Novel nanocomposite and metronidazole detection use thereof

Abstract

The present invention relates to a novel nanocomposite comprising reduced graphene oxide and LFO nanoparticles, and a metronidazole detection use thereof. The LFO / rGO nanocomposite of the present invention was prepared using a simple and eco-friendly method, and it has been identified that, compared to a conventional MTZ sensor, an electrode on which the nanocomposite prepared in this way is deposited can detect and quantify MTZ with a wider linear range, a lower detection limit and superior sensitivity, and thus the present invention can be used for detecting MTZ remaining in a biosample or a food sample.

Description

Novel nanocomposites and their use for detecting metronidazole

[0001] The present invention relates to a novel nanocomposite comprising reduced graphene oxide and LFO nanoparticles and its use for detecting metronidazole.

[0002] Metronidazole (MTZ) is a widely used 5-nitroimidazole derivative first developed in the 1960s for its antibiotic and antimicrobial properties (J. Antimicrob. Chemother. 4 (1978) 97-111.). MTZ is used to treat a variety of diseases, including trichomonas, giardiasis, and anaerobic bacterial infections (Inorg. Chem. Commun. 140 (2022)). It is also effective against Crohn's disease and certain protozoa in humans. However, because MTZ is highly soluble and degrades slowly, it can accumulate in the aqueous environment, posing a serious health risk to humans and wildlife. Furthermore, its long half-life and high levels of the drug can persist for several hours after administration, further increasing the risk during lactation. Overdosage or long-term administration of MTZ in doses exceeding 2 g per day can cause serious neurological symptoms such as headaches, seizures, and nausea, as well as health problems such as optic neuropathy, peripheral neuropathy, and gastric irritation (Electrochim. Acta. 354 (2020), 136723). Therefore, there is an emerging need for the detection of MTZ in human and milk samples.

[0003] Accordingly, various methods have been developed to detect MTZ in biological and environmental samples and foods: flow injection (New Carbon Mater. 29 (2014) 216–224.), titrimetry (Med. Sci. 23 (2000) 20–21.), spectrophotometry (Spectrochim, Acta Part A Mol. Biomol. Spectrosc. 143 (2015) 281–287.), surface-enhanced Raman spectroscopy (Microchem. J. 121 (2015) 6–13.), capillary zone electrophoresis (Electrophor. An, Int. J. 21 (2000) 1409–1414.), chemiluminescence (Spectrochim, Acta Part A Mol. Biomol. Spectrosc. 234 (2020), 118272.), liquid There are chromatography-tandem mass spectroscopy (Analyst 125 (2000) 1533-1535.), thin layer chromatography (J. AOAC Int. 94 (2011) 1427-1439.), gas chromatography-mass spectrometry (Anal. Methods. 6 (2014) 1404-1411. [), and high-performance liquid chromatography (Chemosphere 119 (2015) S28-S34.). However, most of these methods have limitations such as being time-consuming, requiring expensive equipment, requiring specialized knowledge, and requiring complex pretreatment and analysis, which limits their practicality.On the other hand, electrochemical technology has the advantages of low cost, ease of handling, fast speed, high sensitivity, selectivity, accuracy, and excellent repeatability and reproducibility. Since the MTZ structure is a functional group that can be reduced in the electrochemical process, attempts have been made to detect it electrochemically. However, bare electrodes have low selectivity and sensitivity, and are not effective in MTZ detection due to the high potential and shift phenomenon of the electrochemical signal. Therefore, various chemically modified electrodes have been developed as working electrodes, but they still have the problem of low MTZ detection efficiency.

[0004] The purpose of the present invention is to provide a novel nanocomposite.

[0005] In addition, an object of the present invention is to provide an electrode comprising the nanocomposite.

[0006] In addition, it is an object of the present invention to provide a sensor for detecting metronidazole including the electrode.

[0007] In addition, it is an object of the present invention to provide a method for producing the nanocomposite.

[0008] In addition, an object of the present invention is to provide a method for manufacturing the electrode.

[0009] In addition, it is an object of the present invention to provide a method for detecting metronidazole.

[0010] To achieve the above purpose, the present invention provides a nanocomposite comprising reduced graphene oxide and LFO nanoparticles.

[0011] In addition, the present invention provides an electrode comprising the nanocomposite.

[0012] In addition, the present invention provides a sensor for detecting metronidazole including the electrode.

[0013] In addition, the present invention provides a method for producing the nanocomposite.

[0014] In addition, the present invention provides a method for manufacturing the electrode.

[0015] In addition, the present invention provides a method for detecting metronidazole.

[0016] In the present invention, an LFO / rGO nanocomposite was manufactured by a simple and environmentally friendly method, and it was confirmed that an electrode depositing the manufactured nanocomposite can detect and quantify MTZ with a wide linear range, low detection limit, and superior sensitivity compared to a conventional MTZ sensor. Therefore, it can be utilized for the purpose of detecting MTZ remaining in biological or food samples.

[0017] Figure 1 is a schematic diagram showing the synthesis and manufacturing process of LFO / rGO nanocomposites for use in MTZ detection.

