Quinoline-based highly selective and sensitive fluorescent probe specific for Cd2+ detection in mixed aqueous media

Article abstract of DOI:10.1016/j.tetlet.2017.08.068

Quinoline-based fluorescent probe as a recognition unit was designed and synthesized in this study. The probe R1 displayed excellent selectivity and sensitivity for cadmium ions (Cd²⁺) over a wide range of metal ions in acetonitrile-water (MeCN-H₂O) mixed solution. In order to better understand the recognition mechanism between probe and Cd²⁺, the density functional theory calculations were performed. Finally, the colorimetric experiment result was observed and conveniently monitored by the naked eye, and a visual detection limit of 4 × 10^?6 mol L^?1 was achieved. These experimental results indicated the promising potential of the probe to detect Cd²⁺ in biological system. Furthermore, the probe R1 was successfully used for the highly sensitive detection of Cd²⁺ in living cells.

Full text of DOI:10.1016/j.tetlet.2017.08.068

Accepted Manuscript
Quinoline-based highly selective and sensitive fluorescent probe specific for
Cd2+ detection in mixed aqueous media
Xiaohu Ding, Feifei Zhang, Yinjuan Bai, Junxia Zhao, Xia Chen, Man Ge, Wei
Sun
PII:
S0040-4039(17)31088-2
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.08.068
TETL 49258
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 May 2017
24 August 2017
28 August 2017
Please cite this article as: Ding, X., Zhang, F., Bai, Y., Zhao, J., Chen, X., Ge, M., Sun, W., Quinoline-based highly
selective and sensitive fluorescent probe specific for Cd2+ detection in mixed aqueous media, Tetrahedron Letters
(2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.08.068
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Quinoline-based highly selective and sensitive
fluorescent probe specific for Cd2+ detection in mixed
aqueous media
Xiaohu Ding, Feifei Zhang, Yinjuan Bai*, Junxia Zhao, Xia Chen, Man Ge, Wei Sun
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry
of Education, College of Chemistry and Materials Science, Northwest University,
Xi'an , Shannxi 710127 ,P.R. China
Abstract: Quinoline-based fluorescent probe as a recognition unit was designed and synthesized
in this study. The probe R1 displayed excellent selectivity and sensitivity for cadmium ions (Cd2+)
over a wide range of metal ions in acetonitrile-water (MeCN-H2O) mixed solution. In order to
better understand the recognition mechanism between probe and Cd2+, the density functional
theory calculations were performed. Finally, the colorimetric experiment result was observed and
−1
conveniently monitored by the naked eye, and a visual detection limit of 4 × 10−6 mol L was
achieved. These experimental results indicated the promising potential of the probe to detect Cd2+
in biological system. Furthermore, the probe R1 was successfully used for the highly sensitive
detection of Cd2+ in living cells.
Keywords: Fluorescent probe, Quinoline, Cadmium(II) ions, Recognition, Density functional
theory calculations.
Introduction
Pollution caused by heavy metal ions has become a serious and urgent problem because it
causes potential damage to the environment and poses serious health hazards to the human and
animal life even at low concentrations.[1] Among them cadmium ions (Cd2+) are the most toxic and
hazardous ions that are known to lack any vital or beneficial effects on humans.[2] Cd is widely
used in many fields including military affairs, agriculture, and industry. When accumulated in the

