First fluorescent sensor for curcumin in aqueous media based on acylhydrazone-bridged bis-tetraphenylethylene

Article abstract of DOI:10.1016/j.saa.2019.117916

This work designed and synthesized the first organic fluorescent sensor for curcumin in aqueous media based on red-to-green fluorescence change of acylhydrazone-bridged bis-tetraphenylethylene (Bis-TPE). Bis-TPE was prepared by condensation of formyltetra

Full text of DOI:10.1016/j.saa.2019.117916

SAA-117916; No of Pages 9
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (xxxx) xxx
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
First fluorescent sensor for curcumin in aqueous media based on
acylhydrazone-bridged bis-tetraphenylethylene
a,c,
Shengjie Jiang a, Jiabin Qiu a, Bingni Lin a, Hongyu Guo a,b, , Fafu Yang
⁎
⁎
a
College of Chemistry and Materials, Fujian Normal University, Fuzhou 350007, PR China1
Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, PR China
b
c
Fujian provincial Key Laboratory of Advanced Materials Oriented Chemical Engineering, Fuzhou 350007, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
This work designed and synthesized the first organic fluorescent sensor for curcumin in aqueous media based on
red-to-green fluorescence change of acylhydrazone-bridged bis-tetraphenylethylene (Bis-TPE). Bis-TPE was
prepared by condensation of formyltetraphenylethylene with dihydrazide oxalate in 86% yield. It has the large
conjugated electron effect with strong red AIE fluorescence in aqueous solution. It displayed high selective sens-
ing ability for curcumin with red-to-green fluorescence change in THF-H2O (5:95). The detection limit was as low
as 1.15 × 10−7 M. The sensing mechanism was confirmed as 1:1 stoichiometric ratio based on quadruple hydro-
gen bonds. Bis-TPE was successfully applied for analyzing curcumin of ginger and living cell imaging, supplying a
new detecting strategy for curcumin in real sample and living environment.
Received 5 November 2019
Received in revised form 5 December 2019
Accepted 6 December 2019
Available online xxxx
Keywords:
Tetraphenylethylene
Curcumin
© 2019 Elsevier B.V. All rights reserved.
Sensor
Fluorescence
Aqueous media
1. Introduction
electrophoresis and carbon electrode, were reported for measuring
curcumin [5–14]. However, these methods require expensive instru-
Curcumin is a yellow organic compound extracted from the plants of
the Zingiberaceae and Araceae families, which was used extensively as a
natural pigment in food, such as canned foods, cakes and beverages [1].
Also, it possesses the excellent medicinal action including antibacterial,
antitumour, hypoglycaemic, and antioxidant effects for curing various
diseases, for examples, arthritis, colitis, diabetes, Alzheimer, depression,
nephrotoxicity, cardiovascular diseases and diverse types of cancers
[2–4]. However, in 2010, the Food Additives and Nutritional Enhancers
Science Committee of the European Food Safety Authority began to
test the potential hazard of curcumin as a food colouring. The daily ac-
ceptable dose of curcumin might also be controlled for reducing the
possible danger. Thus, the demand for fast and convenient detection
of curcumin is necessary for the safety of food and life body. Up to
now, the classical methods, such as high performance liquid chromatog-
raphy, high performance thin-layer chromatography, HPLC-MS spec-
trometry, UV–Vis spectroscopy, resonance light scattering, capillary
ments, complicated processes of sample treatment and long time-
consuming. Thus, the high efficient and simple detecting method for
curcumin is expected.
