection.
–
Hypochlorite (ClO ) is one of the most important reactive oxygen
species (ROS) in living organisms, which particularly participates in various
physiological and pathological processes and can react with many biological
molecules in living organisms including DNA, RNA, cholesterol, fatty acids,
and a variety of proteins [10-15]. Besides, due to its strong oxidation ability,
2

–
ClO is also widely used as an indispensable disinfectant, household bleach
−
and antimicrobial agent in our daily life [16-18]. Endogenous ClO is mainly
−
produced by myeloperoxidase-catalysed reaction between H O and Cl , and
2
2
it is generally considered as an important antimicrobial agent in the immune
system to defense the invasive bacterial pathogens [19]. However, excessive
−
ClO will increase oxidative stress, and resulting in tissue damage and
various diseases such as lung injury, nephrosis, neurodegeneration,
atherosclerosis, cancer, Alzheimer’s and cardiovascular diseases [20,21].
Consequently, it is highly desirable to develop a reliable analytical method
−
for real-time monitoring of ClO in environmental and biological systems.
Optical sensor technique with outstanding fluorescence and color
changes has been confirmed to be the most convenient and popular
analytical method for efficient identification of various cations, anions and
biomolecules [22-37]. Compared with the electroanalysis, potentiometry and
ion chromatography, reaction-based fluorescent sensor as a promising tool
for the recognition of various analytes has garnered tremendous attentions
because of its unique selectivity, excellent sensitivity, visualization, facile
operation, no damage, reliability, real-time imaging, fast response and
usability to biological system [38-42]. Recently, a numerous reaction-based
−
−
fluorescent sensors have been exploited to detecting CN and ClO [43-52],
which shows better selectivity and can effectively avoid interference of other
3

−
tested species. However, some of them could only detect one single CN or
−
ClO anion, which significantly limited their application. In contrast, the
multi-function fluorescent sensor which could detect multiple targets based
on different mechanisms displayed many unique advantages of simple
operation and multiplicity. Therefore, developing simple and water-soluble
fluorescent sensors with good capability of detecting more than one target in
enviro/biological systems has gained increasing attention. Unfortunately,
only two fluorescent sensors have been reported for simultaneous detection
−
−
of CN and ClO [53-55]. As a result, it is particularly urgent to develop
dual-function fluorescent sensors to quickly, accurately and simultaneously
−
−
detect CN and ClO in biological and environmental samples with excellent
sensitivity and selectivity, which is of significant importance for scientific
investigations, pollution monitoring and medical diagnosis.
Herein, we synthesized a simple dual-function bithiophene-Meldrum's
acid based colorimetric and fluorescent turn on sensor 2TM (Scheme 1) for
−
−
the specific and sensitive simultaneously detection of CN and ClO through
different sensing mechanisms. Sensor 2TM in aqueous media exhibited
−
−
excellent specificity for CN and ClO with visible naked-eye changes, and
−
−
could quantitatively and sensitively detect CN and ClO with low detection
limits of 0.96 µM and 48 nM, respectively. Moreover, excellent recognition
−
properties of 2TM with good water dispersibility, ultrarapid response (CN
4

−
<
30 s, ClO < 12 s), specific selectivity, great sensitivity, and admirable cell
permeability were exhibited, which made the sensor 2TM act as a promising
−
−
tool to monitor CN and ClO in the live cells, environmental water and the
natural food analysis. Furthermore, the sensor 2TM loaded colorimetric test
strips/supported silica measurements further demonstrated to be a portable,
eco-friendly and ultrafast device for real-time and on-site visual detection of
−
−
CN and ClO in water. To the best of our knowledge, our developed sensor
TM is the fourth example to be successfully used for simultaneous
2
−
−
detection of CN and ClO with ultrafast response and great sensitivity.
Scheme 1
2
. Experimental Section
2
.1 Instruments and reagents
The spectra of UV-Vis absorption, fluorescence, FTIR, NMR and
HRMS were recorded using Shimadzu UV-2600 spectrophotometer, Hitachi
F-4600 spectrophotometer, Bruker ALPHA FT-IR spectrometer, Bruker
Advance II 400 MHz instruments and Agilent 6510 Accurate-Mass Q–TOF
LC/MS system, respectively. The pH values were conducted by PHS-25 pH
meter. MTT assay and fluorescence images were obtained using the
microplate reader (MultiskanTM FC Microplate Photometer, Thermo
5

