Construction of a luminescent sensor based on a lanthanide complex for the highly efficient detection of methyl parathion

Article abstract of DOI:10.1039/c9ra01748h

A highly sensitive and selective luminescent sensor for the detection of methyl parathion (MP) pesticide was described in this study. The target molecule HL was synthesized by modifying the structure of 4-hydroxybenzlidene imidazolinone (HBI) with nitrogen-containing heterocyclic 1,10-phenanthroline. In the presence of Eu³⁺, a HL-Eu³⁺ complex was formed which could emit strong red fluorescence due to the removal of coordinated water molecules and an intramolecular energy transfer from HL to Eu³⁺. Addition of MP into the strongly fluorescent solution of HL-Eu³⁺ induced quenching of the complex's fluorescence, and this quenching behavior occurred because of the competition coordination of MP and HL for Eu³⁺. A calibration curve was developed that related the extent of fluorescence quenching to MP concentration, making the HL-Eu³⁺ system a sensitive and selective fluorescent sensor for MP. Under the experimental conditions, the detection limit for MP was down to 95 nM based on LOD = 3σ/S. Moreover, the fluorescence assay developed here allowed the detection of MP in two different types of real samples including pond water and pear juice, and satisfactory results demonstrate that this fluorescent sensor based on HL-Eu³⁺ has potential application in environment and food analysis.

Full text of DOI:10.1039/c9ra01748h

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PAPER
Construction of a luminescent sensor based on
a lanthanide complex for the highly efficient
detection of methyl parathion†
Cite this: RSC Adv., 2019, 9, 13048
Xuan Hu,a Fengyi Wang,a Qianqian Peng,a Jing Hu,a Huaqiao Peng,c Lin Li,c
ab
ab
and Dan Xiaoab
*
*
Baozhan Zheng,
Juan Du
A highly sensitive and selective luminescent sensor for the detection of methyl parathion (MP) pesticide was
described in this study. The target molecule HL was synthesized by modifying the structure of 4-
hydroxybenzlidene imidazolinone (HBI) with nitrogen-containing heterocyclic 1,10-phenanthroline. In
the presence of Eu3+, a HL–Eu3+ complex was formed which could emit strong red fluorescence due to
the removal of coordinated water molecules and an intramolecular energy transfer from HL to Eu3+
.
Addition of MP into the strongly fluorescent solution of HL–Eu3+ induced quenching of the complex's
fluorescence, and this quenching behavior occurred because of the competition coordination of MP and
HL for Eu3+. A calibration curve was developed that related the extent of fluorescence quenching to MP
concentration, making the HL–Eu3+ system a sensitive and selective fluorescent sensor for MP. Under
the experimental conditions, the detection limit for MP was down to 95 nM based on LOD ¼ 3s/S.
Moreover, the fluorescence assay developed here allowed the detection of MP in two different types of
real samples including pond water and pear juice, and satisfactory results demonstrate that this
fluorescent sensor based on HL–Eu3+ has potential application in environment and food analysis.
Received 7th March 2019
Accepted 13th April 2019
DOI: 10.1039/c9ra01748h
rsc.li/rsc-advances
develop more rapid, simple and accurate methods for the
determination of OPs with higher sensitivity and selectivity. As
Introduction
a widely used strategy, the uorescent sensors have aroused
considerable attention due to their advantages of excellent
sensitivity and selectivity, short-time data acquisition, facile
manipulations, low cost and visual detection properties.
Therefore, a number of uorescent sensors based on organic
uorophores, Au nanoparticles, quantum dots and carbon dots
et al. have been constructed for the detection of OPs in real
samples.14–18 Barba-Bon and co-workers designed two Eu3+ and
Au3+ complexes based on commonly used organic uorophore
BODIPY. The BODIPY-containing complexes can effectively
detect V-type nerve agent surrogates, demeton-S, by a colori-
metric and uorescent double-detection assay with high sensi-
tivity and selectivity. The displacement of BODIPY ligand by
demeton-S from the metallic centre resulted in obvious colour
change and uorescence quenching of the detecting system.