[0018] Figure 2 shows the XRD patterns of LFO, rGO, and LFO / rGO (a), the crystallographic structure of LFO (b), the FTIR spectra of LFO, rGO, and LFO / rGO nanocomposites (c), and the Raman spectra (d).

[0019] Figure 3 shows the N2 adsorption-desorption isotherm (a) and the pore diameter (b) of the LFO / rGO nanocomposite.

[0020] Figure 4 shows the XPS survey scans (a and e), C 1 s spectra (inner graph of e) of LFO and LFO / rGO nanocomposites, and high-resolution binding energies of La 3d (b and f), Fe 2p (c and g), and O 1 s (d and h) of LFO and LFO / rGO nanocomposites.

[0021] Figure 5 shows FESEM images of rGO (a), LFO (b and c), and LFO / rGO nanocomposites (d to f).

[0022] Figure 6 shows the TEM images (a to c) of LFO, the HRTEM image (d), the SAED pattern (e) of LFO, the elemental mapping using La (f), Fe (g) and O (h) elements, and the results of EDX analysis (i) of perovskite LFO.

[0023] Figure 7 shows TEM images (a to c), HRTEM images and SAED patterns (d), elemental mapping using La (e), Fe (f), O (g), and C (h) elements, and EDX analysis (i) results of LFO / rGO nanocomposites.

[0024] Figure 8 shows 0.1 M KCl and 5 mM [Fe(CN)6] 3- / 4- Nyquist plots (a) and CV curves (b) of pure GCE, LFO / GCE, rGO / GCE, and LFO / rGO / GCE in electrolyte solution at 50 mV s at 200 μM MTZ. -1 The CV analysis results (c) and the CV analysis results (d) for 200 μM MTZ at different loading volumes of LFO / rGO / GCE are shown in FIG.

[0025] GCE: Pure GCE;

[0026] LFO: LFO / GCE;

[0027] rGO: rGO / GCE; and

[0028] LFO / rGO: LFO / rGO / GCE.

[0029] Figure 9 shows the CV curves (a) and (b) at 200 μM MTZ in the LFO / rGO / GCE sensor using the supporting electrolyte 0.1 M PB (pH 3 to 11) at various pHs. pc vs pH and E pc vs pH plot (b), and the possible electrochemical mechanism of MTZ using the LFO / rGO / GCE sensor (c).

[0030] Figure 10 shows the CV curves (a) and (b) of the LFO / rGO / GCE sensor for various concentrations of MTZ. pc (b) Plots corresponding to the concentration of MTZ (50 to 500 μM) at 200 μM MTZ and at various scan rates (20 to 200 mV s -1 ) CV (c) of LFO / rGO / GCE, I pc and v 1 / 2 Relevance between (d), log I pc Plot of vs logv (e), and E pc This is a plot showing vs logv (all results at pH 7).

[0031] Figure 11 shows DPV curves (a) of various concentrations of MTZ (0.2 to 1221 μM) in the LFO / rGO / GCE sensor, and the MTZ concentration and I pc (b) and DPV curves (c) of LFO / rGO / GCE for MTZ (15 μM) in the presence of 50 μM of ODZ (ornidazole), DA (dopamine), Glu (glucose), AA (ascorbic acid), NaCl, ZnCl2, CaCl2, NaNO3, Na2SO4, Na2CO3 and RU (rutin) at pH 7 and their I pc This is a diagram showing reaction (d).

[0032] Hereinafter, the present invention will be described in detail with reference to the attached drawings and embodiments thereof. However, the following embodiments are provided as examples of the present invention. If a detailed description of a technology or configuration well known to those skilled in the art is judged to unnecessarily obscure the gist of the present invention, such detailed description may be omitted, and the present invention is not limited thereby. The present invention is capable of various modifications and applications within the scope of the following claims and equivalents interpreted therefrom.

[0033] Additionally, the terminology used in this specification is intended to appropriately express preferred embodiments of the present invention, and may vary depending on the intent of the user or operator, or the customs of the field to which the present invention pertains. Therefore, the definitions of these terms should be determined based on the contents throughout this specification. Throughout this specification, when a part is said to "include" a certain component, unless specifically stated otherwise, this does not mean that other components are excluded, but rather that other components may be included.

[0034] Unless otherwise defined, all technical terms used in this invention have the same meaning as commonly understood by those skilled in the art. While preferred methods and samples are described herein, similar or equivalent methods are also included within the scope of the present invention. The contents of all publications cited herein as references are incorporated herein by reference.

[0035] In one aspect, the present invention relates to a nanocomposite comprising reduced graphene oxide (rGO) and lanthanum ferrite (LFO) nanoparticles.

[0036] In one embodiment, the nanocomposite of the present invention may comprise reduced graphene oxide nanosheets and LFO nanoparticles disposed on the nanosheets.

[0037] In one embodiment, the nanocomposite of the present invention may include reduced graphene oxide nanosheets and LFO nanoparticles in a weight ratio of 1:2 to 1:10.

[0038] In one embodiment, the nanocomposite of the present invention has a particle size of 40 to 80 m 2 / g can represent the specific surface area (BET).

[0039] In one embodiment, the nanocomposite of the present invention may be porous.

