Europium-Based Metal-Organic Framework as a Dual Luminescence Sensor for the Selective Detection of the Phosphate Anion and Fe3+ Ion in Aqueous Media

Article abstract of DOI:10.1021/acs.inorgchem.8b02017

A new three-dimensional europium-based metal-organic framework has been synthesized with the newly designed ligand L (6-[1-(4-carboxyphenyl)-1H-1,2,3-triazol-4-yl]nicotinic acid). This compound acts as a dual sensor for the phosphate anion and Fe³⁺ ion in aqueous media. The mechanistic aspect of this selectivity and sensitivity was explored through several spectroscopic methods and then correlated with the corresponding structure.

Full text of DOI:10.1021/acs.inorgchem.8b02017

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Europium-Based Metal−Organic Framework as a Dual
Luminescence Sensor for the Selective Detection of the Phosphate
Anion and Fe3+ Ion in Aqueous Media
Purna Chandra Rao and Sukhendu Mandal*
School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Thiruvananthapuram, Kerala
695551, India
S
* Supporting Information
and chemical and thermal stability.24−26 Luminescent MOFs
ABSTRACT: A new three-dimensional europium-based
metal−organic framework has been synthesized with the
newly designed ligand L (6-[1-(4-carboxyphenyl)-1H-
1,2,3-triazol-4-yl]nicotinic acid). This compound acts as a
dual sensor for the phosphate anion and Fe3+ ion in
aqueous media. The mechanistic aspect of this selectivity
and sensitivity was explored through several spectroscopic
methods and then correlated with the corresponding
structure.
have been used as sensors because of their unique proper-
ties.27−33 Moreover, lanthanide MOFs (LnMOFs) are uniquely
attractive for developing luminescent sensor probes because of
their fascinating optical properties, i.e., large Stokes’ shifts, high
optical purity and quantum yields, visualization, relatively long
luminescence lifetimes, etc.34−38 Herein we report a europium-
based MOF (compound 1) with a designed organic ligand (L;
Figure 1 and Scheme S1). Compound 1 was synthesized by a
hosphate plays a significant role in biological and environ-
P
mental systems.1−5 Detection of the phosphate concen-
tration in body fluids is essential for the diagnosis of severe
diseases like vitamin D deficiency, Fanconi syndrome, and
hyperparathyroidism.6−9 The increase in the concentration of
inorganic phosphates in natural water will engender environ-
mental issues such as eutrophication. Therefore, developing a
selective and sensitive sensor for phosphate detection in aqueous
media is noteworthy to protect the environment and human
health. To do this, various analytical techniques have been
developed including spectrophotometry, fluorometry, chroma-
tography, and electrochemical analysis.10−12 Among these,
fluorescent techniques have a substantial role in sensing
applications because of their remarkable advantages such as
their high level of sensitivity, specificity, fast response, and
simplicity.13,14 The detection of phosphate ions in aqueous
media is a difficult task because of their strong hydration
effects.15,16 Therefore, the sensor probe should be stable and
require suitable detecting sites in aqueous media.
Figure 1. Molecular structure of ligand L.
solvothermal reaction of Eu(NO3)3·5H2O and L in N,N-
dimethylformamide (DMF) for 72 h at 120 °C. Single-crystal
X-ray diffraction (SCXRD) experiments analyzed the colorless
crystals of compound 1, and it was formulated as
{Eu2L3(DMF)}·2DMF. Compound 1 crystallizes in a mono-
clinic crystal system with space group P21/c (No. 14). The
asymmetric unit consists of two independent EuIII ions, three
different ligands (L2−), and one coordinated DMF molecule.