The detection limit for demeton-S reached as low as 9 ppm.19
Wu and co-workers used carbon dots as uorescent probe for
the determination of paraoxon. The uorescence emission
intensity of CDs decreased signicantly in the presence of
AuNPs via uorescence resonance energy transfer (FRET). Upon
addition of acetylthiocholine (ATC) and butyrylcholinesterase
(BChE), the uorescence was recovered because the thiocholine
generated by enzymatic catalysis reaction caused the aggrega-
tion of Au NPs. Furthermore, the uorescence was quenched
again by paraoxon through the inhibition effect on the activity
Organophosphorus pesticides (OPs) have served as the primary
pesticides and insecticides in agriculture since organochlorine
pesticides were banned.1,2 In fact, OPs can also enter the human
body through polluted water, foods or transdermal absorption,3
resulting in several health issues such as neurological disor-
ders, muscular paralysis tremors, language disorders and even
death.4,5 Therefore, great concerns over the damage of OPs have
resulted in the development of a variety of detection technolo-
gies including gas chromatography,6 high performance liquid
chromatography (HPLC),7 mass spectrometry,8 immunoassays,9
spectrophotometry,10 electrochemical methods,11 ow injection
analysis,12 and chemiluminescence methods.13 Despite the high
sensitivity and selectivity of these methods, most of them have
the disadvantages of being time-consuming and laborious and
needing large instruments, which still limit their wide practical
applications. Therefore, it is of great urgency and necessary to
aCollege of Chemistry, Sichuan University, 29 Wangjiang Road, Chengdu 610064,
China. E-mail: dujuanchem@scu.edu.cn; zhengbaozhan@scu.edu.cn
bKey Laboratory of Green Chemistry and Technology, Ministry of Education, College of
Chemistry, SichuanUniversity, Chengdu, Sichuan 610064, China
cThe Second Research Institute of Civil Aviation Administration of China (CAAC),
Chengdu 610041, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c9ra01748h
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of BChE. Therefore, a facile FRET sensing platform for OPs was
constructed.20
The ideal uorescent probe should have the advantages of
controllable uorescence, good stability, fast response, high
selectivity and sensitively. When applied to environmental
analysis, it should also have favorable water solubility and non-
polluting characteristics and function independently of envi-
ronmental factors and interferences. Lanthanide elements have
special luminescence features and excellent coordination
properties.21,22 Compared to other uorescent systems, lantha-
nide uorescent complexes also have the advantages of high
uorescence quantum yield, large Stokes shi, adjustable
photophysical and photochemical characteristics, good
stability, narrow emission peaks and long uorescence life-
time.23,24 Therefore, lanthanides has become an alternative to
organic uorophores especially in considering of background
autouorescence interference. If an analyte can act as
a competitive binder for the lanthanide ion center in the
luminescent Ln-containing complex, then it has the ability to
‘switch off’ the lanthanide emission. In particular, the excellent
abilities of Eu3+ to selectively interact with the phosphate group
in OPs coupled with favourable photophysical characteristics
make the luminescent Eu-containing complexes attractive
choices for the detection of organophosphorus compounds.
