Naphthalimide derivative-functionalized metal-Organic framework for highly sensitive and selective determination of aldehyde by space confinement-induced sensitivity enhancement effect

Article abstract of DOI:10.1021/acs.analchem.1c00916

Facile and sensitive determination of formaldehyde (FA) in indoor environments still remains challenging. Herein, a fluorescent probe, termed PHN@MOF, was synthesized by embedding the fluorescent molecule of N-propyl-4-hydrazinenaphthalimide (PHN) into a metal-organic framework (MOF) for sensitive and visual monitoring of FA. The hydrazine group of PHN acts as the specific reaction group with FA based on the condensation reaction. The host of MOF (UiO-66-NH₂) offers the surrounding confinement space required for the reaction. Owing to the enrichment effect and molecular sieve selection of UiO-66-NH₂ to FA, PHN@MOF, compared with free PHN, exhibits very high sensitivity and selectivity based on space confinement-induced sensitivity enhancement (SCISE). Moreover, the fluorescence of UiO-66-NH₂ offers a reference signal for FA detection. Using this ratiometric fluorescent PHN@MOF probe, a colorimetric gel plate and test paper were developed and used to visually monitor FA in air.

Full text of DOI:10.1021/acs.analchem.1c00916

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Article
Naphthalimide Derivative-Functionalized Metal−Organic
Framework for Highly Sensitive and Selective Determination of
Aldehyde by Space Confinement-Induced Sensitivity Enhancement
Effect
Xiuli Wang, Abudurexiti Rehman, Rong-mei Kong, Yuanyuan Cheng, Xiaoxia Tian, Maosheng Liang,
Lingdong Zhang, Lian Xia,* and Fengli Qu*
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ABSTRACT: Facile and sensitive determination of formaldehyde (FA) in indoor environments still remains challenging. Herein, a
fluorescent probe, termed PHN@MOF, was synthesized by embedding the fluorescent molecule of N-propyl-4-hydrazine-
naphthalimide (PHN) into a metal−organic framework (MOF) for sensitive and visual monitoring of FA. The hydrazine group of
PHN acts as the specific reaction group with FA based on the condensation reaction. The host of MOF (UiO-66-NH2) offers the
surrounding confinement space required for the reaction. Owing to the enrichment effect and molecular sieve selection of UiO-66-
NH2 to FA, PHN@MOF, compared with free PHN, exhibits very high sensitivity and selectivity based on space confinement-
induced sensitivity enhancement (SCISE). Moreover, the fluorescence of UiO-66-NH2 offers a reference signal for FA detection.
Using this ratiometric fluorescent PHN@MOF probe, a colorimetric gel plate and test paper were developed and used to visually
monitor FA in air.
scientists have developed some satisfactory methods of FA
detection, including electrochemical,9,10 SERS,11 fluores-
cence,12,13 and polarographic determination.14 While showing
some success, the development of household FA detection
sensors that can be used in surrounding air is still challenging
by the limited portability. The characteristic of specific
recognition of targets based on a specific reaction has resulted
in the development of highly selective organic fluorescent
probes for detecting FA in the last decades. Among these, two
different kinds of fluorescence probes, including aza-Cope
ormaldehyde (FA), a familiar indoor air pollutant, is
Fusually released from furniture, wood-based flooring,
coating, insulation, textiles, and even cosmetic makeup, posing
a significant threat to human health.1,2 Long-term exposure to
FA leads to such diseases as cancer, asthma, immune system
disorders, and central nervous system damage.3−5 Thus, severe
FA exposure guidelines have been stipulated for indoor air by
WHO (80 ppb) and different countries (e.g., 60 ppb by
China).6,7 This calls for effective and practical ways to monitor
FA concentration in indoor environments, such as new homes,
offices, and chemical factories.
At present, FA is usually detected by on-site sampling
followed by off-site quantification in external analytical
laboratories using sophisticated instruments (e.g., chromatog-
raphy and mass spectrum). This procedure is time-consuming
and labor-intensive.8 Fortunately, chemical sensors show the
potential for on-site monitoring with characteristics of simple
application, miniaturization, and low consumption. Thus far,
Received: March 1, 2021
Accepted: May 19, 2021
Published: June 2, 2021
https://doi.org/10.1021/acs.analchem.1c00916
© 2021 American Chemical Society
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rearrangement-based15,16 and aldehyde-amine condensation
reaction-based probes,17 have drawn interest in FA detection.
Compared to aza-Cope rearrangement, the aldehyde-amine
condensation reaction has shown more rapid reaction kinetics.
Although various small-molecule probes have been developed
for selective detection of FA based on these two mechanisms,
their photobleaching resistance ability still needs to be
improved.
Scheme 1. Schematic Illustration of the PHN@MOF Probe
for the Detection of FA
Recently, space confinement-induced sensitivity enhance-
ment (SCISE)18,19 has attracted attention. SCISE occurs
between porous host and guest and is based on target
enrichment and the interference reduction. First, porous host
nanomaterials adsorb target molecules into their pores through
noncovalent interactions, such as H-bond and electrostatic
adsorption.20 If adsorption is based on specific interaction
between functional groups of host and target molecules,
selective enrichment should occur, thereby not only increasing
the concentration of targets but also decreasing interference
that concentrates around active sites. Therefore, the sensitivity
of the probe can be substantially improved. Second, owing to
the porous structure, the host material also shows the potential
for molecular sieving, which can prevent bulky molecules from
contact with a guest probe, thereby improving selectivity
toward gas molecules of different sizes.
