Synthesis, characterization and Al3+ sensing application of a new chromo-fluorogenic chemosensor

Article abstract of DOI:10.1016/j.molstruc.2019.05.032

A rhodamine B-based chromo-fluorogenic probe BOS is prepared with a good yield by condensating an o-diaminobenzene functionalized rhodamine derivative (RBO) and a large steric hindrance salicylaldehyde, and characterized by elemental analysis, infrared sp

Full text of DOI:10.1016/j.molstruc.2019.05.032

Accepted Manuscript
3+
Synthesis, characterization and Al sensing application of a new chromo-fluorogenic
chemosensor
Xin Leng, Xu Jia, Chengfang Qiao, Wenfeng Xu, Chongting Ren, Ying Long, Bingqin
Yang
PII:
S0022-2860(19)30591-5
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.032
MOLSTR 26539
Reference:
To appear in: Journal of Molecular Structure
Received Date: 22 December 2018
Revised Date: 9 May 2019
Accepted Date: 10 May 2019
Please cite this article as: X. Leng, X. Jia, C. Qiao, W. Xu, C. Ren, Y. Long, B. Yang, Synthesis,
3+
characterization and Al sensing application of a new chromo-fluorogenic chemosensor, Journal of
Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.05.032.
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Synthesis, Characterization and Al3+ Sensing Application of a
New Chromo-Fluorogenic Chemosensor
Xin Leng,‡a Xu Jia,‡a Chengfang Qiao,b,* Wenfeng Xu,a Chongting Ren,a Ying Long,a
Bingqin Yanga,*
a
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of
Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710127,
China
b
Shaanxi Key Laboratory of Comprehensive Utilization of Tailings Resources, College of
Chemical Engineering and Modern Materials, Shangluo University, Shangluo 726000, China
‡ Both authors contributed equally to this work
*Corresponding Authors: Prof. Bingqin Yang (E-mail address: organic_lengxin@163.com);
Prof. Chengfang Qiao (E-mail address: xiaoqiaoqcf@126.com)
Abstract
A rhodamine B-based chromo-fluorogenic probe BOS is prepared with a good yield
by condensating an o-diaminobenzene functionalized rhodamine derivative (RBO)
and a large steric hindrance salicylaldehyde, and characterized by elemental analysis,
1
infrared spectroscopy (IR), H and 13C NMR technology, and high resolution mass
spectrum (HRMS). Spectroscopy experiments reveal that the probe can selectively
and sensitively detect Al3+ from a variety of metal ions with a low detection limit of
1.855 ꢀmol/L. Compared to traditional detection methods, BOS provides an
inexpensive, rapid and straightforward way for Al3+ detection that can be
distinguished
by
“naked
eye”.
The
MTT
(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2-H- tetrazoliubromide) assays and cell
imaging experiments demonstrate that the sensor is low toxic and amicable for Al3+
sensing in living cells.
Keywords: Rhodamine derivative; Fluorescence probe; Bioimaging; Al3+ Detection
1. Introduction
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Aluminium, known as the maximum metallic element on the earth [1-5], has
developed rapidly in the past decades. It is widely applied in daily routine ranging
from water purification, aluminium-ion battery, packing materials, food additives
[6-9]. Meanwhile, due to the accumulation of excessive ingestion, the damage of
dissolved Al3+ in human body has received increasing attention from a number of
different disciplines, among which medical research announces that Alzheimer’s
disease is caused by a typical neurofibril injury from aluminium [10, 11]. This
promotes the invention to quantificationally analyze Al3+ in a fast and visible way.
Technologies that concentrate on Al3+ detection more frequently adopt approaches
like 27Al NMR technology, atomic absorption spectrometry (AAS), inductively
coupled plasma atomic emission spectrometry (ICP-AES), mass spectrometry and
electrochemical methods, while most of them are complicated, time-consuming as
well as expensive due to insufficient spectroscopic characteristics of Al3+ [12-16].
Fluorescence analysis, reported as a convenient, low cost, sensitive and quick
response method [17], has promoted the developement of fluorescence sensing, and
led to the emergence of a large number of effective and sensitive chemosensors.
Given the inherent nature of aluminium ion such as poor bonding capacity and
robust tendency to hydrolysis, micromolecular Al3+ fluorescent sensors with
multidentate coordination sites and strong chromophore are highly promising.
Therefore, among the “off-on” fluorescent sensors [18], rhodamine-based probes
are highlighted because of their extraordinary photophysical properties like good
photostability, relatively higher fluorescence quantum yield, excellent
anti-interference capacity, advanced detection mechanism and special emission
wavelength [19].
