A new fluorescent probe based on quinoline for detection of Al3+ and Fe3+ with "off-on-off" response in aqueous solution

Article abstract of DOI:10.1039/c6ra23296e

A new quinoline-based fluorescent probe 1 has been designed and synthesized. Fluorescence emission spectra of the probe showed red-shift and obvious enhancement of fluorescent intensity upon the addition of Al³⁺ (turn-on). 1-Al³⁺ showed high selectivity for Fe³⁺ over other metal ions, and eliminated the interference of Al³⁺ during Fe³⁺ detection (turn-off). It showed highly selective relay recognition of Al³⁺ and Fe³⁺via a fluorescence "off-on-off" mechanism. Fluorescence spectra indicated that the response of 1-Al³⁺ to Fe³⁺ was caused by central metal displacement. The detection limits for the analysis of Al³⁺ and 1-Al³⁺-Fe³⁺ ions were calculated to be 2.20 × 10^-6 M and 1.96 × 10^-5 M, respectively. Living HeLa cell imaging studies revealed that the probe was cell-permeable and it could be used to detect intracellular Al³⁺ and Fe³⁺ ions.

Full text of DOI:10.1039/c6ra23296e

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A new fluorescent probe based on quinoline for detection of
3
+
3+
Al and Fe with “off-on-off” response in aqueous solution
a
a
a
a
a
a, b*
Yanpeng Dai , Xiaoyan Liu , Peng Wang , Jiaxin Fu , Kun Yao , Kuoxi Xu
Abstract: A new quinolineꢀbased fluorescent probe 1 has been designed and
synthesized. Fluorescence emission spectra of the probe showed redꢀshift and obvious
3
+
3+
enhancement of fluorescent intensity upon the addition of Al (turnꢀon). 1ꢀAl
3
+
showed high selectivity for Fe over other metal ions, and eliminated the interference
of Al during Fe detection (turnꢀoff). It showed highly selective relay recognition
of Al and Fe via a fluorescence “offꢀonꢀoff” mechanism. Fluorescence spectra
indicated that the response of 1ꢀAl to Fe was caused by central metal displacement.
The detection limits for the analysis of Al and 1ꢀAl ꢀ Fe ions were calculated to
be 2.20×10 M and 1.96×10 M, respectively. The living Hela cells imaging studies
revealed that the probe was cellꢀpermeable and it could be used to detect intracellular
3
+
3+
3+
3+
3
+
3+
3
+
3+
3+
ꢀ6
ꢀ5
3
+
3+
Al and Fe ion.
1
.Introduction
Metal ions play an important role in living organisms since they are involved in
many biological processes such as osmotic regulation, catalysis, metabolism,
1
ꢀ6
biomineralization and signaling . However, abnormal concentration levels of metal
3+
ions might cause detrimental effects, for example, Al is an essential metal ion in
7
3+
human health but is also harmful to biological systems in excessive amounts . Al
8
can cause damage to the central nervous system and the immune system of humans ,
9
3+
and affects the absorption and use of other trace elements . Excess of Al can cause
microcytic hypochromic anemia, Alꢀrelated bone disease, encephalopathy and
10ꢀ13
neuronal disorder that will lead to dementia, myopathy and Alzheimer's disease
;
3
+
Fe is an essential transition metal ion in human body, which plays a crucial role in
the growth and development of human body involved in oxygen uptake, oxygen
14ꢀ16
metabolism, and electron transfer process
; It also be involved in the underlying
mechanisms of many neurodegenerative diseases such as Alzheimer’s disease and
17, 18
3+
Parkinson’s disease
; Lack or accumulation of Fe in the body results in a variety
a
Engineering Laboratory for Flame Retardant and Functional Materials of Hennan Province,
Henan University, Kaifeng, 475004
b
*
Institute of Environmental and Analytical Sciences, Henan University, Kaifeng, 475004
Corresponding author, Tel./fax: +86 371 23881589; Eꢀmail address: xukx@henu.edu.cn
1