kidney, thyroid gland, spleen, and so on, Cd can cause serious illness, such as lung cancer, renal
dysfunction, calcium metabolism disorders, prostate disorder, oxidative stress, and high blood
pressure even at very low concentrations.[3,4] Therefore, rapid and efficient detection of Cd2+ is
highly desirable and necessary in order to control its concentration levels in the biosphere and its
direct impact on human health. Though various methods such as atomic emission spectroscopy,
ion-coupled plasma emission-mass spectroscopy, and X-ray fluorescence spectroscopy[5,6] are
available for the detection of content of Cd2+, use of fluorescent probe to recognize Cd2+ is the
most common one. Although these conventional methods provide an extremely sensitive and rapid
analysis approach, they need sophisticated sample-pretreatment procedures, complicated
instrumentation, and rigorous experimental conditions, which limit their use. In recent years, the
fluorescence method has been developed for analysis of Cd2+ and the colorimetric technique has
frequently been applied.[7,8]
Till date, fluorescent probes capable of detecting heavy-metal ions have attracted significant
attention in virtue of their operational simplicity, high sensitivity, high selectivity, low detection
limit, easy operational procedure, and high response speed.[9] The construction of single
fluorescent probes capable of simultaneous detection of multiple targets has drawn increasing
interest due to their cost-effective and real-time applications.[10] However, recognition of multiple
analytes is a great challenge. Presently, among these, a few recent quinoline-based fluorescent
probes as a recognition unit have been reported. Liu et al. reported a novel and efficient
quinoline-based fluorescent sensor for zinc(II) ion (Zn2+) and its application in live-cell
imaging.[11] Mehdi et al. reported a selective “On–Off” switching behavior of a small fluorogenic
molecule, N-(quinolin-8-yl)quinoline-2-carboxamide in acetonitrile (MeCN) solution for detection
of Zn2+.[12] Zhu et al. reported a ratiometric Al3+ ion probe based on the coumarin-quinoline
fluorescence resonance energy transfer system.[13] Montalti et al. reported a fluorescent behavior
of 8-hydroxyquinoline containing chemosensors.[14] However, many of the reported
quinoline-based fluorescent probes have limitations, such as low selectivity and requirement for
long response time and specific reaction conditions such as high temperature and acidic or basic
environment. Moreover, quinoline-based fluorescent probes for detection of Cd2+ have rarely been

reported. Pamuk and Algi reported synthesis of a novel on/off fluorescent Cd2+ probe.[15] However,
extensive research efforts are required to be devoted to the quinolone-based fluorescent probes for
the rapid and highly selective and sensitive detection of Cd2+ at room temperature in mixed
aqueous media.
To address the above mentioned problem herein, a quinoline-based fluorescent probe R1
was designed and synthesized. The new fluorescent probe R1 displayed an excellent selectivity for
Cd2+ over a wide range of metal ions in MeCN-H2O systems. Probe R1 displayed strong
fluorescence enhancement with Cd2+ and other metal ions could not enhance the fluorescence
intensity. Moreover, the colorimetric experiment result was observed and conveniently monitored
−1
by the naked eye and a visual detection limit of 4 × 10−6 mol L was achieved. Finally, the
quinoline-based fluorescent probe was successfully used for detecting Cd2+ in biological system.
Scheme 1.The synthetic route to R1
Results and discussions
The synthesis of R1 is outlined in Scheme 1. It was characterized by 1H NMR, 13C NMR,
and high resolution mass spectroscopy (HRMS), and the corresponding spectra are provided in
supplementary materials.
The solvent affects the fluorescent intensity of the probe in the process of detection of Cd2+.
Therefore, some experiments were conducted to investigate and discuss the effect of solvent and
select an optimal solvent system for the effective detection of Cd2+. Fig. 1a shows that R1
displays a strong fluorescent emission peak in an aprotic polar solvent dimethylformamide (DMF),
and this peak becomes faint in MeCN under no any ions circumstance. Therefore, in order to
reduce the fluorescence response of the solvent itself compared to the probe R1, MeCN was
selected as an optimized solvent. However, whether in nature or in the body to detect metal ions
are inseparable the water, and to improve the usability of the probe, we selected MeCN-H2O as the