Scientific, USA) and Leica TCS SP8 confocal laser scanning microscope
CLSM) with a 63x magnification target oil lens, respectively. All chemical
(
reagents and solvents were purchased from commercial suppliers of
analytical reagent grade and were used directly without further purification
unless otherwise stated. Deionized water was used throughout the test
process. Compounds 2T and 2T-CHO were prepared by the previously
reported procedures [56,57].
2
.2 Synthesis of sensor 2TM
A mixture of compound 2T-CHO (388 mg, 2.0 mmol) and Meldrum's
acid (288 mg, 2.0 mmol) in dry 15 mL EtOH was added 2 drops of acetic
acid glacial as catalyst. The reaction mixture was stirred for overnight under
reflux. The resulting mixed solution was placed in the refrigerator overnight,
and the precipitated solid was suction filtered washed with ethanol and dried
in vacuum to give pure compound 2TM as an orange red solid (325 mg,
1
yield 83.5%). H NMR (400 MHz, DMSO-d , ppm):
δ = 8.64 (s, 1H), 8.25
6
(d, J = 4.0 Hz, 1H), 7.80 (d, J = 4.0 Hz, 1H), 7.72 (d, J = 4.0 Hz, 1H), 7.66
1
3
(
d, J = 4.0 Hz, 1H), 7.24 (t, J = 4.0 Hz, 1H), 1.72 (s, 6H) (Fig. S1); C
= 162.60, 161.15, 151.86, 148.40,
48.09, 135.21, 134.16, 129.50, 129.19, 127.68, 127.59, 125.06, 105.30,
NMR (100 MHz, DMSO-d , ppm):
δ
6
1
1
−1
04.41, 26.85 (Fig. S2); FTIR (KBr, cm ): v = 3077 (C-H), 1717 (O-C=O),
6

+
1
3
558 (C=C) (Fig. S3); HRMS (ESI): m/z calcd for C H O S [M + Na] :
15
12
4 2
43.0075, found: 343.0062 (Fig. S4).
2
.3 General spectroscopic procedures
Stock solution of the 2TM (1.0 mM) was prepared in DMSO. A series
−
−
−
of stock solutions of various anions (10 mM) and ROS including Br , F , Cl ,
2
−
−
3−
4
2−
4
−
−
−
−
−
−
CO , HCO , PO , SO , HSO , SCN , AcO , NO , NO , ClO ,
3
3
3
3
2
4
−
−
−
−
ClO , ClO , I , H O , ROO• and O were dissolved in deionized water and
3
2
2
2
2
used freshly. ROO• was obtained from 2,2'-azobis(isobutyramidine)
dihydrochloride. The test solution of 10 M 2TM was prepared through
μ
pipetted out 2TM stock solution (0.01 mL, 1.0 mM) into a volumetric flask
with 100 mL deionized water and diluted to an appropriate concentration.
All fluorescence and UV-Vis spectra of 2TM were measured at room
temperature. The fluorescence spectra were obtained under the condition of
an excitation wavelength of 350 nm and slit widths of 5 nm/5 nm.
2
.4 Live cell imaging
HeLa cells seeded in 96-well plates were incubated in DMEM medium
o
with 10% fetal bovine serum (FBS) for 24 h (37 C, 5% CO ). For
2
fluorescence imaging, these well-grown cells were treated with sensor 2TM
(15 μM) for 60 min and then washed with PBS buffer for three times.
–
–
Subsequently, the 2TM-treated cells were cultured with 20 μM ClO /CN
7

