A bifunctional probe based on naphthalene derivative for absorbance-ratiometic detection of Ag+ and fluorescence “turn-on” sensing of Zn2+ and its practical application in water samples, walnut and living cells

Article abstract of DOI:10.1016/j.jphotochem.2019.112299

In this work, naphthalene with good biocompatibility was selected, and the probe NBOS was synthesized with 2-Amino-phenol and 2-Amino-benzenethiol. The structure of probe NBOS was confirmed by X-ray Crystallography. Furthermore, the probe showed absorbance-ratiometic sensing for Ag⁺ over a pH range from 6 to 7.5 and fluorescence “turn on” signal response towards Zn²⁺ in the pH range of 6–10 in EtOH/H₂O (9/1, V/V, pH = 7.4) mixture. The detection limit was obtained to be 4.24 μM for Ag⁺ and 3.17 nM for Zn²⁺. Moreover, it could be efficiently recycled by treating Na₂EDTA. The sensing mechanism of probe NBOS toward Ag⁺ and Zn²⁺ was investigated by FT-IR, HNMR, job'plot and ESI-MS. Typically, the coordination mode of NBOS with Zn²⁺ was confirmed by DFT calculation. Moreover, probe NBOS was successfully applied in the detection Ag⁺ and Zn²⁺ in real water samples. Importantly, probe NBOS could be used to detect Zn²⁺ in walnut and living cells. Based on the high throughput analysis strategy, absorbance and fluorescence signals of NBOS could be designed as a NOT and OR logic gate controlled by Ag⁺ (Input 1) and Zn²⁺ (Input 2).

Full text of DOI:10.1016/j.jphotochem.2019.112299

Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
A bifunctional probe based on naphthalene derivative for absorbance-
+
2+
ratiometic detection of Ag and fluorescence “turn-on” sensing of Zn and
its practical application in water samples, walnut and living cells
a
a
a
a
a
a
b
Na-Na Li , Cai-Feng Bi , Xia Zhang , Cun-Gang Xu , Chuan-Bin Fan , Wei-Song Gao , Zi-Ao Zong ,
a
a
a,
Shan-Shan Zuo , Chuan-Feng Niu , Yu-Hua Fan *
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao,
a
Shandong, 266100, PR China
b
Schoolof Laboratory Medicine, Youjiang Medical Universityfor Nationalities, Baise, 533000 Guangxi, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this work, naphthalene with good biocompatibility was selected, and the probe NBOS was synthesized with 2-
Amino-phenol and 2-Amino-benzenethiol. The structure of probe NBOS was confirmed by X-ray
Absorbance-ratiometic
Fluorescence
+
Crystallography. Furthermore, the probe showed absorbance-ratiometic sensing for Ag over a pH range from 6
+
Ag
Zn
2+
2
to 7.5 and fluorescence “turn on” signal response towards Zn in the pH range of 6–10 in EtOH/H O (9/1, V/V,
2+
+
2+
pH = 7.4) mixture. The detection limit was obtained to be 4.24 μM for Ag and 3.17 nM for Zn . Moreover, it
X-ray crystallography
Cells image
+
2+
could be efficiently recycled by treating Na
2
EDTA. The sensing mechanism of probe NBOS toward Ag and Zn
was investigated by FT-IR, HNMR, job’plot and ESI-MS. Typically, the coordination mode of NBOS with Zn
was confirmed by DFT calculation. Moreover, probe NBOS was successfully applied in the detection Ag and
Zn in real water samples. Importantly, probe NBOS could be used to detect Zn in walnut and living cells.
Based on the high throughput analysis strategy, absorbance and fluorescence signals of NBOS could be designed
2+
+
2+
2+
+
2+
as a NOT and OR logic gate controlled by Ag (Input 1) and Zn
(Input 2).
1
. Introduction
So far, many modern techniques were employed for the detection of
Ag+ and Zn , such as atomic absorption spectrometry [13,14], elec-
troanalysis [15] and inductively coupled plasma mass spectrometry
[16]. Compared with those detection methods mentioned above,
fluorescence probes had attracted attention due to its high sensitivity,
simple operation and easy synthesis [17–19]. Therefore, it was used to
2+
The detection of heavy and transition metal ions in biological
samples was challenging and special attentions had been devoted to
+
2+
Ag and Zn . Zinc was an important essential trace element and it
played significant roles in many biological processes, such as regulation
of metalloenzyme, protein expression and apoptosis [1–3]. However,
+
2+
detect metal ions. A number of probes for the detection Ag and Zn
2
+
excess of Zn
in vivo biology could also cause many illnesses, in-
had been developed using fluorescent and/or colorimetric methods.
