A Coumarin-Based Fluorescence Probe for Selective Recognition of Cu<sup>2+</sup> Ions and Live Cell Imaging

He, Guangjie; Ma, Nana; Li, Linlin; Xie, Chenyan; Yang, Linlin; Xu, Jinhe; Wang, Junli

doi:https://doi.org/10.1155/2019/2814947

Journal of Sensors

On this page

Abstract Introduction Results and Discussion Conclusion Data Availability Conflicts of Interest Acknowledgments Supplementary Materials References Copyright Related Articles

Research Article | Open Access

Volume 2019 | Article ID 2814947 | https://doi.org/10.1155/2019/2814947

A Coumarin-Based Fluorescence Probe for Selective Recognition of Cu²⁺ Ions and Live Cell Imaging

Guangjie He,¹Nana Ma,²Linlin Li,¹Chenyan Xie,¹Linlin Yang,¹Jinhe Xu,¹and Junli Wang³

Academic Editor: Hai-Feng Ji

Received13 May 2019

Accepted14 Sept 2019

Published30 Oct 2019

Abstract

A new fluorescence probe L was rationally designed and synthesized for the recognition of Cu²⁺ ions by the combination of coumarin hydrazide and 2-acetylpyrazine. The photochemical properties and selectivity of L for Cu²⁺ ions in a CH₃CN/HEPES (3 : 2, ) buffer were investigated by UV-vis absorption and fluorescence emission spectra. A highly selective and sensitive response of L for Cu²⁺ ions over other competing metal ions was observed with limit of detection in 3 μM. The coordination stoichiometry of L to Cu²⁺ ions was determined to be 1 : 1 by the UV-vis absorption spectrum, the fluorescence titrations, and density functional theory (DFT) calculations. Moreover, L was applied successfully for recognition of intracellular Cu²⁺ ions in living cells.

1. Introduction

The selective and sensitive detection for trace transition metal ions has received great attention in biological samples [1–3]. As a required element in humans, copper plays vital roles during various biochemical processes, such as cellular respiration, neurotransmission, and biosynthesis [4–7]. A copper balance is also maintained in the human body through daily diet and metabolism under normal conditions. However, excessive concentration of copper ions in the human body will cause a wide variety of diseases such as Menkes syndrome, prion disease, and Alzheimer’s disease [8–11]. Therefore, it is significant to develop a highly sensitive method for selective detection of trace Cu²⁺ ions.

Fluorescence detection among various analytical methods is attracting more attention due to its high selectivity, short response time, and great potential for live cell imaging [12–15]. By the virtue of these distinct advantages, fluorescence bioimaging technology has been applied successfully in living cells [16–18]. Typical fluorescent sensors have been documented involving inorganic composites, such as quantum dots @MOFs, or organic fluorophores such as photochromic diarylethene derivatives, coumarin derivatives, rhodamine B-based fluorescent probes, and naphthalimide-rhodamine B derivative [19–27]. Although a variety of fluorescent probes for the recognition of Cu²⁺ ions have been reported, it is still a challenge to directly contact metal ions with fluorophore for signal transduction.

Due to their strong fluorescence emission, efficient cell permeation, large Stokes shift, and a structure that can be easily modified, coumarin is an attractive starting material [28–33]. Besides, the carbonyl group of coumarin can take part in the coordination with metal ions. The introduction of a hydrazide chain at 3-position of coumarin could both increase the intramolecular charge transfer and provide coordination sites for metal ions via carbonyl oxygen and amide nitrogen [34–36]. In order to obtain a new efficient probe, we designed a coumarin derivative for selective recognition of Cu²⁺ ions (Scheme 1). Electron donors of the N,N-diethyl group were introduced at the 7-position to modulate intramolecular charge transfer. L exhibited remarkable fluorescence quenching response to Cu²⁺ ions due to the paramagnetic nature of Cu²⁺ ions and/or photo-induced electron transfer effect. Density functional theory (DFT) calculations confirm the four-coordination configuration of Cu²⁺ ions in complex L-Cu²⁺. Moreover, this probe was successfully applied for the recognition of Cu²⁺ ions in living cells.