Knapton and co-workers prepared some uorescent organo-
metallic sensors for the detection of chemical-warfare-agent
(CWA) mimics by a displacement assay. In this work, several
ligands based on a 2,6-bis(10-methylbenzimidazolyl)pyridine
(Mebip) structure was developed. The complexation of Mebip
with Eu3+ in a 1 : 1 ligand/Eu3+ ratio resulted in a strong lumi-
nescence emission. The addition of triethyl phosphate (TEP) to
the solution of Eu3+–Mebip complex led to the complete and
immediate quenching of the characteristic red luminescence of
Eu3+.25 Zhang and co-workers immobilized Mebip onto
poly(ethylene-glycol)-graed polystyrene micro-spheres, and
the following incorporation of Eu3+ ions resulted in lumines-
cent microspheres. Upon addition of diethyl chlorophosphate
(DCP), the luminescence of the microspheres was immediately
quenched. These results indicated that even be immobilized on
a solid substrate, some ligands for Ln were still able to be
effectively displaced by organophosphorus compounds.26
However, direct excitation of lanthanide ions to luminesce is
difficult because the f–f transitions are Laporte-forbidden, thus
some light-harvesting ligands called ‘antenna ligands’ are
necessary to absorb and transfer the exciting energy to lantha-
nide ions.27,28 For light conversion systems based on Ln3+ ions,
the main requirements are high ligand-absorption coefficients,
efficient ligand-to-metal energy transfer and minimal non-
radiative deactivation of the excited state of the metal.29
Encapsulation of the Ln3+ ion by polydentate/macrocyclic
Scheme 1 (a) The structure of MP; (b) synthesis of Compound 1,
Compound 2 and HL.
However, its detection by uorescent methods was seldom re-
ported, and almost all of them utilized enzymes as catalyst,37,38
which made the analytical process complex and expensive.
Based on the above analysis, herein, a luminescent lanthanide
complex of HL–Eu3+ with red uorescent emission was
synthesized and chosen as the sensing and detecting units for
MP. The aromatic cyclic polyamine ligand HL was designed and
synthesized by modifying the structure of 4-hydroxybenzlidene
imidazolinone (HBI) with nitrogen-containing heterocyclic
1,10-phenanthroline, as shown in Scheme 1(b). HL itself had
very weak uorescence in solution. With the addition of Eu3+
,
HL can act as an effective ‘antenna ligand’ to coordinate with
Eu3+ and form a complex HL–Eu3+ with the characteristic
emission of Eu3+. We foresaw that the Eu3+ emission of HL–Eu3+
could be ‘switched off’ through the displacement of the HL
antenna in the presence of MP caused by the preferable inter-
action between Eu3+ and MP, therefore, an effective MP sensor
can be successfully constructed.
Experimental section
Apparatus
1H NMR and 13C NMR were measured on a BrukerAVII-400 MHz
spectrometer with chemical shis reported in ppm (in DMSO;
TMS as internal standard). Mass spectra were obtained from
a commercial ion trap mass spectrometer (Thermo Fisher
Scientic, San Jose, CA). Thermo Scientic Nicolet 6700 FT-IR
spectrometer (Sugar Land, TX, USA) was used to record the
FT-IR of HL. Fluorescence spectra were determined on F-7000
spectrophotometer equipped with a 1 cm quartz cell (HITA-
CHI, Japan). UV-visible measurements were measured on U-
2900 spectrophotometer (HITACHI, Japan).
Materials reagents
ligands,30 Schiff bases,31 organic acids,32 and even proteins is Europium(III) chloride hexahydrate (EuCl3$6H2O), 2,9-dimethyl-
the most common strategy employed to satisfy these criteria.33 1,10-phenanthroline, N-acetylglycine (AR) were obtained from
As one of the most toxic OPs, methyl parathion (O,O-dimethyl O- Alfa Aesar; selenium dioxide was purchased from Sigma-
4-nitrophenyl phosphorothionate, MP, Scheme 1(a)) was clas- Aladdin; sodium acetate, acetic anhydride and ethanol were
sied as ‘Category Ia’ (extremely toxic) by the World Health purchased from Kelong Chemical Reagent Co., Ltd. (Chengdu,
Organization (WHO) and ‘Toxicity Category I’ (most toxic) by the China); methyl parathion (MP) was purchased from shanghai
United States Environmental Protection Agency (USEPA).34–36 Macklin Biochemical Co., Ltd. All chemicals and reagents were
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of analytical grade and used without further purication.