Recently, the fluorescent sensors were paid much attention due to
their outstanding merits including high sensitivity, low cost, and simple
operation [15,16]. Although curcumin emits yellow fluorescence in
some organic solutions such as CH2Cl2 and CHCl3, its fluorescence
quenched completely in aqueous media due to the strong ACQ effect,
limiting the fluorescence analysis of curcumin in real samples in aque-
ous system and living body [17,18]. Up to now, no organic fluorescence
sensor for curcumin in aqueous media was presented. Lately, the aggre-
gation induced emission (AIE) phenomenon, which eliminates the ACQ
effect effectively, was widely applied in design and preparation of novel
fluorescence sensor [19–21]. Therefore, series of AIE sensors were suc-
cessfully prepared for ion detection, biomolecular recognition and living
cell imaging in water [22–36]. However, the accurate design and syn-
thesis of AIE molecule with excellent sensor ability for complicated
guest, such as curcumin, is still a challenging work. In this paper, we
wish to report the first organic fluorescent sensor for curcumin in aque-
ous media based on an acylhydrazone-bridged bis-tetraphenylethylene,
⁎
Corresponding authors at: College of Chemistry and Materials, Fujian Normal
University, Fuzhou 350007, PR China.
E-mail address: yangfafu@fjnu.edu.cn (F. Yang).
https://doi.org/10.1016/j.saa.2019.117916
1386-1425/© 2019 Elsevier B.V. All rights reserved.
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tetrapheny..., Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, https://doi.org/10.1016/j.saa.2019.117916

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O
O
TiCl4 / Zn / THF
HO
OH
2
1
3
O
O
HOAc,
methenamine
HO
OH
N NH HN N
HC
O
O
CH
H2NHN
NHNH2
EtOH
OHC
Bis-TPE
4
HO
Scheme 1. Synthesis of target acylhydrazone-bridged bis-tetraphenylethylene (Bis-TPE).
which exhibited high selective detection for curcumin with red-to-
green fluorescence change and good performance for analyzing
curcumin in real sample and living cell imaging.
UV–Vis spectra were recorded on Varian UV–Vis spectrometer. Fluo-
rescence spectra were investigated in a conventional quartz cell
(10 × 10 × 45 mm) at 25 °C on a Hitachi F-4500 spectrometer. The fluo-
rescence absolute ΦF values of solution were collected using an Edin-
burgh Instruments FLS920 Fluorescence Spectrometer with a 6-inch
integrating sphere. All theory calculations were obtained by the density
functional theory (DFT) method at the B3LYP/6-31G(d) level by Gauss-
ian 09 program.
2. Experimental section
2.1. Materials and methods
All chemical reagents were obtained from commercial suppliers and
used directly. The other organic solvents and inorganic reagents were
pre-treated by standard anhydrous methods before use. TLC analysis
was performed on pre-coated glass plates. Column chromatography
was carried out by using silica gel (200–300 mesh). NMR spectra were
examined in CDCl3 on a Bruker-ARX 400 instrument at 25 °C. Chemical
shifts were reported in ppm with tetramethylsilane (TMS) as internal
standard. MS spectra were measured from Bruker mass spectrometer.
Compound 3 was synthesized by treating 2-hydroxybenzophenone
and benzophenone in Zn, TiCl4/THF system according to the published
literature [37].
2.2. Synthetic procedure for compound 4
Compound 3 (0.35 g, 1 mmol) and methenamine (0.84 g, 6 mmol)
were added in in 10 mL of HOAc. The mixture was stirred and refluxed
overnight. The reaction process was detected by TLC. After reaction,
50 mL of 1 M HCl solution was poured into the reaction mixture, and
then extracted with CHCl3 (20 mL × 3). Then the organic phase was sep-
arated and concentrated under reduced pressure. The residue was puri-
fied by column chromatography (eluent: CH2Cl2/hexane = 1/2) to
afford compound 4 as pale yellow solid in yield of 54%. 1H NMR
5000
H O fraction
2
0
4000
10
20
30
3000
2000
1000
0
40
50
60
70
80
90
95
450
500
550
600
650
700
Wavelength(nm)
Fig. 1. The emission spectra of Bis-TPE in THF/H2O solutions with different fractions of H2O
(2 × 10−5 M, λex = 360 nm).
Fig. 2. The changes of peak intensities in THF-H2O with different H2O fractions (λex =
360 nm, 2.0 × 10−5 M).