2. Results and Discussion

2.1. Spectral Responses of L to Cu²⁺

The specific bonding of L with Cu²⁺ was first examined by UV-vis absorption spectroscopy in CH₃CN/HEPES (3 : 2, ) buffer (). As shown in Figure 1, the free L exhibited a maximum absorption at 442 nm. With the increase of Cu²⁺ concentration in 0~7.5 equivalents, the maximum absorption intensity gradually decreased and the maximum absorption wavelength exhibited a red shift phenomenon. The former could be ascribed to the transition of the coumarin chromophore, and the latter was attributed to a metal-to-ligand charge transfer (MLCT) caused by binding L and Cu²⁺ ion. Based on the isosbestic point at 458 nm, a 1 : 1 stoichiometry for the L and Cu²⁺ ion is confirmed by the data of Job’s plot (Figure S1a) [37–40].

Besides, the absorption spectra of L were measured in the presence of other potentially relevant metal cations to investigate the selectivity of L for Cu²⁺ ions in CH₃CN/HEPES (3 : 2, ) buffer solutions. Upon addition of 10 equivalents of relevant metal ions such as Pb²⁺, K⁺, Hg²⁺, Co²⁺, Mn²⁺, Al³⁺, Ca²⁺, Cd²⁺, Fe³⁺, Ag⁺, Mg²⁺, Cr³⁺, Na⁺, Fe²⁺, and Zn²⁺, no obvious changes were observed on absorption intensity (Fig. S2). Besides, the addition of Ni²⁺ ions caused a relatively slight absorbance change. In contrast, when 10 equiv. of Cu²⁺ was added to the solution of L, a significant decrease in absorption intensity and a bathochromic shift in absorption wavelength appeared obviously, indicating the excellent selectivity of L for Cu²⁺ over other metal ions. The results could be contributed to the strong coordination ability of Cu²⁺ and its larger association constant.

To calculate the fluorescent response ability of L, the fluorescence emission spectra of L (10 μM) were also investigated in the CH₃CN/HEPES (3 : 2, ) buffer solution. L showed a maximum fluorescence emission at 487 nm upon excitation at 438 nm due to the presence of coumarin chromophore (Figure 2). With the increasing concentration of Cu²⁺ ions, the intensity of fluorescence emission at 487 nm decreased gradually. After the addition of 65 μM Cu²⁺ ions, the fluorescence emission was almost quenched. About 30-fold quenching of fluorescence emission intensity at 487 nm was observed compared with that of free L. The fluorescence quenching effect of L might be attributed to the paramagnetism of Cu²⁺ ions and/or photo-induced electron transfer process [35, 41].

Moreover, the fluorescence emission intensity at 487 nm showed a good linear relationship () against the concentration of Cu²⁺ ions in 1~65 μM (Figure 2 inset). The quenching constant value of L with Cu²⁺ ions was determined from the titration plots. The corrected Stern-Volmer fitting indicates the value of ·L. And Job’s plot and the molar ratio of the fluorescence titrations also revealed a 1 : 1 binding stoichiometry (Fig. S1b). The detection limit of L for Cu²⁺ ions was estimated about 3 μM based on LOD , where and represent the standard deviation of blank measurements and the slope between concentration of Cu²⁺ ions and fluorescence intensity, respectively [42]. Thus, the probe L shows excellent sensitivity and low detection limit for the detection of Cu²⁺.