for 30 min, respectively, and then being washed three times with PBS buffer.
The fluorescence images of the HeLa cells were measured with an CLSM
under blue channel (430–470 nm) upon an excitation at 350 nm.
3
. Result and Discussion
–
3
.1 Spectroscopic response of 2TM towards CN
The UV-Vis absorption and fluorescence spectral response of 2TM
–
towards CN was firstly investigated in DMSO/H O (1/3, V/V) solution. As
2
−
displayed in Fig. 1a, after adding the CN (2.0 equiv.) to the 2TM (10
μ
M),
the strong absorption band at 452 nm disappeared and a new absorption
band appeared at 315 nm, along with an immediate dramatic solution color
change from yellow to colorless by the naked eyes. While, the other anions
−
−
−
2−
−
3−
2−
−
−
−
and ROS (Br , F , Cl , CO , HCO , PO , SO , HSO , SCN , AcO ,
3
3
4
4
3
−
−
−
−
−
−
−
NO , NO , ClO , ClO , ClO , I , O , ROO• and H O ) induced no
3
2
4
3
2
2
2
2
detectable color and spectral changes. As displayed in Fig. 1b, when treated
−
with CN , the fluorescence intensity at 450 nm of 2TM was drastically
enhanced upon an excitation at 350 nm, in accompaniment with a prominent
fluorescence color change into bright blue under 365 nm irradiation,
however, other tested anions and ROS exhibited no distinguished change.
−
These changes indicate that 2TM was only responsive to CN in aqueous
media with high selectivity.
8

Fig. 1
Both excellent selectivity and anti-interference capability are two key
parameters for evaluating the suitability of a developed sensor for biological
and environmental applications. Thus, the specific selectivity of 2TM in
−
DMSO/H O (1:3, V/V) solution for CN was examined by introducing the
2
−
−
−
2−
3
−
3−
2−
4
related co-exist anions including Br , F , Cl , CO , HCO , PO , SO ,
3
4
−
−
−
−
−
−
−
HSO , SCN , AcO , NO , NO , ClO and I . As shown in Fig. S5, in the
3
3
2
4
−
presence of 10.0 equiv. CN and 10.0 equiv. other interfering co-existed
anions, the changes of fluorescence intensity at 450 nm were similar to that
−
−
induced by only CN , indicating that sensor 2TM towards CN in aqueous
media showed excellent selectivity and anti-interference capability.
−
To further investigate the interaction between 2TM and CN , the
−
optical titrations of CN (0–2 equiv.) were carried out in DMSO/H O (1:3,
2
–
V/V) solution. With successive addition of CN to 2TM solution, the
absorption peak at 452 nm decreased progressively with the simultaneous
occurrence of a new peak at 315 nm, indicating that the intramolecular
charge transfer (ICT) transition within the sensor 2TM molecule from the
electron-rich bithiophene unit to the electron-deficient Meldrum's acid unit
is blocked [58,59]. Meanwhile, an isosbestic point appeared at 360 nm,
9

implying a new species was generated during the UV-Vis titration process
–
(
Fig. 2a). On the other hand, with the addition of increasing CN , the sensor
2
TM displayed a turn-on fluorescence emission, the fluorescence intensity
–
at 450 nm increased gradually and reached saturation when 1.0 equiv. CN
was added (Fig. 2b). These great spectral changes can be explained by that
–
the nucleophilic attack of CN to 2TM destroyed the
π
-conjugated system. A
–
good linear relationship between fluorescence intensity at 450 nm and CN
2
concentration at a range of 0–10 µM with a correlation coefficient R =
0
.99857 was obtained (Fig. S6), indicating the 1:1 nucleophilic addition
–
reaction between 2TM and CN . In addition, the 1:1 stoichiometry
–
interaction between 2TM and CN was also confirmed by Job’s plot analysis
–
[
60] (Fig. S7). The detection limit (DL) of sensor 2TM for CN was
estimated to be 0.96 µM based on 3σ/k [61,62], which is much lower than
the maximum level of WHO (1.9 µM) in drinking water, implying 2TM was
–
an effective tool to quantitatively and sensitively detect trace CN in real
water samples.
Fig. 2
1
0