Detection procedure of methyl parathion
Double distilled water was employed for all experiments.
HL stock solution (0.3 mM) was prepared in Tris–HCl buffer (pH
7.0, 25 mM) and further diluted to 60 mM for the assay. The
uorescence spectra were then measured with an excitation
wavelength (lex) of 356 nm, and the uorescence spectrum of
HL–Eu3+ solution was recorded between 600–650 nm with
a maximum emission wavelength of 617 nm (lem). All of the
uorescence intensity measurements were conducted in tripli-
cate. Three polluted water samples were collected from a pond
nearby and ltered prior to analysis. All the stock solutions were
Synthesis of Compound 1
In this paper, HL and its intermediates (Compound 1,
Compound 2) were synthesized via simple steps as depicted in
Scheme 1(b). Typically, 2,9-dimethyl-1,10-phenanthroline (1.0 g,
4.60 mmol), selenium dioxide (2.5 g, 22.5 mmol) were dissolved
in 1,4-dioxane (35 mL) and stirred at 110 ꢀC for 2 h. The formed
precipitate was separated with diatomite thermal ltration and
then recrystallized in DMF/H2O with vacuum dried at 40 ꢀC for
12 h. Thus, 0.70 g (yield 67.6%) yellow solid Compound 1 could
be obtained. Compound 1: 1H NMR (400 MHz, DMSO-d6) dH
(ppm): 10.31 (CHO, s, 2H), 8.71 (Ar–H, d, J ¼ 8.2 Hz, 2H), 8.40
(Ar–H, d, J ¼ 8.4 Hz, 2H), 8.19 (Ar–H, d, J ¼ 4.0 Hz, 2H). (Fig. S1†)
13C NMR (400 MHz, DMSO) dC (ppm): 194.01, 152.3, 148.6,
138.2, 129.7, 120.6. (Fig. S2†).
ꢀ
stored at 4 C in a refrigerator until use.
Results and discussion
Design and characterization of HL–Eu3+
In order to obtain a uorescent system with excellent perfor-
mance, the uorescence behavior of HL toward several lantha-
nide metal ions were rstly examined in Tris–HCl buffer (pH
7.0, 25 mM). As shown in Fig. 1(A), excepting the comparatively
stable and weak uorescence peak of HL at 460 nm, there was
no characteristic uorescence emission of any one of the
lanthanide metal ions including La3+, Nd3+, Tb3+, Yb3+, Er3+ and
Ce3+ that can be detected when they were introduced into HL
solution. In comparison, the uorescence spectrum changed
immediately upon Eu3+ addition and the characteristic peaks of
Eu3+ at 581 nm, 593 nm and 617 nm appeared. This result
demonstrated that Eu3+ can coordinate with HL, which could
transfer the absorbed energy to Eu3+ ions to excite them. The
coordination process of Eu3+ with HL was displayed in Scheme
2(a). In order to explore the optimal concentration of Eu3+ in
HL–Eu3+ system, we analyzed the uorescence intensity of HL–
Eu3+ with different amounts of Eu3+. As shown in Fig. S8,† the
emission intensity at 617 nm increased gradually with contin-
uous addition of Eu3+, then reached the highest level upon
addition of 60 mM Eu3+. Nevertheless, an obvious uorescence
decrease was appeared when the concentration of Eu3+ is higher
than 60 mM. Therefore, 60 mM Eu3+ was selected as the ideal
concentration and used in following experiments. Importantly,
the maximal uorescence intensity of HL–Eu3+ was remained
nearly steady with constant light irradiation (356 nm) for 2 h,
and the unchanged intensity proved its excellent photo-stability
Synthesis of Compound 2
For the synthesis of Compound 2, Compound 1 (0.67 g, 3
mmol), anhydrous sodium acetate (0.5 g, 6 mmol), and N-ace-
tylglycine (0.73 g, 6 mmol) were dissolved in 30 mL acetic
anhydride reuxed at 90 ꢀC for 4 h. When the mixture was
cooled down to room temperature, 250 mL cold water was
added into the solution and yellow precipitate could be formed
quickly. Aer the ltration, washing with cold ethanol and
ꢀ
vacuum-drying at 60 C for 12 h, a yellow solid compound of
Compound
2 could be obtained (0.49 g, yield 41.9%).