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19
of diseases and disorders . However, both metal ions are extensively employed in
industry, military affairs and agriculture, so it is urgent to develop highly sensitive
3+
3+
probes for the effective detection of Al and Fe in biological and environmental
3
+
3+
20ꢀ23
systems, but only few Al and Fe ions probes were reported in the literature
.
3
+
3+
However, synthetic probes for selective detection of trivalent metal ions (Fe , Al
3
+
and Cr ) without interfering from each other counter ions are rare. According to the
3
+
3+
widespread applications of Al and Fe ions in biology and environment, it deserves
24ꢀ 26
to proceed more researches
.
3+
3+
In general, as Al is a hardꢀacid, it has been found that Al prefers a coordination
spherecontaining nitrogen and oxygen atom as hardꢀbase donor sites. 8ꢀHydroxy
quinoline is known to be good ligand for selective detection of alkali, alkaline earth
27ꢀ30
and transition metal ions
. The derivative of 8ꢀhydroxy quinoline contain
nitrogen–oxygenꢀrich coordination sites which provide hardꢀbase environment for the
3+
hardꢀacid Al . Though many fluorescence probes are reported for the detection of
3
+ 31ꢀ34
Al
, most of these probes use fluorescence ‘turnꢀoff’ mechanism, few probes are
3
+
found in the literature use “turnꢀon” mechanism. So develop new fluorescent Al and
3
+
Fe probes are still challenge.
Obviously, different recognition patterns lead to multiple fluorescence behaviors
for detecting analytes, and thus rationally designing fluorescent molecular probes are
indispensable for differential responses towards multiple metal ions. To address the
above issues, we designed a novel probe 1 derived from 8ꢀhydroxyquinaldine and
mꢀxylene fragment (Scheme1) with multiple donor atoms for fluorescence detection
3
+
3+
of Al and Fe ions in aqueous solution. As we anticipated, probe 1 exhibited high
3+
selectivity for both metal ions, and its “turnꢀon” behavior for Al ions distinguished
3+
from the “turn off” recognition behavior for Fe ions maybe because they often cause
the different spectral changes upon binding with their probe molecules. To the best of
our knowledge, probe 1 represents the first example of simultaneous fluorescence
3+
3+
detection and discrimination of Al and Fe ions in a aqueous solution at
physiological pH.
2

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Scheme 1. Synthesis of dipodal compound 1.
2
2
. Experimental Section
.1 General methods:
All reactions were conducted in oven dried glassware. Solvents used for the
experiments were distilled or dried as specified. The following chemicals were
procured commercially and used without further purification, 2ꢀaminopyridine, SeO
2
,
mꢀxcylene, Nꢀbromobutanimide, sodium borohydride and 8ꢀhydroxyquinaldine. All
other reagents and solvents employed for synthesis were commercially available and
used as received without further purification. Column chromatography was done
using 200ꢀ300 mesh silica gel and appropriate mixture of petroleum ether and ethyl
acetate or chloroform and methanol system were used for elution.
2
.2. Synthesis of probe 1
The synthetic route of probe 1 is shown in Scheme 1.
.2.1 Synthesis of compound 3
2
A mixture of 8ꢀhydroxyquinaldine (0.96 g, 6 mmol) and anhydrous potassium
carbonate (1.25g, 9 mmol) in dry acetonitrile (10 mL). This mixture was stirred at
0 ℃ for 10 min. Then, a solution of 1,3ꢀbis(bromomethyl)benzene (0.79 g, 3 mmol)
8
in dry acetonitrile (10 mL) was added slowly to the mixture and the resulting solution
was then stirred at 80 ℃. The reaction mixture was stirred at this temperature until
the reaction was complete as indicated by TLC (12 h). Potassium carbonate was
filtered off and solvent was removed under reduced pressure. The remaining residue
was extracted three times with chloroform. The combined organic layer was washed
3

