Author’s Accepted Manuscript Metal–Organic Frameworks Supported Surface– Imprinted Nanoparticles for the Sensitive Detection of Metolcarb Kun Qian, Qiliang Deng, Guozhen Fang, Junping Wang, Mingfei Pan, Shuo Wang, Yuehong Pu www.elsevier.com/locate/bios
PII: DOI: Reference:
S0956-5663(15)30725-9 http://dx.doi.org/10.1016/j.bios.2015.12.071 BIOS8301
To appear in: Biosensors and Bioelectronic Received date: 15 October 2015 Revised date: 20 December 2015 Accepted date: 21 December 2015 Cite this article as: Kun Qian, Qiliang Deng, Guozhen Fang, Junping Wang, Mingfei Pan, Shuo Wang and Yuehong Pu, Metal–Organic Frameworks Supported Surface–Imprinted Nanoparticles for the Sensitive Detection of M e t o l c a r b , Biosensors and Bioelectronic, http://dx.doi.org/10.1016/j.bios.2015.12.071 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metal–Organic Frameworks Supported Surface–Imprinted Nanoparticles for the Sensitive Detection of Metolcarb
Kun Qiana, Qiliang Denga, Guozhen Fangb, Junping Wangb, Mingfei Panb, Shuo Wangb*, and Yuehong Puc
a
College of Chemical Engineering and Materials Science, Tianjin University of
Science and Technology, Tianjin 300457, China.
b
Key Laboratory of Food Nutrition and Safety, Ministry of Education, Tianjin Key
Laboratory of Food Nutrition and Safety, Tianjin University of Science and Technology, Tianjin 300457, China.
c
Institute of Food Science and Technology, Yunnan Agricultural University, Yunnan
650201, China.
Corresponding Authors * [email protected] (S. Wang) Tel: (+86 22) 60912493 Fax: (+86 22) 60912493 1
Abstract A novel approach to synthesize molecularly imprinted polymer (MIP) nanoparticles using a MIL-101 support (a type of metal–organic framework) is reported herein for the first time; the sample is referred as MIL@MIP. The nanoparticles were well distributed within the polymer films film, and exhibit an octahedral shape, satisfied thermal stability, and a high specific surface area (SSA) of 1579.43 m2 g−1. The adsorption behavior of MIL@MIP toward metolcarb in aqueous solution was subsequently examined. The synthesized MIL@MIP displayed satisfactory high transfer mass rates and a high selective adsorption affinity for metolcarb. Based on these results, a quartz crystal microbalance (QCM) sensor based on MIL@MIP was subsequently constructed and examined for the sensitive detection of metolcarb. Under optimal conditions, the detection limit of the system assessed in pear juice was 0.0689 mg L-1 within a linear concentration range of 0.1–0.9 mg L-1. MIL@MIP–QCM system combines the advantages of MIL-101 and molecularly imprinted technology (MIT), thereby achieving high detection sensitivity and selectivity. The current findings suggest the potential of MIL@MIP for detecting trace level pesticides and veterinary drugs for food safety and environmental control. Keywords: metal–organic frameworks; MIL-101; molecularly imprinted polymer; sol–gel; quartz crystal microbalance sensor; metolcarb.
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1. Introduction
Metal–organic frameworks (MOFs) are a relative relatively new class of crystalline porous hybrid organic–inorganic materials, which are formed by connecting metal ions or metal ion clusters to organic bridging ligands. MOFs display intriguing topological structures and porosities. Recent developments in MOFs have demonstrated the potential of MOFs as candidates for catalysis, sensing, separations, nonlinear optics, gas storage, and drug delivery applications (Eddaoudi et al., 2002; Sudik et al., 2006; Gould et al., 2008; Natarajan et al., 2009; Stock et al., 2012; Bromberg et al., 2012; Yuan et al., 2011; Ling et al., 2015; Xu et al., 2015; Wang et al., 2015; Bertucci et al., 2015). However, the wider application of MOFs is limited by their low hydrolytic and thermal stability. In 2005, a type of MOF, coined as MIL-101, was reported by Férey et al. (Férey et al., 2005). MIL-101 displays good hydro-/solvothermal and chemical stabilities. Since then, the development of multifunctional applications of MOFs has gained increasing scientific interest (Huang et al., 2015; Guo et al., 2014; Fang et al., 2014; Guo et al., 2015). Molecularly imprinted polymers (MIPs) are “antibody mimic” polymers, exhibiting selectivity toward template molecules or relevant structural analogs. MIPs are easy to be prepared, inexpensive, reusable, stable, and feature widespread applications (Schillinger et al., 2012; Azenha et al., 2013; Fernando-Silva et al., 2013; Talance et al., 2012; Piszkiewicz, et al., 2013; Ma et al., 2013; Patra et al., 2015; Singh et al., 2015; Niu et al., 2015; Cieplak et al., 2015). Conventional MIPs are typically synthesized using bulk polymerization methods. Accordingly, the obtained monoliths 3
need to be ground and sieved, producing irregular fragments. To overcome these disadvantages, the development of surface-imprinted polymers was proposed (Hayden et al., 2006; Tatemichi et al., 2007). In recent years, many new solid supports have been studied, such as silica breads, Fe3O4 nanoparticles and quantum dots et al., some of which suffer relative small specific surface area (Dai et al., 2015; Poma et al., 2010). In the our previously work, we reported the encapsulation of metolcarb-MIP into MOF-5 matrix, and the synthesized imprinted polymer, MOF@MIP, featured good properties (Qian et al., 2011). However, the main shortcoming of using MOF-5 as a support is its poor stability in water. To address this problem, in the current study, we describe a novel procedure, whereby MIL-101 is used as the support to synthesize MIP nanoparticles via a sol–gel process. The resulting product exhibits a core–shell architecture. Unlike the traditional matrices used in the MIP field, MIL-101 has numerous inherent advantages e.g., high chemical and hydrothermal stabilities, and high specific surface area. These properties make MIL-101 an ideal support material (Li et al., 1999; Clauzier et al., 2012; Canivet et al., 2013). Specifically, in our method, we combined molecularly imprinting technology (MIT) with MIL-101 to generate a metal–organic frameworks-supported surface–imprinted nanoparticles (MIL@MIP). The latter were subsequently integrated within a sensor device and examined toward the detection of metolcarb, which is widely used in the agriculture sector. Metolcarb inhibits acetylcholine esterase and the N-nitrosocarbamates formed are potent mutagens, which are harmful to the health.
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2. Experimental
Information pertaining to the instruments and reagents used is included in the Supporting Information.