Compound 2: 1H NMR (400 MHz, DMSO-d6) dH (ppm): 8.89 (Ar–
H, d, J ¼ 8.1 Hz, 2H), 8.83 (Ar–H, d, J ¼ 8.2 Hz, 2H), 8.38 (C]
CH, s, 2H), 8.30 (Ar–H, m, 2H), 1.83 (CH3, s, 6H), (Fig. S3†).
Synthesis of HL
Compound 2 (0.49 g, 1.2 mmol), potassium carbonate (0.1 g,
0.72 mmol) and 1 mL 40% aqueous methylamiꢀne solution were
dissolved in 20 mL ethanol and stirred at 90 C for 4 h. Aer
cooling down to room temperature, the mixture was diluted
with 100 mL water, the pH of the solution was adjusted to 3.0
with concentrated HCl, and le overnight at 4 ꢀC in refrigerator.
The formed yellow precipitate was then ltered, washed and
dried. The obtained crude compound was puried by thin layer
chromatography with chloroform/ethylacetate (1 : 3, v/v), thus,
a pure compound of HL (yellow solid (25%)) was synthesized,
which was then used for the characterization of FT-IR, ESI-MS
and 1H NMR. HL: 1H NMR (400 MHz, DMSO-d6) dH (ppm):
8.64–8.38 (Ar–H, d, J ¼ 7.2 Hz, 2H), 8.32–7.9 (Ar–H, d, J ¼ 7.0 Hz,
2H), 7.68 (C]CH, s, 2H), 7.54 (Ar–H, d, J ¼ 8.2 Hz, 2H), 3.75 (N–
CH3, s, 6H), 2.07 (N]C–CH3, s, 6H), (Fig. S4†). The ESI-MS data
of HL showed a peak with m/z 463.0298 ([HL + K]+) (Fig. S5†).
The addition of Eu3+ resulted in the formation of HL–Eu3+
complex, and the MALDI-TOF MS data of HL–Eu3+ showed
a peak with m/z 629.1 ([HL–Eu3+ + 3H2O ꢁ 2H]+) cal.: 629.1
found 629.1 (Fig. S6†). The MALDI-TOF MS data of Eu3+ with the
presence of MP has been added and the peak with m/z 581.3 in
Fig. S7† is assigned to [Eu + MP + K + 7H2O]4+ (cal.: 581.0 found
581.3).
Fig. 1 (A) Fluorescence spectra of HL upon addition of different
lanthanide metal ions (60 mM) of La3+, Nd3+, Eu3+, Tb3+, Yb3+, Er3+ and
Ce3+ with an excitation wavelength of 356 nm. (B) Fluorescence
spectra of HL, next adding Eu3+ and then adding 20 mM MP. Inset:
photograph of HL (a), HL–Eu3+ (b), and HL–Eu3+ + MP (c).
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MP for 10 minutes. These facts made the sensor HL–Eu3+ the
potential candidate for effectively detecting MP.
Investigation of the experimental conditions
In order to explore the inuence of pH on the performance of
HL–Eu3+ towards MP determination, the response of con-
structed uorescent assay pH condition was further optimized
by the addition of various Tris–HCl buffer at pH 2.0–11.0
(Fig. 2(A)). The measured results revealed that the uorescence
intensity of HL–Eu3+ increased gradually to a maximum value
with the increase of pH until pH 7.0 and then slowly decreased.