Yin’s team developed a novel fluorescence probe using terpyridyl tri-
phenylamine derivative, and the probe showed fluorescence turn on
cluding Alzheimer's disease, Parkinson's disease, Epilepsy and Ehlers-
+
Danlos syndromeetc [4–6]. Ag was widely used in jewellery, ther-
apeutic and cosmetics [7]. Besides, Ag+ ion displayed extensive effects
response for Zn
benzothiazole functionalized probe L1, which exhibited colorimetric as
2+
and Cd
2+
in THF [20]. Das’s team synthesized a
on human health including cytotoxicity, failure of several organisms
2+
(
immunity, nervous, and digestive system) and inhibition of mi-
well as fluorometric response to Zn
pH = 7.3) buffered solution, but Cd
in MeOH/H
2
O (7/3, V/V,
+
2+
2+
tochondrial [8,9]. However, Ag and Zn
caused a lot of serious en-
also triggered the emission at
vironmental pollution because of their widespread use in the industry
similai wavelength [21]. Huo etc. team developed a novel fluorescence
10–12]. In view of the roles played by Ag+ and Zn , to develop more
2+
probe by conjugated with benzimidazole and phenol as a fluorophore,
[
+
2+
rapid, sensitive and simple methods for accurate detection of Ag and
Zn
realizing a fluorescent on detection for Zn
in EtOH [22]. Chen etc.
2
+
was necessary and important for biological system and environ-
synthesized a new 9,9′-bianthracene-based thiosemicarbazone fluores-
cence probe, which exhibited a characteristic fluorescence quenching
ment.
⁎
Corresponding author.
E-mail address: fanyuhua301@163.com (Y.-H. Fan).
https://doi.org/10.1016/j.jphotochem.2019.112299
Received 16 August 2019; Received in revised form 9 December 2019; Accepted 10 December 2019
Available online 16 December 2019
1010-6030/ © 2019 Published by Elsevier B.V.

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
2. Experimental
phenomenon in the presence of Ag+ in DMF/H
O (9/1, V/V, pH = 3.0)
2
[
23]. Singh etc. developed a new schiff base probe, which displayed
+
fluorescence turn off response for Ag in CH
3
CN/H
2
O (1/1, V/V,
2.1. General comments
pH = 7.4) medium [24]. Lin etc. developed a fluorescein spirolactam
derivative and used as a turn-on fluorescence probes for the detection of
1H NMR spectra of Compound 2 and NBOS were measured on a
Bruck AV-600 and AV-500 spectrometer in CDCl , respectively. The IR
3
+
Ag in EtOH/H
2
O (1/4, V/V, pH = 9.0) solution [25]. But some of the
2
+
reported probe for Zn
still suffer from the shortcomings such as in-
spectrum was collected with a Perkin-Elmer IR spectrophotometer
using KBr pellet. Pgeneral TU-2550 UV–vis spectrophotometer and
Perkin Elmer LS55 fluorescence spectrometer were employed to mea-
sure absorption and fluorescence spectra, respectively. Mass spectrum
was obtained on an Agilent 6220 Quadruple LC/MS (Agilent Co, USA).
X-ray diffraction data were collected on a Bruker Smart CCD X-ray
single-crystal diffractometer.
All the materials for synthesis and spectral analysis were of analy-
tical grade or higher, purchased from commercial sources, and used
without further purfication. Ultrapure water was used throughout all
the expriments. The solution of various mental ions were prepared from
solubility in water, couldn’t detect under physiological condition or
2
+
interfered by Cd . Moreover, most of fluorescence probes for the de-
+
tection Ag belonged to “on-off” type, which was disadvantageous in
most cases. Even though fluorescent turn-on probe was developed, but
+
it showed significant response to Ag in basic medium, which limited
their practical applications [25]. UV absorbance-ratiometric probes
could conveniently monitor metal ions by the visible range compared to
+
fluorescence probes. So, it was suitable for the detection of Ag . Re-
cently, multi-ion responsive probe attracted more interests because
their advantages of low cost, higher efficiency, easy sample preparation
and time saving. To data, a single probe for the selective detection of
AgNO
Cd(NO
3
, KCl, MgCl
·4H O, Pb(NO
O, HgCl , Na
O, SrCl ·6H O. The pH of NBOS solution was adjusted with
2
·6H
2
O, Ba(ClO
CoSO
SO4, FeCl
4
)
2
, Zn(NO
·7H O, NiCl
·4H O, FeCl
3
)
2
·6H
2
O, Cu(NO
·6H O, CaCl
·6H O, LiNO
3
)
2
·3H
2
,
2
O,
Al
+
2+
Ag and Zn has never been reported except the multi-analyte sensor
3
)
2
2
3
)
2
,
4
2
2
2
array based on fluorescein designed by Li et al., but the probe was used
(NO
(NO
3
)
)
3
·9H
·6H
2
2
2
2
2
2
3
2
3
, La
+
2+
to detect Ag and Zn
in different medium, respectively, which
3
3
2
2
caused the complicated preparation process [26]. Hence, there were
HCl, NaOH and TRIS aqueous solution. For fluorescence measurements,
excitation wavelength was 450 nm and the excitation and emission
wavelength band passes were both set at 5 nm and 5 nm.
strong needs in the development of absorbance-ratiometic and fluor-
+
2+
escence probes for the detection of Ag and Zn
.