Rapid response of a developed sensor towards a special analyte is an
important factor to evaluate its real-time detection performance in practical
–
applications, hence, the time-dependent experiment of 2TM towards CN
was executed in DMSO/H O (1:3, V/V) solution. As illustrated in Fig. 3a,
2
the change of the fluorescence intensity at 450 nm is completed within 30 s
–
with addition of CN and keeps on a steady value as prolonged reaction time,
indicating that the 2TM could be useful for rapid and real-time detection of
–
CN in aqueous media. In addition, the pH effect on real-time detection is
another key parameter in real samples, therefore, the pH effects on the
–
fluorescence response of 2TM (10 µM) in the absence and presence of CN
(
2.0 equiv.) were also measured in DMSO/H O (1:3, V/V) solution. As
2
–
illustrated in Fig. 3b, in the absence of CN , no obvious change in
fluorescence intensity at 450 nm of 2TM was observed over the pH range
–
5
-11. However, in the presence of CN , the fluorescence intensity at 450 nm
of 2TM showed a significant fluorescence enhancement and were
maintained over a wide pH range 5-10, but the fluorescence intensity
decreased below pH 5 owing to the protonation of cyanide anions. Therefore,
–
the 2TM showed highly sensitive fluorescent sensor for CN in the wide pH
–
range 5-10 and could be used to conveniently and effectively detect CN in
both environmental and physiological conditions.
11

Fig. 3
–
3
.2 Spectroscopic response of 2TM towards ClO
The UV–vis absorption and fluorescence responses of 2TM in the
−
−
−
−
2−
3
presence of various anions and ROS including ClO , Br , F , Cl , CO ,
−
3−
2−
4
−
−
−
−
−
−
−
HCO , PO , SO , HSO , SCN , AcO , NO , NO , ClO , ClO ,
3
4
3
3
2
4
3
−
−
−
ClO , I , O , H O and ROO• were investigated in
～
100% aqueous
2
2
2
2
−
solution. As depicted in Fig. 4a, after addition of 2.0 equiv. ClO to 2TM
(10 μM) solution, the strong absorption band at 452 nm disappeared and a
new absorption band emerged at 362 nm, along with a dramatic solution
color change from yellow to colorless, whereas no significant spectral and
solution color changes were noticed in the presence of other tested anions.
As displayed in Fig. 4b, the fluorescence intensity at 452 nm of 2TM in
～
1
00% aqueous solution was greatly enhanced accompanied with a distinct
fluorescence color change from dark blue to bright blue by naked eyes in the
−
presence of 2.0 equiv. ClO , while no color and spectral changes were
detected in the presence of other tested analytes. These investigations
−
indicate that 2TM can selectively sense ClO in
～100% aqueous solution.
−
Subsequently, the specific selectivity of 2TM for ClO was evaluated by
adding 10.0 equiv. of different analytes in
～100% aqueous solution (Fig.
S8). The treatment of other analytes each caused no significant fluorescence
1
2