With the presence of MP, it can be observed that the uores-
cence quenching efficiency was affected by the pH value, and
a maximum quenching rate was obtained at pH 7.0. Hence, pH
7.0 was employed as the favorable pH value. Furthermore, the
uorescence intensity of HL–Eu3+ with or without MP was
comparatively satisfactory stability even in a salty medium with
a NaCl concentration as high as 0.1 M (Fig. 2(B)), indicating its
potential applicability in complex water environmental samples
analysis.
Scheme 2 (a) The coordination process of Eu3+ with HL. (b) The
schematic representation of the fluorescent sensing mechanism for
MP determination based on HL–Eu3+
.
and expectable application potential as an ideal sensor used in
complex environment systems (Fig. S9†).
To understand the stoichiometric nature of HL–Eu3+, the
Job's plot for the binding activity between HL and Eu3+ was
studied, and the result exhibited 1 : 1 stoichiometry from the
uorescence titration (Fig. S10†). The FT-IR spectra of HL and
HL–Eu3+ were reported in Fig. S11.† From which, the charac-
teristic peaks at about 1630 cmꢁ1, 1660 cmꢁ1 and 3320 cmꢁ1
should be attributed to the stretching vibration of C]N, C]O
and N–H of HL, respectively. Compared with the peaks of HL
(1347 cmꢁ1 and 1630 cmꢁ1 for C–N and C]N groups, respec-
tively), the slight peak shis (1319 cmꢁ1 and 1610 cmꢁ1) in HL–
Eu3+ suggested that the N atoms in both of the C–N and C]N
groups were involved in the coordination with Eu3+ in the
formation of HL–Eu3+ complex. In addition, the Eu–N stretch-
ing vibration was observed at 479 cmꢁ1 in HL–Eu3+. The strong
and wide stretching vibration peak of O–H bond at about
3349 cmꢁ1 in HL–Eu3+ could be assigned to the comprised water
molecules of Eu3+. On the basis of the above analysis, the
conclusion can be reached that HL–Eu3+ has been formed.
The uorescence spectra of HL–Eu3+ in the presence of MP
were measured in Tris–HCl buffer (pH 7.0, 25 mM). As illus-
trated in Fig. 1(B), comparing the uorescent emission at
460 nm with HL alone, HL–Eu3+ revealed an extra strong char-
acteristic emission center at 617 nm when excited at 356 nm
with a uorescent color change from weak blue to bright red
(inset of Fig. 1(B)). With the addition of 20 mM MP into the
solution of HL–Eu3+, the complex's uorescence was obviously
quenched and the change was easily discernible to the naked
eye under UV light irradiation as Fig. 1(B) inset showed. More-
over, the uorescent response time of HL–Eu3+ toward MP was
also investigated in this work. The results showed that when MP
was added to HL–Eu3+ solution, about 70% uorescence
intensity quench was detected at 617 nm within one minute and
the uorescent intensity remained almost constant in around
10 min (Fig. S12†). Therefore, all the uorescent spectra
measurement in this work are carried out aer the addition of
Specicity of HL–Eu3+ for MP detection
To examine the selectivity of HL–Eu3+ for MP detection, we
investigated the uorescence behavior of HL–Eu3+ to commonly
existent organic pollute compounds (OPCs), anions and metal
ions (Fig. 3 and S13†), including p-nitrotoluene, 2,4,6-trinitro-
toluene, o-cresol, phenol, 2,5-dimethylphenol, resorcinol,
carbaryl, phoxim, triethylphosphate, dimethoate, PO4
3ꢁ
,
HPO42ꢁ, H2PO4ꢁ, SO42ꢁ, Fꢁ, Brꢁ, NO3ꢁ, Acꢁ, Ba2+, Mg2+, Ca2+,
Hg2+, Na+, Fe3+, Pb2+, Cd2+, Zn2+ and MP. Negligible uores-
cence intensity changes were observed upon the addition of the
above mentioned substances except MP (Fig. 3 blank bars,
Fig. S13A†). Another important feature of HL–Eu3+ was its high
selectivity toward MP in a competitive environment. The
competitive experiments were conducted in coexist of MP and
excess amount of various other OPCs, metal ions and anions
(Fig. 3 red bars, Fig. S13B†). There were no distinct variations of
the uorescence signal caused by the co-existence of these
potential interrupting species. The absorption spectra of HL–
Eu3+ with the addition of as-mentioned OPs (carbaryl, phoxim,
triethyl phosphate, dimethoate and MP) helped to explain the
Fig. 2 (A) Effect of the pH on the fluorescence intensity of HL–Eu3+
with (red line) and without (black line) MP. (B) Effect of the concen-
tration of NaCl on the fluorescence intensity of HL–Eu3+ with (red line)
or without (black line) MP.