[0040] In one embodiment, the nanosheets included in the nanocomposite of the present invention may have a wrinkled surface and a layered structure, and the nanoparticles may be uniformly distributed on the nanosheets.

[0041] In one embodiment, the nanocomposite of the present invention may include a layer of rGO nanosheets and LFO nanoparticles.

[0042] In one embodiment, the rGO nanosheet of the nanocomposite of the present invention may be formed as a monolayer or two or more layers (multi-layer).

[0043] In one embodiment, the nanocomposite of the present invention may be used for electrode modification.

[0044] In the present invention, the term "nanosheet" may resemble a two-dimensional material that may have a single or several single layer thickness and may have a transverse (in-plane) dimension of hundreds of nanometers to tens of micrometers.

[0045] In one aspect, the present invention relates to a composition for forming an electrode comprising the nanocomposite of the present invention.

[0046] In one embodiment, the composition may be an electrode modifier.

[0047] In one aspect, the present invention relates to an LFO-rGO nanocomposite electrode in which the nanocomposite of the present invention is disposed on an electrode surface.

[0048] In one embodiment, the electrode may be a working electrode.

[0049] In one embodiment, the electrode may be a silver (Ag), palladium (Pd), gold (Au), platinum (Pt) or glassy carbon (GC) electrode, and is more preferably a glassy carbon electrode (GCE).

[0050] In one embodiment, the electrode may be for detecting metronidazole (MTZ).

[0051] In one embodiment, the metronidazole may be dissolved in a sample, and the sample may be in a liquid form and may be provided as a biological sample such as a body fluid, urine, plasma, blood, serum, tissue, cells, lymph, and feces; an environmental sample such as a water sample, a soil sample, a soil leachate, and a rainwater sample; a food sample such as milk; and / or an artificial sample that implements conditions similar to the biological sample.

[0052] In one aspect, the present invention relates to a sensor for detecting metronidazole, comprising an electrode of the present invention.

[0053] In one embodiment, the electrode may be a working electrode.

[0054] In one embodiment, the sensor may use a supporting electrolyte having a pH of 6 to 8.

[0055] In one embodiment, the LOD of the sensor may be 0.01 to 0.1 μM, and the sensitivity may be 0.1 to 0.5 μA μM. -1 cm -2 It could be.

[0056] In one embodiment, the sensor may include the electrode and a supporting substrate, wherein the supporting substrate may be glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), or polycarbonate (PC).

[0057] In one aspect, the present invention relates to a method for producing LFO nanoparticles; producing graphene oxide; producing reduced GO (rGO) nanosheets by thermal reduction of the graphene oxide; and producing an LFO-rGO nanocomposite by ultrasonic treatment.

[0058] In one embodiment, the sonication step may be to sonicate the reduced GO nanosheets to dissolve them in a solvent, and then add LFO nanoparticles and sonicate them.

[0059] In one embodiment, 200 to 1000 parts by weight of LFO nanoparticles may be added to 100 parts by weight of the reduced graphene oxide nanosheets.

[0060] In one aspect, the present invention relates to a method for manufacturing an LFO-rGO nanocomposite electrode, comprising the steps of dispersing the nanocomposite of the present invention in a solvent; and depositing the nanocomposite on the surface of an electrode.

[0061] In one aspect, the present invention relates to a method for detecting metronidazole in a sample, comprising the step of contacting the test sample with an electrode of a sensor for detecting metronidazole of the present invention.

[0062] In one embodiment, the method may further include a step of performing DPV (differential pulse voltammetry) after contacting the electrode of the sensor with the sample.

[0063] In one embodiment, the sample may be liquid and may be a biological sample such as body fluid, urine, plasma, blood, serum, tissue, cells, lymph, and feces; an environmental sample such as a water sample, a soil sample, a soil leachate, and a rainwater sample; a food sample such as milk; and / or an artificial sample that implements conditions similar to the biological sample.

[0064] In one aspect, the present invention relates to a method for quantitatively determining MTZ in a sample, comprising the steps of: obtaining a quantitative calibration curve according to the MTZ concentration in the sensor of the present invention; contacting a test sample with an electrode of the sensor for detecting metronidazole of the present invention; and performing DPV (differential pulse voltammetry).

[0065] In one embodiment, metronidazole can be quantified using the above method.

[0066] The present invention is described in more detail through the following examples. However, the following examples are intended only to concretize the content of the present invention and are not intended to limit the present invention.

[0067] Example 1. Preparation of LFO / rGO / GCE electrode

[0068] 1-1. Manufacturing of LFO nanoparticles

[0069] LFO nanoparticles were synthesized using a reflux condenser-based polyol method. Specifically, 5 mM La(NO3) 3· 6H2O and Fe(NO3) 3· 9H2O was dissolved in 100 mL of C2H6O2 in a round-bottom flask and placed in a reflux condenser on an oil bath with a stirrer. When the temperature reached 180°C, it was stirred for an additional 30 minutes, and then an optimized amount of KOH solution was added through the condenser gap. After stirring for an additional 3 hours, the resulting LFO (lanthanum ferrite) was dried in an oven at 50°C for 12 hours and then calcined at 800°C for 4 hours at a ramping rate of 5°C / min.