The carboxylate groups of ligand L have two types of binding
modes in which one of the carboxylate groups belongs to the
chelating−bridging mode and two different carboxylate groups
adopt the chelating mode (Figure S1). Two independent
europium metal ions (Eu1 and Eu2, respectively) are 8-
coordinated and exhibit a bicapped tetragonal-prismatic
geometry (Figure S2). In this, Eu1 is coordinated by seven
oxygen atoms from L2− ligands and one coordinated DMF
molecule, whereas eight oxygen atoms from the carboxylate
moieties coordinate with the Eu2 metal ion. The two carboxylate
moieties are connected by two independent EuIII ions to
generate a binuclear secondary building unit (SBU) with a Eu···
Eu separation of 4.1314 (5) Å. Then another carboxylate moiety
connects these SBUs to form a three-dimensional framework.
It is interesting to note that the carboxylate groups are bound
to EuIII ions, whereas the pyridyl groups of the ligand species are
On the other hand, the Fe3+ ion plays a vital role in biological
systems such as oxygen transport, synthesis of DNA and RNA,
muscle and brain function, and hemoglobin formation.17−19
Moreover, an excess or a deficiency of iron severely affects the
immune and enzyme systems, which can result in several
pathological disorders like skin ailments and insomnia, iron
deficiency anemia, mental decline, etc. Therefore, it is essential
to develop an efficient sensor that can detect the Fe3+ ion in
aqueous media.20−23 Reports on phosphate sensing using
metal−organic frameworks (MOFs) are rare.1,15 The detection
of phosphate and Fe3+ ions in aqueous media using a single
sensor would be an ideal choice for effectiveness and practical
application.
MOFs consist of metal nodesand organic ligands and attribute
hierarchy of structures, high surface area, appropriate active sites,
Received: July 19, 2018
© XXXX American Chemical Society
A
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uncoordinated and freely accessible in the framework. The
topology of compound 1 was represented as a 11,12-connected
2-nodal net with a point symbol of {318.433.54}{318.436.58.64}
(Figure 2).
fonic acid (HEPES) buffer solution (pH = 7; Figure S9). With
the addition of phosphate anions, the fluorescence intensity
decreases, and no significant change was observed in the case of
other pollutant anions (Figure 3c). This confirms that
Figure 2. (a) Three-dimensional view of compound 1. (b) Fragment of
the two-dimensional arrangement of compound 1 along the ac plane.
(c) Coordination environment of dinuclear EuIII metal ions in
compound 1. (d) Topological representation of compound 1.
Figure 3. Photoluminescence spectra of compound 1′ (a) at different
concentrations of PO43− anions and (b) at different concentrations of
Fe3+ ions. Fluorescence response of compound 1′ treated with various
(c) anions (100 μL, 1 mM) and (d) metal ions (100 μL, 10−2 M) in a
HEPES buffer solution (pH = 7).
The simulated and experimental powder X-ray diffraction
(PXRD) data are in good agreement, which confirmed the phase
purity of the compound (Figure S3). Thermogravimetric
analysis showed that the weight loss at 220 °C corresponded
to the removal of coordinated DMF molecules, and then it was
stable up to 340 °C. After that, the framework collapsed (Figure
S4). We activated the compound through a solvent-exchange
method (see the Supporting Information). After activation, the
PXRD pattern of compound 1′ (activated compound) slightly
shifted, and this may be due to the flexible nature of 1′. We have
performed the SCXRD experiment for activated compound 1′.
With the same space group, a slight change in the unit cell
parameters confirmed that shifting of the PXRD pattern might
arise from the flexible nature of the metal nodes or organic linker
(see Table S3). We checked the stability of compound 1′ in
aqueous media by immersing the crystals in a water medium for 3
days. Subsequently, we analyzed the PXRD pattern, which
retains a crystallinity matching that of compound 1′ (Figure S3).
We performed N2 adsorption for compound 1′ at 77 K. The
isotherms showed a low Brunauer−Emmett−Teller surface area
of 19 m2/g, and the pore-size (2.4 nm) distribution profile was
calculated for the activated compound 1′ (Figure S5).
compound 1′ can selectively detect phosphate anions in aqueous
media (Figure 3a). Moreover, we observed that 1′ acts as a
chemosensor and the response time for sensing was 10 min.