ESIPT sensing mechanisms had been widely used to design UV ab-
sorbance-ratiometric and fluorescence “turn on” probe [27–29]. One-
way ESIPT process at the excited state caused fluorescence quenching
2.2. Fluorescence quantum yield measurement
[
30,31]. However, upon addition of metal ions, both ratiometric and
The fluorescence quantum yield was calculated according to fol-
fluorescence “turn on” response appeared by broking ESIPT progress.
Taking the above statements into consideration, probe NBOS was de-
signed and synthesized with 3-hydroxy-2-naphthoic acid, 2-Amino-
phenol and 2-Amino-benzenethiol (Scheme1). Hydroxyl, N, S and O
lowing equation by selecting rhodamine B (Ф = 0.89 in ethanol) as
standard.
x x x x
Φ = Φst (A /Ast) (D /Dst) (η
/ηst)2
+
2+
creating a multipoint binding pocket, which Ag and Zn
could co-
where Φ stands for the fluorescence quantum yield. St subscript denotes
the standard and x means sample. A is the absorbance at excitation
wavelength, D is the integrated area under the flfluorescence emission
spectra, and η is the refractive index of the solvent [32,33].
ordinate in a cooperative breaking Excited-State Intramolecular Proton
+
Transfer (ESIPT). Probe NBOS could detect Ag by absorbance-ratio-
2
+
metic and exhibited high selectivity for Zn by fluorescence “turn on”
2
+
2+
response, especially distinguishing Zn from Cd in EtOH/H
2
O (9/1,
V/V, pH = 7.4) mixture. Comparison of the common methods and
+
2+
2.3. X-ray analysis
probe molecules of NBOS with the previously reported Ag /Zn
probes were shown in Table 1. Moreover, the sensing mechanism of
+
2+
The structure of NBOS was characterized by X-ray crystallographic
analysis. NBOS (10 mg) was dissolved in 10 mL dichlormethane and
petroleum ether (1:1, V/V) mixture, and the solvent was evaporated
slowly at room temperature for 2 days to obtain single crystals of NBOS
suitable for X-ray analysis.
NBOS with Ag and Zn
were confirmed by FT-IR, HNMR, job’plot,
ESI-MS and DFT calculation. The probe NBOS was further applied for
practical water samples, walnut and could be used in the construction
of molecular logic gate. Importantly, fluorescence image of Zn2+ in
living 293T cells confirmed its value in biological system.
2.4. Synthesis of compound 2
Hydroxy-naphthalene-2-carboxylic acid (1.88 g, 10 mmol) and 2-
Amino-phenol (1.09 g, 10 mmol) were dissolved in polyphosphoric acid
PPA, 10 mL) and heated to 180 °C for 3 h with fiercely stirring. After
(
Scheme 1. Synthesis of NBOS.
2

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
Table 1
Comparison of the common methods and probe molecules of NBOH with the previously reported Ag+/Zn2+ probes.
Ref.
probe molecules and synthesi
Methods of detections
Zn2+ Turn on
Media
THF
LOD
[20]
3.7 × 10−7
M
[
21]
22]
Zn2+ colorimetric and fluorometric response
MeOH/H
EtOH
2
O (7/3, V/V, pH 7.3)
6.5 × 10−5
M
M
[
Zn2+ Turn on
2.5 × 10−5
[23]
Ag+ Turn off
DMF/H
2
O (9/1, V/V, pH 3.0)
1.99 × 10−5
M
[
24]
25]
Ag+ Turn off
CH
3
CN/H
2
O (1/1, V/V, pH 7.4)
5 × 10−6
8 × 10−8
M
M
[
Ag+ Turn on
2
EtOH/H O (1/4, V/V, pH 9.0)
+
Ag+ EtOH/H
Ag+ 1 × 10−9
M
[26]
Ag Turn on
2
O (2:8, v/v, pH 7.4)
O (2:8,v/v, pH 7.4)
2
+
2+
2+
−5
Zn
Turn on
Zn
CH
3
CN/H
2
Zn
1 × 10
M
+
Ag+ 4.24 × 10−6
M
This work
Ag UV-vis ratiometic
EtOH/H
2
O (9/1, V/V, pH 7.4)
2
+
2+
−6
Zn
Turn on
Zn 3.17 × 10
M
the reactants were fully consumed (monitored by TLC), the reaction
mixture was cooled down to 100 °C. Then HMTA (2.8 g, 20 mmol) was
added to the solution obtained above and the mixture was stirred at
2.6. Synthesis of [NBOS+Zn2+] complex
To 10 mL solution of compound NBOS (10 mg, 0.025 mmol) in
EtOH/CH Cl (4:1, V/V), Zn(NO ·6H O (7.5 mg, 0.025 mmol) was
100 °C for 5 h and cooled. The reaction mixture was poured in 100 mL
2
2
3
)
2
2
of water. The precipitate was filtered, washed with water and dried.