2.1 Synthesis of MIL-101
MIL-101 was prepared according to a literature procedure with slight modifications (Hwang et al., 2008; Hong et al., 2009). Typically, Cr(NO3)39H2O (4.00 g), terephthalic acid (TPA) (1.64 g) and 40% HF (0.125 mL) mixed with doubly deionized water (DDW) (70.0 mL) were transferred to a 100.0 mL Teflon-lined reaction kettle. Then, the reaction kettle was sealed and heated at 220 °C in an oven. After 8 h, green crystals of MIL-101 were obtained in suspension. After thorough washing with ultrapure water, the green crystals emerged from the hot ethanol and aqueous NH4F solutions at 60 °C for 3 h. The precipitates were collected after centrifuging at 4000 rpm for 15 min to eliminate the unreacted TPA. The resulting MIL-101 was then filtered off, evacuated in vacuum, and activated under reduced pressure at 150 °C for 12 h.
2.2 Synthesis of MIL@MIP
MIL@MIP was synthesized as follows: 0.165 g of template (metolcarb) was dissolved in 3.0 mL tetrahydrofuran (THF). Following dispersion of 0.050 g MIL-101, 0.600 mL functional monomer (3-aminopropyl)triethoxysilane (APTES) was added into the mixture, which was stirred for 60 min. Subsequently, 0.702 mL cross-linker 5
tetraethyl orthosilicate (TEOS) and 1.0 mL 0.2 mol L-1 catalyst (acetic acid) were added. After stirring for 30 min, the pre-polymerized product was sealed and incubated in a temperature-controlled bath at 60 °C for 20 h. Then, the obtained MIL@MIP was washed by Soxhlet extraction (300 mL of methanol/acetic acid; 9: 1 v/v) to remove the template until no metolcarb was detected. MIL@NIP was also prepared using the same procedure as the one described above, however, in the absence of template.
2.3 Preparation of MIL@MIP-modified electrode
Prior to modification, the electrode surface was cleaned by exposure in a solution of 30% H2O2: 98% H2SO4 (1: 3 v/v) for 2 min to remove possible surface chemicals, followed by thorough rinsing with deionized water. MIL@MIP (50.00 mg) was suspended in polyvinyl chloride/dichloromethane (PVC-DCM) (0.7 wt % solution), and then a homogeneous solution was obtained by ultrasonication. The mixture (5.0 μL) was then carefully dispensed onto an immobilized quartz crystal surface. The modified quartz crystal was dried at 25 °C for 30 min and stored at room temperature in a vacuum chamber before use.
2.4 Detection of QCM Sensor
After anchoring of the prepared quartz crystal onto a Teflon holder, the assembled MIL@MIP-modified QCM sensor was immersed in H2O (20.0 mL) at room temperature. A steady resonant frequency (f0; Δf < 1.0 Hz) was obtained after
6
equilibration for 5 min. A small aliquot of metolcarb solution was distributed into the solution. After equilibration for 5 min, a stable frequency change caused by analyte binding was obtained. After each test, the MIL@MIP-modified quartz crystal was washed with HCl (0.1 mol L−1) and DDW until the frequency recovered to f0 and the crystal could be reused. Throughout the entire testing process, the solution was stirred at 240 rpm to accelerate the transmission transfer of analyte. Analyses were performed in triplicate, and the average value of the obtained frequency shift (Δf, Hz) was used to calculate the mass of metolcarb adsorbed onto the crystal surface according to the Sauerbrey equation (Sauerbrey et al., 1959) as follows: Δf = − 2.26 × 10-6Δmf02 /A
(1)
Where f0 is the original frequency of the quartz crystal (Hz), Δm is the mass change (g), and A is the surface area of the electrode (cm2).
2.5 Sample preparation
In this study, pear juice was chosen as a complex sample to assess the application of the prepared MIL@MIP–QCM sensor for detecting metolcarb. Pear juice was obtained from local supermarkets. Pear juice samples (0.25 mL) diluted with an equal volume of H2O were introduced into a polytetrafluoroethylene (PTFE) tube and spiked at three concentrations (0.2, 0.4 and 0.8 mg L−1). Following filtration (0.22 μm filter), the spiked pear juice samples were pumped through the QCM flow cell, anchoring the MIL@MIP Pt electrode. Δf was recorded for analysis until the resulting frequency was stable.
7
3. Results and discussion
In the present study, novel surface–imprinted nanoparticles using MIL-101 as a support were prepared for the sensitivity and selectivity detection of metolcarb. The structure and synthesis procedure of the MIL@MIP is are illustrated in Scheme 1.
Scheme 1
3.1 Characterization of MIL@MIP
The prepared MIL@MIP was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), powder X-ray diffraction (XRD), N2 adsorption–desorption measurements, and thermogravimetric analysis (TGA). The SEM images in Fig. S1 show the morphological features of the MIL-101 (Fig. S1a) and MIL@MIP (Fig. S1b) particles, and bare Pt (Fig. S1c), PVC-DCM-modified (Fig. S1d), MIL-101-modified (Fig. S1e), and MIL@MIP-modified (Fig. S1f) electrodes. The high crystallinity of MIL-101 was characterized by the sharp
8
reflections observed in the Fig. S1a. The average size of the octahedral MIL-101 particles ranged from 100 to 200 nm, and the particles appeared to highly monodisperse. The surface of MIL-101 was smooth, and the needle-like crystals of H2BDC were not observed. Fig. S1(b) shows that MIL-101 was fully encapsulated within the MIP coatings after polymerization. However, after encapsulation, MIL@MIP featured a predominant octahedron morphology, of which the particles ranged from 200 to 300 nm in size. The obtained larger MIL@MIP particles indicated that the MIP shell was successfully formed. The thickness of the MIP coatings was around 100–200 nm and did not influence the shape of the nanoparticles as the reaction only occurred on the surface of MIL@MIP. Compared with bulk MIP, the MOFs-supported
surface–imprinted
nanoparticles
displayed
more
regular
morphological features. As observed, the surface of bare Pt electrode (Fig. S1c) and PVC-DCM-modified electrode (Fig. S1d) exhibited a relatively flat morphology, indicating that there were no specific cavities on the bare Pt electrode and base electrode. The only difference between c and d was that the bare Pt electrode featured a more highly reflective surface than d. As observed from Fig. S1e, MIL-101-modified electrode was uniformly structured. The morphology of MIL@MIP-modified electrode is shown in Fig. S1f. As discussed earlier, MIL-101 was fully encapsulated within the MIP coating after the polymerization, thereby indicating that the ordered MIL@MIP was successfully modified on the electrode surface and greatly changed the surface morphology of the electrode. To assess the formation of the synthesized materials, their respective FT-IR spectra
9
(Fig. S2) were recorded. Fig. S2a displays bands, corresponding to O–C–O and C=C, at 1100 cm-1 and 1600–1700 cm−1, respectively, which originated from the BDC units that comprised benzene rings and carboxylic groups in MIL-101. The band observed at 500 cm−1 was attributed to Cr–O, and the broad band observed at 3400 cm−1 was attributed to adsorbed water. The results obtained confirmed the formation of MIL-101. Fig. S2b shows the FT-IR spectrum of metolcarb that displayed a band around 3300 cm-1, which was assigned to –NH–. The spectrum of MIL@MIP (the template not extracted) in Fig. S2c displayed a band around 1600-1700 cm−1, indicating the existence of MIL-101, and a band at 3000 cm−1 originating from –NH–, which proved the existence of metolcarb. Additionally, Si–O–Si stretching vibrations features around 1100 cm−1 were observed, indicating the occurrence of hydrolysis of the silane coupling agents, thereby confirming the successful encapsulation procedure between MIL-101 and the MIP. The spectrum of MIL@NIP in Fig. S2d featured similar peaks/band characteristics to those featured in Fig. S2c except for the characteristic peaks of metolcarb. MIL-101 and MIL@MIP were further characterized by XRD. The diffractograms of MIL-101 in Fig.S3a agreed with the theoretical XRD patterns of reference Cr-MIL-101 (CSD number: 415697), of which the main characteristic peaks were observed at 2θ 7.98° and 9.06°. Diffraction peaks of recrystallized H2BDC were not detected. It is worth noting that after the surface–imprinted procedure, the intensity of the MIL-101 XRD peaks decreased considerably, indicating the success of the coating procedure.