Many porous materials have been used as host materials of
SCISE-based sensors, such as mesoporous silicon,21,22 layered
double hydroxide,23,24 and metal−organic frameworks
(MOFs).25 Among these materials, MOFs, which are
assembled from metal clusters and organic ligands, stand out
as one kind of promising material owing to their unique
properties.26,27 The inherent characteristics of MOFs, such as
highly specific surface area, ultrahigh porosity, large pore
volume, tunable cage structures, and open metal sites, make
them good candidates for providing a confined environment
for the capture of guest molecules.28−31 Compared with other
MOFs, the amino-functionalized Zr-MOF of UiO-66-NH2 not
only shows high porosity, large surface area, and cage structure
but also exhibits high chemical and thermal stability in both
water and organic solvents. The pore size of UiO-66 was
reported to be 11.5 Å,32 whereas the window opening size was
less than 6 Å.33,34 Such a cage structure can block bulky
molecules such as o-xylene (kinetic diameter around 7.4
Å)35,36 from getting into the pores, thus decreasing
interference based on size preference. The amino groups of
UiO-66-NH2 have a lone pair of electrons, which can easily
adsorb targets with groups of electron acceptors,37 resulting in
the enhancement of preferential adsorption to FA. Moreover,
the strong fluorescence emission at 450 nm of UiO-66-NH2
allows the construction of ratiometric fluorescent probes.
However, to the best of our knowledge, this kind of fluorescent
probe for FA remains elusive.
space confinement that allows PHN to respond to FA, leading
to higher sensitivity and selectivity for FA detection.
Compared with free PHN, PHN@MOF showed enhanced
sensitivity and selectivity to FA. Moreover, the intrinsic
fluorescence emission of UiO-66-NH2 can offer a reference
signal for FA detection (Scheme 2). Using this ratiometric
fluorescent probe, a colorimetric gel plate and test paper were
further developed and successfully used to visualize and
monitor FA in air and alcohol.
EXPERIMENTAL SECTION
■
Chemicals and Reagents. Propylamine was purchased
from McLean Chemical Reagent Co., Ltd. Zirconium chloride
was obtained from Shanghai Darui Fine Chemicals Co., Ltd.
Benzoic acid was received from Tianjin Damao Chemical
Reagent Factory. 2-Amino terephthalic acid was obtained from
Shanghai Darui Fine Chemicals Co., Ltd. Hydrochloric acid
was purchased from Jinan Reagent Factory. Hydrazine hydrate
was obtained from Aladdin Chemistry Co., Ltd. 4-Bromine-1,
8-naphthalic anhydride was purchased from J&K Scientific Ltd.
N,N-dimethylformamide (DMF) and ethanol were purchased
from Sinopharm Chemical Reagent Co., Ltd. In addition, all
other reagents and solvents were obtained commercially and
used without further purification.
Instrumentation and Characterization. Transmission
electron microscopy (TEM) measurements were performed on
a JEOL 2010 microscope (JEOL 2010). Fourier transform
infrared (FTIR) spectra were performed on a WQF-510A
spectrophotometer in the range of 4000−500 cm−1. Detection
of UV−vis spectra was obtained using a UV752pc spectropho-
tometer. Fluorescence spectra were recorded using a Hitachi F-
7000 fluorescence spectrophotometer. The 1H NMR spectrum
was obtained using a Bruker-500 MHz NMR (500 MHz/
AVANCE III HD). High-performance liquid chromatography
(HPLC) (Agilent, 1260) equipped with a fluorescent detector
and C18 column (4.6 × 250 mm, 5 μm) was performed to
obtain the HPLC data. X-ray photoelectron spectroscopy
(XPS) analyses were carried out using an ESCALAB 250XI
spectrometer. N2 adsorption−desorption curves were obtained
using a Kubox1000 specific surface area and an aperture
analyzer. Mass spectrometry was performed on an Agilent
1290InfinityII/6564. Zeta potential was measured using
Malvern Zen3600.
Inspired by the advantages of the aldehyde-amine con-
densation reaction and SCISE, we herein synthesized
fluorescent probe N-propyl-4-hydrazine-naphthalimide
(PHN) and embedded it into UIO-66-NH2 to obtain a
nanocomposite (PHN@MOF), which was subsequently used
to construct a household monitoring device for FA. The
hydrazine group of PHN acts as the response site for FA based
on the condensation reaction, which could react rapidly and
generate a stable methylenehydrazine product. The fluores-
cence of PHN could be recovered because of the prohibition of
fluorescent photoinduced electron transfer (PET) (Scheme
1).38,39 The host of UiO-66-NH2 can offer the surrounding
Preparation of UiO-66-NH2 and PHN. According to the
reported literature with slight modification,40 the synthesis of
UiO-66-NH2 was performed by dissolving ZrCl4 (0.1864 g), 2-
amino-1,4-benzenedicarboxylic acid (0.1328 g), benzoic acid
(1.4640 g), and hydrochloric acid (144 μL) into DMF (28
mL) with ultrasonic vibration for 15 min. Then, the resulting
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Scheme 2. Schematic Illustration of the PHN@MOF Probe for the Detection of FA
Figure 1. (A) TEM image of UiO-66-NH2. (B) XRD of synthetic UiO-66-NH2 (red) and simulated UiO-66-NH2 (black).
mixture was placed into an oil bath and heated for 24 h at 393
K. After cooling to room temperature naturally, the precipitate
was separated by centrifugation and then washed three times
with DMF and ethanol, separately. After drying at 343 K under
vacuum, the yellow powder product was harvested.
interferences (50 μM), including acetone, cysteine, aldehyde,
−
−
2−
H2O2, Ca2+, Mg2+, Na+, Mn2+, Co2+, NO3 , Br−, NO2 , SO4
,
I−, Cl−, methylbenzene, phenol, and resorcinol, and 800 μL of
Tris buffer (pH 6.4) were mixed and incubated for 15 min at
room temperature, followed by recording the fluorescence
intensity.