changes in the sensor 2TM. We further added different analytes to 2TM, and
−
then added 10.0 equiv. ClO to verify the anti-interference ability of 2TM.
The results demonstrated that sensor 2TM showed high specific selectivity
−
and excellent anti-interference for ClO detection.
Fig. 4
The spectroscopic experiment was executed to understand the
−
interaction between 2TM and ClO in
～100% aqueous solution. As shown
−
in Fig. 5a, upon incremental addition of ClO (0–20
μM), the absorption
band at 452 nm was gradually decreased up to disappear and a new
absorption peak at 362 nm was steadily increased, a clear isosbestic point at
3
92 nm was easily observed, indicating a new species was formed during the
titration process. Meanwhile, the changes in the fluorescence spectra of
−
2
TM (10
μ
M) upon addition of ClO (0–2 equiv.) in
～
100% aqueous
solution was exhibited in Fig. 5b. The fluorescence intensity at 452 nm
−
increased gradually by the incremental addition of ClO with a saturation
−
observed at 10 µM ClO . A good linear relationship between fluorescence
−
intensity at 452 nm and ClO concentration (0−10 µM) with a good
2
correlation coefficient R = 0.99808 was derived (Fig. S9), suggesting that
1
3

−
the quantification of ClO in
～100% aqueous solution by 2TM was
feasible. A fitting of this titration data indicates 1:1 ratio interaction between
−
the 2TM and ClO , and this 1:1 stoichiometry was further verified by Job’s
–
plot (Fig. S10). The detection limit of 2TM towards ClO was calculated to
be 48.3 nM based on 3σ/k, which was superior to some reported
−
ClO -sensitive fluorescent sensors [63-65]. These results established that
–
2
TM could achieve sensitive and quantitative detection of ClO in
～100%
aqueous media.
Fig. 5
Response time is of great importance for a sensor to validate its
performance. Consequently, the time-dependent variation in fluorescence
–
intensity at 450 nm for 2TM in response to ClO in
～
100% aqueous
–
solution is evaluated (Fig. 6a). Upon the addition of 2.0 equiv.
～
ClO , the
fluorescence intensity at 452 nm of 2TM dramatically enhanced and reached
–
a plateau within 12 s, indicating that the reaction between 2TM and ClO
was nearly completed within 12 s. Such a quick response endowed the
developed sensor 2TM a promising potential for real-time monitoring of
–
–
ClO in real samples. Next, the fluorescence response of 2TM to ClO in
1
4

different pH values was conducted in
～100% aqueous media. As observed
in Fig. 6b, the fluorescence intensity at 452 nm of free 2TM was pH
–
insensitive over a wide pH range 1–14. When 20
μ
M ClO was added, the
fluorescence intensity at 452 nm increased and kept almost unchanged in a
pH range 2–7. Therefore, 2TM could be used for the real-time and sensitive
–
detection of ClO in environmental and biological samples.
Fig. 6
3
.3 Sensing mechanisms
–
1
To verify the sensing mechanism of 2TM towards CN , H NMR, FTIR,
–
and HRMS spectra were measured before and after adding CN to 2TM. As
–
depicted in Fig. 7a, with addition of 1.0 equiv. CN , the vinyl proton H at
a
8
.64 ppm disappeared and a new proton H at 5.26 ppm appeared, indicating
b
–
the addition process of CN to vinyl group of 2TM. Meanwhile, owing to
−
breaking the conjugation via the CN nucleophilic addition, all the aromatic
protons in 2TM were obviously upfield shifted. In the FTIR spectra (Fig.
−
−1
S11), upon the addition of CN , the ester (O-C=O) group at 1717 cm of
−1
2
TM was shifted to 1620 cm , meanwhile, the appearance of a new
−1
stretching vibration peak at 2143 cm corresponds to the nitrile (C
≡N)
−
group, suggesting the CN addition to vinyl group in 2TM. In the HRMS
1
5