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Fig. 3. Fluorescence spectra of Bis-TPE (λex = 360 nm, 1 × 10−5 M) with guests
(1 × 10−4 M) in THF-H2O 5:95, V/V. (1 = Ag+, 2 = Al3+, 3 = Ba2+, 4 = Bi3+, 5 = Cd2
+, 6 = Zn2+, 7 = Co2+, 8 = Cr3+, 9 = Cs+, 10 = Fe3+, 11 = K+, 12 = Li+, 13 = Mg2
Fig. 5. Fluorescence intensities (516 nm) of Bis-TPE with different equivalent
concentrations of curcumin in THF-H2O (5:95).
+, 14 = Mn2+, 15 = Na+, 16 = Ni2+, 17 = Pb2+, 18 = Pd2+, 19 = Sr2+, 20 = Cu2+
,
21 = Ca2+, 22 = Alizarin, 23 = Curcumin, 24 = Penicillin, 25 = Vanillin, 26 =
Quercetin, 27 = Oxytetracycline, 28 = Carotene, 29 = Lycopene, 30 = Caramel, 31 =
141.00, 139.38, 136.28, 135.35, 134.43, 133.21, 131.33, 133.26, 127.94,
127.81, 127.67, 126.69, 126.43, 116.77, 116.11, 115.24. MALDI-TOF-MS
(C56H42N4O4) Calcd. for m/z = 834.32, found: m/z = 834.35 (M+).
Anal. calcd for C56H42N4O4: C 80.55, H 5.07, N 5.71; found C 80.50, H
5.11, N 5.66.
Annatto, 32
= Zeaxanthin. Inserted images: left = Bis-TPE, right = Bis-
TPE + Curcumin. (For interpretation of the references to color in this figure, the reader
is referred to the web version of this article.)
(400 M Hz, CDCl3): δppm: 10.92 (s, 1H, OH), 9.58 (s, 1H, CHO),
7.02–7.19 (m, 17H, ArH), 6.72 (d, J = 8.0 Hz, 1H, ArH). MALDI-TOF-
MS (C27H20O2) Calcd. for m/z = 376.146, found: m/z = 376.432 (M+).
2.4. The tested procedure of the test paper
The filter papers were soaked in Bis-TPE solution (THF-H2O (5:95),
0.1 mM) for 5 min. Then the filter papers were dried in air at room tem-
perature and tailored as round slices. Five drops of guest solution
2.3. Synthesis procedure of Bis-TPE
The mixture of compound 4 (0.376 g, 1 mmol) and oxalohydrazide
(0.06 g, 0.5 mmol) were added into 20 mL of absolute ethanol, which
was further refluxed and stirred for 24 h under TLC detection. After re-
action, the solvents were removed by reduced pressure and the residue
was recrystallized from CHCl3/MeOH to afford Bis-TPE as pale yellow
powder (86% yield). 1H NMR (400 MHz, CDCl3) δ 10.58 (s, 2H, NH),
10.12 (s, 2H, OH), 8.08 (s, 2H, CH), 7.54 (s, 2H, ArH), 7.17–7.01(m,
30H, ArH), 6.91 (bs,2H, ArH), 6.79 (d, 2H, J = 8.0 Hz, ArH). 13C NMR
(100 MHz, CDCl3), δppm: 157.47, 153.87, 143.58, 143.51, 143.21,
(0.1 mM for each species, including curcumin, Ag+, Al3+, Ba2+, Bi3+
Cd2+, Zn2+, Co2+, Cr3+, Cs+, Fe3+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+
,
,
Pb2+, Pd2+, Sr2+, Cu2+, Ca2+, Alizarin, Penicillin, Vanillin, Quercetin,
Oxytetracycline, Carotene, Lycopene, Caramel, Annatto and zeaxanthin)
were added onto the test paper. After drying, the papers were observed
under UV-light (365 nm).
