Sensors & Transducers, Vol. 186, Issue 3, March 2015, pp. 125-128
Sensors & Transducers
© 2015 by IFSA Publishing, S. L.
http://www.sensorsportal.com
Synthesis and Characterization
of an Al3+-Selective Fluorescent Probe
1
1
Jun Zhang, 1, * Na Li, 1 Fa Dai, 1 Qing Luo, 2, * Yuxiang Ji
Laboratory of Environmental Monitoring, Environmental Sciences, Hainan Medical University,
Haikou, 571101, China
2
Laboratory of Environmental Engineering Management, Environmental Sciences,
Hainan Medical University, Haikou, 571101, China
Tel.: +86 898 66973190, fax: +86 898 66989173
*
E-mail: oknana@163.com, jyxhn2009@sohu.com
Received: 23 February 2015 /Accepted: 23 March 2015 /Published: 31 March 2015
Abstract: A new Schiff base compound derived from benzoyl hydrazine has been synthesized and characterized
as an Al3+-selective fluorescent probe. Compared to other common metal ions, the proposed probe shows high
affinity and sensitibity towards Al3+, and complexing with Al3+ triggers a prominent fluorescence enhancement
at 443 nm, accompanied by the change in the absorption spectrum in ethanol phase. With the optimized
experimental conditions, the probe exhibited a dynamic response range for Al3+ from 5.0×10-7 M to 4.5×10-6 M
with a detection limit of 1.1×10-7 M. Copyright © 2015 IFSA Publishing, S. L.
Keywords: Al3+, Fluorescent probe, Schiff base, Fluorescent enhancement, Synthesis.
1. Introduction
Aluminum is a non-essential element for living
system and can cause severe diseases to human, such
as aluminum toxicity causes microcytic hypochromic
anaemia, encephalopathy, Al-related bone disease
(ARBD) and has the potential to produce some
neurobehavioral and neuro-pathologic changes that
are similar to those found in Alzheimer's disease and
breast cancer [1]. Therefore, the methods to detect
aluminum (Al3+) have attracted much attention
recently [2]. Fluorescent probes have many
advantages compared to other methods such as the
high sensitivity, fast analysis with spatial resolution
for providing in situ and real-time information, and
nondestructive sample preparation, which have been
proved to be useful tools for sensing important
species such as metal ions, anions and amino acids
[3-8]. However, the detection of Al3+ has always
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been problematic due to the lack of spectroscopic
characteristics and poor coordination ability
compared to transition metals [2, 9-10]. For this
reason, the development of Al3+ probes is
comparatively more difficult than those of other
metal ions. In general, Al3+ being a hard acid, prefers
hard donor sites like N and O in its coordination
sphere. With above-mentioned in mind, in this work
a new Schiff base compound containing N and O
donor sites was synthesized and successfully
characterized as Al3+-selective probe (Fig. 1).
Fig. 1. Synthesis route of probe P.
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Sensors & Transducers, Vol. 186, Issue 3, March 2015, pp. 125-128
2. Experimental Section
2.1. Reagents and Instruments
All of the materials were commercial available
reagent grade and used without further purification.
NMR spectra were measured with TMS as an
internal standard. MS spectra were recorded on a
Thermo TSQ Quantum Access Agillent 1100.
Fluorescence emission spectra were conducted on a
Hitachi 4600 spectrofluometer. UV-Vis spectra were
obtained on a Hitachi U-2910 spectrophotometer.
pH values were measured with a pH-meter PBS-3C.
metal ions (K+, Na+, Ca2+, Mg2+, Pb2+, Co2+, Cd2+,
Ag+, Zn2+, Ni2+, Hg2+, Cr3+, Al3+ and Fe3+, 10 equiv.)
was investigated to evaluate the selectivity of
probe P (Fig. 4).
2.2. Synthesis
136 mg benzoylhydrazine (1.0 mmol) and
127.6 μL salicylaldehyde (1.2 mmol) were mixed in
ethanol (20 mL). The reaction mixture was stirred at
80 °C for 4 h, and then cooled to room temperature.
