Metal-organic framework wrapped with molecularly

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C3N4 nanosheets/Metal-organic framework wrapped with molecularly imprinted polymer sensor: Fabrication, characterization and electrochemical detection of furosemide Yanying Wang, Jing Cheng, Xin Liu, Fang Ding, Ping Zou, Xianxiang Wang, Qingbiao Zhao, and Hanbing Rao ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04179 • Publication Date (Web): 08 Nov 2018 Downloaded from http://pubs.acs.org on November 9, 2018

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ACS Sustainable Chemistry & Engineering

C3N4 nanosheets/Metal-organic framework wrapped with molecularly imprinted polymer sensor: Fabrication, characterization and electrochemical detection of furosemide

Yanying Wang1 †, Jing Cheng1 †, Xin Liu1, Fang Ding2, Ping Zou1, Xianxiang Wang1, Qingbiao Zhao3*, Hanbing Rao1*

1

College of Science, Sichuan Agricultural University, Xin Kang Road, Yucheng

District, Ya’an 625014, P. R. China 2

Nanshan District Key Lab for Biopolymers and Safety Evaluation, Shenzhen Key

Laboratory of Polymer Science and Technology, Guangdong Research Center for Interfacial Engineering of Functional Materials, College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, P. R. China 3

Key Laboratory of Polar Materials and Devices, Ministry of Education, Department

of Electronic Engineering, East China Normal University, Shanghai, 200241 P. R. China

†These authors contributed equally to the work. *Corresponding

authors

Qingbiao Zhao E-mail address: [email protected] Hanbing Rao E-mail address: [email protected]

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ABSTRACT: Zeolite imidazole skeleton material 8 (ZIF-8) has high porosity and specific surface area, excellent water stability and is convenient to synthesize. In this study, an original electrochemical imprinting sensor based on the modified glassy carbon electrode (GCE) with C3N4 nanosheets and framework ZIF-8 combined with MIP (ZIF-8@MIP) is developed for the sensitive detection of furosemide. MIP was formed by precipitation polymerization of ZIF-8 with furosemide as template and methacrylic acid (MAA) as monomer, and furosemide was detected by differential pulse voltammetry(DPV).Under the optimized conditions, the DPV response of C3N4/ZIF-8@MIP/GCE to furosemide was linear at 0.08-100 μM, with the detection limit (LOD) as low as 8 nM (S/N = 3). The sensor exhibits good selectivity, high sensitivity, superior stability and reproducibility. Thus, this method possesses high potential for the detection of furosemide in human urine specimens and furosemide tablets.

Key words: Molecularly imprinted polymers; C3N4 nanosheets; ZIF-8; Furosemide; Electrochemical sensor

INTRODUCTION Furosemide (2-(2-furylmethyl)amino-5-(sulfonylamino)-4-chlorobenzoic acid) (Figure. S1) is an anthranilic acid derivative. A significant increase in urine output is caused by obstructing the absorption of salts and fluids in the renal tubules. Furosemide is often used as a diuretic. As the dosage increases, the diuretic effect is significantly enhanced, and the drug dosage range is quite broad. 1 Due to its diuretic properties, furosemide is an effective medicine for renal insufficiency, congestive heart failure, high blood pressure, cirrhosis and chronic renal failure. Like other diuretic drugs, furosemide can be illegally used to mask other drugs by reducing its concentration in the urine,2

and has been classified as a stimulant in sports.

3

Therefore, rapid and precise monitoring of furosemide in biological fluids is very important in stimulant control as well as in clinical practice. Several methods for


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determining pharmaceutical agents and furosemide in biological fluids have been reported,

including

spectrophotometry,4

fluorescence spectrophotometry,

6-8

chemiluminescence

flow

micellar liquid chromatography,9

injection,5

and HPLC.10

Compared with these techniques, electrochemical analysis possesses the advantages of simple operation, low cost, short analysis time and high sensitivity. However, most electrochemical techniques have no specificity or affinity for the analyte. Therefore, molecular imprinting technique was introduced in this study. Molecular imprinting technology (MIT) is a technique in which a functional monomer, a template molecule, an initiator and a crosslinking agent are polymerized in a suitable solvent to obtain a solid polymer, and the template molecule is removed with appropriate method.

11

The obtained polymers (MIPs) have cavities that

correspond to the structure of the target molecule and match the binding sites, and the target molecules can be identified by strong chemical interactions (ion interaction, hydrogen bonding).