In this paper, a newly designed rhodamine-based probe BOS was obtained
based on a three-step synthesis procedure (Scheme 1). In BOS, the flexible benzoic
acid moeity of rhodamine B was substituted by the functional group with
multidentate chelation sites to form the spirolactam form, which benefits to chelate
target ions to display “turn-on” fluorescence signal by the conformational switching
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from spirocyclic to open-cycle structure. Additionally, the large steric hindrance
tertiary butyl groups were introduced on the salicylaldehyde functional group for
trying to improve the sensing selectivity of BOS. This chemosensor can be utilized
to detecte Al3+ in a naked-eye way through the fast and remarkable fluorescence
enhancement and obvious colour variations. The outstanding characterizations of
BOS endow it great potential applications for biological imaging [20-24].
POCl3
COOH
COCl
ClCH2CH2Cl
Reflux
N
O
N
N
O
N
Cl
Cl
Rhodamine B chloride oxide
Rhodamine B
CH3CN
N(CH2CH3)3
RT
NH2
NH2
HO
C(CH3)3
OH
NH2
N
O
N
O
N
(H3C)3C
CH3CH2OH
Reflux
CHO
N
O
N
N
O
N
RBO
BOS
Scheme 1. Synthesis of BOS.
2. Experimental section
2.1. Materials and methods
All materials were purchased commercially without further purification. The
BOS powders were dissolved in ethanol as stock solutions (1 mmol/L), which were
taken quantificationally in different experiments. Fluorescence and absorbance spectra
were performed on a HITACHI F-4500 fluorescence spectrophotometer and a
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Shimadzu UV-1700 spectrophotometer, respectively. Elemental analyses for C, H, and
N were determined on a Vario EL III elemental analyzer. Infrared spectrum was taken
on a Bruker Tensor 27 spectrometer within the range of 4000-400 cm-1 by using KBr
pellets. NMR spectra were obtained on a Varian INOVA-400 MHz spectrometer (at
1
100 MHz for 13C NMR and at 400 MHz for H NMR). A Bruker micro TOF-Q II
ESI-TOF LC/MS/MS Spectroscopy was used to perform mass spectra. Melting point
test was recorded on an XT-4 micromelting apparatus without corrected. Living cells
imaging experiments were preformed on an Olympus FV1000 confocal microscopy.
Cytotoxicity analysis was recorded with the Soft max pro software (version 2.2.1) in
Spectra max190-Molecular Devices. Thermogravimetric analysis was investigated
using a Netzsch STA 449C thermogravimetric analyzer.
2.2. Synthetic procedures
2.2.1. Synthesis of the intermediate product RBO
POCl3 (1 mL, 10 mmol) was added to a 30 mL 1,2-dichloroethane solution of
rhodamine B (1.60 g, 3 mmol), the reaction mixture was refluxed for 8 h. After
cooling to ambient temperature, the solvent was removed under reduced pressure, and
the residue directly reacted with o-phenylenediamine (0.32 g, 3 mmol) in CH3CN. 30
min later, triethylamine (1 mL) was added into the resulting mixture, and stirred for
10 h. After removal of the solvent under reduced pressure, the crude product was
purified by silica gel column chromatography to give RBO in 89.2% yield. The high
resolution mass spectrum (HRMS) analysis for RBO (C34H36N4O2): Calculated: m/z =
1
532.2838, Found: 533.2897 (M+H)+ (Fig. S1). H NMR (400 M, CDCl3), δ:
8.07‒8.09 (d, J = 8 Hz, 1H), 7.57‒7.62 (q, J = 8 Hz, 2H), 7.29‒7.31 (d, J = 8 Hz, 1H),
6.98‒7.01 (t, J = 4 Hz, 1H), 6.80‒6.08 (m, 9H), 3.32‒3.37 (dd, J = 8 Hz, 8H),
1.17‒1.21 (t, J = 8 Hz, 12H) (Fig. S2).