optimized solvent system. In order to reduce the interference of external environment during the
detection of Cd2+ by using probe R1, accurate judgment of the solvent ratio for probe R1 testing
was required; therefore, we tested the probe in solvent systems with different ratios for detecting
the fluorescence response of Cd2+. Fig. 1b exhibits that R1 with Cd2+ shows weak fluorescence
intensity in water alone. Upon gradual addition of MeCN solvent, an obvious enhancement of
fluorescence intensity is observed, and the fluorescence intensity no longer increases when the
MeCN and water ratio reaches 1:1. Thus, the above mentioned results indicate that the best ratio
for MeCN-H2O solvent system is 1:1.
Fig.1. (a) Fluorescence spectra of probe R1 (10 µM) in the presence of various solvents (λex = 375 nm). (b)
Fluorescence probe in response of R1 with Cd2+ under the same solvent conditions in different proportions.
For an ideal probe, a high selectivity for the analyte is a matter of necessity. Related metal
ions, including Ag+, Al3+, Ba2+, Ca2+, Cd2+, Cr3+, Co2+, Cu2+, Fe3+, Hg2+, K+, Li+, Mg2+, Mn2+, Na+,
Ni2+, Pd2+, and Zn2+ were used to monitor the binding abilities of R1 with the metal ions in the
MeCN-H2O (1:1, v/v) solution by fluorescence spectroscopy (Fig. 2a). Upon addition of probe R1,
the fluorescent intensity of metal ions other than Cd2+ did not alter noticeably. Only Cd2+
significantly affected the fluorescent intensity of R1 even in the presence of other interfering
metal ions. This result indicates high selectivity and sensitivity of R1 toward Cd2+. To verify the
effect of R1 on the complexation of Cd2+, following competitive experiment was conducted: the
fluorescence emission of R1 was analyzed upon adding different metal ions. Fig. 2b demonstrates
that the fluorescence of R1 enhances with the addition of Cd2+ to the mixture of R1 with other
interfering ions. Thus, the result reveals that selectivity of R1 toward Cd2+ is not significantly

affected by the commonly coexisting ions. Noteworthy, with the addition of Cd2+, the solution of
R1 immediately becomes dark yellow, which could be distinguished well by the naked eyes.
However, other ions did not exhibit any color change (Fig. 3a), and R1 immediately becomes blue
under 365 nm ultraviolet (UV) light (Fig. 3b). These results indicate that the response of R1
toward Cd2+ was unaffected by the presence of other contaminating ions. Thus R1 is a selective
fluorescent probe for Cd2+.
Fig.2. (a) Fluorescence spectra of probe R1 (10 µM) in the presence of 20 equiv, of various metal cations in
MeCN-H2O (λex = 375 nm). (b) Fluorescence intensity changes of R1 upon the addition of various metal ions in
the presence of R1 with Cd2+ solution. The red bars represent the fluorescence response of R1 and competing ions.
The green bars represent the subsequent addition of R1 with Cd2+ to the above solutions. 1 Ag+, 2 Al3+, 3 Ba2+, 4
Ca2+, 5 Cd2+, 6 Cr3+, 7 Cu2+, 8 Fe3+, 9 Co2+, 10 Hg2+, 11 K+, 12 Li+, 13 Mg2+, 14 Mn2+, 15 Na+, 16 Ni2+, 17 Pd2+, 18
Zn2+
.
Fig.3. (a) Color changes of R1 (10 µM) upon the addition of various metal ions (10 µM) by naked eyes, (b)
and under 365 nm UV light.
The binding behavior of probe R1 toward metal ions was examined by UV–visible (vis)
spectroscopy in MeCN-H2O system. The UV–vis absorption spectrum of probe R1 (10 µM)
exhibited absorption maxima at λ max = 390 nm. Upon addition of different metal ions, such as Ag+,

Al3+, Ba2+, Ca2+, Cd2+, Cr3+, Cu2+, Fe3+, Co2+, Hg2+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pd2+, and Zn2+,
Cd2+ showed enhancement in the intensity of the significant absorbance peak of R1 (λmax = 390
nm), and the other metal ions did not significantly affect the UV–vis spectra of probe R1 (Fig. 4).
Fig.4. The UV-vis spectra of R1 in different metal ion solutions.
In addition to its metal ion sensing properties, the fluorescence behavior of [R1+Cd2+]
−
−
−
−
−
−
2−
−
−
toward various anions, including CH3COO , Br , BrO3 , C2O4 , Cl , ClO3 , CO3 , CrO4 , F ,
−
−
2−
−
−
−
−
−
3−
−
H2PO3 , HCO3 , HPO3 , HSO3 , HSO4 , I , IO3−, NO2 , NO3 , PO4 , S2O3−, S2−, SCN , and
2−
3−
SO4 was also investigated in MeCN-H2O (1:1, v/v) system. Fig. 5 shows that only PO4 causes
−
−
remarkable fluorescence quenching; however, the addition of other anions, such as C2O4 , CrO4 ,
2−
and HPO3 , resulted in only a slight quenching. This indicated that the [R1+Cd2+] complex
3−
exhibited a high selectivity and sensitivity for the PO4 anions. Moreover, the above mentioned
3−
result also indicated that the response of [R1+Cd2+] toward PO4 was unaffected by the presence
of other interfering anions.