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with saturated brine and dried over anhydrous sodium sulphate. After the solvent was
removed, the residue was purified by silica column (eluent ethyl acetate : ethylacetate
1
=
8 : 1) to get a white solid in 80% yield. H NMR (300 MHz, CDCl
3
) δ (ppm) 7.94
(d, J = 8.4 Hz, 2H), 7.63 (s, 1H), 7.43 (d, J = 7.5 Hz, 2H), 7.34 (d, J = 7.4 Hz, 1H),
7
4
2
.27 (d, J = 7.8 Hz, 4H), 7.20 (d, J = 8.1 Hz, 2H), 6.92 (d, J = 7.5 Hz, 2H), 5.42 (s,
H), 2.76 (s, 6H).
.2.2 Synthesis of compound 2
To a solution of 3(1.26 g, 3 mmol) in 1,4ꢀdioxane (25mL), selenium dioxide(0.83 g,
o
7
.5 mmol) was added and reaction mixture was stirred at 90 C for 12 h. The dioxane
was removed under vacuum and the residue obtained was treated with water (30 mL)
and extracted three times with chloroform. The combined organic layer was washed
with saturated brine and dried over anhydrous sodium sulphate. After the solvent was
removed, the residue was purified by silica column (eluent ethyl acetate : ethylacetate
=
6 : 1) to get a yellow solid in 86% yield. 142.4ꢀ144.0 ℃.IR (KBr): 3402.12,
3
9
051.32, 2822.28, 1712.57, 1611.55, 1504.02, 1428.81, 1324.02, 1238.07, 1104.23,
ꢀ1 1
3
86.17, 834.40, 753.22, 696.45, 614.53, 470.53 cm ; H NMR (300 MHz, CDCl ) δ
(ppm) 10.26 (s, 2H), 8.27 (d, J = 8.5 Hz, 2H), 8.06 (d, J = 8.5 Hz, 2H), 7.74 (s, 1H),
7
.55 – 7.50 (m, 3H), 7.46 (t, J = 6.8 Hz, 4H), 7.12 (d, J = 7.4 Hz, 2H), 5.50 (s, 4H).
1
3
C NMR (100 MHz, CDCl
3
): 193.83, 171.17, 155.03, 151.54, 140.21, 137.29, 131.40,
+
1
4
2
29.60, 126.74, 125.61, 120.04, 177.88, 111.03, 70.94; MS: Calcd for: [M+Na] :
71.13 ; Found: 471.21.
.2.3 Synthesis of compound 1
To a solution of 2 (0.45 g, 1 mmol) and 2ꢀaminopyridine (0.24 g, 2.5 mmol) in
ethanol absolute (20 mL) at 60 ℃ stirred for 12 h under nitrogen atmosphere. Then
sodium borohydride (0.14 g, 3.8 mmol) was carefully added to the solution. The
reaction mixture was stirred at this temperature for 12 h. Then, EtOH was removed
under reduced pressure and the residue obtained was treated with water (30 mL) and
extracted three times with chloroform. The combined organic layer was washed with
saturated brine and dried over anhydrous sodium sulphate. After the solvent was
removed, the residue was purified by silica column (eluent chloroform : methanol =
4