2.2.2. Synthesis of BOS
The intermediate RBO (0.53 g, 1 mmol) and 3,5-ditert-butyl salicylaldehyde
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(0.23 g, 1 mmol) were dissolved in 40 mL ethanol solution, stirred and refluxed for 1
h at 80 °C. After cooling to room temperature, the beige precipitate was purified by
recrystallization in ethanol/water to give BOS (beige powder) in 90.8% yield. Melting
point: 157~158 ꢀ. Elemental analysis for C49H56N4O3 (%): Calculated: C, 78.58; H,
7.54; N, 7.48. Found: C, 78.62; H, 7.56; N, 7.46. HRMS (ESI) calcd. for BOS
(C49H56N4O3) m/z = 748.4352, Found: 749.4405 (M+H) +. IR (KBr) υ: 3444, 2962,
2071, 1702, 1616, 1514, 1356, 1223, 1117, 820, 756 cm-1. 1H NMR (400 M, CDCl3) δ:
13.07 (s, 1H), 8.01 (d, J = 8.2Hz, 2H), 5.96‒7.49 (m, 13H), 5.65 (d, J = 8.6 Hz, 1H),
5.21 (s, 1H), 3.29 (q, J = 6.8 Hz, 4H), 3.03 (d, J = 8.2 Hz, 4H), 1.29 (s, 9H), 1.22 (s,
13
9H), 1.11 (t, J = 8.6 Hz, 6H), 0.93 (t, J = 8.2 Hz, 6H). C NMR (100 M, CDCl3) δ:
166.2, 164.32, 158.3, 154.2, 153.3, 152.1, 147.7, 139.7, 136.9, 132.4, 132.4, 130.4,
130.1, 129.2, 129.0, 128.3, 127.8, 126.3, 126.3, 124.1, 123.7, 119.3, 118.4, 108.3,
67.9, 44.5, 35.0, 34.1, 31.5, 29.3, 12.5 (Figs. S3-S6).
2.3. Preparation of the test solution
The stock solution of BOS (100 ꢀmol/L) was prepared in ethanol-water (1:9, v/v,
Tris-HCl, pH =7.2). The solutions of various testing cation species were prepared
from Ca(NO3)2·4H2O, AgNO3, Mg(NO3)2·6H2O, NaNO3, Co(NO3)2·6H2O,
Cd(NO3)2·4H2O,
Zn(NO3)2·6H2O,
Cu(NO3)2·3H2O
,
Mn(NO3)2·4H2O,
Hg(NO3)2·H2O, Ni(NO3)2·6H2O, Pb(NO3)2, Cr(NO3)3·9H2O, Pd(NO3)2·2H2O,
Sn(NO3)2, Ba(NO3)2, KNO3, LiNO3, Fe(NO3)3·9H2O and Al(NO3)3·9H2O using
double distilled water. Before test, the cation solutions with different concentrations
were obtained by diluting the thick solutions. The detailed experimental procedures
are as follows: For the titration tests, 1 mL of the BOS stock solution and different
amounts of Al3+ were mixed and diluted to 10 mL in volumetric flasks using
ethanol-water (1:9 v/v, Tris-HCl, pH = 7.2) solution. For the selectivity tests, 1ꢁmL of
metal ion solution (100ꢁꢀmol/L) and 1ꢁmL of BOS solution (100ꢁꢀmol/L) were added
to a 10ꢁmL volumetric flask and diluted with ethanol-water (1:9 v/v) solution. For the
interference experiments, 1ꢁmL of interference metal ion solution (1ꢁmmol/L) were
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added into the mixed solution containing 1ꢁmL of BOS solution (100ꢁꢀmol/L) and
1ꢁmL of Al3+ solution (100ꢁꢀmol/L).
2.4. Cytotoxicity assays
The toxicity of the probe and metal cation was assessed by using SGC-7901
living cells according to the conventional MTT assays. The 90% confluent cells were
digested by 1 mL trypsin (0.25%) and seeded into a 96-well plate. Cells were
culturing in a mixed medium of Dulbecco's modified eagle medium (DMEM) and 10%
fetal bovine serum (FBS) at 37 °C under a humid environment including 5% CO2 for
24 h. Then, the cells were treated with different concentrations of BOS and Al3+ for
another 24 h, respectively. After that, the medium was removed and washed with
phosphate buffered saline (PBS) for three times. Then the medium was replaced with
the mixed solution of MTT (5 mg/mL) and culture medium, and incubated for an
additional 4 h. Following this, the MTT was removed and washed three times with
PBS. Subsequently, 150 ꢀL DMSO was carefully added to each tube and processed by
ultrasonic oscillation for 10 minutes. All the experiments were conducted in triplicate.
The cell viability (%) was calculated according to the Equation: Cell viability (%) =
[OD490(sample) / OD490(control)] ×100%, where OD490(sample) represents the
optical density of the wells treated with various concentration of probe or metal ions
and OD490(control) represents that of the wells treated with ethanol.