The fluorescence changes of L in response to various relevant species in CH₃CN/HEPES (3 : 2, ) solutions were also studied. As shown in Figure 3, only Cu²⁺ ions induced a significant decrease in the fluorescence intensity, whereas very weak fluorescence variations were observed for the other metal ions such as Pb²⁺, K⁺, Hg²⁺, Co²⁺, Mn²⁺, Al³⁺, Ca²⁺, Cd²⁺, Fe³⁺, Ag⁺, Mg²⁺, Cr³⁺, Na⁺, Fe²⁺, and Zn²⁺ (10 equivalents). Furthermore, Ni²⁺ ions caused a relatively weak fluorescence quenching, which may be attributed to the low associated constant between L and Ni²⁺ ions. Such results indicated that L could be used for selective recognition of Cu²⁺ ions in the presence of other relevant species. Thus, the competing experiments were carried out to observe the selectivity for Cu²⁺ over other transition metal ions. The addition of Cu²⁺ ions still led to a fluorescence quenching of L even in the presence of competing species, suggesting that L had a good selectivity towards Cu²⁺ ions.

2.2. Density Functional Theory (DFT) Calculations of Cu²⁺ Binding L

From a mechanistic viewpoint, the unique selectivity for the Cu²⁺ ion was attributed to various factors, including the suitable coordination conformation of the Schiff-based receptor, the nitrogen (oxygen)-binding affinity character with the Cu²⁺ ion, and the deprotonation ability of L. The fluorescence quenching of L by Cu²⁺ ion could be ascribed to the paramagnetism of Cu²⁺ ions and/or photo-induced electron transfer process. Density functional theory (DFT) calculations were used to determine the possible binding mode of Cu²⁺ to L. The geometry structures of L and metal complexes L-Cu²⁺ and L-Cu²⁺ with all real frequency have been obtained using B3LYP/6–31G(d)/SDD level (the SDD basis set was used for transition metal Cu ion). The optimized geometries (and selected parameters) and electronic energies of metal complexes are shown in Figure 4. The result suggests that L-Cu²⁺ is more stable than L-Cu²⁺ by 23.1 kcal/mol. Thus, the binding model between Cu²⁺ and L should be L-Cu²⁺. Cartesian coordinates were shown in Scheme S1. The results indicated that copper ions coordinated with the ketonic oxygen atom, pyrazine nitrogen atom, and imine nitrogen (C=N) in L molecule. This coordination configuration always appeared in the other similar complexes [29, 43].

2.3. Effect of pH on the Performance of L for Cu²⁺

Because the fluorescence property of L for the detection of Cu²⁺ ions may be affected by pH value, the fluorescence responses of L (10 μM) to pH value were investigated by fluorescence spectroscopy with and without Cu²⁺, respectively. As shown in Figure 5, the fluorescence emission intensity of the free L and complex L-Cu²⁺ was almost independent of pH value in 4.0~10.0. Besides, the addition of Cu²⁺ causes a fluorescence quenching of L. Therefore, L could be applied for the recognition of Cu²⁺ over a wide pH range.

2.4. Live Cell Imaging

Live cell imaging with a fluorescence probe had important significance and application [44–46]. The recognizing ability of L toward Cu²⁺ ions was examined in living cells by using an inverted fluorescence microscope. The clear green fluorescence was observed from the intracellular region in human hepatocellular carcinoma HepG2 after incubation with L (10 μM) for 2.5 hours in 0.01 M PBS buffer solution (Figure 6(a)). However, when the HepG2 cells were further treated with 6 equivalents of Cu²⁺ for 30 minutes, the green fluorescence intensity of L was nearly quenched (Figure 6(b)). During the whole experiment process (about 3 hours), the cells were visualized without obvious side effects. These results manifested that fluorescent L could be used for the recognition of copper ions within biological samples.