The product was purified by silica gel column chromatography (eluent-
dichloromethane) and washed with water to give compound 2 (610 mg,
added and stirred. The end-point of the reaction was confirmed by TLC
when the spot of probe NBOS was disappeared. The solvent was eva-
2
+
porated at room temperature for 2 days to obtain NBOS+Zn
com-
2
1
7
1 %) as green powder [34]. 1H NMR (Fig. S1) (600 MHz, CDCl
3
) δ
plex (yellow powder).
2.58 (s, 1H), 10.97 (s, 1H), 9.13 (s, 1H), 8.73 (s, 1H), 7.80 (d, 1H),
.72 (d, 1H), 7.62 (q, 2H), 7.40 (m, 3H).
2.7. Synthesis of [NBOS+Ag+] complex
3
The solution of NBOS (10 mg, 0.025 mmol) and AgNO (10 mg,
2.5. Synthesis of compound NBOS
0.075 mmol) in 9 mL EtOH and 1 mL H O was stirred for 2 days at room
2
temperature and the reaction was monitored by TLC for completion.
2
-Amino-benzenethiol (125 mg, 1 mmol) and p-MeC
10 mg, 0.2 mmol) were added into a solution of compound 2 (289 mg,
mmol) in EtOH (20 mL). The mixture was stirred for 12 h under reflux
6 4 3
H SO H
(
1
2.8. Cell incubation and fluorescence image
conditions. After cooling to room temperature, the precipitate produced
was filtered and purified by column chromatography using di-
2
93T cells were grown in DMEM medium which supplemented with
1
0 % (v/v) fetal bovine serum, penicillin (100 μg/mL), and strepto-
chlormethane and petroleum ether (1:1, V/V) to give compound NBOS
mycin (100 μg/mL). The 293T cells were seeded on 8-well plates and
incubated 24 h at 37 °C in above culture medium and allowed to grow
to 60–70 % confluence. For imaging of Zn2+ in living cells, the cells was
cultured using fresh medium and the 10 μmol/L probe NBOS was added
to each well. After being incubated for 30 min, the Zn2+ was added into
for another 30 min. Fluorescence image of the cells were observed on a
confocal laser scanning microscope (Olympus FV1000), with green
channal imaging obtained from 500 to 600 nm with 488 nm excitation.
1
(
80 mg, 20 %) as green crystal [35]. H NMR (Fig. S2) (500 MHz,CDCl
3
)
1
H NMR (500 MHz, CDCl
3
) δ 12.20 (s, 1 H), 8.79(s, 1 H), 8.24(d, 1 H),
.10(d, 1 H), 8.04(d, 1 H), 7.94(d, 1 H), 7.75(d, 1 H), 7.70(d, 1 H),
.56(m, 2 H), 7.47(m, 4 H). ESI–MS (Fig. S3): calcd for C24H N O S:
14 2 2
8
7
3
−
93.07 [NBOS-H] , found: 393.07.
3

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
Fig. 1. X-ray crystal structure of NBOS.
Scheme 2. Proposed sensing mechanism of NBOS with Ag+ and Zn2+
.
+
Fig. 2. (a) UV-vis spectral changes of NBOS (10 μM) towards different concentrations of Ag in EtOH/H
2
O (9/1, V/V, pH = 7.4) medium. Inset: The color change of
+
NBOS (20 μM) before and after addition of Ag (50 μM) in EtOH/H
2
O (9/1, V/V, pH = 7.4) medium under normal light. (b) The linear responses of UV–vis ratio at
3
80 nm and 482 nm (A482nm/A380nm) with Ag+ concentractions.
3
. Results and discussion
NBOS (Fig. 1a). The dihedral angle between the naphthalene and
benzooxazole unit and benzothiazole was 63.7° (Fig. S4). The severe
distortion of NBOS may be ascribed to the steric hindrance effect. The
molecular structure of NBOS was stabilized by intramolecular hydrogen
3.1. Crystallographic details for NBOS
The structure of NBOS was further confirmed by single crystal X-ray
diffraction analysis, which clearly revealed the nonplanar structure of
bonding which was clearly visible in Fig. 1b. The intramolecular hy-
drogen bond was formed between OeH of naphthalene ring, N atom of
4

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
2
Fig. 3. (a) UV-absorbance spectra of NBOS (10 μM) in the presence of various metal ions (50 μM) in EtOH/H O (9/1, V/V, pH = 7.4) medium. (b) Color change
2
+
2+
2+
2+
+
2+
2+
2+
2+
2+
2+
2+
2+
3+
3+
+
induced after addition of 5 equiv. of various metal ions (Zn , Ni , Cd , Cu , NBOS, Ag , Co , Mg , Ca , Ba , Hg , Pb , Sr , Fe , Al , Fe , Li
,
+
+
+
2
La , Na , K ) to NBOS (20 μM) in EtOH/H O (9/1, V/V, pH = 7.4) medium.
