Curcumin-Cu(II) Ensemble-Based Fluorescence "turn-On" Mode Sensing the Plant Defensive Hormone Salicylic Acid in Situ and in Vivo

Article abstract of DOI:10.1021/acs.jafc.0c01283

Salicylic acid (SA), a crucial, plant-derived signal molecule, is capable of launching global transcriptional reprogramming to assist plants in obtaining the systemic acquired resistance (SAR) mechanism. Thus, the accurate detection of SA will not only si

Full text of DOI:10.1021/acs.jafc.0c01283

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Article
Curcumin−Cu(II) Ensemble-Based Fluorescence “Turn-On” Mode
Sensing the Plant Defensive Hormone Salicylic Acid In Situ and In
Vivo
Chong Chen,# Lin-Lin Yang,# A-Ling Tang, Pei-Yi Wang,* Rong Dong, Zhi-Bing Wu, Zhong Li,
and Song Yang*
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ABSTRACT: Salicylic acid (SA), a crucial, plant-derived signal molecule, is capable of launching global transcriptional
reprogramming to assist plants in obtaining the systemic acquired resistance (SAR) mechanism. Thus, the accurate detection of SA
will not only significantly contribute to the understanding of the plant SAR but also contribute to crop protection and to the security
of the agricultural production and food supply. However, detection of SA using fluorescent probes is a great challenge for scientists,
because SA analogues can significantly interfere with the detection results. Herein, we first reported using a simple, natural
curcumin−Cu2+ ensemble to selectively and sensitively monitor SA in situ and in vivo, directed by a fluorescence “turn-on” mode. A
binary combination curcumin−Cu2+ was first fabricated with a fluorescence “turn-off” pattern caused by the paramagnetic nature of
Cu2+. Subsequently, a fluorescence “turn-on” response was performed for detecting SA accompanied by the formation of the ternary
complex curcumin−Cu2+−SA due to the high affinity of SA toward Cu2+, which reduced the fluorescent impact caused by the
paramagnetism of Cu2+. Further study revealed that the rationally designed hybrid probe could monitor SA in living cell lines. We
anticipate that this finding can inspire the discovery of a high-performance SA probe.
KEYWORDS: curcumin−Cu2+ ensemble, selective detection, salicylic acid, fluorescence “turn-on”
detect the biological signaling molecule SA in situ and in vivo is
in great demand.
1. INTRODUCTION
Salicylic acid (SA) is one of the significant biogenic immune
signals and regulators existing widely in the plant kingdom.1−3
It is capable of launching global transcriptional reprogramming
to motivate plants to systemically express a type of resistant,
pathogenesis-related species, which is dedicated to resist-
ance.4,5 Through this process, plants can be conferred with
persistent protection abilities against incompatible pathogens,
which is called systemic acquired resistance (SAR).6−8
Generally, SA is generated from the infected tissue and
accumulates in the systemic, uninfected tissue after an invasion
of various offensive pathogens, including viruses, fungi,
bacteria, and oomycetes.9,10 Also, many studies have
demonstrated that SA-induced signal pathways can be
dramatically regulated by the amount of endogenic SA.10,11
Thereby, the accurate detection of SA can elucidate the SA-
induced SAR mechanism, which will significantly help the
staple crops obtain defense mechanisms against various
pathogen infections. Simultaneously, this action may also
initiate the discovery of novel immune activators that offer a
new approach that can reduce the use of traditionally harmful
pesticides, whose use concerns people who handle crop
protection. However, SA analogues, such as methyl salicylate,
2-methoxybenzoic acid, m-hydroxybenzoic acid, o-toluic acid,
benzoic acid, p-hydroxybenzoic acid, and catechol, can
significantly interfere with the detection results, which makes
the detection of SA a big challenge.12−15 Therefore, the
development of simple, reliable, and accurate techniques to
In the past decades, various detection strategies have been
developed to monitor SA, for instance, HPLC,16−19 gas
chromatography,20,21 colorimetry,22 spectrofluorimetry,23−25
surface plasma resonance technology,26 and electrochemical
analysis.27,28 However, these methods had drawbacks,
including expensive instruments, low selectivity, complicated
sample preparation procedures, and time-consuming sample
testing processes. As far as we know, using the above-
mentioned methods cannot achieve the goal of real-time
detection of SA in living organisms.