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Therefore, it can be reasonably presumed that only the addition
of MP can break the combination between HL and Eu3+ and
induce the displacement of HL from HL–Eu3+ complex. These
results clearly manifested that the constructed uorescence
sensor based on HL–Eu3+ has an excellent selective response to
MP with good sensitivity.
Detection of MP and the mechanism
Under the optimized condition, the changes of HL–Eu3+ uo-
rescent were monitored by uorescence emission spectroscopy
with different concentrations of MP (0.75–20 mM). As expected,
the uorescence intensity of HL–Eu3+ at 617 nm gradually
decreased with increasing MP concentration (Fig. 4(A)), and
accurate change monitoring of the uorescence intensity was
realized in the presence of MP as Fig. 4(B) showed. The HL–Eu3+
sensor exhibited a linear response toward the concentration of
Fig. 3 The fluorescence intensity of HL–Eu3+ in the presence of
various organic pollute compounds (OPCs). The black bars represent
the addition of excess OPCs. The red bars represent the subsequent MP (0.75–20 mM), and the tting linear equation was expressed
as y ¼ 0.422x ꢁ 0.0181 with a linear relative coefficient of R2 ¼
addition of MP (20 mM). (a) p-Nitrotoluene (200 mM), (b) 2,4,6-trini-
trotoluene (200 mM), (c) o-cresol (25 mM), (d) phenol (200 mM), (e) 2,5-
dimethylphenol (200 mM), (f) resorcinol (100 mM), (g) carbaryl (200 mM),
(h) phoxim (100 mM), (i) triethyl phosphate (200 mM), (j) dimethoate
0.9944. Furthermore, we also compared our assay with other
reported methods for the determination of MP (Table S1†), and
the results showed that our sensor provided lower detection
limit for the detection of MP.
(200 mM), (k) MP (20 mM).
Considering the above analysis, the detection mechanism of
the uorescence sensor based on HL–Eu3+ toward MP was dis-
played in Scheme 2(b). Aer the addition of Eu3+ into HL
solution, the coordination of HL with Eu3+ could occurred
immediately through four nitrogen atoms and led to the
formation of HL–Eu3+ quaternary complex, which can emit
strong red uorescence due to the removal of coordinated water
molecules and an intramolecular energy transfer from HL to
Eu3+ through the so-called ‘antenna effect’. When MP was
added into the system of HL–Eu3+, it could bind with Eu3+ and
form a more stable complex because of the stronger nucleo-
philicity, leading to the obvious decrease of the uorescence
intensity at 617 nm. This selective binding behavior of Eu3+ also
resulted in the release of free HL ligand, and the uorescence of
HL at 460 nm increased. By employing the uorescent HL–Eu3+
as the sensor, the specic and sensitive detection for MP was
realized and the detection limit reached down to 95 nM with
LOD ¼ 3s/S.
Fig. 4 (A) Fluorescence emission spectra of HL–Eu3+ were measured
upon addition of increasing concentrations of MP. (B) The fluores-
cence intensity at 617 nm of HL–Eu3+ was linearly related to the
concentration of MP.