2.5. MTT assay
Methylthiazolyldiphenyl-tetrazolium (MTT) trials were used for in-
vestigating the toxicity for MCF-7 cancer cells. The Inoculated MCF-7
Fig. 4. Fluorescence spectra of Bis-TPE (λex = 360 nm, 5.0 × 10−6 M) with different
equivalent concentrations of curcumin in THF-H2O (5:95). Inserted images: A = Bis-
TPE, B = Bis-TPE + Curcumin (0.5 eq), C = Bis-TPE + Curcumin (1.0 eq). (For
interpretation of the references to color in this figure, the reader is referred to the web
version of this article.)
Fig. 6. The influence of pH on the fluorescence intensities of Bis-TPE (1 × 10−5 M) in THF-
H2O (5:95) with (red) or without (black) curcumin (1 × 10−5 M), λex = 360 nm. (For
interpretation of the references to color in this figure legend, the reader is referred to
the web version of this article.)
Please cite this article as: S. Jiang, J. Qiu, B. Lin, et al., First fluorescent sensor for curcumin in aqueous media based on acylhydrazone-bridged bis-
tetrapheny..., Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, https://doi.org/10.1016/j.saa.2019.117916

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Under the above identical circumstance of MTT trials, MCF-7 cancer
cells were cultivated for 24 h, and then being dyed by Bis-TPE or
curcumin (1.0 × 10−5 M) with 24 h breeding. After rinsing by PBS-
buffer, the cells tinted by Bis-TPE were fostered in solution of curcumin
(1.0 × 10−5 M) for 1 h at 37 °C, respectively. The cells dyed by Bis-TPE,
curcumin and Bis-TPE + curcumin were examined by a confocal laser
scanning microscope (CLSM, Zeiss LSM 710, Jena, Germany),
respectively.
3. Results and discussion
3.1. Synthesis and characterization
The synthetic route was illustrated in Scheme 1. As curcumin has the
symmetrical structure with two C_O groups, two MeO groups and two
OH groups, it is reasonable to design quadruple hydrogen bonds based
on these functional groups to sensor curcumin. On the other hand, in
order to obtain the excellent performance in living body, the long-
wavelength emission was always expected due to its advantages of
the deep tissue permeation, minimum self-absorption and low back-
ground noise, etc. [38]. Thus, the acylhydrazone-bridged bis-
tetraphenylethylene (Bis-TPE) was designed as target compound. It
possesses the symmetrical structure for matching the symmetrical
structure of curcumin. It also has two OH and two NH groups for pro-
ducing quadruple hydrogen bonds with curcumin, and large conjugated
acylhydrazone-bridging for emitting long-wavelength fluorescence. All
these structural features were favorable for the good sensing abilities for
curcumin. According to the reported procedure [37], mono-hydroxy
tetraphenylethylene 3 was prepared by reacting benzophenone and
monohydrobenzophenone in Zn, TiCl4/THF system in yield of 32%. Sub-
sequently, compound 4 was prepared by the classical formylation pro-
cess of reacting compound 3 and methenamine in HOAc system in the
yield of 54% after column chromatography. Furthermore, the target
Bis-TPE was synthesized by refluxing sample 4 with dihydrazide oxa-
late in yield of 86% after recrystallization. The structure of Bis-TPE was
characterized by 1H NMR and 13C NMR spectra, MALDI-TOF mass
Fig. 7. Fluorescence spectra of Bis-TPE (1 × 10−5 M) with curcumin and other materials
(2 × 10−5 M each) in a mixture of THF-H2O (5: 95) at λex = 360 nm. (1 = curcumin,
2–32 = curcumin with Ag+, Al3+, Ba2+, Bi3+, Cd2+, Zn2+, Co2+, Cr3+, Cs+, Fe3+, K+
,
Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Pd2+, Sr2+, Cu2+, Ca2+, Alizarin, Penicillin, Vanillin,
Quercetin, Oxytetracycline, Carotene, Lycopene, Caramel, Annatto and Zeaxanthin,
respectively).
cancer cells were fostered at 37 °C and 5% CO2 for 24 h, then the solution
of Bis-TPE was tracked in the cells after incubating for 24 h. The fostered
cells were rinsed by PBS buffer and then cultivated for 3 h, in 0.5 mg/mL
MTT-PBS buffer. Next, 100 μL of DMSO was added into dissolving the
generated Formazan crystals, and measured the absorption intensity
at 490 nm.