12

MIPs have strong selectivity and high affinity for the template

molecule. The imprinting sensor combines the MIPs membrane with an electrochemical sensor to measure the target molecule by monitoring the output signal. 13

MIP has been widely used in various fields. However, the molecular imprinting

sensor has lower sensitivity due to poor conductivity.14 The number of molecularly imprinted cavities were increased by the addition of ZIF-8 as the framework. Furosemide has more binding sites with MIP to enhance DPV current response. The conductivity of the modified electrode was enhanced by using C3N4 nanosheets. MOFs, assembled from the apex of metal ions and an organic bridging ligand, are porous coordination polymers. 15 It is an emerging type of porous crystal materials with large surface area and high porosity.

16

Because of their unique properties, such

as the feasibility of external surface modification and pore size adjustability, they been widely used in gas storage and separation, 17 chemical sensing, 18 catalysis19 and drug delivery,20 etc. As an important MOF material, zeolite imidazole skeleton material 8 (ZIF-8) has attracted extensive attention due to its permanent pores, open metal sites, excellent water stability and ease of synthesis.

21

The metal-imidazole

MOF is termed "zeolite" because it has a feature similar to the 145° Si-O-Si angle



observed in the zeolite and has a zeolite-like topology.

22

ZIF-8 (Zn) consists of an

organic imidazole ligand coordinated to a zinc ion. Owing to its high porosity, large surface area, as well as the π-π interaction with furosemide, it is used as a framework in combination with MIP for the detection of furosemide in this study. Graphitic carbon nitride (g-C3N4) is a new class of polymeric semiconductor material. It has a layered structure, and there is a van der Waals interaction between adjacent C-N layers.

23-24

The Single or several layers of structure can significantly

contribute to faster carrier transport from the interior to the surface. It possess unique attributes, such as low density, high hardness, water stability, biocompatibility, chemical inertness and wear resistance,25-26 and are expected to be applied to optoelectronic nano-devices, metal-free photocatalysis and chemical sensors. G-C3N4 has been synthesized in many different forms, such as nanoparticles, nanowires, nanobelts, and hollow containers.27 Also, carbon nitride materials are of low cost, environment-friendly and easy to obtain. Herein, a new kind of electrochemical sensor based on C3N4/ZIF-8@MIP coating is proposed for electrochemical quantitative analysis of diuretic furosemide. As shown in Scheme 1, ZIF-8@MIP was synthesized by precipitation polymerization with furosemide present in the solution. GCE was modified with C3N4 nanosheets and ZIF-8 @ MIP. After removing furosemide from the ZIF-8 @ MIP membrane, the sensor can detect furosemide by DPV through π-π stacking interactions and hydrogen bonding.

12

GCE was coated with C3N4 nanosheets to improve the effective active

surface area of the electrode and increase the conductivity. ZIF-8 (Zn), with a framework structure, increases the molecular imprinting cavities of MIP and improves the sensitivity for electrochemical determination of furosemide. This sensor exhibits good selectivity, reproducibility, high sensitivity, and broad linear range, and was successfully used for determination of furosemide in biological fluids.


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Scheme 1. Flow chart for preparation of C3N4/ZIF-8@MIP/GCE and electrochemical detection of furosemide.

EXPERIMENTAL SECTION All reagents, equipment and experimental procedures are detailed in the Supporting Information.

RESULTS AND DISCUSSION The morphology, crystal structure, elemental composition and valence states of the synthesized materials and MIP were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). From Figure. 1A and Figure. 2A one can observe that the C3N4 nanosheets have a porous sheet structure. As shown in Figure. 1B and C and Figure. 2B, ZIF-8 has a 3-D dodecahedral structure, while ZIF-8 @ MIP has a wrapped irregular spherical morphology. As shown in the TEM image of ZIF-8@MIP (Figure. 1E) and the EDS spectrum of the electrode (Figure. S2), ZIF-8 is completely wrapped by MIP. Figure. 1D shows an SEM images of the C3N4/ZIF-8@MIP on the modified electrode



surface. The C3N4/ZIF-8@MIP/GCE surface has a large number of pores and a rough surface.

Figure. 1 SEM image of (A) C3N4 nanosheets, (B) ZIF-8, (C) ZIF-8@MIP, (D) C3N4/ZIF-8@MIP/GCE and (E) TEM images of ZIF-8@MIP.


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Figure. 2 (a) TEM image of C3N4 nanosheets (b) TEM image of ZIF-8.