Fig.5. (a) Fluorescence spectra of probe [R1+Cd2+] (10 µM) upon addition of 20 equiv, of various anions in
MeCN-H2O (λex = 375 nm). (b) Fluorescence intensity changes of [R1+Cd2+] upon the addition of various anions
in the presence of [R1+Cd2+] with PO43- solution. The red bars represent the fluorescence response of [R1+Cd2+]
3-
and competing anions. The green bars represent the subsequent addition of [R1+Cd2+] with PO4 to the above
−
−
−
−
−
−
2−
−
−
−
−
solutions. 1 CH3COO , 2 Br , 3 BrO3 , 4 C2O4 , 5 Cl , 6 ClO3 , 7 CO3 , 8 CrO4 , 9 F , 10 H2PO3 , 11 HCO3 , 12
2−
−
−
−
−
−
3−
−
2−
HPO3 , 13 HSO3 , 14 HSO4 , 15 I , 16 IO3−, 17 NO2 , 18 NO3 , 19 PO4 , 20 S2O3−, 21 S2−, 22 SCN , 23 SO4
3-
Fig.6. (a) The titration curves of the probe RI with Cd2+, (b) and R1+ Cd2+ with PO4 in the presence of
concentration increased.
Fluorescence titration of R1 was conducted in MeCN-H2O (1:1, v/v) solution. Fig. S1.a
shows that the solution of sensor R1 does not exhibit fluorescence emission without Cd2+ as
expected. Fluorescence titration experiments were conducted by adding Cd2+ (0.0–0.8 equiv).
Upon incremental addition of Cd2+ solution, a gradual enhancement in the fluorescence intensity
of the band was observed, and when 0.8 equiv of Cd2+ was added, it led to a remarkable peak
centered at wavelength of around 500 nm. When the concentration of R1 was twice the
concentration of Cd2+, the fluorescence intensity of R1 was maximal without any further increase
(Fig. 6a). This indicates good ability of R1 to complex Cd2+, and it can be deduced that the
3−
optimized ratio of probe R1 to Cd2+ = 2:1. The sensing ability of [R1+Cd2+] for PO4 was further
determined by fluorescence titration. Fig. S1.b exhibits that the emission intensity of [R1+Cd2+] at
3−
3−
500 nm steadily decreases until 20 equiv. of PO4 is added. Moreover, higher PO4
concentrations did not lead to further quenching (Fig. 6b).

Fig.7. (a) Effect of pH on the fluorescence intensity at 500 nm of R1 (black line) and R1+Cd2+ (red line). (b)
Effect of time on the fluorescence intensity at 500 nm of R1 ( black line) and R1+Cd2+ ( red line).
Job’s plot was obtained by varying the mole fraction of Cd2+ from 0 to 1.0 in a solution of
[Cd2++R1] with a total concentration of 20 µM. Fig. S2 shows a 2:1 stoichiometry between R1
and Cd2+. The association constant was also calculated by using the following formula:[16] 1/(F−F0)
= 1/[Ka(Fmax−F0) (Cd2+)0.5] + 1/( Fmax−F0) based on a 2:1 stoichiometry, where F is the obtained
fluorescence intensity, F0 is the fluorescence intensity of free R1, and Fmax is the saturated
fluorescence intensity for the Cd2+-R1 complex. Fig. S3 shows a linear relationship. The
−1
association constant of R1 was estimated to be 8.48 × 104 M . The peak of [Cd2+ + (R1)2] is
shown in Fig. 7A (Supplementary information).
The influence of pH on fluorescence intensity of R1 toward Cd2+ was also investigated in the
acidic and basic media. Fig. 7a illustrates that probe R1 was non-fluorescent within the pH = 1–12
in the absence of Cd2+. However, when Cd2+ was added under the identical conditions,
fluorescence intensity gradually increased in the pH range of 2 to 6, and R1 fluorescence intensity
remained unchanged, which proved that pH hardly affected the detection of Cd2+ ion in the pH
range of 6 to 10. The fluorescence intensity of [Cd2+]-R1 decreased when the pH > 10, which was
due to the precipitation of cadmium hydroxide in alkaline condition. This result indicated that
fluorescence intensity of coordination compounds almost remained unaffected in the pH range of
6 to 10. Besides, upon addition of Cd2+ into R1 solution, the fluorescence intensity immediately
acquired the maximum value and did not change with further increase the reaction time (Fig.7b)

