Preparation method and application of Fe-NC@CNFs / GCE electrode

Abstract

The application discloses a preparation method of an Fe-NC@CNFs / GCE electrode and application thereof, relates to the technical field of electrochemical detection, and has the technical scheme as follows: a bimetallic ZIF based on Fe / Zn is synthesized, and is calcined at a high temperature of 800 DEG C to obtain a derived nitrogen-doped porous carbon material (Fe-NC@CNFs); the synthesized material has a large specific surface area and rich active sites; the material is configured into a suspension by using ultrapure water; and a traditional drop-coating method is adopted to successfully build an electrode Fe-NC@CNFs / GCE for detecting luteolin; the electrode has high selectivity, sensitivity and stability, and can detect luteolin in a natural sample.

Description

Technical Field

[0001] This invention relates to the field of electrochemical detection technology, and more specifically, to a method for preparing a Fe-NC@CNFs / GCE electrode and its application. Background Technology

[0002] Flavonoids are naturally occurring bioactive compounds widely distributed in various plants, such as fruits, vegetables, and certain medicinal plants. Due to their excellent physiological and pharmacological activities, such as antioxidant, anti-inflammatory, free radical scavenging, and anticancer effects, these compounds have always been a focus of attention in the medical, food, and health care fields. 3',4',5,7-Tetrahydroxyflavone, also known as luteolin (LU), is an important flavonoid that can be extracted from honeysuckle, chrysanthemum, perilla, and other plants. Luteolin possesses good pharmacological activity and biological properties and is widely used clinically in the treatment of cardiovascular diseases, respiratory diseases, and hyperlipidemia. However, excessively high concentrations of luteolin in the human body can inhibit the activity of deoxyribonucleotides, promoting DNA oxidation and leading to damage.

[0003] Currently, the most widely used methods for detecting luteolin include high-performance liquid chromatography (HPLC), ultraviolet spectrophotometry (UV spectrophotometry), mass spectrometry (MS), and immunoassay. While these traditional instrumental methods have many advantages, they also suffer from drawbacks such as large instrument size and inconvenient detection processes. Some methods are time-consuming, costly, or require complex pretreatment processes, hindering their further application. As a relatively new instrumental analytical method, electrochemical determination offers advantages such as high reliability, fast reaction, inexpensive instrumentation, low energy consumption, simple operation, time saving, and high sensitivity and selectivity.

[0004] For electrochemical sensors, suitable electrode materials play a crucial role, significantly impacting detection performance. ZIF, or zeolite imidazolate framework, is a special type of metal-organic framework, typically consisting of divalent metal ions as nodes and 2-methylimidazolium (2-MI) as organic ligands. ZIF materials possess advantages such as high porosity, abundant reactive sites, large specific surface area, and tunable pore size. However, ordinary ZIFs often have unsatisfactory conductivity, resulting in electrochemical performance that fails to meet detection requirements. Therefore, research has shifted towards improving their electrochemical performance. Nitrogen-doped porous carbon materials produced by ZIF pyrolysis exhibit excellent electron transfer capabilities, making them a research hotspot and widely used in energy storage and conversion, electrocatalysis, and electrochemical sensing.

[0005] Therefore, there is an urgent need to explore a green, efficient, and sensitive electrode for detecting luteolin in food, medicinal plants, and human body fluids. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a Fe-NC@CNFs / GCE electrode and its application. This method successfully constructs an Fe-NC@CNFs / GCE electrode for detecting luteolin. This electrode has high selectivity, sensitivity and stability, and can detect luteolin in natural samples.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for preparing a Fe-NC@CNFs / GCE electrode, comprising the following three steps:

[0008] Synthesis of S1.Fe / Zn-ZIF@CNFs;

[0009] Synthesis of S2.Fe-NC@CNFs;

[0010] Preparation of S3.Fe-NC@CNFs / GCE electrode.

[0011] The present invention is further configured as follows: The specific operation for the synthesis of Fe / Zn-ZIF@CNFs in S1 is as follows: Carbon nanofibers (CNFs), Zn(NO3)2·6H2O and FeSO4·7H2O are soaked in methanol and stirred to allow them to react fully. Then, a methanol solution containing 2-methylimidazole is added and ultrasonically dispersed evenly. The mixture is reacted in a reaction vessel. After filtration, the precipitate is thoroughly washed with methanol and deionized water. The precipitate is Fe / Zn-ZIF@CNFs.

[0012] The present invention is further configured as follows: the specific operation of the synthesis of Fe-NC@CNFs in S2 is as follows: the Fe / Zn-ZIF@CNFs obtained in S1 is placed in a tube furnace, heated, calcined at high temperature in a nitrogen atmosphere, and then allowed to cool naturally at room temperature to finally obtain Fe-NC@CNFs nanomaterials. The obtained nanomaterials are dispersed in deionized water under ultrasonic conditions to obtain a suspension.