2.6. The experiment of living cell imaging
Bis-TPE or curcumin (3.0 mg) was dissolved in DMSO (1.0 mL) and
then diluted to concentration of 1.0 × 10−5 M by PBS buffer (pH = 7.4).
Fig. 8. The MALDI-TOF-MS spectrum of Bis-TPE with curcumin (1:4).
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excellent AIE property for Bis-TPE. Moreover, as expected, Bis-TPE
emitted the red fluorescence at 530–650 nm, which exhibited huge
red shift than that of normal TPE derivatives (450–550 nm usually).
This characteristic agreed with the large conjugated structure of
acylhydrazone-bridged bis-tetraphenylethylene and was an obvious
advantage for the probe in living body, because the long wavelength
emission benefits for the deep tissue permeation, minimum self-
absorption and low background noise, etc. [37]. The highest fluores-
cence was observed in THF-H2O solution with fw = 95%, which was cho-
sen as solution system for the further investigation on sensing guests.
3.3. The sensing abilities for series metal ions and biomolecules
As a useful probe, it is expected to achieve a selective and sensitive
detection for the target guest. The sensing ability of Bis-TPE for series
metal ions and biomolecules was investigated by measuring the fluores-
cence change. As shown in Fig. 3, the fluorescence intensities fluctuated
a little when Bis-TPE with series of metal ions and biomolecules (Ag+,
Al3+, Ba2+, Bi3+, Cd2+, Zn2+, Co2+, Cr3+, Cs+, Fe3+, K+, Li+, Mg2+
,
Mn2+, Na+, Ni2+, Pb2+, Pd2+, Sr2+, Cu2+, Ca2+, Alizarin, Penicillin, Van-
illin, Quercetin, Oxytetracycline, Carotene, Lycopene, Caramel, Annatto
and Zeaxanthin), indicating the weak interaction (including the energy
transfer effect, electrostatic interaction and electron transfer effect, etc.)
between host and guest. But these weak interactions did not influence
the fluorescence emission wavelength and fluorescence color.
However, the fluorescence of Bis-TPE with curcumin displayed the
obvious blue shift from 573 nm (red) to 516 nm (green), accompanying
by the color change from red to green under ultraviolet lamp (as shown
in Fig. 3). The fluorescence intensity also increased markedly with the
increasing fluorescence quantum yield from 0.28 to 0.36. Due to pure
curcumin has no fluorescence (ACQ effect) in this system (Fig. S5), the
outstanding fluorescence change after adding curcimin in solution
could be attributed to the strong interaction between these two species,
implying the high sensing selectivity of Bis-TPE for curumin among all
kinds of metal ions and biomolecules.
Fig. 9. Fluorescence Jobs' plot (λem = 516 nm, λex = 360 nm) of Bis-TPE and curcumin in
THF-H2O (5:95), the total concentration of [Bis-TPE] + [curcumin] = 20 μM.
spectrometry and elemental analysis (see SI). All the spectral data were
in accordance with its structure. Especially, the singlet for N_CH, OH
and CH appeared at 10.52, 10.12 and 8.08 ppm, respectively, indicating
the symmetric trans-structure for C_N groups of Bis-TPE in Scheme 1.
3.2. AIE property
The AIE property of Bis-TPE was investigated by fluorescence spec-
troscopy in the THF-H2O mixtures as shown in Figs. 1 and 2. When the
fraction of H2O was b80%, the fluorescence intensities were very weak.