Fluorescence probes offer encouraging opportunities and
promising applications in detecting SA in terms of their
privileged characteristics, including good sensibility and
selectivity,29,30 fast response,31−33 low detection limits,34,35
and real-time monitoring.36,37 In particular, metal-based
fluorescent ensembles have been extensively studied and
developed for monitoring signal species on account of their
convenient synthetic procedures, improved water solubilities,
multifunctional testing purposes, and perceptible detection
Received: February 24, 2020
Revised: April 7, 2020
Accepted: April 10, 2020
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Figure 1. (a) Proposed mechanisms for detecting SA via the 1−Cu2+ ensemble. (b) Structures for SA and SA analogues.
mechanism.38 Curcumin (1,7-bis(4-hydroxy-3-methoxyphen-
yl)-1,6-heptadiene-3,5-dione, 1), found in the rhizomes of
Curcuma longa Linn., not only is an important, bioactive,
naturally occurring product but also is recognized as a
promising fluorescent probe that possesses rich photophysical
and photochemical properties due to the unsaturated β-
diketone moiety in which it can induce a keto−enol
tautomerism. Numerous studies revealed that the pattern of
the 1,3-diketones scaffold can incorporate metals to form
complexes which have already exerted reasonable applications
in photochemistry and photobiology.39−41 Herein, curcumin−
metal complexes were rationally fabricated to monitor SA in
situ and in vivo. As far as we know, no report was performed via
exploiting a curcumin−metal-based fluorescent sensor for
selectively and sensitively sensing SA with a naked-eye
detection feature. Moreover, a plausible detection mechanism
was recommended (Figure 1a): Preliminarily, Cu2+ was
selected and employed to bind the β-diketone part of curcumin
to form the 1−Cu2+ ensemble, which resulted in the
fluorescent “turn-off” of curcumin because of the paramagnetic
nature of Cu2+. SA was added into the system; subsequently,
this led to the formation of the ternary complex 1−Cu2+−SA,
which was accompanied by the fluorescence “turn-on” due to
SA having a high affinity toward Cu2+.42−44 Thus, the
fluorescent impact caused by the paramagnetism of Cu2+ was
reduced. As indicated, the fluorescence of 1 was observed to be
quenched immediately after adding Cu2+, which, subsequently,
was recovered along with the addition of SA, indicating that a
colorimetric sensor for naked-eye monitoring SA should be
discovered.
and the additionally purified curcumin product was obtained by
recrystallization in ethanol.
2.3. Procedures for Fluorescence Spectral Studies. The
initial solution of all of the probes and metal ions was configured as
1.0 mM in DMF/H2O (7:3, v/v) and deionized water, respectively.
The stock solution (1.0 mM) of the 1−Cu2+ ensemble was obtained
by blending probe 1 with the same amount of Cu2+ in DMF/H2O
(7:3, v/v). The stock solution (1.0 mM) of other ensembles, such as
2−Cu2+, 3−Cu2+, and 4−Cu2+, followed the above procedure. The
stock solutions (1.0 mM) of SA and its analogues were prepared in
DMF/H2O (7:3). Sample preparation for the fluorescence testing is
described in the following: A certain amount of detected objects was
added to a volumetric bottle containing 0.1 mL of probes (1.0 mM).
Then, the mixed solution was fixed to 10 mL with the same solvent
before testing.
2.4. Synthetic Protocols for Compounds 2, 3, and 4.
2.4.1. Synthesis of Compound 2. Curcumin (1, 200 mg, 0.54
mmol) and K2CO3 (38 mg, 0.27 mmol) were dissolved in 5 mL of dry
DMF, and the mixture was cooled with an ice bath. Then,
iodomethane (39 mg, 0.27 mmol) in 1 mL of dry DMF was added
dropwise, and the obtained solution was magnetically stirred for about
30 min. After that, 40 mL of EtOAc was added, and the organic layer
was washed by a saturated ammonium chloride solution. A crude
product was provided by vacuum distillation. Finally, the pure
compound 2 was afforded by using a common column chromatog-
raphy with mixed petroleum ether and EtOAc solvents. Yield 34.7%.