Later, we conducted interference experiments with other
−
cointerfering anions (CO32−, SO42−, NO3 , Br−, CrO42−, and
Cr2O72−), and we observed that other anions have a minor effect
on the quenching of 1′ (Figure S10). Quantitatively, the
quenching efficiency effect was rationalized by the Stern−
Volmer (S−V) equation: I0/I = 1 + KSV[M], where I0 and I are
the fluorescence intensities before and after the interaction of
compound 1′ with phosphate anions, respectively, [M] is the
molar concentration of the phosphate anion, and KSV is the
quenching effect coefficient (M−1). The S−V plot is nearly linear
(R2 = 0.967) in the range of 3−30 μM, and a high KSV value (4 ×
104 M−1) was obtained that is comparable to those of known
luminescent LnMOF sensors (Figure S11 and Table S4). The
detection limit was calculated to be 6.62 μM, which is the
relatively lowest concentration for the detection requirement of
phosphate discharge criteria in the water environment, and the
range is reported to be 6.4−320 μM.
In aqueous media, the selective detection of phosphate anions
was attributed to their high hydration energy, with a high charge-
to-radius ratio compared with other pollutant anions.15 Also,
some other factors that can affect the anion binding are the
geometry, charge of the anion, noncovalent interactions between
the metal cluster and anion, nature of the solvent medium, and
lability of the metal cluster.14,39,40 We carried out quenching
studies by dissolving the anions in an isopropyl alcohol/water
mixture (50:1, v/v; Figure S12). It was observed that the
quenching efficiency of the phosphate anions decreased
compared to that of aqueous media. This suggests that aqueous
media are essential for phosphate sensing.
The ligand L absorbs at 270 and 295 nm, respectively, and
emits at 345 nm under excitation at 295 nm in a DMF solvent
(Figure S6). In the solid state, compound 1′ absorbs at 330 nm
(Figure S7). The excitation spectra of 1′ were examined at the
characteristic emission of 611 nm, which resulted in a broad
band with a maximum peak at 345 nm (Figure S8a). Upon
excitation at 330 nm, compound 1′ exhibits strong emissions in
the visible region at 590, 611, 648, and 699 nm, which are
attributed to 5D0 → 7FJ (J = 1−4) transitions of Eu3+ ions (Figure
S8b). The unique optical properties and stability in aqueous
media of the as-synthesized compound provoked us for the
detection of pollutant anions in aqueous media. To do this, we
carried out photoluminescence studies by the addition of various
To investigate the possible mechanism for the sensing of
phosphate with the current fluorescent probe, we conducted
vibrational spectroscopy and X-ray photoelectron spectroscopy
(XPS) analyses. Fourier transform infrared spectroscopy showed
that, upon the addition of low-to-high concentrations of
−
2−
pollutant anions such as Cl−, Br−, NO3 , SO42−, CO32−, CrO4
,
Cr2O72−, P2O74−, HPO42−, H2PO4 , and PO43− to the activated
−
compound 1 in a 4-(2-hydroxyethyl)-1-piperazineethanesul-
B
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phosphate anions to the framework of 1′, there is a decrease in
the peak intensity of carboxylate C−O bonds, and further it
disappears at high concentrations (1657 cm−1). Simultaneously,
we observed a substantial rise in the peak intensity at 1642 cm−1,
which corresponds to the stretching frequency of the P−O
bonds (Figure S13). XPS data before and after phosphate
addition revealed that there is a slight shift in the binding energy
(Figure S14). This red shift in the 3d electron binding energy
(that for Eu 3d3/2 is from 1136.19 to 1137.89 eV, and that for Eu
3d5/2 is from 1166.06 to 1167.35 eV) might be due to the
interaction of phosphate groups with the europium center. The
more electronegative P−O bonds leads to a loss electron density
at the europium center, which, in turn, increases its 3d binding
energy. These experimentalinvestigations confirmed that the P−
O bonds are interacting with the Eu−O cluster and thereby
partial interruption of electron transfer between the organic
ligand and metal center, which might be the reason for the
decrease in the fluorescence intensity. We performed lifetime
measurements, which indicated no change in the lifetimes before
and after the addition of phosphate to 1′ (see Figure S15a). Also,
we observed the change in the UV−visible absorption bands of
1′ after the addition of a phosphate (Figure S15b). It was
concluded that quenching is due to the ground-state complex
formation of phosphate with a fluorophore (1′). Hence, these
analyses showed that phosphate sensing follows a static
quenching process (Figure S15).