(a)

(b)

(c)

(d)

3. Conclusion

In conclusion, a new fluorescence probe L based on coumarin hydrazide and 2-acetylpyrazine moiety was synthesized to detect trace Cu²⁺ ions. A 1 : 1 stoichiometry of L and Cu²⁺ ions was established based on Job’s plot analysis. Density functional theory (DFT) calculations confirm the four-coordination configuration of Cu²⁺ ions. The probe exhibits excellent stability over a wide range of pH, high selectivity, and sensitivity (detection limit of about 3 μM) for Cu²⁺ over other relevant transition metal ions. Further, cell imaging test demonstrated that probe L was also used for the recognition of Cu²⁺ ions in living cells.

Data Availability

The data used to support the findings of this study are included within the article and supplementary information file(s).

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgments

We gratefully acknowledge the financial support from the National Natural Science Foundation of China (Nos. 21801215 and 21371148), the Natural Science Foundation of Henan Province (No. 182300410309), the Key Scientific and Technological Project of Henan Province (No. 182102310648), the Key Research Project of Higher Education Institutions of Henan Province (No. 18A150044), and the National College Students’ Innovation and Entrepreneurship Training Program (No. 201610472020).

Supplementary Materials

The synthesis process of probe L and specific test conditions for spectra and cell imaging reported in this article have been deposited in supplementary material. Figure S1: Job’s plot fitting of probe L with Cu²⁺. Figure S2: UV-vis absorption spectra of probe L upon addition of various metal ions. Scheme S1: the Cartesian coordinate data of complex L-Cu²⁺ and L-Cu²⁺. Figure S3, S4, and S5: the NMR and MS spectra of probe L. (Supplementary Materials)