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5
2
9
0 : 1) to get a light yellow solid in 65% yield. m.p. 57ꢀ59℃. IR (KBr): 3369.98,
928.80, 1600.19, 1567.77, 1504.61, 1430.15, 1321.47, 1261.09, 1151.10, 1100.53,
ꢀ1
1
78.93, 831.50, 772.07, 751.02, 696.22, 525.90, 472.22 cm .; H NMR (300 MHz,
) δ (ppm) 8.09 (d, J = 3.1 Hz, 2H), 7.97 (d, J = 6.7 Hz, 2H), 7.75 (s, 1H), 7.54
d, J = 7.3 Hz, 2H), 7.38 (d, J = 7.5 Hz, 3H), 7.29 (s, 4H), 7.03 (s, 2H), 6.50 (s, 2H),
CDCl
3
(
13
6
.42 (d, J = 8.2 Hz, 2H), 6.18 (s, 2H), 5.39 (s, 4H), 4.81 (s, 4H). C NMR (100 MHz,
): δ158.38, 157.19, 154.03, 147.96, 139.64, 137.69, 137.20, 136.61, 128.91,
28.62, 126.48, 126.25, 120.41, 120.16, 112.85, 111.09, 108.22, 70.94, 47.72; MS:
CDCl
3
1
+
Calcd for: [M + H] : 605.27 ; Found: 605.34.
2
.3. Spectrophotometric experiments
The probe 1 was dissolved in DMF solution. Before spectroscopic measurements,
the solution was freshly prepared in hexamethylenetetramine–HCl (Tris) aqueous
ꢀ1
buffer (20 mmol L , pH 7.4) by diluting the high concentration stock solution to
ꢀ5
3
.33×10 M (DMF: Tris=1:1, pH 7.4). Metal ions (0.1M, 10 mM tris buffer, pH 7.4)
were detected by the addition of different volume stock solutions to probe 1 solution.
+
+
+
The photophysical spectral changes of ligand with the metal ions such as Li , Na , K ,
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
3+
3+
Ag , Zn , Mg , Ba , Ca , Mn , Pb , Hg , Ni , Cd , Co , Cu , Fe , Cr , Fe
3+
and Al were investigated by UV–vis and fluorescence spectra. The fluorescence
emission spectra was recorded in the wavelength range from 300 to 700 nm with
excitation wavelength at 295 nm. Both the excitation and emission slits were set at 5.0
nm.
2
.4. Cell imaging
In vitro experiments were performed using HeLa cells. HeLa cells were cultured
in Dulbecco modied Eagle medium, which were supplemented with 10% fetal bovine
serum in an atmosphere of 5% CO at 37 ℃ for 24 h. Before the experiments, the
2
cells were incubated with 50 mM HL in 0.1M sterile PBS buffer for 30min at room
temperature. After incubation, the cells were washed with PBS buffer and incubated
2
with metal ions for additional 30 min under 5% CO . The cells were washed three
times with PBS buffer. Cells were seeded on dish for fluorescence microscopic
imaging by inversion fluorescence microscope.
5

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3
3
. Results and discussion
.1 pH effect of 1
+
In order to eliminate the disturbance by H during the detection of metal ions and to
find optimal sensing conditions, the fluorescence intensity of compound 1 at various
pH values in the presence and absence of metal ions were determined in DMFꢀH O
2
(1:1, v/v). The effect of pH was evaluated in the pH range of 2—12 as shown in Fig.1.
3+
It was clearly demonstrated that the probe 1–Al system shown strong fluorescence
intensity at the pH less than 7.5 but decrease high than 7.5. This may be due to the
3
protonation of N atom and the formation of Al(OH) , respectively. There were similar
3
+
3+
changes in the fluorescence intensity of the 1+Al +Fe system in different pH
conditions. Therefore, it was demonstrated that probe 1 could be used under
physiological conditions for biological applications with very low background
fluorescence. All spectroscopic measurements were carried out under the physical
conditions simulated the measurements of pH 7.4 at room temperature (10 mM tris
buffer).
500
400
300
200
100
1
3
+
1+Al
3+
3+
1+Al +Fe
2
4
6
8
10
12
pH
ꢀ5
3+
Fig. 1. Fluorescence intensity of probe 1(DMF: Tris=1:1, pH=7.4, 3.33×10 M), 1+Al (4.5
3
+
3+
equiv.) and 1+Al +Fe (4.5 equiv.) at various pH values.
3
+
3
.2 The selectivity of probe 1 to Al
The fluorescence sensing ability of probe 1 was studied by addition of metal ions.
3+
The Fluorescence responses of probe 1 were shown in Fig. 2. The addition of Al to a
solution of 1 induced a significant enhancement of fluorescence intensity. However,
under identical conditions, the fluorescence was completely quenched by addition of
3
+
Fe ions; nearly no fluorescence intensity changes were observed in emission spectra
6