Further, compound 1 has a free pyridyl nitrogen atom and
1,2,3-triazole nitrogen atoms, which can act as Lewis basic sites.
Also, the characteristic features of photoluminescence and water
stability motivated us to check the sensing of metal ions in
aqueous media. We studied the fluorescence sensing experiment
by the addition of equal concentrations of various metal ions
(10−2 M) such as Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+,
Al3+, and Fe3+ to a dispersion of the activated compound 1. Only
the Fe3+ ion was selectively detected in compound 1′ (see
Figures 3b,d and S16). Moreover, the quenching efficiency was
evaluated by the S−V equation with a linear correlation (R2=
0.992) for I0/I versus the concentration of Fe3+ ions. The KSV
value was found to be 6 × 105 M−1, and the limit of detection was
calculated to be 0.793 μM (Figure S17). It is comparable to other
MOF materials with higher binding constants (Table S5). We
carried out an interference experiment for Fe3+; it showed a
minor effect on the luminescence quenching by Cr3+, Zn2+, and
Cd2+, while other cations (Co2+, Fe2+, Cu2+, etc.) had a negligible
effect on the quenching of 1′ (Figure S18). Three aspects that
can iniate the quenching of luminescent MOFs by metal ions are
as follows: (1) collapse of the framework; (2) binding of metal
cations with the organic linker (energy-transfer mechanism); (3)
an ion-exchange approach (replacement of the metal cations in
the framework with targeted metal ions).41 Compound 1′ was
immersed in a Fe3+ ion solution (10−2 M) for 24 h and then
washed with ethanol several times. No change in the PXRD
pattern after treatment with Fe3+ ions in water, which rules out
collapse of the framework (Figure S19a). Then we measured the
UV−visible spectra of various metal ions in aqueous media. The
resulting Fe3+ absorption spectrum was overlapped with the
ligand emission of compound 1′ (Figures S19b and S19c). It is
strongly evident that fluorescence quenching is due to the
competition between the absorbance of the Fe3+ solution and the
emission of compound 1′. Also, we performed lifetime
measurements of 1′ before and after the addition of Fe3+ metal
ions, which shown at 35.6 and 29.11 ns, respectively (Figure
S19d). The change in the lifetimes also concluded that the
quenching of 1′ was more likely to be a dynamic process. To
underscore the interaction between the framework and Fe3+
ions; we collected the XPS data. This showed that the binding
energy of N 1s of the pyridyl and triazole nitrogen atoms slightly
shifted to higher energy (Figure S20). This shift in the binding
energy could be due to the interaction of Fe3+ ions with the
pyridyl and triazolyl nitrogen atoms. This coordination
interaction of the Fe3+ ions with the framework reduces the
antenna efficiency of ligand L2− to f−f transitions of Eu3+,
thereby quenching the luminescence intensity.
In conclusion, we synthesized a new three-dimensional
europium-based framework structure with the newly designed
1,2,3-triazole-based nicotinic acid (L). The polyhedral unit of
europium metal ions are linked to form the dimeric unit, and
these dimeric units are connected with the carboxylate group to
form the three-dimensional architecture. In compound 1, the
pyridyl and triazole nitrogen atoms are uncoordinated and freely
accessible for further functionalization. This MOF can
selectively detect phosphate anions and Fe3+ ions in aqueous
media. The interaction between the europium metal center and
phosphate anions is responsible for the selective and sensitive
detection of phosphate anions, while Fe3+ selective detection is
accountable for binding of these ions with the pyridyl and
triazole nitrogen atoms. There are a few reports on separate
phosphate anion and Fe3+ ion sensing in aqueous media using
MOF materials. However, reports on the dual sensing of
phosphate anions and Fe3+ ions in aqueous media are rare. To
our knowledge, this EuMOF is one of the rare compounds that
can act as a dual sensor for the phosphate anion and Fe3+ ion in
aqueous media.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02017.