[0013] The present invention is further configured as follows: the specific operation for preparing the Fe-NC@CNFs / GCE electrode in S3 is as follows: the glassy carbon electrode (GCE) is polished with alumina powder until the surface is smooth, then it is cleaned with anhydrous ethanol and ultrapure water under ultrasonic conditions to remove surface dirt, and then the clean GCE is dried with an infrared lamp to obtain a clean and dry GCE. The suspension of Fe-NC@CNFs prepared in S2 is taken with a pipette and dropped onto the prepared GCE surface. It is placed at room temperature for drying until the material forms a uniform film on the electrode surface to obtain the Fe-NC@CNFs / GCE electrode.

[0014] Application of a Fe-NC@CNFs / GCE electrode: The Fe-NC@CNFs / GCE electrode can be used to detect the content of luteolin in food, medicinal plants and human body fluids.

[0015] In summary, the present invention has the following beneficial effects: The present invention successfully prepared an electrode Fe-NC@CNFs / GCE for detecting luteolin. This electrode has high selectivity, sensitivity and stability. The electrode has good reliability, fast reaction and low instrument price, low energy consumption, simple operation, time saving, high sensitivity and selectivity for detecting luteolin, and can detect luteolin in natural samples. Attached Figure Description

[0016] Figure 1 A represents the electrochemical impedance spectroscopy of different modified electrodes in the embodiments of the present invention; Figure 1 B is the CV curve of different modified electrodes in 500nM luteolin in the embodiments of the present invention;

[0017] Figure 2 A is the DPV response diagram of Fe-NC@CNFs / GCE at different luteolin concentrations (1 nM, 10 nM, 40 nM, 60 nM, 200 nM, 400 nM, 700 nM, 1000 nM, 1500 nM). Figure 2 B represents the relationship between the Fe-NC@CNFs / GCE detection signal and the luteolin concentration;

[0018] Figure 3 This invention describes the preparation process of the Fe-NC@CNFs / GCE electrode. Detailed Implementation

[0019] The following is in conjunction with the appendix Figure 1-3 The present invention will be described in further detail below.

[0020] Example 1: A method for preparing a Fe-NC@CNFs / GCE electrode, comprising the following three steps:

[0021] Synthesis of S1.Fe / Zn-ZIF@CNFs;

[0022] Synthesis of S2.Fe-NC@CNFs;

[0023] Preparation of S3.Fe-NC@CNFs / GCE electrode.

[0024] The specific steps for synthesizing Fe / Zn-ZIF@CNFs in S1 are as follows: Carbon nanofibers (CNFs), 0.5145 g of Zn(NO3)2·6H2O and 0.0233 g of FeSO4·7H2O were soaked in 25 ml of methanol and stirred for 12 hours to allow for complete reaction; then, 25 ml of methanol solution containing 0.615 g of 2-methylimidazole (2-MI) was added and sonicated for 1 hour to ensure uniform dispersion. Subsequently, the mixture was reacted in a reaction vessel at 100 °C for 2 hours. After filtration, the precipitate was washed several times with methanol and deionized water to obtain Fe / Zn-ZIF@CNFs.

[0025] The specific steps for synthesizing Fe-NC@CNFs in S2 are as follows: The Fe / Zn-ZIF@CNFs obtained in S1 are placed in a tube furnace and heated at 5℃·min. -1 The temperature was slowly increased to 800℃ and calcined at high temperature in a nitrogen atmosphere for 2 hours, then allowed to cool naturally at room temperature to obtain Fe-NC@CNFs nanomaterials. The obtained nanomaterials were dispersed in deionized water under ultrasonic conditions to obtain a concentration of 2 mg·mL⁻¹. -1 A suspension.

[0026] The specific procedures for preparing the Fe-NC@CNFs / GCE electrode in S3 are as follows: The glassy carbon electrode (GCE) is polished using alumina powders of different particle sizes until the surface is smooth. Then, the glassy carbon electrode is cleaned with anhydrous ethanol and ultrapure water under ultrasonic conditions to remove surface contaminants. The clean glassy carbon electrode is then dried using an infrared lamp to obtain a clean and dry glassy carbon electrode. Using a pipette, 6 μL of the Fe-NC@CNFs suspension prepared in S2 is dropped onto the prepared electrode surface and allowed to dry at room temperature until a uniform film forms on the electrode surface, resulting in the working electrode Fe-NC@CNFs / GCE for electrochemical testing.