[0070] 1-2. Manufacturing of LFO / rGO nanocomposite

[0071] Graphene oxide (GO) was prepared using a modified Hummer's method, then thermally reduced to produce reduced GO (rGO). Approximately 2 mg of the product was sonicated for 1 h to completely dissolve it in 30 mL of ethanol. Approximately 10 mg of LFO was then added, sonicated for 1 h, and the resulting product was washed three times with ethanol and dried to obtain an LFO / rGO nanocomposite.

[0072] 1-3. Manufacturing of LFO / rGO / GCE electrodes

[0073] The LFO / rGO nanocomposite prepared above was dissolved in 1 mL of Millipore water and sonicated. Then, 6 μL of the evenly dispersed LFO / rGO solution was ground with alumina paste (0.05 μm) and dried. A glassy carbon electrode (GCE) was dropped onto the surface and treated, and dried at 50°C for 10 minutes to prepare an LFO / rGO / GCE electrode (Fig. 1).

[0074] Example 2. Morphological Characterization of LFO / rGO Nanocomposites

[0075] 2-1. XRD analysis

[0076] The crystalline phase, purity and structure of LFO, rGO and LFO / rGO nanocomposites were analyzed by X-ray diffraction (XRD). Sharp and distinct diffraction peaks of LFO were observed at 2θ values ​​of 22.60°, 32.19°, 39.67°, 46.14°, 51.99°, 57.39°, 67.34°, 72.06° and 76.64° (Fig. 2a), which were in agreement with the orthorhombic structure of LFO (JCPDS No. 00-037-1493) (Fig. 2b) with space group and space number of Pnma and 62, respectively. (204) plane. The crystal parameters were a (Å): 5.5669, b (Å): 7.8547, and c (Å): 5.5530, confirming that the perovskite LFO was highly pure and free of impurities. In addition, a slightly broader peak was observed at 2θ values ​​of approximately 24-26°, which corresponds to the (002) plane of rGO (Fig. 2a). The diffraction peaks of LFO and rGO confirmed in this way were also observed in the analysis results of the LFO / rGO nanocomposite, indicating that the LFO nanoparticles were successfully modified on the rGO nanosheets to form the LFO / rGO structure.

[0077] 2-2. FTIR spectroscopy analysis

[0078] To identify the functional groups of LFO, rGO, and LFO / rGO nanocomposites, they were analyzed by Fourier transform infrared (FTIR) spectroscopy. As a result, the 584 cm -1A sharp band due to the Fe-O stretching mode appeared in the perovskite LFO, confirming octahedral FeO6, and a band at 1639 cm corresponding to the bending vibration and stretching vibration of HOH and OH groups. -1 and 3428 cm -1 A broad band appeared in (Fig. 2c). In addition, the 1231 cm of the rGO spectrum -1 , 1611 cm -1 , 1727 cm -1 and 3438 cm -1 The bands observed in are due to C-OH, C=C, C=O, and OH stretching vibrations, respectively (Fig. 2c). In the FTIR spectrum of LFO / rGO, bands of the functional groups of LFO and rGO were observed (Fig. 2c), confirming the successful composition of the LFO / rGO nanocomposite.

[0079] 2-3. Raman spectroscopy analysis

[0080] The Raman spectra of LFO, rGO and LFO / rGO nanocomposites were analyzed. The Raman active bands in the LFO spectrum were A and B of La-O and Fe-O vibrations, respectively. g and B 3g 286 cm corresponding to the mode -1 and 418 cm -1 It appeared in, “O2 - ” 1301 cm associated with two-photon scattering -1 bands also appeared (Fig. 2d). The rGO spectrum showed structural disorder (or defect) and sp 2 342 cm related to the vibration of the C molecule -1 and 1578 cm -1 Two prominent bands (D and G) were observed in (Fig. 2d). The intensity ratio (I) of rGO and LFO / rGO D / IG ) were calculated as 0.852 and 0.837, respectively, and the reduced I of LFO / rGO D / I G The values ​​were sp during the preparation of LFO / rGO nanocomposites. 2 This indicates an increase in the amount of C atoms. All these Raman active bands were observed in the LFO / rGO nanocomposite, confirming that the LFO particles were effectively integrated into the rGO sheets.

[0081] 2-4. Porosity and surface area analysis

[0082] As a result of checking the surface area and porosity of the LFO / rGO nanocomposite, it was confirmed that the LFO / rGO nanocomposite had a mesoporous structure (Fig. 3), and as a result of calculating the BET (Brunauer-Emmett-Teller) surface area, LFO was 12.75 m 2 / g LFO / rGO nanocomposite is 58.08 m 2 / g, it was confirmed that the surface area of ​​the LFO / rGO nanocomposite was significantly increased compared to LFO.