2.5. Cell culture and fluorescence imaging
The SGC-7901 living cells (human gastric carcinoma cells) were cultured
in DMEM supplemented with 10% FBS. Before the experiments, the cells were
pretreated by BOS (10 ꢀmol/L) for 1 h at 37 °C in humidified air with 5% CO2,
washed three times with PBS and images were obtained. After incubation with
Al3+ (10 ꢀmol/L) for another 1.5 h at 37 °C, the cells were washed three times
with PBS to remove remaining Al3+ before imaging. Confocal fluorescence
imaging was carried out on Olympus FV1000 laser scanning microscope with
80× objective lens.
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3. Results and discussion
3.1. Spectroscopic properties
The spectroscopic properties were explored in both fluorescence and absorption
spectra thoroughly. And the results indicated that the probe showed remarkable
selectivity and sensitivity for the detection of Al3+ in ethanol-water (v/v = 1:9). As can
be seen in Fig. 1a, the reaction of BOS (10 ꢀmol/L) with Al3+ underwent a noticeable
color change from colourless to peach-red, while no change in color was found when
reacting with other metal cations. Similar results also could be observed when
irradiated under a fluorescent light (365 nm), the BOS reacting with Al3+ caused a
dramatic color change from colourless to bright yellow (Fig. 1b). Therefore, the BOS
owned high selectivity towards Al3+ and could be successfully utilized as “naked-eye”
probe for Al3+ detection.
Fig. 1. Visual color (a) and fluorescence (b) change of the ethanol-water solution of BOS upon the
addition of different metal ions.
The sensitivity of BOS towards Al3+ was checked by the fluorescence titration
experiments. As depicted in Fig. 2a, because of the special spirolactam structure of the
free BOS, no fluorescence emission was detected in the wavelength range of 570 –
700 nm. Nevertheless, when Al3+ was gradually added from 0 to 1.0 equiv, the
emission intensity remarkably increased at 595 nm, which indicated that the xanthene
moiety was interfered by the delocalization effect, and BOS was a ture “off-on”
sensor toward Al3+. No significant change in the fluorescence intensity was observed
with further addition of Al3+ (up to 1.25 equiv), which is about 105 times than that of
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the free BOS (Fig. 2b). The remarkable fluorescence enhancement implied that the
ring-opening of spirolactam or the inhibition of the rotation of the “C=N” bond
occurred with the gradual addition of Al3+, and a delocalized π-conjugated moiety
established eventually.
Fig. 2. (a) Fluorescence spectra of BOS (10 ꢀmol/L) and (b) the changes of the fluorescence
intensity at 595nm with the addition of different concentrations of Al3+ (0-1.25 equiv) in
ethanol-water (1:9, v/v, Tris-HCl, pH =7.2) solution.
The results of the titration experiment were analyzed to figure out the
quantitative relationship between the emission intensity of BOS and the Al3+
concentration. And the association constant K of BOS with Al3+ was determined to be
4.204*104 L/mol through the Benesi-Hildebrand equation: (Fmax-F0) / (Fx-F0) = 1 +
(1/K) (1/[Al3+]), where Fmax, F0 and Fx are the fluorescence intensities of probe in the
presence of Al3+ at saturation, free probe, and any intermediate Al3+ concentration,
respectively (Fig. 3a). Additionally, the detection limit of BOS was further determined
from the above results. As shown in Fig. 3b, according to the widely used method
[25,26], linear regression curve was fitted based on the plots of (Fmin - Fx) / (Fmin
-
Fmax) vs log[Al3+], in which the Fx is the emission intensity at various concentration of
Al3+, Fmin and Fmax are respectively the minimum and maximum fluorescence intensity
at 595 nm. After fitting the data, the intercept of the line at x-axis was recorded as the
detection limit of 1.855 ꢀmol/L.
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Fig. 3. (a) Benesi–Hildebrand plot of BOS using 1:1 stoichiometry for association. (b) The plot of
(Fmin - Fx) / (Fmin - Fmax) versus log[Al3+] for the probe BOS.