10
TGA was conducted to assess the thermal stability of MIL-101 and MIL@MIP, and the results are shown in Fig. S4. As observed in Fig. S4 (curve a), MIL-101 displayed an initial weight loss below 100 °C, corresponding to the loss of water molecules from the framework. A second weight loss observed within 140–260 °C was due to the disintegration of OH/F groups of MIL-101. A third weight loss of 40.69% was observed within 300–460 °C, which was ascribed to the collapse of MOF removed the TPA. The thermogram of MIL@MIP is shown in Fig. S4 (curve b). Compared with the slope of curve a, that of curve b seemed less steep. Only one significant weight loss within the temperature range of 25–340 °C was observed. A second weight loss (41.31%) was observed when the temperature was increased further to 1000 °C. This phenomenon shows that the synthesized MOFs-supported surface–imprinted nanoparticles featured feature high thermal stability, which would be a desirable attribute in relevant applications. To determine the Brunauer–Emmett–Teller specific surface area (BET SSA) of MIL@MIP and MIP, N2 adsorption–desorption measurements were performed. MIL@MIP featured a higher BET SSA of 1579.43 m2 g−1 than MIP (138.35 m2 g−1). The results discussed so far demonstrate the superior properties of MIL@MIP over those of conventional MIP. It is worth noting that the octahedral-like morphology of MIL@MIP may be responsible for its high SSA, which would allow fast template loading speed rates.
3.2 Adsorption behavior of MIL@MIP for metolcarb in aqueous solution
11
To evaluate the adsorption behaviors of the MOFs-supported surface–imprinted nanoparticles, static, kinetic and competitive adsorption tests were conducted. In the static adsorption test, MIL@MIP or MIL@NIP was exposed to different metolcarb solutions of varying concentrations (5.0–100.0 mg L−1), separately. As observed from Fig. S5, compared with MIL@NIP, MIL@MIP displayed considerably higher binding ability to the target molecule at all initial concentrations studied. Specifically, the adsorption capacity of the MIL@MIP (up to 3.217 mg g−1) was 1.6-fold higher than that of MIL@NIP (up to 1.994 mg g−1) at a given metolcarb solution concentration of 25.0 mg L−1. This phenomenon might be owing to the structure of the surface–imprinted nanoparticles, which affords a better steric matching between the recognition sites are on the which made and the template, subsequently allowing the imprinted thin films to adsorb more target molecules. Furthermore, in our previous study (Qian et al., 2010), a type of bulk metolcarb-MIP was prepared, and the latter featured a lower adsorption capacity than MIL@MIP. The superior adsorption ability of MIL@MIP was attributed to its high SSA as a result of its octahedral-like particle morphology. To further investigate the adsorption property of the nanoparticles, the rebinding binding kinetics of metolcarb to MIL@MIP was therefore studied. The results are shown in Fig. S6. At the early stages of the adsorption process, the adsorption rate was relatively high and then gradually decreased until equilibrium was achieved. Specifically, within 3 min of reaction, 34.50% of the total amount of kinetic adsorption capacity was obtained, and within 5 min of reaction, 49.64% of the total
12
adsorption capacity was achieved. Adsorption equilibrium was achieved within 20 min. This result further confirmed, the benefit of the higher SSA of MIL@MIP in achieving faster loading rates when compared with bulk metolcarb-MIP (Qian et al., 2010), thereby also suggesting that MIL@MIP has good mass transport properties. A competitive adsorption test was performed to evaluate the selectivity of the binding sites of MIL@MIP. Four kinds of competitive compounds were used i.e., propoxur, carbaryl, isoprocarb and fenobucarb (Fig. S7). The results showed that MIL@MIP displayed a significantly higher metolcarb loading (1.3425 mg g−1) in the competitive environment examined (Table 1). Moreover, the metolcarb loading was higher than that obtained for MIL@NIP (0.4534 mg g-1). Also, it was noted that the adsorption capacity of MIL@MIP in the competitive environment was lower than that obtained from the single-pesticide adsorption system (static adsorption test). Among the four competitors studied, the loading capacities of isoprocarb and fenobucarb were higher than those of carbaryl and propoxur (Table 1). The structures of isoprocarb and fenobucarb are comparable with that of metolcarb, but with different R groups. Conversely, propoxur features a more complex R group, which result results in a lower adsorption capacity. However, the greater steric hindrance effects of the naphthalene ring in carbaryl result in the lower adsorption capacity obtained.