[0083] Example 3. Analysis of chemical composition and elemental oxidation state of LFO / rGO nanocomposites

[0084] The chemical composition and elemental oxidation states of LFO and LFO / rGO nanocomposites were determined using X-ray photoelectron spectroscopy (XPS) (LFO: Fig. 4a and LFO / rGO nanocomposites (La 3d, Fe 2p, O 1s, and C 1s elements): Fig. 4e). As a result, three different peaks of C 1s spectra at 284.8 eV, 286.4 eV, and 288.9 eV were assigned to C-C or C=C, C-O, and C=O bonds, indicating the presence of rGO in the LFO / rGO nanocomposites (inserted graph in Fig. 4e). In Fig. 4b, La 3d in LFO 5 / 2and 3d 3 / 2 It exhibited deconvoluted peaks at 834.6 eV, 838.3 eV, 851.4 eV, 855.2 eV and 864.2 eV corresponding to La 3d and at binding energies of 834.1 eV, 837.7 eV, 850.9 eV, 854.8 eV and 863.8 eV in LFO / rGO, respectively. 5 / 2 and 3d 3 / 2 The peaks are shown in Fig. 4f. Two peaks (La 3d 5 / 2 and 3d 3 / 2 ) was 16.8 eV in both LFO and LFO / rGO, indicating that the oxidation state of La ion was +3. In addition, the Fe 2p spectrum of LFO was Fe 2p 3 / 2 and Fe 2p 1 / 2 Two prominent peaks corresponding to (Fig. 4c) were observed, which can be deconvoluted into four peaks at 710.5 eV, 712.2 eV, 723.6 eV, and 725.3 eV. The four peaks correspond to Fe in the LFO phase. 2+ (710.5 eV and 723.6 eV) and Fe 3+ (712.2 eV and 725.3 eV). Similarly, the LFO / rGO nanocomposite exhibited four main peaks of Fe 2p, with peaks at 709.6 eV and 711.5 eV corresponding to Fe 2+ and Fe 3+ Fe 2p of 3 / 2 is assigned to, and the peaks at 722.6 eV and 724.4 eV are Fe 2+ and Fe 3+ Fe 2p of 1 / 2are respectively assigned to (Fig. 4g). In addition, the O 1s spectrum exhibits two high-resolution peaks at 527.9 eV and 530.3 eV, which are associated with lattice oxygen (OL) and hydroxyl oxygen (OH), respectively, in LFO (Fig. 4d), while slightly shifted peaks at 527.5 eV and 529.8 eV for OL and OH in LFO / rGO nanocomposites (Fig. 4h). The results indicate that LFO nanoparticles are successfully integrated onto the rGO architecture, and the electron transfer between rGO nanosheets and LFO nanoparticles can be helpful for improving the electrochemical performance during the detection of substances such as metronidazole (MTZ).

[0085] Example 4. Surface morphology analysis of LFO / rGO nanocomposites

[0086] Since uniform distribution of LFO nanoparticles on the surface of rGO in the LFO / rGO nanocomposite is important for achieving excellent electrochemical performance, the surface morphologies of rGO, LFO, and LFO / rGO nanocomposite were analyzed by field emission scanning electron microscopy (FESEM). As a result, the rGO sheets showed a wrinkled surface and a layered structure (Fig. 5a), and LFO appeared as spherical particles almost uniformly distributed in the nanoscale (Figs. 5b and c). These uniformly formed LFO nanoparticles were found to be completely integrated with the rGO sheets (Figs. 5d to f), confirming that the LFO / rGO nanocomposite has a high surface area, which enhances the electrochemical performance, and prevents aggregation of LFO on the rGO surface, which is advantageous for maintaining the stability and durability of the nanocomposite.

[0087] Example 5. Structural Characterization of LFO / rGO Nanocomposites

[0088] 5-1. LFO

[0089] LFO was analyzed by transmission electron microscopy (TEM) to determine its structural and elemental properties. As a result, the TEM image of LFO showed that spherical particles with a size of less than 100 nm were uniformly formed and joined together in a chain-like structure (Figs. 6a to 6c). In Fig. 6d, a transparent lattice fringe with a d-space value of 0.278 nm corresponds to the (121) plane of perovskite LFO. The selected area electron diffraction (SAED) pattern showed diffraction planes of (121) and (220) for LFO, suggesting a single crystalline nature with an orthorhombic structure (Fig. 6e). Additionally, the elemental composition (Figs. 6f-h) and elemental spectrum (Fig. 6i) of LFO showed a uniform elemental distribution of La, Fe, and O with weight ratios of 55.1%, 19.7%, and 25.2%, respectively.

[0090] 5-2. LFO / rGO

[0091] TEM analysis of the LFO / rGO nanocomposite confirmed that LFO nanoparticles were successfully incorporated onto the rGO surface with effectively controlled particle agglomeration (Figs. 7a to c). The HRTEM image of the LFO / rGO nanocomposite showed a d-space lattice fringe of 0.278 nm (Fig. 7d), which was well matched with the orthorhombic structure of rGO nanosheets and LFO. The SAED pattern showed bright spots assigned to the diffraction planes of LFO / rGO, indicating the polycrystalline structure of the fabricated nanocomposite (inset of Fig. 7d). The presence of the LFO / rGO nanocomposite was verified using elemental mapping and EDX techniques, and the LFO / rGO nanocomposite was confirmed to be composed of La (50.27%), Fe (11.31%), O (19.43%), and C (18.99%) atoms (Figs. 7e to i).

[0092] Therefore, FESEM and TEM analyses confirmed that LFO nanoparticles were incorporated into rGO nanosheets, resulting in high surface area and conductivity, and enabling rapid electron transfer between the electrolyte and electrode interface.