According to the reported literature with slight modification,
the PHN product was prepared as follows:41 ten mmol 4-
bromine-1, 8-naphthalic anhydride, and 30 mmol propylamine
were dissolved into 60 mL of ethanol. Then, the mixture was
refluxed under 90 °C for 6 h to yield the condensate. After
that, the resultant reaction solution was poured into 1000 mL
of deionized water and then dewatered using a vacuum pump.
The resultant intermediate product was redissolved into 80 mL
of ethanol, and a condensation reaction was carried out at 90
°C for 8 h. One mmol hydrazine hydrate per hour was added
into the mixture. The resultant mixture was poured into 1000
mL of deionized water and then dewatered using a vacuum
pump. The product was dried at 333 K overnight.
Detection of FA in Liqueur and Air Samples. One
hundred μL of PHN@MOF suspension (300 μg/mL), 100 μL
of 10% liqueur, and 100 μL of different concentrations of
HCHO were added into 700 μL of Tris buffer (pH 6.4). The
mixture was reacted for about 15 min, and then, the
fluorescence spectra were measured. The test paper was
dipped in a vial containing PHN@MOF suspension (300 μg/
mL) and dried in an oven at 40 °C. The process was repeated
five times. FA detection in air samples: the test paper was hung
in a 30 mL bottle containing a drop of 0.1 M methylbenzene,
phenol, resorcinol, and FA, respectively, and the bottles were
heated at 100 °C. Photographs of the test paper were taken
after 15 min of response under a 365 nm UV light. The
preparation process of silica gel plates was as follows: the silica
gel plates were immersed in PHN@MOF dispersions (0.3 mg/
mL) and then dried in an oven at 40 °C. The process was
repeated three times. We wrote “QF” on the silica gel sheets
using the solutions of water, cysteine, acetaldehyde, H2O2,
1H NMR (400 MHz, DMSO, d6): δ 10.2 (3H, s, N−H),
7.63 (1H, d, Ar−H), 8.02 (1H, t, Ar−H), 8.24 (1H, d, Ar−H),
8.36 (1H, d, Ar−H), 8.59 (1H, d, Ar−H), 2.45 (2H, t,CH2)
1.70 (2H, m, CH2), 1.12 (3H, t, CH3).
Preparation of PHN@MOF. PHN@MOF was synthesized
using the same method as that for preparing UiO-66-NH2
except that PHN (0.05 g) was added into the precursor
solution of UiO-66-NH2.
Fluorescence Sensing Experiment. One hundred μL of
PHN@MOF suspension (300 μg/mL) and 100 μL of different
concentrations of HCHO aqueous solution were added into
800 μL of Tris buffer (pH 6.4). The mixture was incubated for
about 15 min at room temperature, followed by the
measurement of the fluorescence spectrum. To evaluate the
selectivity of PHN@MOF for FA detection, 100 μL of PHN@
MOF suspension (300 μg/mL), 100 μL of different potential
−
−
Ca2+, Mg2+, Na+, Mn2+, Co2+, NO3 , Br−, NO2 , SO42−, I−, and
Cl− (100 μM) and FA (10 μM) as ink, respectively.
Photographs of the silica gel plates were taken after 15 min
of response under a 365 nm UV light.
RESULTS AND DISCUSSION
■
Characterization of PHN@MOF. The synthesis process of
PHN is shown in Scheme S1. The successful synthesis of PHN
was confirmed by mass spectrometry and 1H NMR. As shown
in Figure S1, the resultant PHN produced an intense molecular
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Figure 2. (A) TEM image of PHN@MOF. (B) XRD of UiO-66-NH2 (black) and PHN@MOF (red). (C) FT-IR of UiO-66-NH2 (blue), PHN
(red), and PHN@MOF (black). (D) XPS spectra of UiO-66-NH2 (black), PHN (red), and PHN@MOF (blue). (E) N2 adsorption and
desorption isotherms of UiO-66-NH2 (a) and PHN@MOF (b). (F) UV−vis absorption spectra of UiO-66-NH2 (black), PHN (red), and PHN@
MOF (blue).
ion peak at m/z 269.6, which was consistent with the
morphology of the resultant PHN@MOF was the same as that
of pristine UiO-66-NH2, revealing that the loaded PHN caused
no structural change in UiO-66-NH2. From Figure 2B, we can
see the XRD patterns of PHN@MOF, showing all peaks in the
same positions as those of pristine UiO-66-NH2, indicating
that no contraction or change in the symmetry of the crystals
happened as a result of the rigidity of UiO-66-NH2. This
suggested that the crystal structure of UiO-66-NH2 had
maintained the load of PHN molecules into its cavity. The FT-
IR spectra comparing UiO-66-NH2, PHN, and PHN@MOF
are shown in Figure 2C. The absorption peaks at 1701 and
1069, which were derived from the CO stretch vibration of
dicarboximide and the N−N stretch vibration of hydrazine,
were both observed in PHN and PHN@MOF, whereas
pristine UiO-66-NH2 did not show these characteristic
absorption peaks.43,44 Furthermore, XPS was used to verify
the successful coupling of UiO-66-NH2 with PHN molecules.