The selectivity and anti-interference performance of probe are significant for its
application. Hence, the fluorescence response of BOS (10 ꢀmol/L) towards Al3+ ions
and other various metal ions in ethanol-water (1:9 v/v, Tris-HCl, pH =7.2) was
investigated. As shown in Fig. 4a, the free BOS exhibited negligible fluorescence
emission. When different metal cations (Mn2+, Pb2+, Cd2+, Co2+, Fe3+, Al3+, Cu2+, Ni2+,
Ag+, Zn2+, Cr3+, Hg2+, Pd2+, Sn2+, K+, Li+, Na+, Ca2+, Mg2+, Ba2+) were added into the
BOS system, only Al3+ caused a significant fluorescence enhancement at 595nm, and
no obvious fluorescence signals were detected for other ions, indicating the good
selectivity of BOS as Al3+ sensor. For the interference experiment (Fig. 4b), when
10.0 equiv of competitive ions (K+, Li+, Na+, Ca2+, Mg2+, Ba2+, Mn2+, Pb2+, Cd2+, Co2+,
Fe3+, Cu2+, Ni2+, Ag+, Zn2+, Cr3+, Hg2+, Pd2+, Sn2+) were respectively added into the
BOS test solutions, almost no change in emission intensity was found. On the
contrary, upon the further addition of 1.0 equiv of Al3+, a rapid fluorescence
enhancement occurred, which suggested that the sensing response of BOS to Al3+
could hardly be influenced by other coexisting metal ions. The characteristics of high
selectivity and sensitivity as well as the excellent anti-interference performance
enabled BOS to be potentially used for Al3+ ions detection in complex systems.
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Fig. 4. (a) Fluorescence spectra of BOS (10 ꢀmol/L) in ethanol-water (1:9, v/v, Tris-HCl, pH =7.2)
solution upon the addition of different metal ions (10 ꢀmol/L). (b) The emission intensities of
BOS (10 ꢀmol/L) at 595 nm in the presence of 10.0 equiv of different interference metal ions
(dark cyan bars) or when 1.0 equiv of Al3+ coexiting with 10.0 equiv of competing ions added
(wine bars).
The Al3+ sensing ability of BOS was also examined by UV-vis spectroscopy
experiment. As depicted in Fig. S7, the titration experiments indicated that the
absorption intensity markedly increased at 568 nm upon the gradual addition of Al3+
from 0 to 1.0 equiv. Similarly, the absorption intensity stayed still with the
concentration of Al3+ further increasing to 1.25 equiv, suggesting a possible 1:1
binding. The different absorption intensities were detected to explore the selectivity
by mixing BOS with the above-mentioned 20 kinds of distinct metal ions. Only the
BOS-Al3+ system displayed a remarkable absorption enhancement, whereas
negligible changes could be found in other test systems (Fig. S8). The results
confirmed the excellent selectivity of BOS for Al3+. For the application in complex
biological environments, the probes with low background interference are preferred.
Therefore, the interference experiments were illustrated by mixing BOS (10 ꢀmol/L)
with 10.0 equiv of interference metal ions in the presence or absence of 1.0 equiv of
Al3+ (Fig. S9). After the introduction of Al3+, the significant absorption enhancement
in these competitive systems further demonstrated the good anti-interference of BOS
for Al3+ recognition.
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Fig. 5. Effects of pH (a) and time (b) on the Al3+ recognition of BOS (10 ꢀmol/L) in ethanol-water
(1:9, v/v, Tris-HCl, pH =7.2) solution.
Given the outstanding Al3+ sensing performance, BOS is proposed to be used in
biological detection. So the effects of pH and time on the Al3+ response of BOS were
further investigated through a serious of experiments. Commonly, the spirolactam ring
of the rhodamine derivative opens in acidic medium and presents the fluorescence of
rhodamine. As a consequence, the optimum pH conditions for BOS should be
explored to confirm its stability in potential practical applications. In the presence or
absence of Al3+, the pH dependent fluorescence responses of BOS were recorded in
the pH range of 2 – 12 (Fig. 5a). When pH < 4, both the fluorescence intensities of
BOS and BOS-Al3+ species were strong enough because of the ring-opening of
spirolactam induced by the strong protonation of the tertiary amine-N atom in acid
conditions. The free BOS showed negligible emission when pH > 5, while strong
emissions were detected after the addition of Al3+ within the pH value range from 5 to
9. When the pH value was greater than 9, the emissions of BOS-Al3+ were rapidly
quenched due to the formation of Al(OH)3 and the regeneration of spirolactam ring.
The results suggested that the response of BOS to Al3+ worked well in a suitable pH
region of 5 – 9 that approximated the physiological environment.
Response time is also a key index for chemosensors. The time-dependent
fluorescence responses of BOS towards Al3+ were proceed in a simulated in vivo
environment (ethanol-water = 1:9, v/v, Tris-HCl, pH = 7.2) at ambient temperature.