[0093] Example 6. Charge transfer characteristics analysis

[0094] To investigate the charge transfer characteristics between the electrode surfaces of GCE, LFO / GCE, rGO / GCE, and LFO / rGO / GCE and the electrolyte, 0.1 M KCl and 5 mM [Fe(CN)6] 3- / 4- 0.1 Hz-10 using electrolyte 5 The analysis was performed using EIS at a voltage frequency of kHz and an amplitude potential of 5 mV. As a result, the R of pure GCE ct (charge transfer resistance) is 203 Ω, which is the same as that of the pure electrode and [Fe(CN)6]3- / 4- The behavior of the solution was shown, and the semicircle diameter of the EIS curve in the modified LFO / GCE was larger due to the lower electroconductivity of the LFO nanoparticles, resulting in a larger R ct The value (860 Ω) was obtained (Fig. 8a). After modifying rGO with GCE, the diameter of the semicircle was significantly reduced, indicating that R ct The R value decreased to 489 Ω, which was inferred to be due to the high surface area and conductivity of rGO (Fig. 8a). However, LFO / rGO / GCE had a smaller semicircle and lower R than LFO / GCE and rGO / GCE. ct (246 Ω), confirming that the synergistic action of the nanocomposite increases the conductivity of the electrode interface and reduces the resistance (Fig. 8a). This shows that the LFO / rGO / GCE electrode has a fast electron transfer rate and low charge resistance, which is advantageous for electrochemical reactions. In addition, the LFO / rGO / GCE electrode exhibited a high electron transfer rate and low charge resistance at 50 mV s -1 In 0.1 M KCl and 5 mM [Fe(CN)6] 3- / 4- The CV responses of various electrodes were confirmed in the redox probe, which were consistent with the EIS results (Fig. 8b). Compared to other electrodes, LFO / rGO / GCE showed the highest redox peak currents, confirming that LFO was incorporated into the rGO sheet and had excellent electrochemical activity. In addition, the electrochemically active surface area (EASA) values ​​of each electrode were calculated using the following mathematical equation (Randles-Sevcik Equation 1), and were 0.290, 0.306, and 0.319 cm for the LFO / GCE, rGO / GCE, and LFO / rGO / GCE electrodes, respectively. 2It was confirmed that LFO particles fused with rGO nanocomposites significantly increased the EASA of the electrode, providing more infiltration space for the electrolyte and thus faster electron transfer.

[0095]

[0096] * I p : I pa / I pc response;

[0097] n: electron transfer number in the redox probe (n = 1);

[0098] A: active electrode surface area (cm 2 );

[0099] D: diffusion coefficient (cm 2 s -1 );

[0100] C: concentration of ferricyanide solution (mol cm -3 ); and

[0101] v: scan rate (mV s -1 ).

[0102] Example 7. Electrochemical behavior analysis of MTZ of LFO / rGO / GCE electrode

[0103] 50 mV s -1 The electrochemical behavior of 200 μM MTZ in pure GCE, LFO-modified GCE, rGO-modified GCE, and LFO / rGO nanocomposite-modified GCE was analyzed in 0.1 M phosphate buffer (pH 7) solution with an optimized potential window of 0.3 V to -1.0 V using CV. As a result, in pure GCE, a lower reduction peak for MTZ was observed at -0.68 V (I pc= -7.04 μA) appeared (Fig. 8c), indicating a slow electron transfer rate. LFO / GCE was -0.69 V (E pc ) and an increased I of -10.10 μA. pc , which is attributed to the excellent electrocatalytic activity of perovskite LFO (Fig. 8c). In addition, rGO / GCE showed an improved I of -12.48 μA compared to pure GCE and LFO / GCE. pc It showed a potential reduction shift at -0.64 V, which was inferred to be due to the larger surface area of ​​rGO. LFO / rGO / GCE had a high I of -15.90 μA pc and was found to be significantly shifted toward MTZ at a reduction potential of -0.67 V (Fig. 8c). In addition, the I of MTZ in LFO / rGO / GCE pc The response was increased by 1.26, 1.56, and 2.25 times compared to rGO / GCE, LFO / GCE, and pure GCE, respectively. This confirmed that the electrocatalytic activity of the LFO / rGO nanocomposite toward MTZ was significantly higher.

[0104] Example 8. Selection of optimal parameters for MTZ detection of LFO / rGO / GCE

[0105] To improve the MTZ detection sensitivity of the electrochemical sensor, the catalyst loading volume, accumulation time, and supporting electrolyte of the modified electrode were optimized. For this purpose, 50 mV s -1 In the presence of 200 μM MTZ, the effect of various catalyst loadings (2, 4, 6, and 8 μL) on the modified LFO / rGO / GCE was investigated. As a result, the reduction current increased as the amount of modified electrode increased up to 6 μL, but when the amount of modifier increased from 8 μL, I pcThe reaction was found to decrease (Fig. 8d), which was inferred to be due to the thickening of the LFO / rGO layer, which increased the transfer resistance at the electrode interface and hindered electron transmission. Therefore, the optimal catalyst loading amount on the electrode was selected to be 6 μL. In addition, the I of MTZ pc The response increased with time and remained constant after 60 s due to surface saturation (data not shown), so the optimal accumulation time for voltammetric analysis was selected as 60 s. In addition, to confirm the effect of pH, CVs of 200 μM MTZ were performed in various supporting electrolytes (pH 3-11), and the results showed that I for MTZ pc As the pH increased from 3 to 7, it increased significantly, and as it increased from 9 to 11, it decreased (Fig. 9a), so the optimal electrolyte for MTZ detection was selected as 0.1 M PB at pH 7. In addition, using the regression equation of the following mathematical expression 2, E pc A linear plot was drawn between and pH (Fig. 9b). In addition, to calculate the m / n ratio, the slope of -0.037 obtained here was used in the following mathematical equation (Nernst Equation).