benzooxazole and S atom of benzothiazole preferentially, which was
necessary for occurrence of the desired ESIPT process. Furthermore,
due to the coplanar of naphthalene and benzooxazole, the proton would
hop between hydroxy of naphthalene ring and imine of benzooxazole at
excited state preferentially, the so-called ESIPT process (Scheme 2). All
the significant crystallographic data and refinement parameters were
shown in Tables S1 and S2.
assumption that NBOS and NBOS+Ag+ were coexisting in the solution
[36]. Obviously, the UV–vis titration experiments exhibited that the
UV–vis ratio at 380 nm and 482 nm (A482 nm/A380 nm) increased from
0.1 to 1.8. In addition, the UV–vis ratio at 368 nm and 442 nm (A442 nm
/
+
A
368 nm) was plotted as a function of the various concentration Ag
added. The good linearity between UV–vis ratio of A482 nm/A380 nm and
+
Ag concentractions ranging from 3 μM to 80 μM were observed and
the detection limit was obtained to be 4.24 μM by applying equation 3
δ/S [37].
.2. UV–vis absorbance-ratiometic detection of Ag+
The selectivity of probe NBOS for Ag+ was investigated by UV–vis
3
absorbance spectrometry in EtOH/H
2
O (9/1, V/V, pH = 7.4) mixture.
The investigation of probe NBOS sensing ability was carried out by
In Fig. 3, probe NBOS exhibited major absorption peak at 380 nm.
Addition Zn2+, Cd , Cu , Ni red shifted the absorbance peak from
380 nm to 440 nm and resulted in slightly yellow green color appear-
ance. However, addition of Ag+ showed the reduction of origin ab-
sorption band at 380 nm and appeared a new absorption band at
482 nm. Such a large red shift in absorption spectrum lead to an ob-
vious color change from colourless to pale pink. These phenomena
2+
2+
2+
UV–vis absorbance titrations (Fig. 2) in EtOH/H
2
O (9/1, V/V,
pH = 7.4) mixture. The absorption maximum of probe NBOS was
+
3
3
80 nm. With gradual addition of Ag , the origin absorption band at
80 nm decreased gradually while a new absorption band at 482 nm
increased accompanied by a visual color change from colourless to pale
yellow. A well-defined isosbestic point was observed at 396 nm, in-
dicating that only one new species was fomed, supporting the
5

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
2
+
Fig. 4. (a) Fluorescence spectral changes of NBOS (10 μM) towards different concentrations of Zn in EtOH/H
2
O (9/1, V/V, pH = 7.4) medium. Inset: Photograph
O (9/1, V/V, pH = 7.4) medium under UV light of
2
+
of the fluorescence change of the solution of NBOS (10 μM) before and after addition of Zn (50 μM) in EtOH/H
2
2
+
365 nm. (b) The linear responses of fluorescence intensity at 550 nm with Zn
concentractions.
Fig. 6. Fluorescence spectral of NBOS (10 μM) in the presence of various metal
ions (50 μM) in EtOH/H O (9/1, V/V, pH = 7.4) medium (λex = 450 nm).
2
Fig. 5. CIE diagram of the probe NBOS and NBOS with Zn2+ (5 equiv.) in
EtOH/H
2
O (9/1, V/V, pH = 7.4) medium (λex = 450 nm).
suggested that NBOS could be used as a Ag probe. But, when Zn2+,
+
2
+
2+
2+
+
Cd , Cu
and Ni
were present, the detection of Ag almost cer-
tainly interfere.
Furthermore, the effect of pH on the UV–vis ratio sensing ability of
+
NBOS towards Ag was investigated. Probe NBOS exhibited negligible
relative absorbance ratios at 482 nm and 380 nm (A482 nm/A380 nm) over
+
a wide pH range (2–10). Upon addition of Ag , a remarkable increase
of absorbance ratios (A482 nm/A380 nm) in the pH range from 6 to 7.5
(
Fig. S5). Hence, the suitable pH range of 6–7.5 made it possible to
+
detect Ag using probe NBOS.
Fig. 7. Fluorescence intensity at 550 nm of NBOS (10 μM) upon addition of
3
.3. Fluorescence titration spectra for Zn2+
2+
various metal ions (50 μM) in the presence Zn (50 μM) in EtOH/H
V, pH = 7.4) mixture (λex = 450 nm).