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with the other ions. The results indicated that probe 1 were a highly selective
3
+
3+
fluorescence “turnꢀon” probe for Al and “turnꢀoff” probe for Fe . Achieving high
3
+
selectivity toward Al over the other competitive species coexisting was a very
important feature to evaluate the performance of the fluorescent probe 1. Therefore,
the competition experiments were also conducted for probe 1. Fig. 3 indicated that
3+
when Al were added into the solution of probe 1 in the presence of other ions, the
3
+
3+
emission spectra displayed a similar pattern to that with Al only except for Fe ion.
3+
3+
The competition experiments indicated that Fe induced disturbance to Al detection,
3+
which meant that probe 1 could perform as a highly selective probe for Al via
fluorescence “turnꢀon” mechanism. The competition experiments demonstrated
3
+
eminent relay recognition of Fe as well. So far, the “offꢀonꢀoff” mechanism has
3
+
3+
been achieved with sequence specificity (Al ꢀFe ) .
300
250
200
150
100
3
+
Al
2
+
Cu
3+
Cr
2
+
+
+
+
2+
2+
Fe
Blank, Li , Na , K , Zn , Mg
,
2+
2+
2+
2+
2+
Ba , Ca , Mn , Pb , Hg
,
2+
2+
2+
Ni , Cd , Co
+
Ag
3+
Fe
50
0
300
350
400
450
500
550
Wavelength (nm)
Fig. 2. Changes in fluorescent intensity (λex=295 nm) of probe 1 upon the addition of different
+
+
+
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
metal ions Li , Na , K , Ag , Zn , Mg , Ba , Ca , Mn , Pb , Hg , Ni , Cd , Co ,Cu , Fe ,
3
+
3+
3+
Cr , Fe and Al (4.5 equiv.) .
1
1 + Al3+
1 + Al3+ + metalions
3
2
2
1
1
00
50
00
50
00
5
0
0
Al3+ Li+ Na+ K+ Ag+ Zn2+ Mg2+ Ba2+ Ca2+ Mn2+ Pb2+ Ni2+ Cd2+ Co2+ Fe2+ Cu2+ Hg2+ Fe3+ Cr3+
ions
7

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ꢀ5
Fig. 3. The fluorescence intensity of solution probe 1 (DMF: Tris = 1:1, pH=7.4, 3.33×10 M) to
various metal ions. The blue bars represent the fluorescence intensity of only probe 1, the red bars
represent the fluorescence intensity of the above solution upon subsequent addition of 4.5 equiv.
3
+
of Al . The green bars represent the fluorescence intensity of the above solution upon subsequent
3
+
addition of 4.5 equivalent of Al and 4.5 equiv. of other metal ions.
3
.3. Absorption properties of probe 1
The UVꢀvis absorption spectrum responses of probe 1 recognition of Al and Fe
were also studied (Fig. 4). The absorption spectrum of free probe 1 exhibited only one
3
+
3+
3
+
absorbance peak at 300 nm. When 4.5 equiv. of Al was added to the solution, the
UV–vis response of probe 1 shown red shift of the maximum absorption, moreover,
3
+
3+
with the addition of 4.5 equiv. of Fe to the 1+Al system, the intensity of the
absorption at about 302 nm increased. The UV–vis response of probe 1 shown red
shift of the maximum absorption indicating the formation of a complex between probe
1
and metal ion. Furthermore, the band appearing in the UV–vis region (285–455 nm)
which is typical for internal charge transfer (ICT) due to imines’ linkage is
characteristics of the ligand.
1
1
0
0
.5
.0
.5
.0
1
1
1
3
+
+
+Al
3
3+
+Al +Fe
3
00
350
400
450
Wavelength (nm)
ꢀ5
3+
3+
Fig. 4. UVꢀvis spectra of prob 1(DMF: Tris = 1:1, pH = 7.4, 3.33×10 M), 1+Al and 1+Al +
3
+
Fe .
3
.4 Ions-titration and spectral responses
The fluorescence intensity changes of probe 1 in the presence of Al were
3
+
ꢀ5
investigated. As shown in Fig. 5a, the free probe 1 (3.33×10 M) emitted
fluorescence at 357 nm. The fluorescence intensity of probe 1 increased gradually
3+
with gradually red shifted to 375 nm on addition of Al (0–4.5 equiv.), which agreed
8