[0027] Example 2: Includes the following 3 steps:

[0028] Synthesis of S1.ZIF-8@CNFs;

[0029] Synthesis of S2.NC@CNFs;

[0030] Fabrication of S3.NC@CNFs / GCE electrode.

[0031] The specific steps for synthesizing ZIF-8@CNFs in S1 are as follows: Carbon nanofibers (CNFs) and 0.5145 g of Zn(NO3)2·6H2O were soaked in 25 ml of methanol and stirred for 12 hours to allow for complete reaction; then, 25 ml of methanol solution containing 0.615 g of 2-methylimidazole (2-MI) was added, and the mixture was sonicated for 1 hour to ensure uniform dispersion. Subsequently, the mixture was reacted in a reaction vessel at 100 °C for 2 hours. After filtration, the precipitate was washed several times with methanol and deionized water to obtain ZIF-8@CNFs.

[0032] The specific steps for synthesizing NC@CNFs in S2 are as follows: The ZIF-8@CNFs obtained in S1 are placed in a tube furnace and heated at 5℃·min. -1 The temperature was slowly increased to 800℃ and calcined at high temperature in a nitrogen atmosphere for 2 hours, then allowed to cool naturally at room temperature to obtain NC@CNFs nanomaterials. The obtained nanomaterials were dispersed in deionized water under ultrasonic conditions to obtain a concentration of 2 mg·mL⁻¹. -1 A suspension.

[0033] The specific procedures for preparing the NC@CNFs / GCE electrode in S3 are as follows: The glassy carbon electrode (GCE) is polished using alumina powder of different particle sizes until the surface is smooth. Then, the glassy carbon electrode is cleaned with anhydrous ethanol and ultrapure water under ultrasonic conditions to remove surface contaminants. The clean glassy carbon electrode is then dried using an infrared lamp to obtain a clean and dry glassy carbon electrode. Using a pipette, 6 μL of the NC@CNFs suspension prepared in S2 is dropped onto the prepared electrode surface and allowed to dry at room temperature until a uniform film forms on the electrode surface, resulting in the working electrode NC@CNFs / GCE for electrochemical testing.

[0034] Example 3: CNFs were directly dispersed in deionized water under ultrasonic conditions to obtain a concentration of 2 mg·mL⁻¹. -1 A suspension of CNFs was prepared by polishing a glassy carbon electrode (GCE) with alumina powder of different particle sizes until the surface was smooth. The GCE was then cleaned with anhydrous ethanol and ultrapure water under ultrasonic conditions to remove surface contaminants. The cleaned GCE was then dried using an infrared lamp to obtain a clean and dry glassy carbon electrode. 6 μL of CNFs suspension was pipetted onto the prepared electrode surface and allowed to dry at room temperature until a uniform film formed on the electrode surface, resulting in a CNFs / GCE working electrode for electrochemical testing.

[0035] The electrochemical measurements were performed on a CHI660 electrochemical workstation using a standard three-electrode system. The auxiliary electrode was a platinum wire electrode, the reference electrode was a saturated AgCl solution-filled electrode, and the prepared modified electrode served as the working electrode. The electrolyte solution used for the electrochemical detection was 0.1 M phosphate-buffered saline (PBS), and the measurements were conducted under a nitrogen atmosphere throughout. The cyclic voltammetry (CV) potential range was set to -0.1 V to 0.7 V, and the scan rate was set to 50 mV·s. -1 The potential range for differential pulse voltammetry (DPV) was also set to -0.1V to 0.7V. Electrochemical impedance spectroscopy (EIS) was performed in a 1.0M potassium ferricyanide / potassium ferrocyanide mixed solution containing 0.1M potassium chloride.

[0036] The three working electrodes prepared in Examples 1, 2, and 3, along with a bare glassy carbon electrode, were placed in an AC impedance electrolyte for electrochemical impedance spectroscopy (EIS) testing. The test results are as follows: Figure 1 As shown in Figure A, in EIS, the semicircle diameter of the curve in the Nyquist plot is proportional to the impedance (Rp) of the working electrode surface material. It is evident that the bare glassy carbon electrode has the highest impedance. The impedance of CNFs / GCE is slightly lower than that of the bare glassy carbon electrode, but its semicircle diameter is still relatively large. The curve radius corresponding to NC@CNFs / GCE is smaller, while the curve corresponding to Fe-NC@CNFs / GCE is almost a straight line, indicating that the Fe-NC@CNFs material has the best electron transfer capability.