■
S
Synthesis of ligand and compound 1, NMR, IR analysis,
crystallographic data of compound 1, characterization
data, and additional figures (PDF)
Accession Codes
CCDC 1841354 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: sukhendu@iisertvm.ac.in.
■
ORCID
Sukhendu Mandal: 0000-0002-4725-8418
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) Yang, J.; Dai, Y.; Zhu, X.; Wang, Z.; Li, Y.; Zhuang, Q.; Shi, J.; Gu, J.
Metal-organic frameworks with inherent recognition sites for selective
phosphate sensing through their coordination-induced fluorescence
enhancement effect. J. Mater. Chem. A 2015, 3, 7445−7452.
(2) Jia, X.; Chen, D.; Bin, L.; Lu, H.; Zhang, R.; Zheng, Y. Highly
selective and sensitive phosphate anion sensors based on AlGaN/GaN
C
DOI: 10.1021/acs.inorgchem.8b02017
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
high electron mobility transistors functionalized by ion imprinted
polymer. Sci. Rep. 2016, 6, 27728.
(3) Camarero, L.; Catalan, J. Atmospheric phosphorus deposition may
cause lakes to revert from phosphorus limitation back to nitrogen
limitation. Nat. Commun. 2012, 3, 1118.
(4) Upadhyay, L. S. B.; Verma, N. Alkaline phosphatase inhibition
based conductometric biosensor for phosphate estimation in biological
fluids. Biosens. Bioelectron. 2015, 68, 611−616.
(22) Li, H.; Han, Y.; Shao, Z.; Li, N.; Huang, C.; Hou, H. Water-stable
Eu-MOF fluorescent sensors for trivalent metal ions and nitrobenzene.
Dalton Trans 2017, 46, 12201−12208.
(23) Wang, D.; Sun, L.; Hao, C.; Yan, Y.; Liang, Z. Lanthanide metal-
organic frameworks based on a 1,2,3-triazole-containing tricarboxylic
acid ligand for luminescence sensing of metal ions and nitroaromatic
compounds. RSC Adv. 2016, 6, 57828−57834.
(24) Dhakshinamoorthy, A.; Asiri, A. M.; Garcia, H. Tuneable nature
of metal organic frameworks as heterogeneous solid catalysts for alcohol
oxidation. Chem. Commun. 2017, 53, 10851−10869.
(5) Zhao, H. X.; Liu, L. Q.; Liu, Z. D.; Wang, Y.; Zhao, X. J.; Huang, C.
Z. Highly selective detection of phosphate in very complicated matrixes
with an off-on fluorescent probe of europium-adjusted carbon dots.
Chem. Commun. 2011, 47, 2604−2606.
(25) Lin, Z.-J.; Lu, J.; Hong, M.; Cao, R. Metal-organic frameworks
based on flexible ligands (FL-MOFs): structures and applications.
Chem. Soc. Rev. 2014, 43, 5867−5895.
(6) Berchmans, S.; Issa, T. B.; Singh, P. Determination of inorganic
phosphate by electroanalytical methods: A review. Anal. Chim. Acta
2012, 729, 7−20.
(26) Sculley, J.; Yuan, D.; Zhou, H.-C. The current status of hydrogen
storage in metal-organic frameworks-updated. Energy Environ. Sci. 2011,
4, 2721−2735.
(7) Cheng, W.-L.; Sue, J.-W.; Chen, W.-C.; Chang, J.-L.; Zen, J.-M.
Activated Nickel Platform for Electrochemical Sensing of Phosphate.
Anal. Chem. 2010, 82, 1157−1161.
(27) Hao, J.-N.; Yan, B. Highly sensitive and selective fluorescent
probe for Ag+ based on a Eu3+ post-functionalized metal-organic
framework in aqueous media. J. Mater. Chem. A 2014, 2, 18018−18025.