[0106]

[0107]

[0108] *m: e who participated in MTZ reduction - number of; and

[0109] n: H who participated in MTZ reduction + The number of.

[0110] The m / n calculated through the above mathematical equation 3 is -62 mV / pH, which is close to the Nernst theoretical value of -59 mV / pH, and is used in the electrochemical detection of MTZ. - ) and proton (H +) indicates that the equivalent transfer occurred. The possible electrochemical mechanism of MTZ is shown in Fig. 9c, and in step I, the reduction (R) of MTZ in LFO / rGO / GCE is 4e from the nitro group (-NO2) to the hydroxylamine derivative (-NHOH). - and 4H + , and then in step II, 2e from a hydroxylamine derivative to a nitroso derivative (-NO) - and 2H + participates in the oxidation (O) of MTZ in LFO / rGO / GCE.

[0111] Example 9. Analysis of MTZ detection performance of LFO / rGO / GCE

[0112] 9-1. MTZ detection suitability analysis

[0113] In order to confirm the MTZ detection ability of the LFO / rGO / GCE of the present invention, CV curves were derived for MTZ at various concentrations (50 to 500 μM) at pH 7. As a result, as the concentration of MTZ increased, I pc was significantly increased (Fig. 10a), and MTZ concentration and I pc A linear relationship was obtained between I pc The excellent electrochemical performance of GCE modified with LFO / rGO for MTZ reduction was demonstrated by the following mathematical equation 4 (Fig. 10b). In addition, to confirm the electrochemical reaction kinetics of MTZ, the electrochemical potentials of LFO / rGO / GCE were measured at 20 to 200 mV s at 200 μM MTZ. -1 As a result of performing CV at a scan rate of 200 mV s -1 Until I pc was found to increase linearly (Fig. 10c). I pc Wow v 1 / 2The relationship between (the square root of the scan rate) was linear, and the regression equation was expressed as Equation 5 below, indicating a diffusion-controlled electrochemical process on the surface of the modified LFO / rGO electrode (Fig. 10d). As shown in Fig. 10e, the log I pc And the log v showed a linear graph, and the regression equation was fitted with mathematical equation 6. The slope value of 0.45 corresponded to 0.5, further confirming the diffusion-controlled electrochemical reaction mechanism of MTZ in LFO / rGO / GCE. In addition, by changing the scan sweep, the reduction potential (E) of MTZ pc ) moved to the opposite side (negative side). E pc The plot between and log v is shown in Fig. 10f, and the linear regression equation is expressed by Equation 7. The number of electrons transferred (n) during the electrochemical reduction of MTZ in LFO / rGO / GCE was calculated using Equations 8 and 9 assuming that the slope value of 0.035 is equal to 2.303RT / αnF. The α value for the electrochemical detection of MTZ using LFO / rGO / GCE calculated through Equation 9 was calculated to be 0.412, and the number of electrons n derived by applying this to Equation 8 was 4.10 (~4e - ) was determined. Therefore, it was confirmed that four electrons and four protons were transferred during the irreversible electrochemical reduction of MTZ in LFO / rGO / GCE. This confirmed that LFO / rGO / GCE is suitable for MTZ detection.

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] * R: gas constant;

[0120] F: Faraday constant;

[0121] T: temperature; and

[0122] α: Electron transfer coefficient determined by mathematical expression 9.

[0123]

[0124] * E p : formal potential;

[0125] E p / 2 : 1 / 2 of the format potential value.

[0126] 9-2. Detection limit

[0127] MTZ was detected using the LFO / rGO / GCE sensor by differential pulse voltammetry (DPV), an electrochemical method with high sensitivity and low detection limit, under the optimal detection conditions derived from Example 8 above. As a result, as the MTZ concentration increased from 0.2 to 1221 μM, I pc The response increased linearly at -0.61 V (Fig. 11a). MTZ concentration and I pc The calibration curve showed a single linear range from 0.2 to 1221 μM, and the regression equation was expressed as Equation 10, showing good linearity for the determination of MTZ (Fig. 11b). The limit of detection (LOD) and sensitivity of MTZ in LFO / rGO / GCE were calculated using Equations 11 and 12 below. The calculated LOD and sensitivity were 0.048 μM and 0.241 μA μM. -1 cm -2, which showed significantly superior performance in MTZ detection with lower LOD and wider linear range compared to previously known MTZ detection sensors (Table 1). This excellent performance is attributed to the high surface area, better conductivity, and excellent electrocatalytic activity of the rGO nanocomposite containing LFO.