1H NMR (500 MHz, CDCl3, δ): 7.58 (dd, 2H, J = 7.5 Hz, −CH),
7.12 (dd, 2H, J = 10.0 Hz, Ar−H), 7.07 (s, 2H, Ar−H), 6.89 (dd, 2H,
J = 10.0 Hz, CH−), 6.47 (dd, 2H, J = 10.0 Hz, Ar−H), 5.91 (s, 1H,
−CH), 5.80 (s, 1H, −OH), 3.93 (s, 6H, −OCH3), 3.92 (s, 3H,
−OCH3). 13C NMR (125 MHz, CDCl3, δ): 183.5, 183.2, 151.1,
149.3, 147.9, 146.9, 140.7, 140.5, 128.1, 127.7, 123.0, 122.7, 122.1,
121.8, 114.9, 111.2, 109.8, 109.7, 101.3, 56.1, 56.0, 55.9. HRMS
(ESI): [M − H]− calcd for C22H21O6, 381.1344; found, 381.1342.
2.4.2. Synthesis of Compound 3. The synthesis of 3 followed the
protocol of compound 2. The difference is that the dosages of K2CO3
and iodomethane were changed to 150 mg (1.08 mmol) and 153 mg
(1.08 mmol), respectively. Yield 75.3%. 1H NMR (500 MHz, CDCl3,
δ): 7.69 (d, 2H, J = 15.0 Hz, −CH), 7.19 (dd, 2H, J = 10.0 Hz,
Ar−H), 7.10 (s, 2H, Ar−H,), 6.98 (d, 2H, J = 15.0 Hz, CH−), 6.89
(dd, 2H, J = 10.0 Hz, Ar−H), 6.51 (s, 1H, −CH), 3.95 (s, 12H,
−OCH3). 13C NMR (125 MHz, CDCl3, δ): 182.6, 151.0, 149.3,
141.4, 128.6, 122.6, 118.8, 111.2, 110.2, 105.8, 56.1, 56.0. HRMS
(ESI): [M − H]− calcd for C23H23O6, 395.1500; found, 395.1504.
2.4.3. Synthesis of Compound 4. The synthetic protocol followed
the literature procedure reported by Sharma et al.45 Boron oxide (0.49
g, 7.0 mmol) and acetylacetone were dissolved in ethyl acetate (10
mL) and stirred for 30 min in a 45 °C oil bath. Then, 3,4-
dihydroxybenzaldehyde (2.76 g, 20.0 mmol) and tributyl borate (0.46
g, 20.0 mmol) were added, and the obtained solution was
magnetically stirred for about 30 min. Later, butylamine (1.10 g,
15.0 mmol), in 10 mL of ethyl acetate, was added dropise. The
obtained mixture was stirred for anothor 24 h. Subsequently, 10 mL
of 10% hydrochloric acid was added and incubated at 60 °C for 1 h.
2. MATERIALS AND METHODS
2.1. Instruments. NMR data were recorded by JEOL-ECX-500
devices (tetramethylsilane was the internal standard, deuterated
dimethyl sulfoxide (DMSO-d6) or chloroform (CDCl3) was the
solvent). High-resolution mass spectra were recorded by Agilent LC/
MSD Trap VL and Thermo Scientific Q Exactive mass spectrometers.
Fluorescence spectra were measured by a Fluoromax-4 (Horiba
LTD). Cell imaging was carried out by an Olympus FVMPE-RS
multiphoton confocal laser scanning microscope.