2
O (9/1, V/
Moreover, as shown in Fig. 4, upon addition of Zn2+, the fluores-
cence intensity at 550 nm increased gradually, and probe NBOS with
6

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
Fig. 8. The calculated molecular orbitals and the HOMO-LUMO gaps of NBOS and NBOS+Zn2+
.
Zn2+ showed visual color change from colorless to yellow under
Fe2+ were low but detectable. The fluorescence of NBOS+Zn
plexation was completely quenched by Cu
2+
com-
2+
3+
365 nm UV lamp. Furthermore, there was a good linear relationship
and Fe . Therefore,
between the maximal fluorescence intensity of NBOS and the con-
NBOS could be applied as an effective probe for Zn2+ in the presence of
most competing metal ions.
2
+
centration of Zn
varied from 2 μM to 20 μM. The detection limits of
+ −9
2
probe NBOS for Zn was confirmed to be 3.17 × 10 M by applying
equation 3 δ/S [37]. The nonfluorescent nature of the probe NBOS was
caused by the ESIPT progress at the excited state. Because of chelating
of the probe NBOS with Zn , the ESIPT processes in corresponding
were inhibited, resulting in significant enhancement of the fluores-
cence.
The time response of probe represented the sensitivity. Therefore,
we further investigated the time response on fluorescence intensity of
the probe NBOS to Zn2+ (2.0 equiv) in EtOH/H
O (9/1, V/V, pH = 7.4)
2
2
+
mixture. The fluorescence response signal showed instant enhancement
and reached saturation with 2 s upon addition of Zn2+ (Fig. S6). In
addition, the fluorescence intensity was almost unchanged over a
period of time, indicating that complexation process of probe NBOS
with Zn2+ was fast and stable, which had potential application for
CIE chromaticity diagram was usually used to better explain the
colour variation in the emission spectrum of luminescent materials
[
38,39]. To better understand chromaticity changes of the probe upon
quickly detection Zn2+
.
complexation, CIE chromaticity coordinates were also calculated from
the fluorescence spectrum. The CIE system identified the colour of the
fluorescent emission more precisely by a two-dimensional space (XY
In order to demonstrate whether probe NBOS had a good perfor-
mance under physiological conditions, the pH effect of on the fluores-
cence and UV–vis response of probe NBOS toward Zn2+ in a pH range
from 2.0 to 12.0 was investigated. As shown in Fig. 8, probe NBOS
exhibited negligible relative fluorescence intensity at 550 nm over a
wide pH range (2–10) (Fig. S7). For the mixture of probe NBOS with
2
+
plane). The CIE chromaticity coordinates of NBOS-Zn
complex was
found to be x = 0.4084, y = 0.5792 at room temperature. These color
point data suggested that the color coordinates shifts gradually from
yellowwish green to yellowgreen color region upon progressive addi-
2+
Zn , a strong fluorescence emission at 550 nm was observed in a wide
pH range from 6.0 to 10.0, indicating that probe NBOS could detect
2
+
tion of Zn
in to the solution of probe NBOS (Fig. 5).
2+
To investigate selectivity of probe NBOS, it was incubated with each
Zn
under physiological condition.
+
2+
2+
+
+
2+
2+
+
of various metal ions including Ag , Cd , Co ,Na , K , Ba , Fe
Co , Ni , Ca , Zn , Cd , Cu , Mg2+, Pb , Fe , Li , La ,
2
+
2+
2+
2+
2+
2+
2+
3+
+
3.4. Mechanism study
3
+
Sr
and the fluorescence spectroscopy was measured. As shown in
Fig. 6, probe NBOS alone and other metal ions all exhibited very weak
In order to explore the combination code of the probe NBOS with
2
+
Ag+ and Zn , the FT-IR (Fig. S8), H NMR (Fig. S9) of NBOS+Ag
2+
1
+
single fluorescence emisson band at 550 nm except for Zn . After
2
+
2+
addition of Zn , probe NBOS showed a prominent fluorescence en-
hancement. In addition, the fluorescence quantum yield of probe NBOS
and NBOS+Zn complex were measured. The FT-IR spectra of NBOS
+Zn2 complex exhibited a wide peak at 3376 cm , because of pre-
+
−1
2
+
before and after addition of Zn was determined to be as high as 0.03
and 0.62 (using rhodamine B as standard), respectively. This property
indicated that probe NBOS could specifically fluorescence “turn on”
sence of H O molecules in the complex. The FT-IR spectra of NBOS
2
+
2+
+Ag and NBOS+Zn
complex appeared obviously strong peaks at
respectively, which attributed to NeO vi-
−
1
−1
1350 cm
and 1381 cm
2
+
3−
test Zn
.
bration of the NO . Compared to the FT-IR spectra of NBOS, the
−
1
Additionally, the competition experiments were performed by
characteristic eCeSe absorption peak at 1153 cm widen and shifted
to the lower wavenumber in the presence of Ag+ and Zn , indicating
that the intramolecular hydrogen bond was broken.