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Table 1. Competitive loading of metolcarb, propoxur, carbaryl, isoprocarb and fenobucarb by MIL@MIP and MIL@NIP MIL@MIP
MIL@NIP
metolcarb
1.3245
0.4534
Loading capacity
propoxur
0.1523
0.2378
(mg g−1)
carbaryl
0.1348
0.2094
isoprocarb
0.3513
0.4207
fenobucarb
0.2344
0.2564
metolcarb
152.67
47.49
propoxur
15.47
24.36
carbaryl
13.67
21.39
isoprocarb
36.41
43.92
fenobucarb
24.00
26.31
propoxur
9.87
1.95
carbaryl
11.17
2.22
isoprocarb
4.19
1.08
fenobucarb
6.36
1.81
propoxur
5.06
carbaryl
5.03
isoprocarb
3.88
fenobucarb
3.51
Kd
K
K'
Kd, distribution coefficient, K {(C C ) / C } {volume of solution (mL)}/{mass of gel (g)} . d
i
f
f
Where Ci and Cf represent the initial and final concentrations, respectively. K, selectivity coefficient, K K (metolcarb)/K (competitors) . d
d
K ', relative selectivity coefficient, K' K / K . MIP
NIP
14
3.3 Evaluation of binding of the MIL@MIP-modified QCM crystal electrode
A PVC-modified QCM sensor did not show any detectable frequency response to metolcarb at selected concentrations, thus indicating that PVC, which was used to immobilize the MIP on the electrode surface, did not affect the specific recognition of metolcarb by the proposed sensor. The binding capacity of the prepared MIL@MIP is one key parameter that must be determined. Accordingly, solutions containing the analyte molecule at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, and 2.0 mg L−1 in H2O were exposed to the MIL@MIP–QCM sensor, and results are presented in Fig. 1. As observed, Δf increased with increasing metolcarb concentrations. This increase was attributed to the imprinting of MIP with metolcarb, whereby cavities formed during polymerization. The generated cavities could specifically fit the target molecule (metolcarb) in terms of spatial structure and functional groups. At metolcarb concentrations greater than 1.00 mg L−1, the frequency response remained constant owing to the saturation of MIP with metolcarb. A good linear relationship between the frequency change and concentration was obtained within a metolcarb concentrations range of 0.1–0.9 mg L−1 (r2 = 0.9868). The standard deviations (SDs) of the results were 1.3–4.2% (n = 3); indicating that the analysis of metolcarb in pear juice samples using the prepared MIL@MIP-QCM sensor is stable and reproducible.
15
Fig. 1
3.4 Reproducibility and stability
The reproducibility and stability of the developed QCM are important features for successful metolcarb detection. Therefore, the frequency response of the MIL@MIP–QCM sensor in H2O containing metolcarb (1.0 mg L−1) was measured consecutively 10 times. After each test, the imprinted sensor was washed with 0.1 M HCl and DDW until the original resonance frequency was recovered. The frequency change during the repeated testing decreased slightly from 700.3 to 680.1 Hz, corresponding to a loss of just 2.9% only, thereby confirming the good recyclability and stability of the MIL@MIP–QCM sensor toward metolcarb detection. The stability of the MIL@MIP–QCM sensor over a long period of time was also demonstrated. After hermetic storage at room temperature for 6 months, the average frequency shift 16
of the quartz crystal was 665.0 Hz, which was only 5.0% lower than the initial frequency shift of 700.3 Hz. This result further confirmed the excellent stability of the developed MIL@MIP–QCM sensor and MIL@MIP.
3.5 Evaluation of sample analysis
Using the established sample pretreatment method, the concentration of metolcarb in pear juice samples, which were spiked at three concentrations (0.2, 0.4 and 0.8 mg L−1), was measured using the MIL@MIP–QCM sensor. The recovery for the measurements ranged from 74.16% to 96.2%, indicating that the prepared MIL@MIP–QCM sensor could be used in practical application to accurately determine metolcarb. The measured detection limit was 0.0689 mg L-1 within the linear range of 0.1–0.9 mg L−1 in pear juice with a relative standard deviations (RSDs) of 0.24–2.27% (n = 3).
4. Conclusion
The current study presented an efficient method to synthesize novel porous hybrid materials, specifically, MOFs-supported surface–imprinted nanoparticles. The synthesized MIL@MIP featured improved thermal stability, BET SSA, and the kinetic adsorption rate when compared with MIP. In view of the satisfactory performance of MIL@MIP, we believe that the findings of the current study could be used further to advance progress in MIT.
Acknowledgments 17
This work was supported by Project supported by the National Science Foundation for Distinguished Young Scholars of China (Grant No. 31225021), National Basic Research Program (973) of China (Project No.2012CB720803), Innovation Talents of Science and Technology Plan of Yunnan Province (Project No. 2012HA009), and National High-tech R&D Program (863 Program) financial supports from the Ministry of Science and Technology of China (Project No. 2012AA101604).
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Figure Captions Scheme 1.
Synthesis
procedure of MIL-101 supported surface–imprinted
nanoparticles. Fig. 1. Frequency responses of MIL@MIP–QCM sensors in solutions containing metolcarb at different concentrations.
21
Scheme 1. Synthesis procedure of MIL-101 supported surface-imprinted nanoparticles.
22
Fig. 1. Frequency responses of MIL@MIP-QCM sensors in solutions containing metolcarb at different concentrations.
Table 1. Competitive loading of metolcarb, propoxur, carbaryl, isoprocarb and fenobucarb by MIL@MIP and MIL@NIP MIL@MIP
MIL@NIP
metolcarb
1.3245
0.4534
Loading capacity
propoxur
0.1523
0.2378
(mg g−1)
carbaryl
0.1348
0.2094
isoprocarb
0.3513
0.4207
fenobucarb
0.2344
0.2564
metolcarb
152.67
47.49
propoxur
15.47
24.36
carbaryl
13.67
21.39
isoprocarb
36.41
43.92
Kd
23
K
K'
fenobucarb
24.00
26.31
propoxur
9.87
1.95
carbaryl
11.17
2.22
isoprocarb
4.19
1.08
fenobucarb
6.36
1.81
propoxur
5.06
carbaryl
5.03
isoprocarb
3.88
fenobucarb
3.51
Kd, distribution coefficient, K {(C C ) / C } {volume of solution (mL)}/{mass of gel (g)} . d
i
f
f
Where Ci and Cf represent the initial and final concentrations, respectively. K, selectivity coefficient, K K (metolcarb)/K (competitors) . d
d
K ', relative selectivity coefficient, K' K / K . MIP
NIP
Highlights
Metal–organic frameworks supported surface–imprinted nanoparticles (MIL@MIP) had been prepared.
A quartz crystal microbalance sensor based on of MIL@MIP for the sensitive detection of metolcarb is constructed, and could be used for other small-molecules analysis.