(28) Cao, L. H.; Shi, F.; Zhang, W. M.; Zang, S. Q.; Mak, T. C. W.
Selective Sensing of Fe3+ and Al3+ Ions and Detection of 2,4,6-
Trinitrophenol by a Water-Stable Terbium-Based Metal−Organic
Framework. Chem. - Eur. J. 2015, 21, 15705−15712.
(8) Wygladacz, K.; Qin, Y.; Wroblewski, W.; Bakker, E. Phosphate-
selective fluorescent sensing microspheres based on uranyl salophene
ionophores. Anal. Chim. Acta 2008, 614, 77−84.
(9) Karthikeyan, R.; Berchmans, S. Inorganic-Organic Composite
Matrix for the Enzymatic Detection of Phosphate in Food Samples. J.
Electrochem. Soc. 2013, 160, B73−B77.
(29) Zhou, J.-M.; Shi, W.; Xu, N.; Cheng, P. Highly Selective
Luminescent Sensing of Fluoride and Organic Small-Molecule
Pollutants Based on Novel Lanthanide Metal−Organic Frameworks.
Inorg. Chem. 2013, 52, 8082−8090.
(30) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T.
Luminescent Metal-Organic Frameworks. Chem. Soc. Rev. 2009, 38,
1330−1352.
(31) Mahata, P.; Ramya, K. V.; Natarajan, S. Pillaring of CdCl2-Like
Layers in Lanthanide Metal−Organic Frameworks: Synthesis,
Structure, and Photophysical Properties. Chem. - Eur. J. 2008, 14,
5839−5850.
(32) Mahata, P.; Ramya, K. V.; Natarajan, S. Synthesis, structure and
optical properties of rare-earth benzene carboxylates. Dalton Trans
2007, 4017−4026.
(33) Singha, D. K.; Bhattacharya, S.; Majee, P.; Mondal, S. K.; Kumar,
M.; Mahata, P. Optical detection of submicromolar levels of nitro
explosives by a submicron sized metal-organic phosphor material. J.
Mater. Chem. A 2014, 2, 20908−20915.
(34) Hu, Z.; Deibert, B. J.; Li, J. Luminescent metal-organic
frameworks for chemical sensing and explosive detection. Chem. Soc.
Rev. 2014, 43, 5815−5840.
(35) Lin, R. B.; Liu, S. Y.; Ye, J. W.; Li, X. Y.; Zhang, J. P.
Photoluminescent Metal−Organic Frameworks for Gas Sensing. Adv.
Sci. 2016, 3, 1500434.
(36) Li, D.-S.; Wu, Y.-P.; Zhao, J.; Zhang, J.; Lu, J. Y. Metal-organic
frameworks based upon non-zeotype 4-connected topology. Coord.
Chem. Rev. 2014, 261, 1−27.
(37) Zheng, X.; Zhou, L.; Huang, Y.; Wang, C.; Duan, J.; Wen, L.;
Tian, Z.; Li, D. A series of metal-organic frameworks based on 5-(4-
pyridyl)-isophthalic acid: selective sorption and fluorescence sensing. J.
Mater. Chem. A 2014, 2, 12413−12422.
(38) Zhao, J.; Wang, Y.; Dong, W.; Wu, Y.; Li, D.; Liu, B.; Zhang, Q. A
new surfactant-introduction strategy for separating the pure single-
phase of metal-organic frameworks. Chem. Commun. 2015, 51, 9479−
9482.
(39) Ojida, A.; Nonaka, H.; Miyahara, Y.; Tamaru, S. i.; Sada, K.;
Hamachi, I. Bis(Dpa-ZnII) Appended Xanthone: Excitation Ratio-
metric Chemosensor for Phosphate Anions. Angew. Chem., Int. Ed.
2006, 45, 5518−5521.
(40) Steed, J. W. Coordination and organometallic compounds as
anion receptors and sensors. Chem. Soc. Rev. 2009, 38, 506−519.