spectrum, a new peak appeared at m/z = 351.0236 was attributed to the
4
+
3
TBN-CN adduct [2TM + CN + 4H] (351.0208), which revealed that the
−
nucleophilic reaction between 2TM and CN was proceeded in a molar ratio
of 1:1 (Fig. S12). Together with the optical instruments, the plausible
−
nucleophilic addition reaction between 2TM and CN was well proposed
−
and shown in Scheme 2. The nucleophilic attack of CN toward 2TM
interrupted the well π-conjugated system and effectively inhibited the ICT
process, thus caused a significant fluorescence turn on response [66,67].
−
Next, the possible reaction between 2TM and ClO was carefully
1
analyzed by H NMR, FTIR and HRMS spectra. After the reaction between
−
2
TM and ClO , there was a new proton peak appeared at about 9.80 ppm,
which was attributed to the aldehyde proton (H ) of the oxidative cleavage
b
1
product 2T-CHO (Fig. 7b), well matched with the H NMR analysis of free
−
compound 2T-CHO. In the FTIR spectra (Fig. S13), after treatment of ClO ,
−1
the ester (O-C=O) group at 1717 cm of 2TM disappeared, and a new
−1
stretching vibration peak at 1655 cm was observed corresponding to the
aldehyde (HC=O) group. Moreover, in the HRMS spectra (Fig. S14), the
peak at m/z = 194.9926 was assigned to the oxidative cleavage product of
+
2
T-CHO [2T-CHO + H] (194.9860). In addition, the significant optical
−
spectral changes of 2TM after treatment of excess ClO were well matched
with that of free compound 2T-CHO (Fig. S15). The aforementioned
1
6

−
evidences demonstrated that the reaction between 2TM and ClO in
～
−
1
00% aqueous solution was the ClO -promoted oxidative cleavage of
olefinic C=C bond to release the free fluorophore 2T-CHO [68-70], led to
prominent color and spectral changes (Scheme 2).
Fig. 7
Scheme 2
3
.4 Practical applications
−
To explore the practical utility of 2TM for qualitative analysis of CN
in real life, the food samples including the sprouted potato, cassava,
immature sorghum and bitter seed were chosen for the experiments. The the
sprouted potato, cassava, immature sorghum and bitter seed were separately
smashed and soaked in 100 mL water for 3 days until the extract became
turbid. The mixture was then filtered and washed three times with NaOH
(
100 mL, 100 mmol/L) to give a cyanide-containing solution and remained
the solution pH < 8. As displayed in Fig. 8, when the four different cyanide
solutions were added to 2TM (10 M), it’s well worth noting that the
μ
fluorescence intensity increased significantly and the color changed to bright
blue could be distinguished by the naked eyes under 365 nm UV light. These
1
7

investigated results showed that the recognition process is simple, handy,
and fast response, thus, the 2TM can be effectively utilized for real-time
−
detection of CN in the natural food samples.
Fig. 8
To further exploit the practical application of 2TM for quantitative
−
–
analysis of CN and ClO in real water, we selected the distilled water, river
water, tap water, the Yellow River water, lake water of Ji’nan Garden Expo
as water samples for the experiment. The detection accuracy and relative
standard deviation (RSD) was calculated by adding known concentrations of
–
–
standard CN and ClO (1, 5 and 10
μM) to these samples. As displayed in
Tables 1 and 2, the values of recovery were determined from 98% to 103%
–
−
of 2TM to CN , and from 98.6% to 102.1% of 2TM to ClO , together with
the obtained RSD values down to < 3.5%. The good recovery and excellent
analytical precision showed that sensor 2TM is feasible, accurate and
–
–
reliable in the determination of CN and ClO in environmental samples.
Table 1
Table 2
1
8

Based on the excellent characteristics of the sensor 2TM, we applied
–
–
2
TM to HeLa intracellular imaging to detect exogenous CN and ClO . The
MTT assay showed that 2TD has little cytotoxicity and was capable of
bio-imaging application (Fig. S16). After the HeLa cells were incubated
with 2TM (15
μM) for 60 min, almost no fluorescence was exhibited under
the blue channel (Fig. 9a,b). When the HeLa cells were incubated with 20
–
–
μ
M CN /ClO for 30 min, respectively, an obvious blue fluorescence signal
occurred under blue channel (Fig. 9c,d). All the results illustrated that sensor
TM has good cell-membrane permeability and was capable of imaging
2
–
–
intracellular CN and ClO in live cells.
Fig. 9
3
.5 Detection on test strips
The development of colorimetric test strips for fast and convenient
−
–
detection of CN and ClO could be important and useful for environmental
samples. To verify the possibility of 2TM as a fast and convenient
–
economical portable tool for colorimetric and instant detection of CN and
–
ClO in environmental water, the easy-to-use inexpensive test strips were
fabricated by soaking filter papers/TLC plates in 2TM solution (1 mM,
1
9