References

H. Huang, R. Chen, J. Ma et al., “Graphitic carbon nitride solid nanofilms for selective and recyclable sensing of Cu²⁺ and Ag⁺ in water and serum,” Chemical Communications, vol. 50, pp. 15415–15418, 2014.
View at: Publisher Site | Google Scholar
A. Rai, A. K. Singh, K. Tripathi et al., “A quick and selective rhodamine based “smart probe” for “signal-on” optical detection of Cu²⁺ and Al³⁺ in water, cell imaging, computational studies and solid state analysis,” Sensors and Actuators B: Chemical, vol. 266, pp. 95–105, 2018.
View at: Publisher Site | Google Scholar
H. Kang, C. Fan, H. Xu, G. Liu, and S. Pu, “A highly selective fluorescence switch for Cu²⁺ and Fe³⁺ based on a new diarylethene with a triazole-linked rhodamine 6G unit,” Tetrahedron, vol. 74, no. 33, pp. 4390–4399, 2018.
View at: Publisher Site | Google Scholar
M. Yu, M. Shi, Z. Chen et al., “Highly sensitive and fast responsive fluorescence turn-on chemodosimeter for Cu²⁺ and its application in live cell imaging,” Chemistry - A European Journal, vol. 14, no. 23, pp. 6892–6900, 2008.
View at: Publisher Site | Google Scholar
Z. Liu, W. He, M. Pei, and G. Zhang, “A fluorescent sensor with a detection level of pM for Cd²⁺ and nM for Cu²⁺ based on different mechanisms,” Chemical Communications, vol. 51, pp. 14227–14230, 2015.
View at: Publisher Site | Google Scholar
R. Uauy, M. Olivares, and M. Gonzalez, “Essentiality of copper in humans,” The American Journal of Clinical Nutrition, vol. 67, no. 5, pp. 952S–959S, 1998.
View at: Publisher Site | Google Scholar
D. Maity, D. Karthigeyan, T. K. Kundu, and T. Govindaraju, “FRET-based rational strategy for ratiometric detection of Cu²⁺ and live cell imaging,” Sensors and Actuators B: Chemical, vol. 176, pp. 831–837, 2013.
View at: Publisher Site | Google Scholar
G. J. Brewer, “Copper excess, zinc deficiency, and cognition loss in Alzheimer’s disease,” BioFactors, vol. 38, pp. 107–113, 2012.
View at: Publisher Site | Google Scholar
L. Wang, X. Gong, Q. Bing, and G. Wang, “A new oxadiazole-based dual-mode chemosensor: colorimetric detection of Co²⁺ and fluorometric detection of Cu²⁺ with high selectivity and sensitivity,” Microchemical Journal, vol. 142, pp. 279–287, 2018.
View at: Publisher Site | Google Scholar
C. Li, Z. Yang, and S. Li, “1,8-Naphthalimide derived dual-functioning fluorescent probe for “turn-off” and ratiometric detection of Cu²⁺ based on two distinct mechanisms in different concentration ranges,” Journal of Luminescence, vol. 198, pp. 327–336, 2018.
View at: Publisher Site | Google Scholar
Y. S. Yang, S. S. Ma, Y. P. Zhang, J. X. Ru, X. Y. Liu, and H. C. Guo, “A novel biphenyl-derived salicylhydrazone Schiff base fluorescent probes for identification of Cu²⁺ and application in living cells,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 199, pp. 202–208, 2018.
View at: Publisher Site | Google Scholar
Y. Jiao, L. Zhou, H. He et al., “A novel rhodamine B-based “off-on” fluorescent sensor for selective recognition of copper (II) ions,” Talanta, vol. 184, pp. 143–148, 2018.
View at: Publisher Site | Google Scholar
M. Pannipara, A. G. Al-Sehemi, A. Irfan, M. Assiri, A. Kalam, and Y. S. Al-Ammari, “AIE active multianalyte fluorescent probe for the detection of Cu²⁺, Ni²⁺ and Hg²⁺ ions,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 201, pp. 54–60, 2018.
View at: Publisher Site | Google Scholar
F. Nouri Moghadam, M. Amirnasr, S. Meghdadi, K. Eskandari, A. Buchholz, and W. Plass, “A new fluorene derived Schiff-base as a dual selective fluorescent probe for Cu²⁺ and CN⁻,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 207, pp. 6–15, 2019.
View at: Publisher Site | Google Scholar
Q. Zhao, Q. Wu, P. Ma et al., “Selective and sensitive fluorescence detection method for pig IgG based on competitive immunosensing strategy and magnetic bioseparation,” Talanta, vol. 195, pp. 103–108, 2019.
