An easy and accessible water-soluble sensor for the distinctive fluorescence detection of Zn2+ and Al3+ ions

Article abstract of DOI:10.1039/c5ra15126k

A water-soluble fluorescence sensor (SA) was facilely synthesized via a one-step condensation reaction between commercially available salicylaldehyde and 2-(2-aminoethylamino)ethanol with high yield. The addition of Zn²⁺ and Al³⁺ to SA showed drastic enhancements of the emission intensities at 458 nm and 376 nm, respectively, while exhibiting negligible interference in the presence of typical competitive ions such as Fe³⁺, Cr³⁺, Hg²⁺ and Cd²⁺. This phenomenon indicates that SA may be helpful for rapid, quantitative and qualitative detection of Zn²⁺ and Al³⁺.

Full text of DOI:10.1039/c5ra15126k

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An Easy and Accessible Water-soluble Sensor for the
2
+
3+
Distinctive Fluorescence Detection of Zn and Al
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
ions†
Tianqi Liu,a,b Yunsheng Dong, Xuejuan Wan, Weibin Li, and Youwei Yaob,**
b
c
a, *
DOI: 10.1039/x0xx00000x
www.rsc.org/
water-soluble fluorescence sensor (SA) was facilely increase the risk for diverse diseases. Al3 toxicity is believed to
synthesized via a one-step condensation reaction between
+
A
9
retard plant growth and arouse neuronal disorders which may
induce Alzheimer’s disease and Parkinson’s disease10, 11. Until
now, numerous fluorescence sensors for Zn2+ ion12-17 and Al3+
ion18-21 have been reported, but most of them have tedious
synthetic step-outs. Besides, the detection of Al3+ is usually
disturbed by other trivalent ions (Fe3+ and Cr ) while the
detection of Zn2+ can be interfered by Cd , owing to the
similar electron configuration23 in the recognition process.
Consequently, relatively scarce fluorescence sensors capable of
simultaneous discrimination of Zn2+ and Al3+ without any other
interference have been reported9, 24-30. A water-soluble unit, 2-
commercially
available
salicylaldehyde
and
2-(2-
aminoethylamino)ethanol with high yield. The addition of
Zn2+ and Al3+ to SA showed drastic enhancements of the
emission intensities in 458 nm and 376 nm respectively,
whereas exhibited a negligible interference in the presence of
typical competitive ions such as Fe , Cr Hg2+ and Cd2+.
3+ 22
2+
3
+
3+
This phenomenon indicates that SA may be helpful for rapid
quantitative and qualitative detection of Zn2+ and Al3+.
Fluorescence sensing1-4 has gradually emerged as a significant
(
2-aminoethylamino)ethanol, was strategically attached to
and effective approach for the recognition of metal ions due to
its simplicity, high sensitivity and instantaneous response. In
the past decade, a considerable amount of sensors with
excellent detection sensitivity and selectivity for diverse metal
ions have been reported, however, there are still many
challenges to be overcome. For example, most of the
fluorescence detection process is conducted in pure organic or
organic-water mixed solution ascribing to the insufficient water
solubility of the sensor, which is inconvenient in practical
quantitative and qualitative detection of the water
salicylaldehyde template to improve the water solubility of
probe thus meeting the needs of actual detection31-33. To the
best of our knowledge, herein, it is the first time to develop the
easy and accessible water-soluble fluorescence sensor for the
distinct detections of Zn2+ and Al3+ ions with different
fluorescence emission peak, which is convenient and
economical for the quantitative determination of Zn2+ and Al3+
ions.
5
contamination . Besides, complicated multiple synthesis and
purification steps accompanied with relatively low product
yield of the chemosensor are also severe limitations for the
large scale production and application. Consequently, it is
highly desirable to design a sensor which is readily available
with high yield, and is sensible for target ion in 100% aqueous Scheme 1 Schematic illustration of the synthesis of fluorescent chemosensor SA.
solution.