Compared with PHN, Figure 2D shows that PHN@MOF had
molecular weight of PHN,41 together with the results of H
1
NMR, demonstrating that PHN had been successfully
synthesized. The synthesis of UiO-66-NH2 was characterized
by SEM, TEM, and XRD. As shown in Figures S2 and 1A, we
can see that the synthesized UiO-66-NH2 exhibited an
“octahedron-like” morphology with an average length of
about 60 nm, which was consistent with that previously
reported.40 Figure 1B shows the XRD diffraction patterns of
the synthesized UiO-66-NH2, which highly matched those of
the simulation,42 suggesting that UiO-66-NH2 had been
successfully synthesized.
On the basis of the successful synthesis of PHN and UiO-
66-NH2, the PHN@MOF was then synthesized under the
hydrothermal reaction and characterized. In order to
investigate the influence of PHN load on the structure of
UiO-66-NH2, the morphology of PHN@MOF was first
evaluated. As shown in Figures S3 and 2A, the structural
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Figure 3. (A) Emission (Em) spectrum of PHN@MOF with λEx = 362 nm (red); excitation (Ex) spectra of PHN@MOF with λEm = 434 nm
(black). (B) Fluorescence emission spectra of PHN, UiO-66-NH2, and PHN@MOF before and after the addition of 5 μM FA. (C) Time-resolved
fluorescence decay profiles of the aqueous suspension of PHN@MOF before and after the addition of FA. (D) Emission spectra of PHN (black),
UiO-66-NH2 (red), and PHN@MOF (blue) and the UV−vis spectrum (pink) of HCHO (pink).
an additional peak at 185.22 and 183.02 eV, which could be
attributed to Zr 3d.45 Especially, the N and C percent in
PHN@MOF was obviously higher than that in UiO-66-NH2
after coupling with PHN, which further indicated the
successful combination of PHN with MOF. In addition, the
zeta potentials of UiO-66-NH2, PHN, and PHN@MOF were
obtained in Tris-HCl solution at room temperature (Table.
S1). The results showed that the zeta potentials of UiO-66-
NH2 and PHN were about 38.8 and −29.9 mV, respectively.46
Therefore, PHN molecules could combine with UiO-66-NH2
tightly, according to the charge attraction, and suitable
electrostatic repulsion could give rise to the homogeneous
dispersion of PHN. As a result, the zeta potential of PHN@
MOF (34.17 mV) fell between that of UiO-66-NH2 and PHN
after coupling. These results suggested that PHN had been
successfully loaded into the cavity of UiO-66-NH2 without any
changes in the molecular structure.
The N2 sorption−desorption isotherm was used to confirm
the porosity of UiO-66-NH2 and PHN@MOF. As shown in
Figure 2E, the sorption−desorption processes of UiO-66-NH2
and PHN@MOF were both classified as type-II isotherm,
indicating that both UiO-66-NH2 and PHN@MOF possessed
a porous structure. The BET surface area and the pore value of
the synthesized UiO-66-NH2 and PHN@MOF were also
measured by N2 adsorption at 77 K. The results showed that
the Brunauer, Emmett, and Teller (BET) surface area of UiO-
66-NH2 was 1034.8956 m2/g47 and that the pore size was 20
Å. After loading with PHN, the resultant PHN@MOF showed
a slight decrease in the BET surface area and pore size, which
were 923 m2/g and 17 Å, respectively. These results indicated
that crystal UiO-66-NH2 had a large surface area and big pore
size and that the load of PHN only had slight influence on
these characteristics. Figure 2F shows the UV−vis absorption
spectra of UiO-66-NH2, PHN, and PHN@MOF. UiO-66-NH2
(black) showed one absorption peak at 369 nm,48 and PHN@
MOF (blue) exhibited two absorption bands at 340 and 431
nm,41 respectively, which largely resembled those of PHN
(red).
Feasibility of PHN@MOF for Detecting FA. The
fluorescence property of PHN@MOF was further investigated.
Figure 3A demonstrates that PHN@MOF emits blue
fluorescence centered at 434 nm upon excitation of 362 nm.
In order to highlight the better performance of PHN@MOF,
the fluorescence property of PHN, UiO-66-NH2, and PHN@
MOF before and after reacting with FA was investigated
(Figure 3B). Under an excitation wavelength of 362 nm, the
UiO-66-NH2 nanoparticle showed a single fluorescence
emission at 456 nm, which decreased slightly after being
treated with FA. PHN exhibited a single emission at 417 nm in
the absence of FA. However, after incubation with FA for 15
min, the fluorescence intensity at 417 nm showed a slight
decrease, and a new fluorescence peak at 553 nm appeared.
This is because the fluorescence at 553 nm of pristine PHN
was initially suppressed by the PET effect between the
hydrazine group and its chromophore. After reaction with FA,
the PET effect was blocked by the formed hydrazone group,
turning on fluorescence.49−51 To further study the interaction
of PHN@MOF and FA, time-resolved fluorescence decay
experiments of PHN@MOF before and after the reaction with
FA were performed. According to Figure 3C, we can see that
the fluorescence lifetime of PHN@MOF obviously increased
after the reaction with FA, which further confirmed the
inhibition of the PET process between them. Here, PHN@
MOF also showed a single emission at 434 nm in the absence
of FA, resulting from the overlap of UiO-66-NH2 emission at
456 nm and PHN emission at 417 nm. However, after reacting
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Figure 4. (A) Fluorescence spectra of the PHN@MOF probe in response to FA at varied concentrations (0−5 μM); inset: photographs of the
sensing mixture with various concentrations (1−3 μM) of FA. (B) Fluorescence intensity ratio (F553/F434) of the PHN@MOF probe in response to
FA.