Theoretical calculations for probe R1.
To better understand the nature of R1, energy optimized structures of R1 were obtained by
using density functional theory (DFT) calculations based on the Fukui function f+(r). All the
calculations were performed with the Gaussian 09 program with B3LYP/6-31G**/dgdzvp
level.[17–19] The optimized structure of the ground state S0 is shown in Fig. S4.a. Clearly, the
dihedral angle between the quinoline and thiazole is 137.60°. According to NBO analysis,[17b] the
larger the atomic value, the more active it is, and it combines easily with Cd2+. For R1, the
condensed Fukui functions are O (0.037), N3 (0.067), N2 (0.023), S (0.009), and N1 (−0.031),
which indicate that the O, N3, and N2 should be better active sites using which the probe R1 can
bind with one Cd2+. The energy-minimized structure of probe R1 with Cd2+ is shown in Fig. S4.b.
DFT calculations show that the Cd2+ ions are essentially coordinated with oxygen of the –OH
group [d(Cd–O1) = 2.16 Å, labeled r1], thiazole nitrogen [d(Cd–N2) = 2.28 Å, labeled r2], and
enamine [d(Cd–N3) = 2.34 Å, labeled r3]. The difference in distances between phenolic oxygen
and Cd2+ could determine the extent of ESIPT inhibition, resulting in extensive variations in
fluorescence emission after complexation, and to be the better active site that probe R1 could bind
with Cd2+(2:1).
Fig.8. HOMO, LUMO and band gap energies (-∆E = EHOMO–ELUMO) of probe R1 and R1 with Cd2+.
Our calculations show that the S1–S0 transition in R1 and the Cd2+-coordinated complex
corresponds to the transition from the highest occupied molecular orbital (HOMO) to the lowest

unoccupied molecular orbital (LUMO) (Fig. 8). This reveals that electron density variations
caused observable changes in the UV–vis and fluorescence spectra, which were mainly attributed
to the different points of interaction with the respective analytes. The different fluorescence
response observed with R1 and R1+Cd2+ indicated the extent with different binding modes. The
band gap energy (−∆E = EHOMO–ELUMO) in R1+Cd2+ (1.84 eV) was found to be smaller than that
of R1 (2.11 eV). At the same time, calculations were also performed for the combination of other
ions with R1; nonetheless, the band gap energy (−∆E = EHOMO–ELUMO) in R1+Cd2+ (1.84 eV) was
found to be smaller than that of other ions (−∆EFe = 1.86 eV). In general, lower band gap energy
indicates easier combination of the probe with the metal ion, thus it was the easiest for R1 probe
to combine with Cd2+. This result further supported that the complexation was thermodynamically
stable. As discussed above, the sensing mechanism is schematically shown in scheme 2.
Scheme 2.Proposed mechanism of interaction between R1 with Cd2+
Colorimetric Detection
Currently, paper-based analytical devices have aroused significant attention because of their
flexibility, low cost, and high speed detection.[22–24] This is perhaps the simplest of detection
techniques, as a change in color can be observed by the naked eyes. Several reports have been
demonstrated for application in disease markers, food safety, and environmental monitoring.[25,26]
Therefore, in this study, paper-based analytical device was used for the rapid detection of metal
ions. For detecting the Cd2+, a series concentration of Cd2+ in water was dropped, respectively, on
−4
−1
the filter paper coated with the 0.1 mL solution of R1 (2.0 × 10 mol L ) in MeCN-H2O, and
then dried at 25 °C. Fig. 9a shows an image depicting the color changes on test paper in the
presence of Cd2+ solutions with different concentrations under 365 nm UV light, and an image of
sensors with variations in color intensity. The image clearly presents a decrease in the dark yellow