As the fraction of H2O was higher than 80%, the fluorescence intensities
increased greatly by 147.7 times at 95% of H2O, in which the absolute
fluorescence quantum yield attained 0.28. These results indicated the
Fig. 10. The 1H NMR spectrum of Bis-TPE with curcumin (1:1).
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3.4. Fluorescence titration for curcumin
Fluorescence titration of Bis-TPE for curcumin was studied and the
results were exhibited in Fig. 4. It can be seen that, with the increase
of concentration of curcumin, a new fluorescence emission at about
516 nm appeared and enhanced gradually, the red color of solution
also turned into green as inserted in Fig. 4. Based on Fig. 4, the change
of peak intensities at 516 nm vs fractions of H2O was summarized in
Fig. 5. The inserted figure of peak intensities vs fractions of H2O from 0
to 0.1 eq was in a good linear relationship. According to the calculation
formula of DL = K × Sb1/S (where K = 2 or 3, in this case the value is 2,
Sb1 is the standard deviation of the blank solution, and S is the value of
the slope of the standard curve), the detection limit was evaluated as
1.15 × 10−7 M. It was worthy of noting that this DL value reached the
level of other methods such as electrochemical, carbon dots and
voltammetric Sensor [10–13].
3.5. pH influence and interference experiments on sensing curcumin
Fig. 11. The FT-IR spectra of Bis-TPE, curcumin and Bis-TPE with curcumin (1:1).
The influence of pH on the fluorescence emission of Bis-TPE in THF-
H2O (5:95) with or without curcumin was measured as shown in Fig. 6.
Fig. 12. (A) The binding model of Bis-TPE with curcumin; (B) The LUMO and HOMO of Bis-TPE; (C) The LUMO and HOMO of Bis-TPE with curcumin.
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Fig. 13. Photographs of test strips containing different ions or biomolecules under UV light (365 nm). (1 = Curcumin, 2 = Ag+, 3 = Al3+, 4 = Ba2+, 5 = Bi3+, 6 = Cd2+, 7 = Zn2+, 8 = Co2
+, 9 = Cr3+, 10 = Cs+, 11 = Fe3+, 12 = K+, 13 = Li+, 14 = Mg2+, 15 = Mn2+, 16 = Na+, 17 = Ni2+, 18 = Pb2+, 19 = Pd2+, 20 = Sr2+, 21 = Cu2+, 22 = Ca2+, 23 = Alizarin, 24 =
Penicillin, 25 = Vanillin, 26 = Quercetin, 27 = Oxytetracycline, 28 = Carotene, 29 = Lycopene, 30 = Caramel, 31 = Annatto, 32 = Zeaxanthin). (For interpretation of the references to
color in this figure, the reader is referred to the web version of this article.)
One can see that the fluorescence intensities of Bis-TPE was stable be-
tween pH = 2 and 10. After adding curcumin, the fluorescence intensi-
ties were enhanced greatly. When pH N 9, the fluorescence intensities
decreased rapidly, which might be attributed to the conversion of the
phenolic hydroxyl groups of curcumin to phenolate under alkaline con-
dition. This conversion enhanced the solubility of curcumin in water
and weakened the interaction between Bis-TPE and curcumin, resulting
in the decrease of fluorescence intensity finally. These results indicated
that both Bis-TPE and Bis-TPE with curcumin possessed the stable fluo-
rescence emission in pH range of 2–9, exhibiting the good application
prospects in analyzing actual sample. On the other hand, the interfer-
ence experiments were examined by the fluorescence spectra of Bis-
TPE with curcumin or curcumin and other species. In Fig. 7, pure Bis-
TPE emitted fluorescence at 570 nm, Bis-TPE with curcumin or
curcumin and other species possessed the similar strong fluorescence
at 516 nm, although the maximum emission intensities fluctuated a lit-
tle with different interference species. These results suggested good
sensing selectivity for curcumin among these tested metal ions and or-
ganic biomolecules.