Figure 5. Selectivity of the sensing method against other interferences. Concentrations of FA and other interferences (acetone, cysteine, aldehyde,
−
−
acetaldehyde, H2O2, Ca2+, Mg2+, Na+, Mn2+, Co2+, NO3 , Br−, NO2 , SO42−, I−, Cl−, methylbenzene, phenol, and resorcinol) were 5 and 50 μM,
respectively. (A) Fluorescence intensity spectra showing the response of the sensing system to different interferences. (B) Fluorescence intensity
ratio (F553/F434) of the PHN@MOF probe toward various interferences. Inset: photographs at various interferences.
with FA, it was found that the fluorescence intensity of PHN@
MOF initially decreased at 434 nm but then increased at 553
nm. The sensitivity of PHN@MOF to FA was much higher
than that of PHN to FA. The reaction mechanism of PHN
with FA, as shown in Schemes 1 and S2, was confirmed by
HPLC (Figure S4) and HR-MS (Figure S5). As shown in
Figure S4a, the retention time of PHN was 7.2 min. From
Figure S4b, we can see that a new chromatographic peak at 5.8
min was observed after PHN reacting with FA, which we
concluded to be the product of hydrazone. Then, HR-MS was
performed to verify the product. From Figure S5, we can see
that the molecular ion peak at m/z 282.3 was observed after
PHN reacts with FA, which was consistent with the molecular
weight of hydrazone. Therefore, after the reaction between
PHN and FA, the resultant product of hydrazone was expected
to be formed. In order to investigate why the reference signal
decreased with increasing FA concentration, the UV−vis
adsorption of PHN, UiO-66-NH2, and PHN@MOF was
detected, respectively. As shown in Figure 3D, the fluorescence
emission spectra of PHN (black), UiO-66-NH2 (red), and
PHN@MOF (blue) considerably overlapped with the UV−vis
absorption spectra of FA (black), indicating that the decrease
in the reference signal at 434 nm could be attributed to the
inner filter effect (IFE).52 3D emission profiles were then used
to investigate the fluorescence properties of PHN@MOF.
PHN@MOF exhibited maximum emission/excitation wave-
lengths at 434/362 nm (Figure S6A). However, after
incubating with formaldehyde for 15 min, a new strong
emission fluorescence peak at 553 nm appeared in the 3D
emission of PHN@MOF (Figure S6B). To prove the stability
of PHN@MOF for FA detection, the fluorescence intensity
ratio at F553/F434 was investigated at different times (Figure
S7). The results showed that the fluorescence intensity ratio at
F553/F434 exhibited negligible change in 72 h. The morphology
of PHN@MOF after the addition of FA was further
investigated, and the results are shown in Figure S8. The
SEM image (Figure S8A) and the TEM image (Figure S8B)
show that the morphology of PHN@MOF after the addition of
FA was the same as that of pristine PHN@MOF, revealing that
incubation with FA did not cause structural collapse of PHN@
MOF. Therefore, PHN@MOF can be employed as an ideal
ratiometric probe for the detection of FA with excitation at 362
nm.
Performance of PHN@MOF for Detecting FA. To
investigate the fluorescence titration of FA using PHN@MOF
as the sensing platform, PHN@MOF water solution (0.3 mg/
mL) was incubated with different concentrations of FA (0−5
μM) for 15 min at room temperature. The optimization
process of the sensing condition is shown in Figure S9. Based
on the data shown in Figure 4A, as FA concentration
increased, the fluorescence intensity at 434 nm decreased,
and the emission at 553 nm gradually increased. The inset of
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Figure 4A shows the photograph of the sensing mixture with
different FA concentrations under a UV light at 365 nm. With
increasing FA concentration, results showed that the emission
of the sensing mixture changed gradually from blue to bright
yellow. Figure 4B shows that the fluorescence intensity ratio
(F553/F434) of PHN@MOF had good linear relationships with
FA concentration in the range of 1−3 and 3−4 μM (R2 =
0.9933 and 0.9935). Based on the signal-to-noise ratio of S/N
= 3, the limit of detection (LOD) was calculated to be 0.173
μM, which was lower than the LOD of PHN (3.2 μM).
Compared to single PHN, PHN@MOF was more sensitive to
FA by the SCISE of MOF host. Since UiO-66-NH2 was rich
with amine, the hydrogen bonds of amine could easily form
with FA (Figure S10), facilitating surface adsorption. There-
fore, local concentration of FA around the MOF increased,
leading to higher response sensitivity. These results suggested
that the established sensing platform presented a satisfactory
fluorescence and naked-eye detection method for FA.
Figure 6. Photographs of silica gel plates under a 365 nm UV light
upon coating with interferences (water, cysteine, acetaldehyde, H2O2,
−
−
Ca2+, Mg2+, Na+, Mn2+, Co2+, NO3 , Br−, NO2 , SO42−, I−, and Cl−)
The selectivity of the PHN@MOF for FA was investigated
by performing fluorescence tests in the presence of potential
interference species, including acetone, cysteine, aldehyde,
and FA. Concentrations of FA and other interferences (cysteine,
−
−
acetaldehyde, H2O2, Ca2+, Mg2+, Na+, Mn2+, Co2+, NO3 , Br−, NO2 ,
SO42−, I−, and Cl−) were 10 and 100 μM, respectively.