Among the common metal ions, Zn2+ is the second most
The fluorescence probe was obtained via one-step
condensation reaction between salicylaldehyde and 2-(2-
abundant transition metal ion in the human body which plays a
aminoethylamino)ethanol at room temperature34, 39, as is
significant role in various biological activities6-8, and a
deviation of Zn2+ concentrations from normal levels can
illustrated in Scheme 1. The yield is as high as 93%. Molecular
structure of the probe was confirmed by H NMR, 13C NMR
1
a
Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China. E- and HR-MS analysis (Fig. S1-S3). The modification of 2-(2-
mail: wbli@tsinghua.edu.cn.
b
aminoethylamino)ethanol endows the probe SA with excellent
water solubility, which is advantageous for the following heavy
metal ion detection process.
Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University,
Shenzhen 518055, P. R. China. E-mail: yaoyw@sz.tsinghua.edu.cn.
c
Shenzhen Key Laboratory of Special Functional Materials, College of Materials
Science and Engineering, Shenzhen University, Shenzhen 518060, P.R. China.
The fluorescence response of SA
(50 μM) toward various
†
Electronic supplementary information (ESI) available. See DOI:
XXXXXXX
metal ions 250 μM) was investigated in Tris buffer (10 mM, pH
(
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=
7.0). As shown in Fig. 1, free SA gave almost no fluorescence buffer (10 mM, pH = 7.0). As shown in Fig. 2, relative weak
emission changes and was silent toward most of the metal ion fluorescence emission was observed in the absent of any metal
+
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
such as Na , K , Mg , Ni , Ba , Cd , Ca , Hg , Cu , Pb , ion. With the increasing concentration of Zn , the fluorometric
Fe3+ and Cr . However, the fluorescence signal of SA showed titration curve firstly showed a steady and smooth enhancement,
immediate changes upon the addition of Zn2+ and Al3+ ions. and then gradually reached equilibrium as the concentration of
Surprisingly, Zn2+ and Al3+ can be distinguished through the Zn2+ ion was greater than 50 μM, indicating that the recognition
different fluorescence emission peak. An emission band centered molar ratio of probe SA to Zn2+ ion might be 1:1. Plotting of the
at 458 nm was observed with an obvious fluorescence turn-on fluorescence intensity (458 nm) versus the concentration of Zn2+
after the addition of Zn2+ ion. As for Al3+ ion, a much more (0-50 μM) afforded a good linear relationship as shown in the
significant fluorescence blue shift from 496 nm to 376 nm was inset of Fig. 2. The detection limit (DL) of SA toward Zn2+ ion
3+
achieved, accompanied with
fluorescence intensity. These fluorescence changes can be Sb
a distinctive enhancement of was calculated to 0.643 μM according to the equation DL = 3
3
7
1
1
/ S , where Sb is the standard deviation of the blank sample,
attributed to the formation of a chelate complex between metal S is the slope of the calibration curve.
ions and SA, causing the chelation-enhanced fluorescence (CHEF)
effect35, 36
.
other ion
2
+
Zn + other ion
1
0
0
0
0
0
.0
.8
.6
.4
.2
1.0
0.8
0.6
0.4
0.2
0.0
3
Al
+
2+
Zn
+
+
2+
2+
2+
Blank and Na , K , Cd , Hg ,Cu
,
2
+
2+
2+
2+
2+
3+
3+
Mg , Pb , Ni , Ca , Ba , Fe , Cr
.0 Zn2+
Na
K Mg Cu Ni Pb Ba Cd Hg Fe Al Cr
+
+
2+
2+
2+
2+
2+
2+
2+
3+
3+
3+
3
50
400
450
500
550
600
Fig. 3 Fluorescence intensity at 458 nm of SA (50 μM) in the presence of
selected metal ions (250 μM) in Tris buffer solution (10 mM, pH = 7.0). The
black bars represent the intensity of SA in the presence of selected cations;
the red bars represent the intensity upon an addition of Zn2+ (250 μM) to a
solution of SA in the presence of selected cations
Wavelength (nm)
Fig .1 Fluorescence spectra of SA (50 μM) in Tris buffer (10 mM, pH = 7.0) in
the absence and presence of 250 μM of various metal ions, λex =310 nm
Possible interference from other cations in the
fluorescence detection of Zn2+ ions was also tested.