The phase of g-C3N4 (Figure. 3A a) and C3N4 porous nanosheets (Figure. 3A b) was analyzed by XRD. The XRD pattern of the g-C3N4 has two characteristic diffraction peaks at 12.8° (100) and 27.4° (002).28 The two characteristic peaks are due to the interlayer packing of the aromatic system and inter-layer structure filling of the tetragonal g-C3N4 phase (JCPDS 87-1526).29 For the XRD pattern of the C3N4 porous nanosheets treated by ultrasonic hydrothermal process, the peak intensity of (002) was significantly reduced, the peak of (100) almost disappeared, and the structure was changed. The XRD pattern of the prepared ZIF-8 crystal (Figure. 3B a) shows a sharp peak consistent with the simulated XRD pattern of ZIF-8 obtained from the Cambridge Crystallography Data Center (CCDC 602542).22, 30 The peak shape of the XRD pattern (Figure. 3B b, c) of ZIF-8@MIP obtained by precipitation polymerization changed significantly, and the characteristic peak of ZIF-8 did not appear, further indicating that ZIF-8 was completely encapsulated by MIP. After elution of the template molecule, the XRD pattern changed, indicating the generation of imprinted pores.



Figure. 3 (A) XRD patterns of g-C3N4(a) and C3N4 porous nanosheets (b) (B) XRD patterns of ZIF-8(a), ZIF-8@MIP before (b)and after(c) removing the template molecule.

As shown in Figure. 4, XPS analysis was performed for the C3N4 nanosheets (A-D). C1s peak at 284.6 eV in Figure. 4B is assigned to C=C or C-C, and the peak at 287.8 eV is derived from N-bonded sp2 C in the aromatic ring (N=C-(N)2), and the C 1s peak centered at 288.1 eV corresponds to sp2 C atoms in the N=C(N)-OH. The N 1s peak centered at 398.4 eV in Figure. 4C is attributed to nitrogen bonded to the sp2 hybrid aromatic carbon atom (C-N = C). The N 1s peak centered at 399.3 eV is associated with a hydrogen-carrying amino group (HN-(C)2, H2N-C) while the N 1s peak with 400.5 eV as the peak center corresponds to the nitrogen atom bonded to the carbon atom in the aromatic cycle. In Figure. 4D, the O 1s peak at 531.6 eV is attributed to N=C(N)-OH, and the peak at 532.9 eV is attributed to the adsorbed water.31 Figure. 4, E-H show the XPS spectrums of ZIF-8@MIP. As shown in Figure. 4F, C 1s is present as C-H or -C-C (284.8 eV), O-C or N-C (286.6 eV) and O=C-O (288.8 eV). Devolution of the N 1s peak (Figure. 4G) yielded two components, i.e., pyridine N (398.6 eV) and pyrrole N (399.5 eV).32 This phenomenon possibly results from a strong acid-base interaction between the amine site and the carboxyl group. In addition, the O 1s peak (Figure. 4H) at 532 eV was assigned to -OH, while the peak at 533.5 eV was because of the C=O bond in the polymer.


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Figure. 4 XPS spectrums of C3N4 nanosheets (A: full spectrum B:C 1s; C: N 1s; D: O 1s) and ZIF-8@MIP (E: full spectrum F:C 1s; G: N 1s; H: O 1s).



Element mapping was performed o study the elemental distribution of ZIF-8@MIP composites, ZIF-8, and C3N4 nanosheets. The result is shown in Figure. S3. ZIF-8@MIP (Figure. S3 A, B, C, D) contains elements such as C, N, O, and Zn. Among them, C and O elements are concentrated, while N and Zn elements are evenly distributed, indicating that ZIF-8 is more evenly distributed in MIP. The distribution of C, N, O and Zn in ZIF-8 (Figure. S3 E, F, G, H) is uniform. The O element is also included in the C3N4 (Figure. S3 I, J, K) nanosheets material, which is consistent with the XPS results. Brunner-Emmet-Teller measurement (BET) was performed to assess the porosity characteristics and specific surface area of ZIF-8. A distinct isotherm hysteresis loop was found from the N2 adsorption-desorption isotherm diagram for ZIF-8 (Figure. 5A). On the basis of the International Union of Pure and Applied Chemistry (IUPAC) classification system, the adsorption isotherm of ZIF-8 prepared is classified as type IV, revealing that the material has a mesoporous framework.33 The pore size distribution of ZIF-8 is shown in Figure. 5B. The pores are mainly mesopores from 2 nm to 50 nm, and there are also large pores of >50 nm in size and no micropores (

Metal-organic framework wrapped with molecularly

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