H2O2, Ca2+, Mg2+, Na+, Mn2+, Co2+, NO3 , Br−, NO2 , SO4
,
−
−
2−
I−, Cl−, methylbenzene, phenol, and resorcinol (Figure 5). As
shown in Figure 5A, the fluorescence emission at 553 nm is
greatly enhanced after reacting with FA. However, even with
10 times concentration of FA, the interference species exhibit
negligible fluorescence change at 553 nm. Figure 5B shows that
the fluorescence intensity ratio (F553/F434) of PHN@MOF
gives a remarkable increase with response to FA and negligible
responses to interference species, which is highly consistent
with Figure 5A, suggesting that PHN@MOF has high specific
recognition of FA. Compared to the free PHN, the selectivity
of PHN@MOF is better for the SCISE (Figure S11). The pore
size of UiO-66-NH2 synthesized in this work was determined
to be 20 Å, whereas the window opening size is less than 6 Å,
which permits the small molecules, such as FA, entering but
blocks the bulky molecules, such as toluene and phenol, getting
into the pores (Figure S12). Therefore, the PHN@MOF
shows higher selectivity and sensitivity to FA than the free
PHN.
Figure 7. Photographs of the test paper under a visible light (A) and a
365 nm UV light. (B) Photographs of the test paper hanging upon 30
mL bottles containing contaminated air and methylbenzene (C),
phenol (D), resorcinol (E), and FA (F) solutions (0.1 M),
respectively, under a 365 nm UV light.
Practical Application of PHN@MOF for Detecting FA.
In order to study the practical applications of PHN@MOF for
FA detection, a silica gel plate and filter paper were coated with
PHN@MOF dispersive solution (0.3 mg/mL) as a test paper
to detect FA. The letters “QF” were written on the silica gel
plates using water, cysteine, acetaldehyde, H2O2, Ca2+, Mg2+,
Practical Application. To further evaluate the feasibility of
PHN@MOF as a sensor for practical FA detection, assay tests
were carried out to detect FA in liqueur. The original samples
were spiked with different concentrations of FA standards,
followed by sensing performance. The experimental results are
shown in Table 1. From Table 1, we can see that the recoveries
of FA for all the samples with different concentrations range
from 93.33 to 105.00% with RSD less than 5%. These results
demonstrated that the PHN@MOF sensor had satisfactory
accuracy and precision for detecting FA in liqueur.
Na+, Mn2+, Co2+, NO3 , Br−, NO2 , SO42−, I−, and Cl− (100
μM) and FA (10 μM) as ink, respectively. As shown in Figure
6, under UV light irradiation at 365 nm, no obvious changes
were observed in the silica gel sheets written by interference
species, while the script “QF” appears in yellow-green on the
silica gel sheet coated in FA. In addition, a simulation of
contaminated air was prepared by mixing air and benzenes,
including methylbenzene, phenol, and resorcinol. This was
used to further examine the practical ability of the developed
test paper for FA monitoring. As shown in Figure 7, the air
contaminated with FA reported out a remarkable change from
blue to yellow, whereas the contaminated air without FA, but
with interference species, showed no obvious color change.
These results revealed that the developed test paper pretreated
with PHN@MOF could be used as a satisfactory test strip for
FA monitoring with characteristics of easy operation, high
economy, high safety, and advanced efficiency.
−
−
Table 1. Recovery of 10% Liqueur Samples Containing
Different Concentrations of FA Measured by Fluorescence
Spectrometry
sample added (μM) found (μM) recovery (%) RSD (%, n = 3)
1
2
3
1.00
2.00
3.00
1.05
2.04
2.80
105.00
102.22
93.33
1.89
2.70
3.62
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pubs.acs.org/ac
Article
In order to highlight the application of the proposed method
for detecting FA, the analysis parameters of FA detection with
different methods were compared (Table S2). As shown in
Table S2, the method proposed in this study had the
advantages of simple design, low synthesis cost, high selectivity,
low instrument price, and low LOD, when compared with
methods reported in the previous literature.
Lingdong Zhang − Chemistry and Chemical Engineering
College, Qufu Normal University, Qufu 273165, PR China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.analchem.1c00916
Author Contributions
All authors have given approval to the final version of the
manuscript.
CONCLUSIONS
■
Notes
In summary, a ratiometric fluorescent probe for FA sensing
was successfully synthesized by embedding the fluorescent
probe PHN into UiO-66-NH2 through one-pot. The hydrazine
group of PHN acts as the specific reaction group with FA
based on the condensation reaction. The host of MOF (UiO-
66-NH2) offers surrounding space confinement for the
reaction. Compared with free PHN, PHN@MOF with
SCISE shows higher selectivity and sensitivity to FA, owing
to the molecular sieve selection and enrichment effect of UiO-
66-NH2 for FA. The fluorescence emission of UiO-66-NH2
also offers a reference signal for FA detection. Based on this
ratiometric fluorescent probe, a simple method was developed
and used for successful visual monitoring of FA in air and
alcohol. The strategy of embedding guest recognition
molecules into host porous nanomaterials to improve
selectivity and sensitivity can provide prospective potential
for monitoring trace targets in complex samples.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is supported by grants awarded by the National
Natural Science Foundation of China (no. 21505084,
21775089, and 22074080), Changjiang Scholar Program of
the Ministry of Education of China, Natural Science
F ou n d a t io n P r o j e c ts o f S h a n d o n g P r o v in c e
(ZR2020MB056), Key Research and Development Program
of Shandong Province (no. 2017GSF19109), Innovation
Project of Shandong Graduate Education (no. SDYY16091),
Taishan Scholar Program of Shandong Province
(tsqn201909106), and College Students Innovation and
Entrepreneurship Training Project of Shandong Province
(no. S201910446019).