Ultrasensitive, selectivity and specific quantification of metolcarb had been achieved.
This study presented an efficient method to synthesize novel porous hybrid materials.
24
PII: DOI: Reference:
S0956-5663(15)30725-9 http://dx.doi.org/10.1016/j.bios.2015.12.071 BIOS8301
To appear in: Biosensors and Bioelectronic Received date: 15 October 2015 Revised date: 20 December 2015 Accepted date: 21 December 2015 Cite this article as: Kun Qian, Qiliang Deng, Guozhen Fang, Junping Wang, Mingfei Pan, Shuo Wang and Yuehong Pu, Metal–Organic Frameworks Supported Surface–Imprinted Nanoparticles for the Sensitive Detection of M e t o l c a r b , Biosensors and Bioelectronic, http://dx.doi.org/10.1016/j.bios.2015.12.071 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metal–Organic Frameworks Supported Surface–Imprinted Nanoparticles for the Sensitive Detection of Metolcarb
Kun Qiana, Qiliang Denga, Guozhen Fangb, Junping Wangb, Mingfei Panb, Shuo Wangb*, and Yuehong Puc
a
College of Chemical Engineering and Materials Science, Tianjin University of
Science and Technology, Tianjin 300457, China.
b
Key Laboratory of Food Nutrition and Safety, Ministry of Education, Tianjin Key
Laboratory of Food Nutrition and Safety, Tianjin University of Science and Technology, Tianjin 300457, China.
c
Institute of Food Science and Technology, Yunnan Agricultural University, Yunnan
650201, China.
Corresponding Authors * [email protected] (S. Wang) Tel: (+86 22) 60912493 Fax: (+86 22) 60912493 1
Abstract A novel approach to synthesize molecularly imprinted polymer (MIP) nanoparticles using a MIL-101 support (a type of metal–organic framework) is reported herein for the first time; the sample is referred as MIL@MIP. The nanoparticles were well distributed within the polymer films film, and exhibit an octahedral shape, satisfied thermal stability, and a high specific surface area (SSA) of 1579.43 m2 g−1. The adsorption behavior of MIL@MIP toward metolcarb in aqueous solution was subsequently examined. The synthesized MIL@MIP displayed satisfactory high transfer mass rates and a high selective adsorption affinity for metolcarb. Based on these results, a quartz crystal microbalance (QCM) sensor based on MIL@MIP was subsequently constructed and examined for the sensitive detection of metolcarb. Under optimal conditions, the detection limit of the system assessed in pear juice was 0.0689 mg L-1 within a linear concentration range of 0.1–0.9 mg L-1. MIL@MIP–QCM system combines the advantages of MIL-101 and molecularly imprinted technology (MIT), thereby achieving high detection sensitivity and selectivity. The current findings suggest the potential of MIL@MIP for detecting trace level pesticides and veterinary drugs for food safety and environmental control. Keywords: metal–organic frameworks; MIL-101; molecularly imprinted polymer; sol–gel; quartz crystal microbalance sensor; metolcarb.
2
1. Introduction
Metal–organic frameworks (MOFs) are a relative relatively new class of crystalline porous hybrid organic–inorganic materials, which are formed by connecting metal ions or metal ion clusters to organic bridging ligands. MOFs display intriguing topological structures and porosities. Recent developments in MOFs have demonstrated the potential of MOFs as candidates for catalysis, sensing, separations, nonlinear optics, gas storage, and drug delivery applications (Eddaoudi et al., 2002; Sudik et al., 2006; Gould et al., 2008; Natarajan et al., 2009; Stock et al., 2012; Bromberg et al., 2012; Yuan et al., 2011; Ling et al., 2015; Xu et al., 2015; Wang et al., 2015; Bertucci et al., 2015). However, the wider application of MOFs is limited by their low hydrolytic and thermal stability. In 2005, a type of MOF, coined as MIL-101, was reported by Férey et al. (Férey et al., 2005). MIL-101 displays good hydro-/solvothermal and chemical stabilities. Since then, the development of multifunctional applications of MOFs has gained increasing scientific interest (Huang et al., 2015; Guo et al., 2014; Fang et al., 2014; Guo et al., 2015). Molecularly imprinted polymers (MIPs) are “antibody mimic” polymers, exhibiting selectivity toward template molecules or relevant structural analogs. MIPs are easy to be prepared, inexpensive, reusable, stable, and feature widespread applications (Schillinger et al., 2012; Azenha et al., 2013; Fernando-Silva et al., 2013; Talance et al., 2012; Piszkiewicz, et al., 2013; Ma et al., 2013; Patra et al., 2015; Singh et al., 2015; Niu et al., 2015; Cieplak et al., 2015). Conventional MIPs are typically synthesized using bulk polymerization methods. Accordingly, the obtained monoliths 3
need to be ground and sieved, producing irregular fragments. To overcome these disadvantages, the development of surface-imprinted polymers was proposed (Hayden et al., 2006; Tatemichi et al., 2007). In recent years, many new solid supports have been studied, such as silica breads, Fe3O4 nanoparticles and quantum dots et al., some of which suffer relative small specific surface area (Dai et al., 2015; Poma et al., 2010). In the our previously work, we reported the encapsulation of metolcarb-MIP into MOF-5 matrix, and the synthesized imprinted polymer, MOF@MIP, featured good properties (Qian et al., 2011). However, the main shortcoming of using MOF-5 as a support is its poor stability in water. To address this problem, in the current study, we describe a novel procedure, whereby MIL-101 is used as the support to synthesize MIP nanoparticles via a sol–gel process. The resulting product exhibits a core–shell architecture. Unlike the traditional matrices used in the MIP field, MIL-101 has numerous inherent advantages e.g., high chemical and hydrothermal stabilities, and high specific surface area. These properties make MIL-101 an ideal support material (Li et al., 1999; Clauzier et al., 2012; Canivet et al., 2013). Specifically, in our method, we combined molecularly imprinting technology (MIT) with MIL-101 to generate a metal–organic frameworks-supported surface–imprinted nanoparticles (MIL@MIP). The latter were subsequently integrated within a sensor device and examined toward the detection of metolcarb, which is widely used in the agriculture sector. Metolcarb inhibits acetylcholine esterase and the N-nitrosocarbamates formed are potent mutagens, which are harmful to the health.
4
2. Experimental
Information pertaining to the instruments and reagents used is included in the Supporting Information.