3.6. The sensing mechanism
The sensing mechanism of Bis-TPE for curcumin was investigated by
MS spectroscopy, fluorescence Job's plot, FT-IR spectroscopy and 1H
NMR spectroscopy. In the MS spectroscopy of Bis-TPE with excess
curcumin (1:4), only
a strong binding peak at 1202.9 [(Bis-
TPE + curcumin)+] was observed, suggesting the formation of 1:1 stoi-
chiometric ratio of Bis-TPE with curcumin (Fig. 8). The fluorescence
Job's plot indicated an inflection point at fcurcumin = 0.5 (Fig. 9), also in-
dicating a stoichiometric ratio of 1:1. In Fig. 10, the comparison of 1
H
NMR of Bis-TPE, curcumin, Bis-TPE and curcumin (1:1) suggested the
obvious shifts of the OH and NH protons of Bis-TPE from high fields
(10.12 and 10.58) to low fields (10.25 and 10.63), implying the forma-
tion of hydrogen bonds between Bis-TPE and curcumin as expected.
The FT-IR absorption of OH, NH and C_O of Bis-TPE with curcumin
also exhibited remarkable change in comparison with that of Bis-TPE
and curcumin (Fig. 11). The OH and NH groups shifted from
3417 cm−1, 3441 cm−1 to 3425 cm−1 and 3475 cm−1, respectively.
The C_O groups shifted from 1628 cm−1 and 1681 cm−1 to
1685 cm−1. These phenomena were in accordance with the changes
from intramolecular hydrogen bond before detection to intermolecular
hydrogen bond after detection. Based on these data, the binding model
of Bis-TPE for curcumin was proposed as Fig. 12A, in which the quadru-
ple hydrogen bonds existed between Bis-TPE and curcumin. Moreover,
the theoretical calculation for this binding model was performed by a
Gaussian 09 B3LYP/6-31G*. The HOMO-LUMO energy gap increased
from 0.691 eV for Bis-TPE to 1.146 eV for Bis-TPE with curcumin
(Fig. 12B and C). This increased energy gap was in consistent with the
blue shift of fluorescence wavelength of Bis-TPE after sensing curcumin.
3.7. Application in test paper
Test strip was a common method to evaluate the actual application
of a sensor. Therefore, the test paper of Bis-TPE was prepared by im-
mersing a neutral filter paper in a 0.1 mM of Bis-TPE solution for
5 min. The filter paper was then evaporated to dryness at room temper-
ature and customized into round sections. Subsequently, 5 drops of
0.1 mM solution containing the ions or biomolecules (curcumin, Ag+
Al3+, Ba2+, Bi3+, Cd2+, Zn2+, Co2+, Cr3+, Cs+, Fe3+, K+, Li+, Mg2+
,
,
Fig. 14. Emission spectra of Bis-TPE and Bis-TPE with the curcumin extract of ginger.
Mn2+, Na+, Ni2+, Pb2+, Pd2+, Sr2+, Cu2+, Ca2+, Alizarin, Penicillin,
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Fig. 15. Confocal fluorescence images of MCF-7 cells incubated with curcumin, Bis-TPE and Bis-TPE + curcumin (1.0 × 10−5 M, each), respectively. (A)–(C) MCF-7 cells with curcumin;
(D)–(F) MCF-7 cells with Bis-TPE; (G)–(I) MCF-7 cells with Bis-TPE + curcumin. Left, middle and right images were bright field images, fluorescence images, and the merged images of
fluorescence and bright field, respectively. (λex = 405 nm). The same scale bar for all images. (For interpretation of the references to color in this figure, the reader is referred to the web
version of this article.)