2
+
2+
adding 5 equiv. Zn to the solution of probe NBOS in the presence of 5
equiv. above metal ions. As shown in Fig. 7, negligible interference was
2
+
2+
2+
+
1
observed for the detection of Zn in the presence of Cd , Co , Na ,
H NMR experiments was performed in CDCl . The hydroxyl proton
3
K , Ba , Co , Ni , Ca , Mn2+, Mg , Pb , Bi , Li , La
Sr . The probe NBOS responses to Zn
+
2+
2+
2+
2+
2+
2+
3+
+
3+
,
of the naphthalene ring part was not observed in the spectrum of NBOS
2
+
2+
3+
+
2+
in the presence of Al
and
+Ag
and NBOS+Zn
complex, suggested the occurrence of
7

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
Fig. 9. UV–vis ratio detection of Ag+ and fluorescence determination of Zn2+ in distilled water and lake water by NBOS (10 μM) in EtOH/H
O (9/1, V/V, pH = 7.4)
+
2
mixture.
This result suggested certain complex formation of NBOS and Ag /
2+
Zn
.
The detailed binding mode was confirmed by mass spectrometry
+
analysis. The mass spectrum was measured in the presence of Ag /
2+
2
Zn in EtOH/H O (9/1, V/V, pH = 7.4) mixture. The peak at 538.43
+
+
was observed, assigned as [NBOS-H+Ag +K] (calc = 538.9) (Fig.
S10), providing a powerful evidence for formation of 1:1 coordination
complex between Ag+ and NBOS. The peak at m/z 393.07 and m/z
−
2
54.02 corresponding to [NBOS-H] (calc = 393.07) and [1/2(NBOS-
2+
− −
H + Zn +3OH )] (calc = 254.00) (Fig. S11), respectively, in-
dicating NBOS+Zn2+ comprised by a receptor, a Zn+ and 3 OH .
2+
−
2+
Moreover, the job’t plot of the probe NBOS with Ag and Zn
was
carried in EtOH/H
total concentration remained unchanged of NBOS+Ag (5 × 10
2
O (9/1, V/V, pH = 7.4) mixture, respectively. The
+
−5
2+
−5
+
mol/L) and NBOS+Zn
(10
mol/L) with the molar ratio of Ag /
2+
Zn
varied from 0.1 to 0.9 (Fig. S12). Both maximum absorbance
ratios (A482 nm/A380 nm) and fluorescent intensity at 550 nm exhibited at
around 0.5 M fraction, suggesting a 1:1 ratio for the probe NBOS with
Ag /Zn , which was consistent with the result of mass analysis.
2
+
Fig. 10. Fluorescence spectra of NBOS (10 μM) for determination Zn
walnut in EtOH/H O (9/1, V/V, pH = 7.4) mixture.
in
+
2+
2
According to the UV–vis/fluorescence titration data and 1:1 binding
+
stoichiometry, the association constant (K) of probe NBOS with Ag /
deprotonation during the coordination of the hydroxyl group with
2+
+
2+
Zn was determined by using Benesi-Hildebrand (B–H) equation (Fig.
Ag /Zn . All signal of aromatic protons in the spectrum of NBOS
4
−1
+
2+
S13) [18,40]. The K value was calculated to be 1.81 × 10
M
and
+
Ag and NBOS+Zn
complex were observed to be decreased and
4
−1
+
9.62 × 10 M
by curves of [1/(A − Amin)] against 1/[Ag ] and 1/
shifted a little downfield as compared to the spectrum of free NBOS.
8

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
Fig. 11. Fluorescence image of Zn2+ in 293T cells.
Scheme 3. Truth table and logic gate diagram based on Ag+ and Zn2+ by means of absorbance and fluorescence intensity.
(
F
550 nm − Fmin) against 1/[Zn2+], respectively.
Based on above experimental supports from various spectroscopic
3.5. DFT study
+
2+
techniques, the proposed mechanism for the detection of Ag /Zn
using the probe NBOS was well presented in Scheme 2.
To further understand the electronic structures of NBOS and NBOS
+Zn2 complex, density functional theory (DFT) calculation using
Gaussian 09 programme was performed [41,42]. As shown in Fig. 8, the
+
9

N.-N. Li, et al.