(41) Wang, J.; Wang, J.; Li, Y.; Jiang, M.; Zhang, L.; Wu, P. A europium
(III)-based metal-organic framework as a naked-eye and fast response
luminescence sensor for acetone and ferric iron. New J. Chem. 2016, 40,
8600−8606.
(10) Sun, H.; Scharff-Poulsen, A. M.; Gu, H.; Jakobsen, I.; Kossmann,
J. M.; Frommer, W. B.; Almdal, K. Phosphate Sensing by Fluorescent
Reporter Proteins Embedded in Polyacrylamide Nanoparticles. ACS
Nano 2008, 2, 19−24.
(11) Li, C. M.; Li, Y. F.; Wang, J.; Huang, C. Z. Optical investigations
on ATP-induced aggregation of positive-charged gold nanoparticles.
Talanta 2010, 81, 1339−1345.
(12) Fibbioli, M.; Berger, M.; Schmidtchen, F. P.; Pretsch, E.
Polymeric Membrane Electrodes for Monohydrogen Phosphate and
Sulfate. Anal. Chem. 2000, 72, 156−160.
(13) Yang, Z.-C.; Wang, M.; Yong, A. M.; Wong, S. Y.; Zhang, X.-H.;
Tan, H.; Chang, A. Y.; Li, X.; Wang, J. Intrinsically fluorescent carbon
dots with tunable emission derived from hydrothermal treatment of
glucose in the presence of monopotassium phosphate. Chem. Commun.
2011, 47, 11615−11617.
(14) Bai, J. M.; Zhang, L.; Liang, R. P.; Qiu, J. D. Graphene Quantum
Dots Combined with Europium Ions as Photoluminescent Probes for
Phosphate Sensing. Chem. - Eur. J. 2013, 19, 3822−3826.
(15) Asha, K. S.; Bhattacharjee, R.; Mandal, S. Complete Trans-
metalationina Metal−Organic Frameworkby Metal Ion Metathesisin a
Single Crystal for Selective Sensing of Phosphate Ions in Aqueous
Media. Angew. Chem., Int. Ed. 2016, 55, 11528−11532.
(16) Beer, P. D.; Gale, P. A. Anion Recognition and Sensing: The State
of the Art and Future Perspectives. Angew. Chem., Int. Ed. 2001, 40,
486−516.
(17) Liu, J. Q.; Li, G. P.; Liu, W. C.; Li, Q. L.; Li, B. H.; Gable, R. W.;
Hou, L.; Batten, S. R. Two Unusual Nanocage-Based Ln-MOFs with
Triazole Sites: Highly Fluorescent Sensing for Fe3+ and Cr2O2−, and
Selective CO2 Capture. ChemPlusChem 2016, 81, 1299−1304.
(18) Yan, W.;Zhang, C.; Chen, S.; Han, L.; Zheng, H. TwoLanthanide
Metal−Organic Frameworks as Remarkably Selective and Sensitive
Bifunctional Luminescence Sensor for Metal Ions and Small Organic
Molecules. ACS Appl. Mater. Interfaces 2017, 9, 1629−1634.
(19) Dang, S.; Ma, E.; Sun, Z.-M.; Zhang, H. A layer-structured Eu-
MOF as a highly selective fluorescent probe for Fe3+ detection through a
cation-exchange approach. J. Mater. Chem. 2012, 22, 16920−16926.
(20) Das, A.; Banesh, S.; Trivedi, V.; Biswas, S. Extraordinary
sensitivity for H2S and Fe(III) sensing in aqueous medium by Al-MIL-
53-N3 metal-organic framework: in vitro and in vivo applications of H2S
sensing. Dalton Trans 2018, 47, 2690−2700.
(21) Liang, Y.-T.; Yang, G.-P.; Liu, B.; Yan, Y.-T.; Xi, Z.-P.; Wang, Y.-Y.
Four super water-stable lanthanide-organic frameworks with active
uncoordinated carboxylic and pyridyl groups for selective luminescence
sensing of Fe3+. Dalton Trans 2015, 44, 13325−13330.
D
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