2.2. Chemicals. The used chemical reagents, including N,N-
dimethylformamide (DMF), ethyl acetate (EtOAc), petroleum ether,
and dichloromethane, were acquired from reliable suppliers without
additional treatment. Deionized water was exploited in all of the
experiments. All of the metallic compounds were composed of nitrate
ions. Potassium carbonate (K2CO3), ammonium chloride, iodo-
methane, boron oxide, acetylacetone, 3,4-dihydroxybenzaldehyde,
tributyl borate, and butylamine were purchased from Aladdin Reagent
(Shanghai) Co., Ltd. Curcumin (purity >98%) was purchased from
Energy Chemical of Saen Chemical Technology (Shanghai) Co., Ltd.,
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Finally, the organic layer was obtained by simple separation and was
evaporated under reduced pressure to give the crude product. The
pure compound 4 was provided by using column chromatography
with the mixed eluting agents of dichloromethane and EtOAc. Yield
1.3%. 1H NMR (500 MHz, DMSO-d6, δ): 9.60 (s, 2H), 9.15 (s, 2H),
7.46 (d, J = 15.0 Hz, 2H), 7.01 (d, J = 10.0 Hz, 2H), 6.78 (d, J = 10.0
Hz, 2H), 6.57 (d, J = 15.0 Hz, 2H), 6.07 (s, 2H). 13C NMR (125
MHz, DMSO-d6, δ): 183.1, 148.4, 145.6, 140.7, 126.3, 121.5, 120.6,
115.8, 114.7, 100.9. HRMS (ESI): [M − H]− calcd for C19H15O6,
339.0874; found, 339.0874.
result from HRMS, affording the peak at m/z 430.0473 that
corresponds to [1−Cu2+] (Figure S4). Further study revealed
that the related detection limit of probe 1 toward Cu2+ was 15
nM. Based on the above results, the curcumin−Cu2+ ensemble
was successfully constructed, in which curcumin exerted a high
specificity and sensitivity toward Cu2+ with a fluorescent “turn-
off” mode.
3.2. Selective Detection of SA by the Curcumin−Cu2+
Ensemble. The prepared 1−Cu2+ was employed to examine
the selectivity for SA analogues by using fluorescence
microscopy and UV light. Before the detection of SA, the
solvent was first screened. As shown in Figure S5a, the 1−Cu2+
ensemble displayed the highest response to SA in DMF
solvent, providing a 26-fold enhancement in the fluorescence
intensity (Figure S5b). To extend its potential applications, the
solvent water was introduced into the system. However, along
with the increase in the ratio of water, the fluorescence
intensity of 1−Cu2+−SA was significantly decreased (Figure
S5c). Because of this, the solution of DMF/H2O with the
volume ratio 7:3 afforded the better response (20.6-fold
enhancement) for detecting SA (Figure S5d). Based on the
above results, the detection of SA by the 1−Cu2+ ensemble was
performed in the DMF/H2O (7:3, v/v) solution. Clearly, a
remarkable, induced fluorescence “turn-on” pattern (Figure
3a) was observed only upon the addition of SA within 10 s
(Figure S6). This occurrence simultaneously promoted the
variation of fluorescence quantum yields from 0.002 (1−Cu2+)
to 0.025 (1−Cu2+−SA). The presented green fluorescence
under the UV light (Figure 3b) further confirmed that the 1−
Cu2+ binary complex possessed the specific selectivity and
sensitivity in response to SA compared to those of other SA
analogues, including 4-hydroxybenzoic acid (4-OHBA), 3-
hydroxybenzoic acid (3-OHBA), benzoic acid (BA), 2-
methoxybenzoic acid (2-MeOBA), 2-methylbenzoic acid (2-
MeBA), methyl salicylate (MeSate), catechol, phenol,
acetylsalicylic acid (AcetylSA), anthranilic acid, and 5-amino-
salicylic acid (Figure S7). Moreover, the 1−Cu2+ ensemble
could selectively distinguish SA in MES buffer (4-morpholi-
neethanesulfonic acid; 20 mM; DMF/MES buffer = 7/3 or
5:5, v/v; pH 7.2) from pyrophosphate and adenosine
triphosphate (Figure S8). Additionally, the 1−Cu2+ ensemble
could monitor SA in a wide pH range in DMF/MES buffer;
however, the better detection system was in a neutral or weakly
basic solution (Figure S9). Competition experiments were
further performed to evaluate the anti-interference perform-
ance of the 1−Cu2+ ensemble toward SA via the addition of SA
into the premixed solution containing 1−Cu2+ with other SA
analogues. Dramatically, the significantly increased fluorescent
intensity could be achieved due to the latter addition of SA
(Figure 3c), further confirming that the 1−Cu2+ ensemble can
be exploited as a highly selective sensor for monitoring SA with
an attractive anti-interference feature. The titration experiment
of the 1−Cu2+ ensemble toward SA demonstrated that the
fluorescent intensity at 530 nm was gradually elevated with
increments of SA and was afforded the binding constant of
5.22 × 104 M−1 (Figure S10a−c). Therefore, an appreciable
linear detection range was obtained from 10 to 150 μM
(Figure S10d). Further study revealed that the related
detection limit of the 1−Cu2+ ensemble toward SA was 3
μM. Given the above results, the rationally designed 1−Cu2+
complex can be considered as a promising colorimetric probe
for sensing SA with the appreciable feature.