Table 1 Determination of MP in spiked real samples
Added
(mM)
RSD (n
¼ 3%)
Sample
Found (mM)
Recovery (%)
Detection of MP in real samples
Pond water
2.00
4.00
6.00
2.00
4.00
6.00
2.13
3.96
5.84
2.06
4.06
5.95
106.62
99.15
97.37
102.82
101.51
96.23
3.28
2.53
1.78
2.97
1.08
2.68
To demonstrate the feasibility of the present method for selec-
tive probing MP in real samples, different concentrations of MP
in the spiked pond water and pear juice samples were deter-
mined and the results were listed in Table 1. It can be seen that
good recoveries ranging from 96.23% to 106.62% were obtained
and the RSD were less than 4.0% for all indicating that the
present method is reliable and applicable for MP assay in
environmental and food samples.
Pear juice
observed selectivity of HL–Eu3+ toward MP. As displayed in
Fig. S14,† HL–Eu3+ had two distinct absorption bands centred at
232 nm and 282 nm, respectively. The addition of MP induced
an obvious disappearance of the absorption band centred at
232 nm and a minor blue-shi from 282 nm to 280 nm.
Otherwise, there was no apparent change of the absorption
bands of HL–Eu3+ with the presence of other OPs except MP.
Conclusions
In summary, a lanthanide complex sensor HL–Eu3+ based on
aromatic cyclic polyamine ligand was constructed by modifying
the structure of 4-hydroxybenzlidene imidazolinone (HBI) with
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nitrogen-containing heterocyclic 1,10-phenanthroline. In this 16 N. Fahimi-Kashani and M. R. Hormozi-Nezhad, Anal. Chem.,
system, the competition coordination of MP and HL for Eu3+
2016, 88, 8099–8106.
transformed the uorescence and established a uorescence 17 X. Gao, G. Tang and X. Su, Biosens. Bioelectron., 2012, 36, 75–
sensor for MP. HL–Eu3+ displayed excellent selectivity and
80.
sensitivity toward MP detection, and the detection limit reached 18 J. Chang, H. Li, T. Hou and F. Li, Biosens. Bioelectron., 2016,
95 nM. At the same time, it showed good recovery performance 86, 971–977.
in actual pond water and pear juice samples, indicating that the 19 A. Barba-Bon, A. M. Costero, S. Gil, F. Sancenon and
´
´
´˜
sensor has the potential application for detecting MP in
complex real samples.
R. Martınez-Manez, Chem. Commun., 2014, 50, 13289–13291.
20 X. Wu, Y. Song, X. Yan, C. Zhu, Y. Ma, D. Du and Y. Lin,
Biosens. Bioelectron., 2017, 94, 292–297.
˜
21 S. V. Eliseeva and J. C. BaNzli, Chem. Soc. Rev., 2009, 39, 189–
Conflicts of interest
227.
There are no conicts to declare.
22 K. Mikami, M. Terada and H. Matsuzawa, Angew. Chem.,
2002, 114, 3704–3722.
23 A. T. Bui, M. Beyler, A. Grichine, A. Duperray, J. C. Mulatier,
Y. Guyot, C. Andraud, R. Tripier, S. Brasselet and O. Maury,
Chem. Commun., 2017, 53, 6005–6008.
24 K. Binnemans, Chem. Rev., 2009, 109, 4283–4374.
25 D. Knapton, M. Burnworth, S. J. Rowan and C. Weder, Angew.
Chem. Int. Ed., 2006, 45, 5825–5829; Angew. Chem., 2006, 118,
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Acknowledgements
We are grateful for nancial support from National Natural
Science Foundation of China (No. 21876117, U1833124 and
U1833202). We also appreciate Analytical & Testing Centre of
Sichuan University for the characterizations.
26 H. Zhang, X. Hua, X. Tuo, C. Chen and X. Wang, J. Rare
Earths, 2012, 30, 1203–1207.
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