Vanillin, Quercetin, Oxytetracycline, Carotene, Lycopene, Caramel, An-
natto and zeaxanthin) were added into the sections. Fig. 13 displayed
the photographs of these sections under ultraviolet light (365 nm),
showing no color change in all species except curcumin. The test
paper of Bis-TPE with curcumin exhibited the obvious color change
from red to green. These tests strongly suggested the practical applica-
tion of Bis-TPE in the detection of curcumin.
working curve and compared with the result of high performance liquid
chromatography (99 μg/100 g). The results of these two methods were
almost identical with a deviation of b3%, although the contents of
curcumin were lower than the theoretical content due to incomplete
extraction of curcumin in the sample. This result indicated the good po-
tential of Bis-TPE for determining curcumin in actual samples.
3.9. Application in living cell imaging
3.8. Applications in curcumin analysis of real sample
The application of Bis-TPE in live cell imaging was investigated by
confocal laser scanning microscopy (CLSM). The metabolic activity of
MCF-7 cells was obtained by MTT assay at a concentration of
0–5.0 × 10−5 M. The cell viability was higher than 80% as concentrations
were b2.5 × 10−5 M (Fig. S6). On the other hand, MCF-7 cells were fixed
after incubating with samples for 1 h in the medium at 37 °C. Fluores-
cence imaging was examined at λex = 405 nm. The corresponding fluo-
rescent images were shown in Fig. 15. Cells with curcumin displayed no
fluorescence. But cells with Bis-TPE and Bis-TPE + curcumin exhibited
red and green fluorescence, respectively. These results were in
Furthermore, a common turmeric-containing vegetarian (ginger)
was used as a real sample to detect the curcumin. Ginger was pulverized
and then leached with tetrahydrofuran. The obtained turbid solution
was filtered, evaporated to dryness and then dissolved in THF-H2O
(5:95), which was further studied by fluorescence sensing analysis of
Bis-TPE. As shown in Fig. 14, Bis-TPE with the curcumin extract of gin-
ger exhibited blue-shift and enhanced fluorescence in comparison of
pure Bis-TPE, which was consistent with previous fluorescence studies.
The curcumin content was calculated as 96 μg/100 g by the standard
Please cite this article as: S. Jiang, J. Qiu, B. Lin, et al., First fluorescent sensor for curcumin in aqueous media based on acylhydrazone-bridged bis-
tetrapheny..., Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, https://doi.org/10.1016/j.saa.2019.117916

S. Jiang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (xxxx) xxx
9
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4. Conclusion
In conclusion, an acylhydrazone-bridged bis-tetraphenylethylene
was designed and synthesized as the first organic fluorescent senor for
curcumin in aqueous media. It displayed high selective detection for
curcumin with red-to-green fluorescence change in THF-H2O (5:95).
The detection limit was as low as 1.15 × 10−7 M. The sensing mecha-
nism was confirmed by MS spectroscopy, fluorescence Job's plot, FT-IR
spectroscopy and 1H NMR spectroscopy, indicating the 1:1 stoichiomet-
ric ratio based on quadruple hydrogen bonds. It was successfully applied
for analyzing curcumin of ginger and living cell imaging for the first
time, supplying a new detecting strategy for curcumin in real samples
and living environment.
Author contributions
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Dr. Jiabin Qiu was responsible for the characterization of target
compound.
Mr. Bingni Lin was responsible for the investigation of photophysical
properties.
Mr. Hongyu Guo was responsible for the data analysis.
Prof. Yang was responsible for direction of experiment and writing
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Declaration of competing interest
The authors declared that there is no conflict of interest.
Acknowledgment
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Financial support from the National Natural Science Foundation of
China (No: 21406036), Fujian Science and Technology Project (No.
2019N0010), Science and Technology Planning Project of Fuzhou
(2018-G-44), and Undergraduate Innovation Program of FJNU (2019)
were greatly acknowledged.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.saa.2019.117916.
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Please cite this article as: S. Jiang, J. Qiu, B. Lin, et al., First fluorescent sensor for curcumin in aqueous media based on acylhydrazone-bridged bis-
tetrapheny..., Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, https://doi.org/10.1016/j.saa.2019.117916