REFERENCES
■
ASSOCIATED CONTENT
(1) Li, Y.; Chen, N.; Deng, D.; Xing, X.; Xiao, X.; Wang, Y. Sens.
Actuators, B 2017, 238, 264−273.
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.analchem.1c00916.
(2) Salthammer, T. Angew. Chem., Int. Ed. 2013, 52, 3320−3327.
(3) Wang, X.; Si, Y.; Wang, J.; Ding, B.; Yu, J.; Al-Deyab, S. S. Sens.
Actuators, B 2012, 163, 186−193.
(4) Kukkar, D.; Vellingiri, K.; Kaur, R.; Bhardwaj, S. K.; Deep, A.;
Kim, K.-H. Nano Res. 2019, 12, 225−246.
Synthesis of the fluorescent formaldehyde probe PHN;
illustration of the mechanism of the PHN reaction with
FA; HRMS spectral analysis of PHN; SEM image of
UiO-66-NH2; SEM image of PHN@MOF, and so on
(PDF)
(5) Wu, K.; Kong, X. Y.; Xiao, K.; Wei, Y.; Zhu, C.; Zhou, R.; Si, M.;
Wang, J.; Zhang, Y.; Wen, L. Adv. Funct. Mater. 2019, 29, 1807953.
(6) Feng, L.; Musto, C. J.; Suslick, K. S. J. Am. Chem. Soc. 2010, 132,
4046−4047.
(7) Fu, J.; Zhang, L. Anal. Chem. 2018, 90, 8080−8085.
(8) Taprab, N.; Sameenoi, Y. Anal. Chim. Acta 2019, 1069, 66−72.
(9) Sun, J.; Sun, L.; Bai, S.; Fu, H.; Guo, J.; Feng, Y.; Luo, R.; Li, D.;
Chen, A. Sens. Actuators, B 2019, 285, 291−301.
AUTHOR INFORMATION
■
Corresponding Authors
̌
̌
̌
̌
̌
(10) Trafela, S.; Zavasnik, J.; Sturm, S.; Rozman, K. Z. Electrochim.
Acta 2019, 309, 346−353.
Lian Xia − Chemistry and Chemical Engineering College, Qufu
Normal University, Qufu 273165, PR China; orcid.org/
0000-0001-6117-7596; Email: xialian01@163.com
Fengli Qu − Chemistry and Chemical Engineering College,
Qufu Normal University, Qufu 273165, PR China;
orcid.org/0000-0001-6311-3051; Phone: +86 537
4456301; Email: fengliquhn@hotmail.com; Fax: +86 537
4456301
(11) Lv, Z.-Y.; Mei, L.-P.; Chen, W.-Y.; Feng, J.-J.; Chen, J.-Y.;
Wang, A.-J. Sens. Actuators, B 2014, 201, 92−99.
(12) Dou, K.; Chen, G.; Yu, F.; Liu, Y.; Chen, L.; Cao, Z.; Chen, T.;
Li, Y.; You, J. Chem. Sci. 2017, 8, 7851−7861.
(13) Ma, Y.; Tang, Y.; Zhao, Y.; Lin, W. Anal. Chem. 2019, 91,
10723−10730.
(14) Septon, J. C.; Ku, J. C. Am. Ind. Hyg. Assoc. J. 1982, 43, 845−
852.
(15) Brewer, T. F.; Chang, C. J. J. Am. Chem. Soc. 2015, 137,
10886−10889.
Authors
Xiuli Wang − Chemistry and Chemical Engineering College,
Qufu Normal University, Qufu 273165, PR China
Abudurexiti Rehman − Chemistry and Chemical Engineering
College, Qufu Normal University, Qufu 273165, PR China
Rong-mei Kong − Chemistry and Chemical Engineering
College, Qufu Normal University, Qufu 273165, PR China
Yuanyuan Cheng − Chemistry and Chemical Engineering
College, Qufu Normal University, Qufu 273165, PR China
Xiaoxia Tian − Chemistry and Chemical Engineering College,
Qufu Normal University, Qufu 273165, PR China
Maosheng Liang − Chemistry and Chemical Engineering
College, Qufu Normal University, Qufu 273165, PR China
(16) Feng, X.; Wei, Q.; Li, S.; Wei, X.; Yang, X.; Song, Z.; Geng, B.;
Li, Z.; Zhang, J.; Yan, M. Sens. Actuators, B 2021, 330, 129342.
(17) Bruemmer, K. J.; Brewer, T. F.; Chang, C. J. Curr. Opin. Chem.
Biol. 2017, 39, 17−23.
(18) Trivedi, K.; Yuk, H.; Floresca, H. C.; Kim, M. J.; Hu, W. Nano
Lett. 2011, 11, 1412−1417.
(19) Ning, Z.; Chen, Z.; Zhang, Q.; Yan, Y.; Qian, S.; Cao, Y.; Tian,
H. Adv. Funct. Mater. 2007, 17, 3799−3807.
(20) Wu, Z.; Zhao, D. Chem. Commun. 2011, 47, 3332−3338.
(21) Ma, L.; Zhang, M.; Yang, A.; Wang, Q.; Qu, F.; Qu, F.; Kong,
R.-M. Analyst 2018, 143, 5388−5394.
(22) Yu, Y.; Li, G.; Liu, J.; Yuan, D. Chem. Eng. J. 2020, 401, 126139.