View at: Publisher Site | Google Scholar
X. Tang, Z. Zhu, R. Liu et al., “A novel OFF-ON-OFF fluorescence probe based on coumarin for Al³⁺ and F⁻ detection and bioimaging in living cells,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 211, pp. 299–305, 2019.
View at: Publisher Site | Google Scholar
Z. Wang, Y. Zhang, J. Song et al., “A highly specific and sensitive turn-on fluorescence probe for hypochlorite detection based on anthracene fluorophore and its bioimaging applications,” Dyes and Pigments, vol. 161, pp. 172–181, 2019.
View at: Publisher Site | Google Scholar
Q. H. You, P. S. Chan, W. H. Chan et al., “A quinolinyl antipyrine based fluorescence sensor for Zn²⁺ and its application in bioimaging,” RSC Advances, vol. 2, pp. 11078–11083, 2012.
View at: Publisher Site | Google Scholar
A. Zhang, C. Fan, W. Sun et al., “Cu²⁺ and Fe²⁺ sensor based on CdTe QD@ZIF-8 composites,” Journal of Nanoscience and Nanotechnology, vol. 19, pp. 8088–8094, 2019.
View at: Publisher Site | Google Scholar
Q. Zhang, P. Yang, J. Shen, and J. Yu, “Graphene-amplified photoelectric response of CdS nanoparticles for Cu²⁺ sensor,” Journal of Nanoscience and Nanotechnology, vol. 19, pp. 7871–7878, 2019.
View at: Publisher Site | Google Scholar
Y. Fu, C. Fan, G. Liu, and S. Pu, “A colorimetric and fluorescent sensor for Cu²⁺ and F⁻ based on a diarylethene with a 1,8-naphthalimide Schiff base unit,” Sensors and Actuators B: Chemical, vol. 239, pp. 295–303, 2017.
View at: Publisher Site | Google Scholar
C. Zhang, C. Fan, S. Pu, and G. Liu, “A highly selective chemosensor for Cu²⁺ based on a diarylethene linking an aminoquinoline unit,” Chinese Journal of Chemistry, vol. 33, pp. 1310–1316, 2015.
View at: Publisher Site | Google Scholar
H. Jia, S. Pu, C. Fan, G. Liu, and C. Zheng, “A highly selective ratiometric fluorescent Cu₂₊ and HSO₄^- probe based on a new photochromic diarylethene with a 6-aryl[1,2-c]quinazoline unit,” Dyes and Pigments, vol. 121, pp. 211–220, 2015.
View at: Publisher Site | Google Scholar
Z. Liu, L. Liu, J. Li et al., “A new coumarin-based fluorescent probe for selective recognition of Cu²⁺ and S²⁻ in aqueous solution and living cells,” Tetrahedron, vol. 75, pp. 3951–3957, 2019.
View at: Publisher Site | Google Scholar
J. Mao, J. Cheng, X. Wang, S. Wang, N. Cheng, and J. Wang, “A rhodamine-based fluorescent probe for Cu(II) determination in aqueous solution,” Luminescence, vol. 30, no. 2, pp. 221–227, 2015.
View at: Publisher Site | Google Scholar
K. Ghosh, S. Rathi, P. Gupta, P. Vashisth, and V. Pruthi, “A simple fluorescent probe derived from naphthylamine for selective detection of Hg^II, Fe^II and Fe^III ions in mixed aqueous media: applications in living cells and logic gates,” European Journal of Inorganic Chemistry, vol. 2015, no. 2, pp. 311–317, 2015.
View at: Publisher Site | Google Scholar
S. Wang, H. Ding, Y. Wang et al., “An “off–on–off” sensor for sequential detection of Cu²⁺ and hydrogen sulfide based on a naphthalimide–rhodamine B derivative and its application in dual-channel cell imaging,” RSC Advances, vol. 8, no. 58, pp. 33121–33128, 2018.
View at: Publisher Site | Google Scholar
A. Helal, M. H. Or Rashid, C. H. Choi, and H. S. Kim, “Chromogenic and fluorogenic sensing of Cu²⁺ based on coumarin,” Tetrahedron, vol. 67, no. 15, pp. 2794–2802, 2011.
View at: Publisher Site | Google Scholar
A. Bekhradnia, E. Domehri, and M. Khosravi, “Novel coumarin-based fluorescent probe for selective detection of Cu(II),” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 152, pp. 18–22, 2016.
View at: Publisher Site | Google Scholar
Z. Zhou, N. Li, and A. Tong, “A new coumarin-based fluorescence turn-on chemodosimeter for Cu²⁺ in water,” Analytica Chimica Acta, vol. 702, pp. 81–86, 2011.
View at: Publisher Site | Google Scholar
S. R. Liu, C. Y. Chang, and S. P. Wu, “A fluorescence turn-on probe for cysteine and homocysteine based on thiol-triggered benzothiazolidine ring formation,” Analytica Chimica Acta, vol. 849, pp. 64–69, 2014.