2.1 Synthesis of MIL-101
MIL-101 was prepared according to a literature procedure with slight modifications (Hwang et al., 2008; Hong et al., 2009). Typically, Cr(NO3)39H2O (4.00 g), terephthalic acid (TPA) (1.64 g) and 40% HF (0.125 mL) mixed with doubly deionized water (DDW) (70.0 mL) were transferred to a 100.0 mL Teflon-lined reaction kettle. Then, the reaction kettle was sealed and heated at 220 °C in an oven. After 8 h, green crystals of MIL-101 were obtained in suspension. After thorough washing with ultrapure water, the green crystals emerged from the hot ethanol and aqueous NH4F solutions at 60 °C for 3 h. The precipitates were collected after centrifuging at 4000 rpm for 15 min to eliminate the unreacted TPA. The resulting MIL-101 was then filtered off, evacuated in vacuum, and activated under reduced pressure at 150 °C for 12 h.
2.2 Synthesis of MIL@MIP
MIL@MIP was synthesized as follows: 0.165 g of template (metolcarb) was dissolved in 3.0 mL tetrahydrofuran (THF). Following dispersion of 0.050 g MIL-101, 0.600 mL functional monomer (3-aminopropyl)triethoxysilane (APTES) was added into the mixture, which was stirred for 60 min. Subsequently, 0.702 mL cross-linker 5
tetraethyl orthosilicate (TEOS) and 1.0 mL 0.2 mol L-1 catalyst (acetic acid) were added. After stirring for 30 min, the pre-polymerized product was sealed and incubated in a temperature-controlled bath at 60 °C for 20 h. Then, the obtained MIL@MIP was washed by Soxhlet extraction (300 mL of methanol/acetic acid; 9: 1 v/v) to remove the template until no metolcarb was detected. MIL@NIP was also prepared using the same procedure as the one described above, however, in the absence of template.
2.3 Preparation of MIL@MIP-modified electrode
Prior to modification, the electrode surface was cleaned by exposure in a solution of 30% H2O2: 98% H2SO4 (1: 3 v/v) for 2 min to remove possible surface chemicals, followed by thorough rinsing with deionized water. MIL@MIP (50.00 mg) was suspended in polyvinyl chloride/dichloromethane (PVC-DCM) (0.7 wt % solution), and then a homogeneous solution was obtained by ultrasonication. The mixture (5.0 μL) was then carefully dispensed onto an immobilized quartz crystal surface. The modified quartz crystal was dried at 25 °C for 30 min and stored at room temperature in a vacuum chamber before use.
2.4 Detection of QCM Sensor
After anchoring of the prepared quartz crystal onto a Teflon holder, the assembled MIL@MIP-modified QCM sensor was immersed in H2O (20.0 mL) at room temperature. A steady resonant frequency (f0; Δf < 1.0 Hz) was obtained after
6
equilibration for 5 min. A small aliquot of metolcarb solution was distributed into the solution. After equilibration for 5 min, a stable frequency change caused by analyte binding was obtained. After each test, the MIL@MIP-modified quartz crystal was washed with HCl (0.1 mol L−1) and DDW until the frequency recovered to f0 and the crystal could be reused. Throughout the entire testing process, the solution was stirred at 240 rpm to accelerate the transmission transfer of analyte. Analyses were performed in triplicate, and the average value of the obtained frequency shift (Δf, Hz) was used to calculate the mass of metolcarb adsorbed onto the crystal surface according to the Sauerbrey equation (Sauerbrey et al., 1959) as follows: Δf = − 2.26 × 10-6Δmf02 /A
(1)
Where f0 is the original frequency of the quartz crystal (Hz), Δm is the mass change (g), and A is the surface area of the electrode (cm2).
2.5 Sample preparation
In this study, pear juice was chosen as a complex sample to assess the application of the prepared MIL@MIP–QCM sensor for detecting metolcarb. Pear juice was obtained from local supermarkets. Pear juice samples (0.25 mL) diluted with an equal volume of H2O were introduced into a polytetrafluoroethylene (PTFE) tube and spiked at three concentrations (0.2, 0.4 and 0.8 mg L−1). Following filtration (0.22 μm filter), the spiked pear juice samples were pumped through the QCM flow cell, anchoring the MIL@MIP Pt electrode. Δf was recorded for analysis until the resulting frequency was stable.
7
3. Results and discussion
In the present study, novel surface–imprinted nanoparticles using MIL-101 as a support were prepared for the sensitivity and selectivity detection of metolcarb. The structure and synthesis procedure of the MIL@MIP is are illustrated in Scheme 1.
Scheme 1
3.1 Characterization of MIL@MIP
The prepared MIL@MIP was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), powder X-ray diffraction (XRD), N2 adsorption–desorption measurements, and thermogravimetric analysis (TGA). The SEM images in Fig. S1 show the morphological features of the MIL-101 (Fig. S1a) and MIL@MIP (Fig. S1b) particles, and bare Pt (Fig. S1c), PVC-DCM-modified (Fig. S1d), MIL-101-modified (Fig. S1e), and MIL@MIP-modified (Fig. S1f) electrodes. The high crystallinity of MIL-101 was characterized by the sharp
8
reflections observed in the Fig. S1a. The average size of the octahedral MIL-101 particles ranged from 100 to 200 nm, and the particles appeared to highly monodisperse. The surface of MIL-101 was smooth, and the needle-like crystals of H2BDC were not observed. Fig. S1(b) shows that MIL-101 was fully encapsulated within the MIP coatings after polymerization. However, after encapsulation, MIL@MIP featured a predominant octahedron morphology, of which the particles ranged from 200 to 300 nm in size. The obtained larger MIL@MIP particles indicated that the MIP shell was successfully formed. The thickness of the MIP coatings was around 100–200 nm and did not influence the shape of the nanoparticles as the reaction only occurred on the surface of MIL@MIP. Compared with bulk MIP, the MOFs-supported
surface–imprinted
nanoparticles
displayed
more
regular
morphological features. As observed, the surface of bare Pt electrode (Fig. S1c) and PVC-DCM-modified electrode (Fig. S1d) exhibited a relatively flat morphology, indicating that there were no specific cavities on the bare Pt electrode and base electrode. The only difference between c and d was that the bare Pt electrode featured a more highly reflective surface than d. As observed from Fig. S1e, MIL-101-modified electrode was uniformly structured. The morphology of MIL@MIP-modified electrode is shown in Fig. S1f. As discussed earlier, MIL-101 was fully encapsulated within the MIP coating after the polymerization, thereby indicating that the ordered MIL@MIP was successfully modified on the electrode surface and greatly changed the surface morphology of the electrode. To assess the formation of the synthesized materials, their respective FT-IR spectra
9
(Fig. S2) were recorded. Fig. S2a displays bands, corresponding to O–C–O and C=C, at 1100 cm-1 and 1600–1700 cm−1, respectively, which originated from the BDC units that comprised benzene rings and carboxylic groups in MIL-101. The band observed at 500 cm−1 was attributed to Cr–O, and the broad band observed at 3400 cm−1 was attributed to adsorbed water. The results obtained confirmed the formation of MIL-101. Fig. S2b shows the FT-IR spectrum of metolcarb that displayed a band around 3300 cm-1, which was assigned to –NH–. The spectrum of MIL@MIP (the template not extracted) in Fig. S2c displayed a band around 1600-1700 cm−1, indicating the existence of MIL-101, and a band at 3000 cm−1 originating from –NH–, which proved the existence of metolcarb. Additionally, Si–O–Si stretching vibrations features around 1100 cm−1 were observed, indicating the occurrence of hydrolysis of the silane coupling agents, thereby confirming the successful encapsulation procedure between MIL-101 and the MIP. The spectrum of MIL@NIP in Fig. S2d featured similar peaks/band characteristics to those featured in Fig. S2c except for the characteristic peaks of metolcarb. MIL-101 and MIL@MIP were further characterized by XRD. The diffractograms of MIL-101 in Fig.S3a agreed with the theoretical XRD patterns of reference Cr-MIL-101 (CSD number: 415697), of which the main characteristic peaks were observed at 2θ 7.98° and 9.06°. Diffraction peaks of recrystallized H2BDC were not detected. It is worth noting that after the surface–imprinted procedure, the intensity of the MIL-101 XRD peaks decreased considerably, indicating the success of the coating procedure.