8226
https://doi.org/10.1021/acs.analchem.1c00916
Anal. Chem. 2021, 93, 8219−8227

Analytical Chemistry
pubs.acs.org/ac
Article
(23) Tian, R.; Zhang, S.; Li, M.; Zhou, Y.; Lu, B.; Yan, D.; Wei, M.;
Evans, D. G.; Duan, X. Adv. Funct. Mater. 2015, 25, 5006−5015.
(24) Song, L.; Shi, J.; Lu, J.; Lu, C. Chem. Sci. 2015, 6, 4846−4850.
(25) Ni, J.; Li, M.-Y.; Liu, Z.; Zhao, H.; Zhang, J.-J.; Liu, S.-Q.;
Chen, J.; Duan, C.-Y.; Chen, L.-Y.; Song, X.-D.; Li, D. ACS Appl.
Mater. Interfaces 2020, 12, 12043−12053.
(26) Wang, X.; Xiao, H.; Li, A.; Li, Z.; Liu, S.; Zhang, Q.; Gong, Y.;
Zheng, L.; Zhu, Y.; Chen, C.; Wang, D.; Peng, Q.; Gu, L.; Han, X.; Li,
J.; Li, Y. J. Am. Chem. Soc. 2018, 140, 15336−15341.
(27) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M.
Science 2013, 341, 1230444.
(28) Gu, Z.-Y.; Wang, G.; Yan, X.-P. Anal. Chem. 2010, 82, 1365−
1370.
(29) Zhang, Z.; Huang, Y.; Ding, W.; Li, G. Anal. Chem. 2014, 86,
3533−3540.
(30) Yan, M.; Ye, J.; Zhu, Q.; Zhu, L.; Huang, J.; Yang, X. Anal.
Chem. 2019, 91, 10156−10163.
(31) Xu, G.; Yamada, T.; Otsubo, K.; Sakaida, S.; Kitagawa, H. J.
Am. Chem. Soc. 2012, 134, 16524−16527.
(32) Katz, M. J.; Brown, Z. J.; Colón, Y. J.; Siu, P. W.; Scheidt, K. A.;
Snurr, R. Q.; Hupp, J. T.; Farha, O. K. Chem. Commun. 2013, 49,
9449−9451.
(33) Kandiah, M.; Usseglio, S.; Svelle, S.; Olsbye, U.; Lillerud, K. P.;
Tilset, M. J. Mater. Chem. A 2010, 20, 9848−9851.
(34) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti,
C.; Bordiga, S.; Lillerud, K. P. J. Am. Chem. Soc. 2008, 130, 13850−
13851.
(35) Lennox, M. J.; Du
18658.
̈
ren, T. J. Phys. Chem. C 2016, 120, 18651−
(36) Chang, N.; Yan, X.-P. J. Chromatogr. A 2012, 1257, 116−124.
(37) Wang, K.; Gu, J.; Yin, N. Ind. Eng. Chem. Res. 2017, 56, 1880−
1887.
(38) Bi, A.; Gao, T.; Cao, X.; Dong, J.; Liu, M.; Ding, N.; Liao, W.;
Zeng, W. Sens. Actuators, B 2018, 255, 3292−3297.
(39) Tang, Y.; Kong, X.; Liu, Z.-R.; Xu, A.; Lin, W. Anal. Chem.
2016, 88, 9359−9363.
(40) Gao, X.; Cui, R.; Ji, G.; Liu, Z. Nanoscale 2018, 10, 6205−6211.
(41) Tang, Y.; Kong, X.; Xu, A.; Dong, B.; Lin, W. Angew. Chem., Int.
Ed. 2016, 128, 3417−3420.
(42) Chen, Q.; He, Q.; Lv, M.; Xu, Y.; Yang, H.; Liu, X.; Wei, F.
Appl. Surf. Sci. 2015, 327, 77−85.
(43) Johnston, C. T.; Bish, D. L.; Eckert, J.; Brown, L. A. J. Phys.
Chem. B 2000, 104, 8080−8088.
̈
(44) Quante, H.; Mullen, K. Angew. Chem., Int. Ed. 1995, 34, 1323−
1325.
(45) Wu, T.; Yan, T.; Zhang, X.; Feng, Y.; Wei, D.; Sun, M.; Du, B.;
Wei, Q. Biosens. Bioelectron. 2018, 117, 575−582.
(46) Du, X.-D.; Yi, X.-H.; Wang, P.; Zheng, W.; Deng, J.; Wang, C.-
C. Chem. Eng. J. 2019, 356, 393−399.
(47) Garibay, S. J.; Cohen, S. M. Chem. Commun. 2010, 46, 7700−
7702.
(48) Zhang, J.; Hu, Y.; Qin, J.; Yang, Z.; Fu, M. Chem. Eng. J. 2020,
385, 123814.
(49) Ge, H.; Liu, G.; Yin, R.; Sun, Z.; Chen, H.; Yu, L.; Su, P.; Sun,
M.; Alamry, K. A.; Marwani, H. M.; Wang, S. Microchem. J. 2020, 156,
104793.
(50) Liu, C.; Cheng, A.-W.; Xia, X.-K.; Liu, Y.-F.; He, S.-W.; Guo,
X.; Sun, J.-Y. Anal. Methods 2016, 8, 2764−2770.
(51) Nandi, S.; Sharma, E.; Trivedi, V.; Biswas, S. Inorg. Chem. 2018,
57, 15149−15157.
(52) Liu, H.; Li, M.; Xia, Y.; Ren, X. ACS Appl. Mater. Interfaces
2017, 9, 120−126.
8227
https://doi.org/10.1021/acs.analchem.1c00916
Anal. Chem. 2021, 93, 8219−8227