[0128]

[0129]

[0130]

[0131]

[0132] a : Polydopamine / carboxylic multi-walled carbon nanotubes;

[0133] b : Ag-nanoparticles / ionic-liquid modified screen-printed carbon electrode;

[0134] c : Duplex molecularly imprinted polymer modified carbon paste electrode;

[0135] d : Boron doped diamond electrode;

[0136] e : Copper-poly (cysteine);

[0137] f : Partially reduced graphene oxide;

[0138] g : Poly(diallyldimethylammonium chloride)-graphene oxide hydrogel;

[0139] h: Nanoporous carbon;

[0140] i : Nitrogen-doped graphene nanosheets decorated gold nanoparticles;

[0141] j : Poly(chromotrope 2B);

[0142] k : Molecularly imprinted polymer;

[0143] l : Layered double hydroxide@carbon quantum dots;

[0144] m : Square wave voltammetry;

[0145] n : Linear sweep voltammetry; and

[0146] o : Amperometry.

[0147] Example 10. Verification of selective detection of LFO / rGO / GCE

[0148] To verify whether the LFO / rGO / GCE sensor of the present invention selectively detects MTZ even in the presence of organic or inorganic interfering compounds, samples in which ODZ (ornidazole), DA (dopamine), Glu (glucose), AA (ascorbic acid), NaCl, ZnCl2, CaCl2, NaNO3, Na2SO4, Na2CO3, and RU (rutin) (50 μM) were combined with MTZ (15 μM) were analyzed by the DPV method using the LFO / rGO / GCE sensor. As a result, even in the presence of interfering substances, I of 15 μM MTZ pc No significant changes were observed in (Fig. 11c and d).

[0149] Example 11. Confirmation of MTZ detection ability in actual samples

[0150] The ability of the LFO / rGO / GCE sensor of the present invention to detect MTZ in actual urine and food (milk) samples was verified using the DPV method. For this purpose, urine samples were collected from healthy volunteers, and milk samples were purchased from a local market in Taiwan. The samples were centrifuged at 6000 rpm for 30 min, and the supernatant was separated and used for analysis. MTZ at various concentrations (2.5-10.0 μM) was added to 0.1 M PB solution (pH 7) at each spiking concentration, and three independent samples were analyzed simultaneously. As shown in Table 2, the recoveries of urine and milk samples ranged from 98.80% to 99.86% and from 98.40% to 99.80%, respectively, and the relative standard deviation (RSD) values ​​were 1.98% and 1.83%, respectively. These results indicate that the LFO / rGO nanocomposite electrochemical sensor of the present invention has high efficiency and accuracy in detecting MTZ in actual urine and milk samples.

[0151]

Claims

1. A nanocomposite comprising reduced graphene oxide (rGO) and lanthanum ferrite (LFO) nanoparticles.

2. A nanocomposite comprising reduced graphene oxide nanosheets and LFO nanoparticles arranged on the nanosheets in claim 1.

3. A nanocomposite in claim 1, wherein the weight ratio of the reduced graphene oxide nanosheets and LFO nanoparticles is 1:2 to 1:

10.

4. In paragraph 1, 40 to 80 m 2 Nanocomposites exhibiting a surface area (BET) of / g.

5. A porous nanocomposite according to claim 1.

6. A nanocomposite in the first paragraph, wherein the nanosheet has a wrinkled surface and a layered structure.

7. A nanocomposite in the first paragraph, wherein the nanoparticles are uniformly distributed on a nanosheet.

8. An electrode having the nanocomposite of clause 1 arranged on its surface.

9. In the 8th paragraph, the electrode is a silver (Ag), palladium (Pd), gold (Au), platinum (Pt) or glassy carbon (GC) electrode.

10. An electrode for detecting metronidazole (MTZ) in clause 8.

11. A sensor for detecting metronidazole, comprising the electrode of clause 8.

12. A sensor according to claim 11, wherein a supporting electrolyte having a pH of 6 to 8 is used. 13.a) Step of manufacturing LFO nanoparticles; b) a step of manufacturing graphene oxide; c) a step of producing reduced GO (rGO) nanosheets by thermal reduction of graphene oxide; and d) A method for producing LFO-rGO nanocomposite by ultrasonic treatment.

14. In the 13th paragraph, the step d) is a method for producing an LFO-rGO nanocomposite, wherein the reduced GO nanosheet is dissolved in a solvent by ultrasonic treatment, and then LFO nanoparticles are added and ultrasonic treatment is performed.

15. A method for producing an LFO-rGO nanocomposite, wherein 200 to 1,000 parts by weight of LFO nanoparticles are added to 100 parts by weight of reduced graphene oxide nanosheets in the 14th paragraph. 16.a) a step of dispersing the nanocomposite of paragraph 1 in a solvent; and b) A method for producing an LFO-rGO nanocomposite electrode, comprising the step of depositing on the surface of an electrode.

17. A method for detecting metronidazole in a sample, comprising the step of contacting the test sample with the electrode of the sensor of claim 11.

18. A method for detecting metronidazole, further comprising the step of performing DPV (differential pulse voltammetry) in claim 17.

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