DMSO) and air-drying. As shown in Fig. 10a, the yellow-colored TLC
−
–
plates were dipped in CN /ClO solutions (1 mM, water) showed
immediately naked-eye discernible color change to colorless under daylight
as well as an obvious fluorescence color change from green to blue. Further,
−
–
the 2TM-coated filter papers were immersed in CN /ClO solutions of
different concentrations and dried in air. According to the increasing
−
–
concentration of CN /ClO , the color was changed gradually from yellow to
gray were clearly viewed under daylight, along with the fluorescence color
changes from green to blue under 365 nm illumination (Fig. 10b). These
observations implied that the test strips served as a practical tool to
−
–
colorimetrically and conveniently monitor CN and ClO in water.
In addition, the silica loaded 2TM was prepared and used for the
−
–
selective detection of CN /ClO . The silica gels (100 mesh, 1 g) were loaded
with 2TM solution (1.0 mM) and dried under vacuum to obtain the yellow
−
–
color. The dried silica was then added to CN /ClO (1.0 mM, water), the
color immediately changed to colorless and blue under sunlight and UV light,
respectively (Fig. 10c), which insisted on the real application of 2TM for
−
–
rapid and qualitative identification of CN and ClO . These results
–
demonstrated that sensor 2TM could selectively and visually recognize CN
–
and ClO in water as a portable device by the naked eyes.
2
0

Interestingly, due to the above good fluorescent sensing performance,
sensor 2TM could serve as a rewritable small-molecular smart fluorescent
−
−
display material. The CN /ClO solution (10 µM, water) was loaded into a
−
−
pen without any modification and was used to write a letter of “CN , ClO
and QLU”, number of “2019” and Chinese characters (such as “Qilu
University of Technology”) on the 2TM-based filter papers, respectively,
and the results were visualized under 365 nm UV light. As displayed in Fig.
1
0 (d), all the letter, number, and the Chinese characters on the handwritten
filter paper gave bright blue fluorescence, further confirming 2TM could be
−
−
used as a convenient and inexpensive test tool for sensing CN and ClO in
water.
Fig. 10
4
. Conclusions
In summary, a novel dual-function bithiophene-Meldrum's acid based
colorimetric and fluorescent sensor 2TM was synthesized and characterized.
On account of the outstanding advantages of excellent selectivity, great
sensitivity, ultrafast response time and wide working pH range, sensor 2TM
−
−
was successfully applied to detecting CN and ClO in aqueous media with
2
1

naked-eye colorimetric and fluorescent turn-on responses, and its practical
utility as an on-site testing reagent has been verified in live cells and
environmental water samples. Moreover, the sensor 2TM was also capable
−
of monitoring CN in the natural food samples. In addition, colorimetric test
strips demonstrated a promising application of 2TM as a portable,
eco-friendly and ultrafast device for real-time and on-site visual detection of
−
−
CN and ClO in water with great sensitivity.
Acknowledgments
The authors gratefully acknowledge the financial support from the National
Natural Science Foundation of China (Nos. 21776143, 21376125, 51702178
and 21801144), the Natural Science Foundation of Shandong Province (No.
ZR2017LB009), the Program for College Students' Innovation and
Entrepreneurship Training of Shandong Province (No. S201910431035), the
Youth Innovative Talents Recruitment and Cultivation Program of Shandong
Higher Education, and the Program for Scientific Research and the Program
for Scientific Research Innovation Team in Colleges and Universities of
Shandong Province (No. 0308150302).
2
2

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