10
TGA was conducted to assess the thermal stability of MIL-101 and MIL@MIP, and the results are shown in Fig. S4. As observed in Fig. S4 (curve a), MIL-101 displayed an initial weight loss below 100 °C, corresponding to the loss of water molecules from the framework. A second weight loss observed within 140–260 °C was due to the disintegration of OH/F groups of MIL-101. A third weight loss of 40.69% was observed within 300–460 °C, which was ascribed to the collapse of MOF removed the TPA. The thermogram of MIL@MIP is shown in Fig. S4 (curve b). Compared with the slope of curve a, that of curve b seemed less steep. Only one significant weight loss within the temperature range of 25–340 °C was observed. A second weight loss (41.31%) was observed when the temperature was increased further to 1000 °C. This phenomenon shows that the synthesized MOFs-supported surface–imprinted nanoparticles featured feature high thermal stability, which would be a desirable attribute in relevant applications. To determine the Brunauer–Emmett–Teller specific surface area (BET SSA) of MIL@MIP and MIP, N2 adsorption–desorption measurements were performed. MIL@MIP featured a higher BET SSA of 1579.43 m2 g−1 than MIP (138.35 m2 g−1). The results discussed so far demonstrate the superior properties of MIL@MIP over those of conventional MIP. It is worth noting that the octahedral-like morphology of MIL@MIP may be responsible for its high SSA, which would allow fast template loading speed rates.
3.2 Adsorption behavior of MIL@MIP for metolcarb in aqueous solution
11
To evaluate the adsorption behaviors of the MOFs-supported surface–imprinted nanoparticles, static, kinetic and competitive adsorption tests were conducted. In the static adsorption test, MIL@MIP or MIL@NIP was exposed to different metolcarb solutions of varying concentrations (5.0–100.0 mg L−1), separately. As observed from Fig. S5, compared with MIL@NIP, MIL@MIP displayed considerably higher binding ability to the target molecule at all initial concentrations studied. Specifically, the adsorption capacity of the MIL@MIP (up to 3.217 mg g−1) was 1.6-fold higher than that of MIL@NIP (up to 1.994 mg g−1) at a given metolcarb solution concentration of 25.0 mg L−1. This phenomenon might be owing to the structure of the surface–imprinted nanoparticles, which affords a better steric matching between the recognition sites are on the which made and the template, subsequently allowing the imprinted thin films to adsorb more target molecules. Furthermore, in our previous study (Qian et al., 2010), a type of bulk metolcarb-MIP was prepared, and the latter featured a lower adsorption capacity than MIL@MIP. The superior adsorption ability of MIL@MIP was attributed to its high SSA as a result of its octahedral-like particle morphology. To further investigate the adsorption property of the nanoparticles, the rebinding binding kinetics of metolcarb to MIL@MIP was therefore studied. The results are shown in Fig. S6. At the early stages of the adsorption process, the adsorption rate was relatively high and then gradually decreased until equilibrium was achieved. Specifically, within 3 min of reaction, 34.50% of the total amount of kinetic adsorption capacity was obtained, and within 5 min of reaction, 49.64% of the total
12
adsorption capacity was achieved. Adsorption equilibrium was achieved within 20 min. This result further confirmed, the benefit of the higher SSA of MIL@MIP in achieving faster loading rates when compared with bulk metolcarb-MIP (Qian et al., 2010), thereby also suggesting that MIL@MIP has good mass transport properties. A competitive adsorption test was performed to evaluate the selectivity of the binding sites of MIL@MIP. Four kinds of competitive compounds were used i.e., propoxur, carbaryl, isoprocarb and fenobucarb (Fig. S7). The results showed that MIL@MIP displayed a significantly higher metolcarb loading (1.3425 mg g−1) in the competitive environment examined (Table 1). Moreover, the metolcarb loading was higher than that obtained for MIL@NIP (0.4534 mg g-1). Also, it was noted that the adsorption capacity of MIL@MIP in the competitive environment was lower than that obtained from the single-pesticide adsorption system (static adsorption test). Among the four competitors studied, the loading capacities of isoprocarb and fenobucarb were higher than those of carbaryl and propoxur (Table 1). The structures of isoprocarb and fenobucarb are comparable with that of metolcarb, but with different R groups. Conversely, propoxur features a more complex R group, which result results in a lower adsorption capacity. However, the greater steric hindrance effects of the naphthalene ring in carbaryl result in the lower adsorption capacity obtained.