3. RESULTS AND DISCUSSION
3.1. Preparation of Nonfluorescent Curcumin−Cu2+
Ensemble. In order to prepare the fluorescent “turn-off”
curcumin−metal ensemble, various metal ions were screened
by using fluorescence spectroscopy. As illustrated in Figure 2a,
Figure 2. (a) Fluorescent spectra of 1 (10 μM) toward 1 equiv of
various cations. (b) Competition experiments for adding Cu2+ (red
bars, 1 equiv, 3−18) into the premixed solution consisting of probe 1
(10 μM) and various interfering metal ions (blank bars, 2 equiv, 3−
18): (1) probe 1 itself, (2) probe 1 + Cu2+, (3) Co2+, (4) Ni2+, (5)
Pb2+, (6) Hg2+, (7) Zn2+, (8) Cd2+, (9) Ca2+, (10) Ba2+, (11) Mg2+,
(12) Fe3+, (13) Cr3+, (14) Al3+, (15) Li+, (16) K+, (17) Na+, and (18)
Ag+. Conditions: DMF/H2O (7:3, v/v), λex/λem = 433/530 nm, slits =
3 nm/3 nm.
Cu2+ can not only quench the fluorescence of 1 within 10 s
(Figure S1) but also be selectively distinguished in comparison
to other metal ions, indicating that the natural, fluorescent
curcumin can detect Cu2+ with a high specificity. Competition
experiments were further conducted to explore the selectivity
of 1 toward Cu2+ by testing the variations of the fluorescent
intensity before and after the addition of Cu2+ into the
premixed ingredients that contained 1 with other metal ions.
The fact that the fluorescence can be significantly quenched
only by the later introduction of Cu2+ further supports that
excellent anti-interference performance is achieved by probe 1
in the detection of Cu2+ (Figure 2b). The Job’s plot
experiment revealed that a 1:1 stoichiometry was provided
for probe 1 and Cu2+ with the binding constant of 5.54 × 104
M−1 (Figures S2 and S3), which was in accordance with the
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Figure 3. (a) Fluorescent spectra of 1−Cu2+ (10 μM) toward 20 equiv of salicylic acid or its analogues in DMF/H2O (7:3, v/v) (λex/λem = 433
nm/530 nm, slits = 3 nm/3 nm). (b) Photographs of 1 (10 μM), 1−Cu2+ ensemble, and 1−Cu2+ ensemble after the addition of 20 equiv of SA and
its analogues: (1) 1, (2) 1 + Cu2+, (3) 1 + Cu2+ + SA, (4) 1 + Cu2+ + BA, (5) 1 + Cu2+ + 3-OHBA, (6) 1 + Cu2+ + 4-OHBA, (7) 1 + Cu2+ + 2-
MeOBA, (8) 1 + Cu2+ + 2-MeBA, (9) 1 + Cu2+ + MeSate, (10) 1 + Cu2+ + Catechol, (11) 1 + Cu2+ + Phenol, and (12) 1 + Cu2+ + AcetylSA in
DMF/H2O (7:3, v/v) under a UV lamp with an excitation of 365 nm. (c) Competition experiments for adding SA (red bars, 20 equiv, 3−11) into
the premixed solution consisting of 1−Cu2+ (10 μM) and various interfering SA analogues (blank bars, 20 equiv, 3−11): (1) 1−Cu2+, (2) SA, (3)
2-CH3BA, (4) catechol, (5) BA, (6) phenol, (7) 2-MeOBA, (8) 3-OHBA, (9) 4-OHBA, (10) AcetylSA, and (11) MeSate.