[0037] The four electrodes were placed in 0.1 M PBS solution containing 500 nM luteolin at pH 5.5, and cyclic voltammetry (CV) experiments were performed on each modified electrode pair. The electrochemical response results are as follows: Figure 1 As shown in Figure B, it can be clearly seen that Fe-NC@CNFs / GCE exhibits the strongest electrochemical response signal for the analyte luteolin, followed by NC@CNFs / GCE, with CNFs / GCE showing the weakest response. This result is consistent with the EIS results, indicating that Fe-NC@CNFs / GCE has the best detection effect for luteolin, and its electrochemical response signal is approximately three times that of NC@CNFs / GCE.

[0038] After finding the optimal parameters for the detection process through numerous experiments, differential pulse voltammetry (DPV) was used to conduct the following tests to investigate the linear equation, linear range, and detection limit of LU (luteolin) detection by the Fe-NC@CNFs / GCE electrode. The experimental results are shown below. Figure 2 As shown, Figure 2A is a superimposed graph of the electrochemical response results of luteolin at different concentration gradients (1 nM, 10 nM, 40 nM, 60 nM, 200 nM, 400 nM, 700 nM, 1000 nM, 1500 nM). The results show that in 1.0 M PBS (pH = 5.0) solution, the oxidation peak current gradually increases with increasing luteolin concentration. Figure 2 As shown in Figure B, within the range of 1-1500 nM, the peak current value exhibits a good linear correlation with the concentration of the detectable substance, and the equation for this linear relationship is shown below:

[0039] Ip(μA)=0.0254C(nM)+0.9357(R 2 =0.9972)

[0040] Calculations showed that the limit of detection was 0.47 nM when the signal-to-noise ratio was 3 (S / N = 3). Therefore, this invention successfully constructed a novel electrochemical sensing platform for detecting luteolin: Fe-NC@CNFs / GCE. This sensing platform features simple electrode material preparation and a relatively sensitive electrochemical response.

[0041] Furthermore, this invention also applies the Fe-NC@CNFs / GCE electrode to the detection of actual samples, employing the standard addition method to determine the concentration of chrysanthemum extract. First, 20 μL of chrysanthemum extract was added to PBS solution, and the concentration of LU was determined using DPV technology. Then, 1.0, 1.5, and 2.0 times the actual sample concentration of luteolin standard analyte were added for further determination. The experimental results are shown in Table 1.

[0042] Table 1. Detection of Dried Chrysanthemum Extract from Actual Samples

[0043]

[0044]

[0045] Calculations showed that the recovery rate of the actual sample detection ranged from 98.0% to 101.1%, and the relative standard deviation (RSD) was 0.68% to 3.46%. This result indicates that Fe-NC@CNFs / GCE can be used for the detection of luteolin in actual samples.

[0046] The same method was used to determine the luteolin content in actual chrysanthemum tea beverage samples again. The calculated recoveries and RSDs were 99.8%–103.0% and 0.89%–4.08%, respectively, indicating good detection performance. This further confirms that Fe-NC@CNFs / GCE can be used for the detection of luteolin in actual samples. The experimental results are shown in Table 2.

[0047] Table 2. Detection of actual chrysanthemum tea beverage samples

[0048]

[0049] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a Fe-NC@CNFs / GCE electrode, characterized by comprising the following: 3 steps: S1. Synthesis of Fe / Zn-ZIF@CNFs: Carbon nanofibers (CNFs), Zn(NO3)2·6H2O and FeSO4·7H2O were soaked in methanol and stirred to allow them to react fully. Then, a methanol solution containing 2-methylimidazole was added and ultrasonically dispersed evenly. The mixture was reacted in a reaction vessel, filtered, and the precipitate was thoroughly washed with methanol and deionized water. The precipitate is Fe / Zn-ZIF@CNFs. S2. Synthesis of Fe-NC@CNFs: The Fe / Zn-ZIF@CNFs obtained in S1 were placed in a tube furnace, heated, and calcined at high temperature in a nitrogen atmosphere. After being allowed to cool naturally at room temperature, Fe-NC@CNFs nanomaterials were finally obtained. The obtained nanomaterials were dispersed in deionized water under ultrasonic conditions to obtain a suspension. S3. Preparation of Fe-NC@CNFs / GCE electrode: The glassy carbon electrode (GCE) was polished with alumina powder until the surface was smooth. Then, it was cleaned with anhydrous ethanol and ultrapure water under ultrasonic conditions to remove surface dirt. The clean GCE was then dried with an infrared lamp to obtain a clean and dry GCE. The suspension of Fe-NC@CNFs prepared in S2 was taken with a pipette and dropped onto the prepared GCE surface. It was placed at room temperature to dry until a uniform film was formed on the electrode surface, thus obtaining the Fe-NC@CNFs / GCE electrode.

2. The application of the Fe-NC@CNFs / GCE electrode prepared by the method according to claim 1, characterized in that: The electrode can be used to detect the luteolin content in food, medicinal plants, and human body fluids.

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