color intensity with decreasing Cd2+ concentration by naked eye (Fig. 9b). The result was
−6
−1
observed by naked eye and a visual detection limit of 4 × 10 mol L was achieved. It is a
practical low-cost approach which rapidly detects the Cd2+ even in low concentrations, and it can
be further successfully applied in the areas of medical health and environmental monitoring.
Fig.9.(a) Color changes on test paper in the presence of different concentration of Cd2+under 365 nm UV light, (b)
and by naked eye.
Fluorescence imaging
For investigating the practical bio-imaging applications of R1, it was utilized to set up the
fluorescence assay to analyze Cd2+ in live HCCLM3 cells by laser scanning confocal microscopy.
The cells were incubated with R1 (20 µM) buffer for 1 h at 37 °C in a CO2 incubator (5% CO2,
95% relative humidity). Subsequently, the cells were washed with PBS buffer three times to
remove unbound probe. Further Cd2+ (10 µM) was added to the cells for another 30 min. Fig. 10
presents the results of confocal fluorescence imaging of Cd2+ in live HCCLM3 cells. As expected,
in the absence of Cd2+, free R1 showed no detectable fluorescence signal in living cells (Fig. 10
top). In contrast, blue fluorescence was observed when a deposited HCCLM3 cell was incubated
with Cd2+ (10 µM) for 30 min (Fig. 10 bottom). Thus, the results indicated that the remarkable
fluorescence enhancement was because of the complexation of R1 with Cd2+ in the live cells,
which was employed for sensing of Cd2+.

Figure.10. Images of HCCLM3 cells treated with R1 (20 µM) in the absence or presence of Cd2+ (10 µM). (a,b)
Confocal fluorescence image of HCCLM3 cells with R1. (c) Confocal fluorescent image of HCCLM3 cell with
Cd2+ and R1 (scale = 10 µm). (d) Confocal fluorescent image of HCCLM3 cell with Cd2+ and R1 (scale = 20 µm).
Excitation wavelengths of R1 and R1-Cd2+ are 390 nm.
Conclusions
In summary, we designed and synthesized a quinoline-based fluorescent probe R1. It
displayed a high selectivity for Cd2+ over other ions in MeCN-H2O (1:1, v/v) system. Probe R1
and Cd2+ system could form a new fluorescent probe [R1+Cd2+] relay identification. [R1+Cd2+]
3−
exhibited better specificity for PO4 without interference from other ions, and could quantitatively
3−
detect PO4 . A B3LYP/6-31G** basis set was employed for optimization of R1 and R1-Cd2+
complex. The colorimetric detection experiment explained that probes R1 could rapidly detect the
Cd2+ in a cost-effective manner and act as potential candidates for further application in the areas
of medical health and environmental monitoring. Furthermore, the probe R1 was successfully
used for the highly sensitive detection of Cd2+ in living cells.
Acknowledgements
We gratefully acknowledge financial support from the National Natural Science Foundation
of China (Grant no.21042002).
References
1. Zhang, C. H.; Gao, B. Z.; Zhang, Q. Y. Talanta. 2016, 154, 278-283
2. (a) Kim. H. N.; Ren. W. X.; Kim. J. S.; Yoon. J. Chem. Soc. Rev. 2012, 41, 3210–3244; (b)
Waisberg, M.; Joseph, P.; Hale, B.; Beyersmann, D. Toxicology. 2003, 192, 95–117; (c)
Erdemir, S.; Malkondu, S. Sens. Actuators, B. 2013, 188, 1225–1229; (d) Tchounwou, P. B.;