Competitive ions were first added into the detection solution,
and Zn2+ ions were added 20 minutes later. The fluorescence
1
.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2+
0.8
Zn
0.6
0.4
0.2
0.0
emission curves were then recorded and the changes of
fluorescence intensity at 458 nm before and after the addition
Zn2+ were displayed in Fig. 3. It is obvious that most of the
detection systems exhibited minimum interference in the
detection of Zn2+ even in the presence of typical competitive
y = 8897.4 x + 0.1288
2
R
= 0.9951
DL = 0.643 μM
0
2.5
5
7.5
10
2+
-5
[
Zn ] / 10 mol/L
ions Cd2+ and Hg . However, the detection process of Zn can
2+
2+
3
+
be affected by Al , suggesting that SA has a binding affinity
toward Al3+ higher than that of Zn . The association constant
2+
a
(K ) between the probe and the two ions was then calculated
3
8
according to the reported work . The equilibrium constant K
a
between SA and Zn2 ion was 3.06 × 10 , while the data was
.96 × 10 for SA and Al ion. The formation of more stable
SA-Al3+ complex can be ascribed to that hard Lewis acid Al3+
+
8
350
400
450
500
550
600
8
3+
4
Wavelength (nm)
Fig. 2 Fluorescence spectra of SA (50 μM) in the presence of increasing tends to have a high binding affinity toward the probe under the
concentrations of Zn2+ in Tris buffer (10 mM, pH = 7.0). Inset: fluorescence hard base environment offered by SA . We tried to select
26
2+
ammonium fluoride and tartaric acid as screening agent of Al3+
intensity at 458 nm as a function of [Zn ], λex =310 nm
in HAc-NaAc buffer ( 60 mM, pH=6, ωNH =0.02, ωtartaric
acid=0.07) (Fig. S4). The results indicate that there was no
4
F
The fluorescence detection capacity of SA (50 μM) toward
Zn2+ was evaluated by fluorescence titration experiments in Tris
2
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obvious interferences (fluorescence intensity decreased to 94% fluorescence sensing of Al3+ (Fig. S9-S10). The fluorescence
of original intensity) in detecting Zn2+ in the presence of 5 intensity increased linearly (R = 0.9945) upon the addition of
equivalents of Al3+ under the above detection system. Al3+ (0-50 μM).
2
Fluorescence spectroscopic titration experiments (Fig. S5-S6)
showed that there was a negligible fluorescence enhancement
(
blue line, slope K
1
= 0.017) with the concentration of Zn2+
other ion
ranging from 0 μM to 15 μM (0 - 0.3 eq.). With increasing
concentrations of Zn , the titration reaction curve showed a
steady enhancement (red line, slope K =1.073), and gradually
reached equilibrium as the concentration of Zn2+ was greater
than 60 μM. This phenomenon means that sensitive detection of
Zn2+ in the presence of Al3+ when the concentration of Zn2+ is
less than 15 μM has not been achieved using this method.
3
+
Al + other ion
2+
1.0
0.8
0.6
2
0
0
0
.4
Similarly, the fluorescence detection capacity of SA (50 μM)
toward Al3+ was recorded in Fig. 4. With the increasing
.2
3
+
concentration of Al , the fluorometric titration curve showed a
steady and smooth enhancement, accompanied with a much more
fluorescence blue shift, which is significant to the distinctive
detection of Zn2+ and Al3+ ions respectively. Plotting of the
.0 Al3+
Na
K Mg Cu Ni Pb Ba Zn Cd Hg Fe Cr
+
+
2+
2+
2+
2+
2+
2+
2+
2+
3+
3+
fluorescence intensity (376 nm) versus the concentration of Al3+ (0- Fig. 5 Fluorescence intensity at 376 nm of SA (50 μM) in the presence of selected
metal ions (250 μM) in Tris buffer solution (10 mM, pH = 7.0). The black bars
5
0 μM) also afforded a good linear relationship as shown in the inset
of Fig. 4. The detection limit of probe SA toward Al3+ was 0.611 μM,
represent the intensity of SA in the presence of selected cations; the red bars
represent the intensity upon an addition of Al3+ (250 μM) to a solution
3
+
3+
there were no obvious interferences in the presence of Fe , Cr ,
2
+
Zn , and other cations as shown in Fig. 5.