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with that in the UV–vis spectra. The obvious red shift could be explained that the ICT
3
+
3+
phenomenon was inhibited upon binding Al ion. The coordination of Al to probe 1
induces an intramolecular electron transfer process (ICT) from the nitrogen atom of
3+
the nitrogen atom of the quinoline was coordinated with Al to cause an enhanced
3
5, 36
ICT process from donor (methoxy group) to acceptor (quinoline)
, so an obvious
3
7
red shift in both fluorescence and absorption wavelength could be observed .
3+
The binding association constant (Ka) the stoichiometry of 1ꢀAl complex were
determined from Benesei–Hildebrand equation by changes in the fluorogenic
3
+
3+
response in the presence of varying Al concentrations between probe 1 and Al .
The results indicated the formation of a 1:1 complex and the binding association
3
−1
constant (Ka) was determined to be 2.11×10 M (Fig. 5b). Moreover, the Job’s plot
3+
analysis showed 1:1 binding stoichiometry complex between the probe 1 and Al
38, 39
(Fig. 6)
. Additionally, the estimated limit of detection (LD) was came out to be
ꢀ6
3+
40
2
.20×10 M for 1ꢀAl complex (Fig. 7) . The results indicated that probe 1 was
3
+
3+
sensitive to Al and could be potentially used to quantitatively detect Al
concentration.
3
00
B
A
1.2
ꢀ6
Y = 3.5133*10 x ꢀ 0.01178
2
R = 0.9960
250
3
1.0
K = 2.106 x 10
3+
Al
0
4.5 equiv.
200
0.8
0.6
0.4
0.2
0.0
1
50
100
5
0
0
3
0
50000
100000 150000 200000 250000 300000
00
350
400
450
500
550
3
+
Wavelength (nm)
1/[Al
]
ꢀ5
Fig.5(A). Fluorescent spectra of probe 1 (DMF: Tris = 1:1, pH = 7.4, 3.33×10 M) with the
3+
addition of various concentration of Al (λex=295 nm). (B). Benesi–Hildebrand plot of fluorescent
3
+
probe (1+ Al ) at λ = 295 nm.
ex
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1
1
1
4
2
0
8
6
4
2
0
0.0
0.2
0.4
0.6
3+
0.8
1.0
3+
[
Al ] / ([1]+[Al ])
Fig. 6. 1:1 Stoichiometry of the host guest relationship was realized from the job’s plot.
0.08
Y=0.26+0.04595 * X
R=0.9935
0
.07
-6
DL=2.1962 * 10
0.06
0.05
0.04
0.03
0.02
0.01
0.00
-5.6
-5.4
-5.2
-5.0
-4.8
-4.6
-4.4
-4.2
-4.0
3
+
Log [Al
]
3
+
ꢀ6
Fig. 7. The detection limit (DL) of probe 1 for Al was calculated as 2.1962×10 M.
3+
3+
In the competition experiments, upon addition of Fe to the 1ꢀAl system, as
3+
shown in Fig.8(a), with the addition of Fe (0ꢀ13.0 equiv.) to the solution, the
fluorescence intensity at 375 nm was dramatically decreased to quenching completely
Fig.8(b) and gradually red shifted to 410 nm, the fluorescence was quenched and
3
+
3+
transformed into that of the LꢀFe system. Whereas upon addition of Al to the
3
+
1
ꢀFe system, the fluorescence profile did not change obviously. Obviously, the
41
fluorescence changes could be ascribed to the ligandꢀtoꢀligand charge transfer , as
3+
3+
illustrated in Fig. 9. When probe 1 coordinated with Fe ions, the structure of 1ꢀFe
3
+
became more stable than that of 1ꢀAl . The selective fluorescence quenching of
3+
3+
probe 1 upon Fe ion addition may be due to paramagnetic nature of Fe which on
10