Ayensu, W. K.: Ninashvili, N.; Sutton, D. Environ. Toxicol. 2003, 18, 149–175; (e) Harada,
M.; Crit. Rev. Toxicol. 1995, 25, 1–24.
3. Safe, S. Nat. Med. 2003, 9, 1000.
4. (a) Waalkes, M. P. J. Inorg. Biochem. 2000, 79, 241–244; (b) Wang, P.; Wu, J.; Liu, L. X.;
Zhou, P. P.; Ge, Y. S.; Liu, D.; Liu, W. S.; Tang, Y. Dalton Trans. 2015, 44, 18057–18064.
5. Haribhau, S. K.; Balu, L. G.; Ganapati, S. S. Sens. Actuators, B. 2016, 222, 35–42.
6. Meel, K. Van.; Smekens, A.; Behets, M.; Kazandjian, P.; Grieken, R. V.; Anal. Chem. 2007,
79, 6383–6389.
7. Taher, M. A.; Daliri, Z.; Fazelirad, H.; Chin. Chem. Lett. 2014, 25, 649–654.
8. Kumar, A.; Rao, G. K.; Singh, A. K.; RSC Adv. 2012, 2, 12552–12574.
9. Houk, R. J. T.; Wallace, K. J.; Hewage, H. S.; Anslyn, E. V.; Tetrahedron Lett.2008, 64,
8271–8278.
10. (a) Yang, X. F.; Guo, Y. X.; Strongin, R. M. Angew. Chem. 2011, 123, 10878–10881; (b)
Maity, D.; Govindaraju, T.; Chem. Commun. 2012, 48, 1039–1041; (c) He, X.; Yam, V. W.
W.; Org. Lett. 2011, 13, 2172–2175.
11. Liu, H. Y.; Dong, Y. S.; Zhang, B.; Sensors and Actuators B.2016, 234, 616-624.
12. Amirnasr, M.; Meghdad, S. I. Sensors and Actuators B.2016, 233, 355-360.
13. Zhu, Q.; Li, L.; Mu, L. Journal of Photochemistry and Photobiology A: Chemistry.2016, 328,
217-224.
14. Bronson, R. T.; Montalti, M. Tetrahedron.2004, 60, 11139-11144.
15. Pamuk, M.; Algi, F. Tetrahedron Letters, 2012, 53, 7010-7012.
16. Schade, A. E.; Schieven, G. L.; Townsend, R.; Jankowska, A. M.; Susulic, V.;
Blood.
2008, 111, 1366-1377.
17. Bao, X. F.; Cao, X. W.; Nie, X. M.; Xu, X.; Guo, W. H.; Zhou, B. J.; Zhang, L.Y.; Liao, H.;
Pang, T. Sensors and Actuators B. 2015, 208, 54-66. (b) Reed, A. E.; Curtiss, L. A.;
Weinhold, F. Chem. Rev. 1988, 88, 899-926.
18. Kumar, A.; Pandith, H.-S. Kim. RSC Adv. 2015, 5, 81808–81816.
19. Kumar, A.; Pandith, H.-S. Kim. Dyes Pigm. 2015, 122, 351–358.
20. Qi, D.; Zhang, L.; Zhao, L.; Cai, X.; Jiang, J. Chem. Phys. Chem. 2012, 13, 2046-2050.

21. Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899-926.
22. Liana, D. D.; Raguse, B.; Gooding, J. J.; Chow, E. Sensors (Basel). 2012, 12, 11505-11526.
23. Liu, J.; Wang, H.; Manicke, N. E.; Lin, J. M.; Cooks, R. G.; Ouyang, Z. Anal. Chem. 2010,
82, 2463-2471.
24. Liana, D. D.; Raguse, B.; Gooding, J. J.; Chow, E. Sensors. 2012, 12, 11505.
25. Sameenoi, Y.; Panymeesamer, P.; Supalakorn. N.; Koehler, K.; Chailapakul, O.; Henry, C. S.;
Volckens, J. Environ, Sci. Technol. 2013, 47, 923-940.
26. Apilux, A.; Siangproh, W.; Praphairaksit, N.; Chailapakul, O.; Talanta. 2012, 97, 388.

1. The probe exhibited highly selective and sensitive recognition toward Cd2+.
2. Colorimetric detection can show the detection line.
3-
3. The probe-Cd2+ complex could detect PO4 .
4. The recognition mechanism was explored through theoretical calculations.
5. The probe exhibited excellent fluorescence imaging in living cells.

Quinoline-based highly selective and sensitive fluorescent probe
specific for Cd2+ detection in mixed aqueous media
Xiaohu Ding, Feifei Zhang, Yinjuan Bai*, Junxia Zhao, Xia Chen, Man Ge, Wei Sun