With the addition of Al3+, the emissions of BOS at 595 nm remarkably increased to
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the maximum value at 57 seconds and remained unchanged in the subsequent time
(Fig. 5b), revealing that BOS is a promising instantaneously responsive colorimetric
sensor for Al3+.
3.2. Cytotoxicity assays and biological imaging applications
Cytotoxicity experiments are crucial to the application of probes in biological
environment [27], and MTT assays were operated on SGC-7901 living cells to
investigate the biotoxicity of BOS and Al3+. As illustrated in Fig. 6 and Table S1, the
cell viability decreased slowly with the increase of the concentration of BOS or Al3+,
and the viability still stayed above 85% when 25 ꢀmol/L BOS or Al3+ treated, which
showed that BOS was low cytotoxic to living cells and suitable for bioimaging.
Fig. 6. SGC-7901 living cells viability of BOS and Al3+ quantified by the MTT assay.
So the fluorescence imaging experiments were carried out in SGC-7901 cells. As
expected, free BOS presented no detectable fluorescence signals in cells without Al3+
(Fig. 7a), and bright fluorescence signals were observed after the incubation BOS
with Al3+ (Fig. 7c). Bright-field transmission images of cells treated with BOS-Al3+
indicated that the cells were viable during the imaging experiments (Fig. 7b). These
results revealed that BOS could readily penetrate the cell membrane and be used for
in vitro imaging of Al3+ in living cells.
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Fig. 7. The fluorescence images and of SGC-7901 cells treated with BOS (20 ꢀmol/L) either in
absence (a) or presence (c) of 20 ꢀmol/L Al3+ for 1h at 37 °C, and the bright-field image of cells
shown in panel (b) as well as the overlay image (d) of (b) and (c).
3.5. Probable mechanism for the interactions of BOS with Al3+
Fig. 8. The Al3+-sensing mechanism of BOS.
Based on the spectral response of BOS to Al3+, the possible sensing mechanism
should be due to the chelation-induced ring opening of rhodamine spirolactam (Fig. 8).
To be more specific, a conjugated moiety was generated when the multidentate
coordination sites (carbonyl and hydroxy oxygen atoms as well as imino nitrogen
atoms) chelated Al3+, and at the same time the spirolactam ring was induced to be
opened, exhibiting remarkable fluorescence enhancements [28,29].
As displayed in Fig. S10, binding analysis was carried out by using the
continuous variations with a total concentration of [BOS] + [Al3+] as 10 ꢀmol/L to
determine the binding stoichiometry between them (Job's plot) [30,31]. The
fluorescence emission intensity showed a maximum at 595 nm when the mole fraction
of Al3+ approached 0.5, which demonstrated the 1:1 binding stoichiometry of
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Al3+–BOS.
EDTA was added into the BOS-Al3+ system to test the binding reversibility of
BOS. As shown in Figs. S11 and S12, after the introduction of EDTA, the intensities
of fluorescence and absorbance rapidly decreased with the fluorescent color changing
from bright yellow to colorless, while the spectral signals recovered with the addition
of Al3+ again (Fig. S12). The decreasing-reproducing processes of fluorescence
intensity can be repeated several cycles without obvious changes, suggesting that
BOS is a true reversible probe for Al3+.
4. Conclusion
A novel chromo-fluorogenic probe BOS displaying specific color change and
fluorescence response towards Al3+ was designed, synthesized and characterized. The
probe shows good selectivity and high sensitivity towards Al3+ via a 1:1 binding mode
in ethanol-water solution over a wide range of tested metal ions. The “turn on”
fluorescence response produced by the chelation-induced ring opening of spirolactam
indicates that BOS can be applied to rapid “naked-eyes” Al3+ detection in the pH
range of 5 – 9. Fluorescence imaging of Al3+ in SGC-7901 living cell suggests that
this probe is promising for the practical applications to Al3+ ion assays in
environmental and biological samples.
Acknowledgements
This work was supported by the National Natural Science Foundation of China
(Grant Nos. 21703135 and 21803042), the Natural Science Foundation of Shaanxi
Province (No. 2019JQ-249), the Natural Science Foundation of the Department of
Education of Shaanxi Province (No. 17JS034), the Outstanding Young Talents Fund
of University in Shaanxi Province (No. 18SKY001) and the Doctoral Scientific
Research Starting Foundation of Shangluo University (No. 17SKY028).
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1. A novel rhodamine-based probe BOS is designed and synthesized.
2. BOS is able to high selectively and sensitively detect Al3+.
3. The detection process can be identified through naked eye.
4. BOS is capable of detecting Al3+ in complex biological environment.