The yellow precipitate so obtained was filtered and
used directly. Yields: 85.6 %. MS m/z:
263.1 [M+Na]+, 239.0 [M-H]-. 1H NMR ( δ p p m ,
D M S O - d 6 ) : 12.14 (s, 1H), 11.32 (s, 1H),
8.65 (s, 1H), 7.95 (d, 2H, J=7.5), 7.62 (t, 1H, J=7.25),
7.55 (t, 3H, J=7.25), 7.31 (t, 1H, J=8.5), 6.94 (t, 2H,
J=9.75). 13C NMR ( δ p p m , D M S O - d 6 ) : 163.33,
157.93, 148.77, 133.25, 132.48, 131.89, 130.00,
129.04, 128.11, 119.84, 119.13, 116.89.
Fig. 2. Spectra of P (10 µM) with Al3+ (100 µM)
in ethanol.
2.3. General Spectroscopic Methods
All of the UV-Vis and fluorescence titration data
were recorded at 25 oC. Test solutions were prepared
by placing 50 μL of the P stock solution (1 mM) and
an appropriate aliquot of individual ions stock
solution into a test tube, and then diluting the
solution to 5 mL with ethanol. For all fluorescent
measurements, excitation and emission slit widths
were 10 nm, respectively. Excitation wavelength was
375 nm.
Fig. 3. Changes in UV-vis spectra of P (10 μM) in ethanol
with various amounts of Al3+ (0-10 μM).
3. Results and Discussion
3.1. Uv/vis Response of P
The absorption spectra of P in the absence and
presence of Al3+ were recorded for the purpose of
obtaining an insight into the response mechanism of
P with Al3+ (Fig. 2). The results showed that the
addition of Al3+ cause an obvious red shift of the
absorption spectrum of probe P, which clearly
suggested the binding of P with Al3+. Notably, upon
sequential addition of Al3+ to the P solution induced
an obvious red-shift of the absorption of P (Fig. 3).
Fig. 4. Fluorescence response of P (10 µM) with different
metal ions (100 µM) in ethanol.
3.2. Fluorescence Spectral Response of P
The fluorescent spectra (ex=375 nm) of P
(10 µM) in ethanol with the addition of respective
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Compared to other tested ions, only Al3+
generated a significant “turn-on” fluorescent
Sensors & Transducers, Vol. 186, Issue 3, March 2015, pp. 125-128
response at 443 nm with a prominent fluorescence
enhancement, and only Zn2+ has a negligible
interference. It suggested that P has a better
selectivity toward Al3+ than other metal ions.
To further investigate the interaction of Al3+ with
the proposed probe P, the fluorescent titration
experiment was carried out. Upon titration with Al3+,
the fluorescence intensity of the monomer peak at
443 nm increased gradually (Fig. 5), and the
fluorescent intensity of P was proportional to the
concentration of Al3+ in the range of 5.0×10-7 M to
4.5×10-6 M with a detection limit of 1.1×10-7 M Al3+.
This clearly demonstrated that probe P could
sensitively
detect
environmentally
relevant
levels of Al3+.
Fig. 6. Job’s plot curve of P with Al3+ in ethanol.
The total concentration of P and Al3+ was kept 10 μM.
Fig. 7. Proposed binding mode of P with Al3+.
Acknowledgments
Fig. 5. Fluorescence response of P (10 μM) with different
concentrations of Al3+ in ethanol.
Inset: the fluorescence of P (10 μM) as a function of Al3+
concentrations (0.5–10 μM).
3.3. Proposed Binding Mode of P with Al3+
The linear dependence of the intensity at 480 nm
within the equivalent range of the Al3+ showed that a
1:1 complex was formed between P and Al3+.
Moreover, binding analysis using the method of
continuous variations (Job’s plot) was measured
(Fig. 6), and a maximum fluorescent intensity at
443 nm was observed when the molecular fraction of
P was close to 0.5, which established the
1:1 complex formation between P and Al3+. Thus,
according to the obtained results and reported work,
the binding mode of P and Al3+ was proposed as
shown in Fig. 7.
4. Conclusions
In summary, a simple “off-on” type probe P for
Al3+ was presented. The conception may expand a
promising approach to develop selective detection
method for Al3+ and lead to the development “offon” type probes for other metal ions.
This work was financially supported by the
National Natural Science Foundation of China
(No. 81260268, 81360266), the Natural Science
Foundation of Hainan Province (No. 812188,
413131), the Colleges and Universities Scientific
Research Projects of the Education Department of
Hainan Province (Hjkj2013-29), the Research and
Training Foundation of Hainan Medical University
(HYCX201209), the National Training Programs of
Innovation and Entrepreneurship for Undergraduates
(201311810042).
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