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coordination with the heteroatoms of ligands triggered the nonradiative deactivation
process instead of fluorescent emission signal led to the efficient fluorescence
42, 43
3+
3+
quenching
.
Besides, the above calculated binding constant of 1ꢀAl ꢀFe
3
−1
3+
3+
(
5.58×10 M ) (Figs. 1). Thus, the Al in the formed complex 1ꢀAl could be
3+
3+
replaced by Fe forming 1ꢀFe , accompanied by fluorescence quenching. The
−5
corresponding LOD was calculated to be 1.96×10 M (Figs. 2).
300
250
200
150
100
A
B
3
00
250
3
+
Fe
0
13 equiv.
200
150
100
5
0
50
0
0
300
350
400
450
500
550
0
2
4
6
8
10
12
3
+
Wavelength (nm)
Fe equiv.
3
+
3+
Fig. 8. A: Fluorescence emission spectra of 1+Al upon addition of Fe (0 to 13.0 equiv.) with
3
+
an excitation of 295 nm. B: Changes of the emission intensity with the addition of Fe .
3
+
Fig. 9 The illustration of fluorescence “turnꢀon” of probe 1 for selective detection of Al and
3
+
fluorescence “turnꢀoff” of probe 1 for selective detection of Fe .
3
.5 Fluorescence imaging
To demonstrate the potential of probe 1 to image Al and Fe in living matrices,
We next sought to investigate the utility of probe 1 for monitoring the intracellular
3+
3+
3
+
3+
(
living Hela cells) exogenous Al and Fe . As shown in Fig. 10, Hela cells treated
with probe 1 (10 µM) alone in the growth medium for 30 min gave a very weak
fluorescence (Fig.10 a–c), indicating the efficient loading of probe 1. When the cells
11

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DOI: 10.1039/C6RA23296E
3
+
were further incubated with 20 µM Al for 30 min, a bright blue fluorescence was
observed (Fig.10 d–f). Bright field measurements after treatment with probe 1 and
3
+
Al confirmed that the cells were viable throughout the imaging experiments,
showing the formation of the probe 1ꢀAlCl complex in the cells. While for the cells
in cubated with probe 1 and FeCl , the faint blue fluorescence disappeared and turned
3
3
3
dark inside cells, attributed to the quenching role of FeCl that got into the cells. Thus,
3+
probe 1 can detect intracellular Al very efficiently.
Fig. 10 Confocal fluorescence images of live Hela cells. a) Brightꢀfield transmission image of
cells incubated with 10 µM probe 1 for 30 min; b) Bright image of the cells; c) Merged image of a
3
+
and b; d) Fluorescence image when treated with sensor followed by 20 µM Al ; e) Bright field
image of d; f) An overlay image of d and e.
4
. Conclusions
In summary, we synthesized a new quinolineꢀbased fluorescent probe for Al and
3
+
3
+
3+
Fe . The probe displayed different fluorescence responses toward Al (turnꢀon) and
3
+
Fe (turnꢀoff) in aqueous environment, respectively, showing high sensitivity and
3
+
selectivity. Probe exhibited a strong preference for Al over other metal ions in
3
+
3+
DMFꢀH O solution. Importantly, probeꢀAl shown high selectivity for Fe over
2
3+
3+
other metal ions, and could eliminate the interference of Al during Fe detection.
3
+
These suggested that probe could serve as a nice probe for the detection of Al and
3
+
Fe via the “offꢀonꢀoff” mechanism with sequence specificity in DMFꢀH O solution.
2
Finally, in living cell imaging demonstrated that the new probe was cellꢀpermeable
3
+
and could be used to monitor the Al in biosystems. This work may provide a new
3+
strategy to design probes for discriminating Al in biological systems.
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DOI: 10.1039/C6RA23296E
Acknowledgements
We thank the Program for He’nan Innovative Research Team in University
15IRTSTHN005) and the National Natural Science Foundation of China (Grant No.
(
U1404207) for financial support.
Supplementary data
Some plots of fluorescence spectrometry experiments, characterization of the
compounds were given.
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A new fluorescent probe based on quinoline for detection of
3
+
3+
Al and Fe with “off-on-off” response in aqueous solution
a
a, b∗
a
a
a
a
Yanpeng Dai , Kuoxi Xu , Xiaoyan Liu , Peng Wang , Jiaxin Fu , Kun Yao
3
+
3+
A new quinoline-based fluorescent probe for Al and Fe has been designed and
3+
3+
synthesized. It showed highly selective relay recognition of Al and Fe via a
fluorescence “off-on-off” mechanism by central metal displacement. The living Hela
cells imaging studies revealed that the probe was cell-permeable and could be used to
3
+
3+
detect intracellular Al and Fe ion.