Journal of Photochemistry & Photobiology A: Chemistry 390 (2020) 112299
electron cloud in HOMO (−5.49 eV) of NBOS was spread on the ben-
zothiazole and naphthalene subunit. The result suggested that hydroxyl
and nitrogen atom were likely to chelate with metal ions. Furthermore,
the calculated energy gaps between HOMO and LUMO were 3.38 eV for
3.10. Logic gate
Absorbance peak at 482 nm appeared only occurring coordination
between NBOS and Ag . The fluorescence intensity at 550 nm of probe
NBOS increased only after addition of Zn . Therefore, when we con-
sidered the absorbance at 482 nm and fluorescence intensity at 550 nm
as outputs, the two signals were Input 1 (Ag ) and Input 2 (Zn ), OR
and INHIBIT logic gate was constructed [46,47]. When Input 1 (Ag )
was present and Input 2 (Zn ) was absent or Input 1 (Ag ) was absent
and Input 2 (Zn2+) was present, the output 2 and output 1 respectively
were 0 state, which presented combination gate (blue period). When
the opposite situation appeared, it exhibited OR gate (gray period). The
logic gate was showed in Scheme 3.
+
2
+
2+
NBOS and 1.08 eV for NBOS+Zn , which suggested the higher sta-
2
+
bility of NBOS+Zn
than the free NBOS. As we expected, the ex-
+
2+
perimental results agree with that of theoretical calculation.
+
2+
+
+
3
.6. Reversibility of NBOS for Ag and Zn2+
The reversibility was crucial for cost efficiencies of the probe.
Therefore, we designed experiments to improve the reversibility of
+
2+
probe NBOS to Ag and Zn
mixture using ethylenediaminetetraacetic acid (Na
erful chelator for metal ions. Upon addition of Na
in EtOH/H
2
O (9/1, V/V, pH = 7.4)
EDTA) as a pow-
EDTA, the UV–vis
absorbance spectra of NBOS+Ag and fluorescence spectra of NBOS
2
4. Conclusion
2
+
In summary, a novel naphthalene based probe NBOS for detection
2
+
+
Zn
almost back to the state of free NBOS (Figs. S14 and S15).
Ag+ and Zn by using two different optical modes in EtOH/H
2+
2
O (9/1,
These results suggested that NBOS could serve as a reversible probe for
V/V, pH = 7.4) medium based on the inhibition of ESIPT progress was
+
2+
detection Ag and Zn
in physiological condition.
developed. The binging mode of NBOS with Ag+ and Zn
2+
was con-
firmed. Moreover, probe NBOS was successfully applied in real water
.7. Detection Ag+ and Zn2+ in water samples
Considering the pollution of Ag+ and Zn2+ in the environment, the
samples detection Ag+ and Zn+ with good accuracy and exhibited a
2+
3
2+
logic gate with two inputs Ag and Zn . Importantly, probe NBOS
2+
could be used to detect Zn
in walnut and living cells.
+
2+
probe NBOS was applied in the detection of Ag and Zn in real water
samples by the proposed UV–vis ratio and fluorimetric method, re-
spectively. The tap water was collected from chemistry building in
Ocean university of China. The lake water was collected from lake that
located in Ocean university of China. These water samples were spiked
with Ag (5, 10, 15, 20, 25, 30 μM) and Zn
respectively. As shown in Fig. 9, the relative absorbance ratios at
4
5
CRediT authorship contribution statement
Na-Na Li: Conceptualization, Methodology, Software, Data cura-
tion, Writing - original draft. Cai-Feng Bi: Supervision. Xia Zhang:
Supervision. Cun-Gang Xu: Software, Validation. Chuan-Bin Fan:
Writing - review & editing. Wei-Song Gao: Software, Validation. Zi-Ao
Zong: Software, Validation. Shan-Shan Zuo: Investigation. Chuan-
Feng Niu: Investigation. Yu-Hua Fan: Supervision.
+
2+
(5, 6, 7, 8, 9, 10 μM),
82 nm and 380 nm (A482 nm/A380 nm) and fluorescence intensity at
50 nm showed nice linearity for tap and lake water. In addition, it
displayed good recovery values (97–104 %) (Table S1). These results
further indicated that the practical value of the probe NBOS for de-
Acknowledgements
+
2+
tection Ag and Zn
NBOS could be used for the detection Ag and Zn accurately in real
in environment. These results suggested that
+
2+
This work was supported by the Fundamental Research Funds for
the Central Universities (No. 201822012), the National Natural Science
Foundation of China (Nos. 21476218 and 21601171).
water samples.
3
.8. Detection Zn2+ in walnut
Appendix A. Supplementary data
In order to evaluate the practical application of probe NBOS for
detection Zn in our daily life, the walnut containing trace amount of
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.jphotochem.2019.
2
+
2
+
Zn
and immersed in HNO
taining solution [43–45]. In Fig. 10, the probe NBOS (5 mL) showed
was used in the sample analysis. The walnut (0.5 g) were broke
112299.
(10 mL), then added NaOH and al Zn2+-con-
3
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revealed that Zn content in walnut was 0.0211 mg/g. The result was
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