HR-MS measurements (Fig. S11) and FT-IR (Fig. S13) were
utilized to analyse the binding mode of sensor SA towards Zn2+
ion. In Fig. S11, the peak located at m/z 271.0409
(calcd=271.0420) corresponding to [SA+Zn -H ] can be clearly
observed when 5 equiv. of ZnCl was added to the solution
containing probe SA. In Fig. S13 the characteristic absorption
peak of C=N double bond at 1577 cm−1 shifted to 1544 cm−1, and
the characteristic absorption peak of C-O bond at 1045 cm−1
shifted to 1014 cm−1 in the presence of Zn2+ ion, indicating that
the N atom of the Schiff base and the O atom of alcoholic
1.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
3
Al
+
2+
+ +
0.8
0
.6
.4
2
0
y = 9826.1 x + 0.0089
2
0.2
.0
R = 0.9947
DL = 0.611 μM
0
0
2.5
5
7.5
10
3
+
-5
[
Al ] / 10 mol/L
2
hydroxyl (-CH OH) were actually involved in the recognition of
Zn . Considering the strong acidity (δ=13.38 ppm) of the
2+
phenolic hydroxyl group in SA, the H of phenolic hydroxyl was
easy to leave, which also agreed with reported work25, 26, 39. The
350
400
450
500
550
600
binding mode of sensor SA towards Al3+ was further confirmed
Wavelength (nm)
by high-resolution mass spectrum (Fig. S12), in which the peak at
3+
+ +
m/z 233.0861 (calcd=233.0865) corresponding to [L+Al -2H ]
was clearly observed when 5 equiv of Al(ClO was added to
Fig. 4 Fluorescence spectra of SA (50 μM) in the presence of increasing
concentrations of Al3+ in Tris buffer (10 mM, pH = 7.0). Inset: fluorescence
intensity at 376 nm as a function of [Al3+], λex =310 nm
4 3
)
probe SA. According to these results, the probable binding modes
of SA with Zn2+ and Al3+ ions were proposed as shown in Fig.
A sample with tap water background has been detected to S14.
evaluate the potential application of chemosensor SA in detecting
In conclusion, we report the one-step synthesis and
Zn2+ and Al . Zn and Al3+ was deliberately introduced to characterization of a new fluorescence chemosensor for the
simulate contaminated tap water. 200 mL tap water was obtained distinct detections of Zn2+ and Al , and it can be used in pure
from tap faucet (Nanshan District, Shenzhen, China. Sampling aqueous solution. An obvious fluorescence turn-on with a slight
time: 14:00 on August 18th, 2015). The water sample in the blue shift (centered at 458 nm) was observed after the addition of
beaker was kept still for 24 hours. Then the tap water could be Zn2+ ion. However, much more significant fluorescence blue shift
3+
2+
3+
used as testing solution for fluorescent analysis. As shown in Fig. was achieved for SA-Al3+ complex, accompanied with
a
2
S7-S8, the fluorescence intensity increased linearly (R = 0.9954) distinctive intensity enhancement (centered at 376 nm). The
upon the addition of Zn2+ (0-50 μM). The result indicated the detection limit of SA for Zn2+ and Al3+ are both at the micromolar
suitability of this chemosensor for the determination of Zn2+ in level without the disturbances from Na , K , Mg , Ni , Ba ,
+
+
2+
2+
2+
2+
2+
2+
2+
3+
3+
real sample. Similar phenomenon can also be observed in the Cd , Hg , Cu , Pb , Fe and Cr , which is comparable to the
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