Figure 4. (a) Synthesis of probes 2 and 3. (b) Synthesis of probe 4.
3.3. Preparation of Curcumin Derivatives 2, 3, and 4
for Detecting SA by Their Related Cu2+ Ensembles. In
order to explore and search for better-performance probes for
monitoring SA, curcumin derivatives 2 and 3 were first
designed and synthesized by the partial or complete
methylation reactions on probe 1 (Figure 4 and Figures
S11−S16). Undesirably, the two probes exerted a weaker
selectivity for SA detection (Figures S17 and S18), indicating
that the free hydroxyl groups on the benzene rings may serve
as one of the critical roles in specifically distinguishing SA.
Therefore, compound 4, bearing four hydroxyl groups, was
subsequently prepared (Figures S19−S21). Although probe 4
demonstrated a better selective detection capability toward SA
than those of compounds 2 and 3, it only resulted in an
approximately 6-fold fluorescence enhancement at 550 nm
(Figure S22), further confirming that the natural framework
curcumin can be regarded as a considerable colorimetric probe
for detecting SA with the privileged performance.
3.4. Possible Detection Mechanism Investigations.
The 1H NMR titration experiments were conducted to
understand the possible mechanism and the natural
interactions of 1−Cu2+ and 1−Cu2+−SA. Upon addition of
1.0 equiv of Cu2+ to 1 (Figure 5a), the protons located at the
benzene ring and olefin of 1 shifted upfield and became
broadened due to the paramagnetic nature and shielding effect
of Cu2+ (Figure 5b). Followed by the addition of 1.0 equiv of
SA into the system, all of the protons belonging to SA shifted
upfield due to the formation of new coordination bonds
between copper ions and SA, suggesting a ternary complex 1−
Cu2+−SA might be fabricated (Figure 5c,d), which was
confirmed by the result from the HRMS spectrum, which
provided the peak at m/z 566.4279, corresponding to the
ternary complex [1−Cu2+−SA] (Figure S23). Further study
revealed that there were negligible interactions between probe
1 and SA (Figures S24 and S25). Another way titration
experiments were carried out was by the addition of probe 1
into the premixed solution of SA and Cu2+ (Figure 5e,f). A
D
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3.5. Fluorescence Imaging. Because probe 1−Cu2+
displays promising applications in monitoring SA, NRK-52E
cells were used for SA imaging. Briefly, NRK-52E cells were
incubated with 30 μM probe 1 for 1 h at 37 °C and then
washed with 0.01 M PBS buffer (pH 7.4) thrice before
imaging. A considerable fluorescence was presented for tested
cells in Figure 6a, indicating that probe 1 had a good ability to
penetrate the cell membrane. Cells were then incubated with
culture medium containing 60 μM Cu2+ for another 2 h at 37
°C and then washed with 0.01 M PBS buffer thrice.
Subsequently, SA-free culture medium was added into cells
treated with the 1−Cu2+ ensemble; no fluorescent cells were
observed (Figure 6b), suggesting neither the components from
the culture medium nor the ingredients inside the cell could
recover the fluorescence. Finally, a strong emerging fluo-
rescence response with different levels from the intracellular
area was observed after adding different concentrations of SA
for 2.5 h at 37 °C (Figure 6c,d). These results suggested that
the 1−Cu2+ ensemble could be used for detecting SA in living
cell lines.
In conclusion, we have developed a simple, rapid, and
reliable approach for detecting SA in vitro and in vivo by
utilizing the natural hybrid combination of curcumin and Cu2+.