View at: Publisher Site | Google Scholar
J. Li, C. F. Zhang, S. H. Yang, W. C. Yang, and G. F. Yang, Analytical Chemistry, vol. 86, no. 6, pp. 3037–3042, 2014.
View at: Publisher Site
S. B. Warrier and P. S. Kharkar, “A coumarin based chemosensor for selective determination of Cu (II) ions based on fluorescence quenching,” Journal of Luminescence, vol. 199, pp. 407–415, 2018.
View at: Publisher Site | Google Scholar
G. He, J. Li, Z. Wang et al., “Synthesis of a fluorogenic probe for thiols based on a coumarin schiff base copper complex and its use for the detection of glutathione,” Tetrahedron, vol. 73, no. 3, pp. 272–277, 2017.
View at: Publisher Site | Google Scholar
Y. Wang, Q. Meng, Q. Han et al., “Selective and sensitive detection of cysteine in water and live cells using a coumarin–Cu²⁺ fluorescent ensemble,” New Journal of Chemistry, vol. 42, no. 19, pp. 15839–15846, 2018.
View at: Publisher Site | Google Scholar
G. He, J. Li, L. Yang et al., “The synthesis of a coumarin carbohydrazide dinuclear copper complex based fluorescence probe and its detection of thiols,” PLoS One, vol. 11, no. 2, article e0148026, 2016.
View at: Publisher Site | Google Scholar
N. Behera and V. Manivannan, “Selective recognition of Zn²⁺ion using 2,4-bis(2-pyridyl)-5-(4-pyridyl)imidazole: spectra and molecular structure,” ChemistrySelect, vol. 1, no. 13, pp. 4016–4023, 2016.
View at: Publisher Site | Google Scholar
A. A. Dar, S. Hussain, D. Dutta, P. K. Iyer, and A. T. Khan, “One-pot synthesis of functionalized 4-hydroxy-3-thiomethylcoumarins: detection and discrimination of Co²⁺ and Ni²⁺ ions,” RSC Advances, vol. 5, no. 71, pp. 57749–57756, 2015.
View at: Publisher Site | Google Scholar
A. Karmakar and B. Singh, “Spectroscopic analysis and theoretical investigation of hydrogen bonding interaction of quercetin with different acceptor molecules,” Journal of Molecular Structure, vol. 1180, pp. 698–707, 2019.
View at: Publisher Site | Google Scholar
Y. Yang, B. Li, L. Zhang, and Y. Guan, “Triphenylamine based benzimidazole and benzothiazole: synthesis and applications in fluorescent chemosensors and laser dyes,” Journal of Luminescence, vol. 145, pp. 895–898, 2014.
View at: Publisher Site | Google Scholar
X. Tang, Z. Zhu, Y. Wang et al., “A dual site controlled probe for fluorescent monitoring of intracellular pH and colorimetric monitoring of Cu²⁺,” Sensors and Actuators B: Chemical, vol. 270, pp. 35–44, 2018.
View at: Publisher Site | Google Scholar
J. Xu, J. Li, C. Liu et al., “Design and synthesis of a dinuclear copper(II) probe for selective fluorescence sensing of pyrophosphate,” Journal of Sensors, vol. 2019, Article ID 5349124, 8 pages, 2019.
View at: Publisher Site | Google Scholar
K. Karaoglu, F. Yilmaz, and E. Mentese, “A new fluorescent “turn-off” coumarin-based chemosensor: synthesis, structure and Cu-selective fluorescent sensing in water samples,” Journal of Fluorescence, vol. 27, no. 4, pp. 1293–1298, 2017.
View at: Publisher Site | Google Scholar
Q. Qiao, W. Liu, J. Chen et al., “A naphthalimide-derived fluorogenic probe for SNAP-tag with a fast record labeling rate,” Dyes and Pigments, vol. 147, pp. 327–333, 2017.
View at: Publisher Site | Google Scholar
M. Shimi, V. Sankar, M. K. A. Rahim et al., “Novel glycoconjugated squaraine dyes for selective optical imaging of cancer cells,” Chemical Communications, vol. 53, pp. 5433–5436, 2017.
View at: Publisher Site | Google Scholar
A. Wieczorek, P. Werther, J. Euchner, and R. Wombacher, “Green- to far-red-emitting fluorogenic tetrazine probes – synthetic access and no-wash protein imaging inside living cells,” Chemical Science, vol. 8, no. 2, pp. 1506–1510, 2017.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2019 Guangjie He et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

1373

Downloads

1043

Citations