13
Table 1. Competitive loading of metolcarb, propoxur, carbaryl, isoprocarb and fenobucarb by MIL@MIP and MIL@NIP MIL@MIP
MIL@NIP
metolcarb
1.3245
0.4534
Loading capacity
propoxur
0.1523
0.2378
(mg g−1)
carbaryl
0.1348
0.2094
isoprocarb
0.3513
0.4207
fenobucarb
0.2344
0.2564
metolcarb
152.67
47.49
propoxur
15.47
24.36
carbaryl
13.67
21.39
isoprocarb
36.41
43.92
fenobucarb
24.00
26.31
propoxur
9.87
1.95
carbaryl
11.17
2.22
isoprocarb
4.19
1.08
fenobucarb
6.36
1.81
propoxur
5.06
carbaryl
5.03
isoprocarb
3.88
fenobucarb
3.51
Kd
K
K'
Kd, distribution coefficient, K {(C C ) / C } {volume of solution (mL)}/{mass of gel (g)} . d
i
f
f
Where Ci and Cf represent the initial and final concentrations, respectively. K, selectivity coefficient, K K (metolcarb)/K (competitors) . d
d
K ', relative selectivity coefficient, K' K / K . MIP
NIP
14
3.3 Evaluation of binding of the MIL@MIP-modified QCM crystal electrode
A PVC-modified QCM sensor did not show any detectable frequency response to metolcarb at selected concentrations, thus indicating that PVC, which was used to immobilize the MIP on the electrode surface, did not affect the specific recognition of metolcarb by the proposed sensor. The binding capacity of the prepared MIL@MIP is one key parameter that must be determined. Accordingly, solutions containing the analyte molecule at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, and 2.0 mg L−1 in H2O were exposed to the MIL@MIP–QCM sensor, and results are presented in Fig. 1. As observed, Δf increased with increasing metolcarb concentrations. This increase was attributed to the imprinting of MIP with metolcarb, whereby cavities formed during polymerization. The generated cavities could specifically fit the target molecule (metolcarb) in terms of spatial structure and functional groups. At metolcarb concentrations greater than 1.00 mg L−1, the frequency response remained constant owing to the saturation of MIP with metolcarb. A good linear relationship between the frequency change and concentration was obtained within a metolcarb concentrations range of 0.1–0.9 mg L−1 (r2 = 0.9868). The standard deviations (SDs) of the results were 1.3–4.2% (n = 3); indicating that the analysis of metolcarb in pear juice samples using the prepared MIL@MIP-QCM sensor is stable and reproducible.
15
Fig. 1
3.4 Reproducibility and stability
The reproducibility and stability of the developed QCM are important features for successful metolcarb detection. Therefore, the frequency response of the MIL@MIP–QCM sensor in H2O containing metolcarb (1.0 mg L−1) was measured consecutively 10 times. After each test, the imprinted sensor was washed with 0.1 M HCl and DDW until the original resonance frequency was recovered. The frequency change during the repeated testing decreased slightly from 700.3 to 680.1 Hz, corresponding to a loss of just 2.9% only, thereby confirming the good recyclability and stability of the MIL@MIP–QCM sensor toward metolcarb detection. The stability of the MIL@MIP–QCM sensor over a long period of time was also demonstrated. After hermetic storage at room temperature for 6 months, the average frequency shift 16
of the quartz crystal was 665.0 Hz, which was only 5.0% lower than the initial frequency shift of 700.3 Hz. This result further confirmed the excellent stability of the developed MIL@MIP–QCM sensor and MIL@MIP.
3.5 Evaluation of sample analysis
Using the established sample pretreatment method, the concentration of metolcarb in pear juice samples, which were spiked at three concentrations (0.2, 0.4 and 0.8 mg L−1), was measured using the MIL@MIP–QCM sensor. The recovery for the measurements ranged from 74.16% to 96.2%, indicating that the prepared MIL@MIP–QCM sensor could be used in practical application to accurately determine metolcarb. The measured detection limit was 0.0689 mg L-1 within the linear range of 0.1–0.9 mg L−1 in pear juice with a relative standard deviations (RSDs) of 0.24–2.27% (n = 3).
4. Conclusion
The current study presented an efficient method to synthesize novel porous hybrid materials, specifically, MOFs-supported surface–imprinted nanoparticles. The synthesized MIL@MIP featured improved thermal stability, BET SSA, and the kinetic adsorption rate when compared with MIP. In view of the satisfactory performance of MIL@MIP, we believe that the findings of the current study could be used further to advance progress in MIT.
Acknowledgments 17
This work was supported by Project supported by the National Science Foundation for Distinguished Young Scholars of China (Grant No. 31225021), National Basic Research Program (973) of China (Project No.2012CB720803), Innovation Talents of Science and Technology Plan of Yunnan Province (Project No. 2012HA009), and National High-tech R&D Program (863 Program) financial supports from the Ministry of Science and Technology of China (Project No. 2012AA101604).
18
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Figure Captions Scheme 1.
Synthesis
procedure of MIL-101 supported surface–imprinted
nanoparticles. Fig. 1. Frequency responses of MIL@MIP–QCM sensors in solutions containing metolcarb at different concentrations.
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Scheme 1. Synthesis procedure of MIL-101 supported surface-imprinted nanoparticles.
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Fig. 1. Frequency responses of MIL@MIP-QCM sensors in solutions containing metolcarb at different concentrations.
Table 1. Competitive loading of metolcarb, propoxur, carbaryl, isoprocarb and fenobucarb by MIL@MIP and MIL@NIP MIL@MIP
MIL@NIP
metolcarb
1.3245
0.4534
Loading capacity
propoxur
0.1523
0.2378
(mg g−1)
carbaryl
0.1348
0.2094
isoprocarb
0.3513
0.4207
fenobucarb
0.2344
0.2564
metolcarb
152.67
47.49
propoxur
15.47
24.36
carbaryl
13.67
21.39
isoprocarb
36.41
43.92
Kd
23
K
K'
fenobucarb
24.00
26.31
propoxur
9.87
1.95
carbaryl
11.17
2.22
isoprocarb
4.19
1.08
fenobucarb
6.36
1.81
propoxur
5.06
carbaryl
5.03
isoprocarb
3.88
fenobucarb
3.51
Kd, distribution coefficient, K {(C C ) / C } {volume of solution (mL)}/{mass of gel (g)} . d
i
f
f
Where Ci and Cf represent the initial and final concentrations, respectively. K, selectivity coefficient, K K (metolcarb)/K (competitors) . d
d
K ', relative selectivity coefficient, K' K / K . MIP
NIP
Highlights
Metal–organic frameworks supported surface–imprinted nanoparticles (MIL@MIP) had been prepared.
A quartz crystal microbalance sensor based on of MIL@MIP for the sensitive detection of metolcarb is constructed, and could be used for other small-molecules analysis.
Ultrasensitive, selectivity and specific quantification of metolcarb had been achieved.
This study presented an efficient method to synthesize novel porous hybrid materials.
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