During the fabrication of the curcumin−Cu2+ ensemble, we
found that Cu2+ could be selectively recognized by curcumin
with the detection limit of 15 nM directed by a fluorescence
“turn-off” mode. By introducing SA into the prepared
curcumin−Cu2+ ensemble, the fluorescence “turn-on” pattern
Figure 5. Partial 1H NMR titration experiments of SA toward 1−Cu2+
and of 1 toward SA−Cu2+ in CD3OD: (a) 1, (b) 1 + 1.0 equiv of
Cu2+, (c) 1−Cu2+ + 1.0 equiv of SA, (d) SA, (e) SA + 1.0 equiv of
Cu2+, and (f) SA−Cu2+ + 1.0 equiv of 1.
phenomenon was observed that the protons of SA shifted low
field, which might be explained by the decreased shielding
effect caused by the newly involved coordination bonding
forces between probe 1 and Cu2+, suggesting that Cu2+, as a
mediate bridge, plays the significant role in the detection of SA.
The above results validated our proposed mechanism (Figure
1a).
Figure 6. Confocal fluorescence microscopic images of NRK-52E cell lines under different conditions: (a) 1, (b) 1 + Cu2+, (c) 1 + Cu2+ + SA (10.0
equiv), and (d) 1 + Cu2+ + SA (20.0 equiv). The samples were washed with PBS buffer (0.01 M, pH 7.4) three times before imaging. λex = 885 nm
(two-photon excited mode), and scale bars are 40 μm.
E
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was observed with high selectivity, providing the detection
limit of 3 μM. Further study revealed that the rationally
designed 1−Cu2+ ensemble could sense SA in cell lines.
Considering the simple, natural structure and conveniently
prepared protocols for the ensemble, we anticipate that this
finding can initiate the discovery of a high-performance SA
probe.
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China
Zhong Li − College of Pharmacy, East China University of
Science & Technology, Shanghai 200237, China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jafc.0c01283
Author Contributions
ASSOCIATED CONTENT
#C.C. and L.-L.Y. contributed equally to this work.
■
sı
* Supporting Information
Notes
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jafc.0c01283.
The authors declare no competing financial interest.
Supplementary data, Job’s plot experiment, titration
profiles, HRMS spectrum, calculation of detection limit,
solvent selection for the detection of SA, calculation of
fluorescence quantum yields, fluorescence studies, pH
ACKNOWLEDGMENTS
■
We acknowledge the National Natural Science Foundation of
China (21877021, 21702037, 31860516, 21662009), the
Research Project of Ministry of Education of China
(20135201110005, 213033A), and the Guizhou Provincial
S&T Program (LH [2017]7259, [2017]5788).
1
influences, H NMR, 13C NMR and HRMS spectra,
selectivities of ensembles, HRMS spectrum, and
comparison of the limit of detection (PDF)
REFERENCES
■
AUTHOR INFORMATION
■
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Corresponding Authors
Pei-Yi Wang − State Key Laboratory Breeding Base of Green
Pesticide and Agricultural Bioengineering, Key Laboratory of
Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China; orcid.org/0000-0002-
9904-0664; Email: pywang888@126.com
Song Yang − State Key Laboratory Breeding Base of Green
Pesticide and Agricultural Bioengineering, Key Laboratory of
Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China; College of Pharmacy, East
China University of Science & Technology, Shanghai 200237,
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Authors
Chong Chen − State Key Laboratory Breeding Base of Green
Pesticide and Agricultural Bioengineering, Key Laboratory of
Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China
Lin-Lin Yang − State Key Laboratory Breeding Base of Green
Pesticide and Agricultural Bioengineering, Key Laboratory of
Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China
A-Ling Tang − State Key Laboratory Breeding Base of Green
Pesticide and Agricultural Bioengineering, Key Laboratory of
Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China
Rong Dong − State Key Laboratory Breeding Base of Green
Pesticide and Agricultural Bioengineering, Key Laboratory of
Green Pesticide and Agricultural Bioengineering, Ministry of
Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang 550025, China
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