GO / Mg-Fe-LDH modified electrode and electrochemical sensor

Abstract

The invention discloses a GO / Mg-Fe-LDH modified electrode and an electrochemical sensor, and relates to the technical field of electrode materials. The invention discloses a GO / Mg-Fe-LDH modified electrode. The GO / Mg-Fe-LDH modified electrode is composed of a working electrode, a magnesium-iron double-metal hydroxide layer and a graphene oxide layer, wherein the magnesium-iron double-metal hydroxide layer and the graphene oxide layer wrap the surface of the working electrode from inside to outside. The prepared GO / Mg-Fe-LDH modified electrode serves as a working electrode to be applied to an electrochemical sensor, the electrochemical sensor is suitable for detecting the content of mycophenolic acid in feed, the prepared modified electrode has a large specific surface area, more active sites can be provided for reaction, and the electrochemical sensor can be used for detecting the content of mycophenolic acid in feed. Therefore, the sensitivity of the sensor to target molecules is remarkably improved, and the charge transfer rate can be remarkably improved due to the good catalytic performance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and particularly to a GO / Mg-Fe-LDH modified electrode and an electrochemical sensor. Background Art

[0002] An electrochemical sensor is a device that senses the type, content, etc. of a target substance by detecting electrical signals (such as current, voltage, resistance, etc.) generated by redox reactions occurring in an electrolyte or buffer solution. This is an application field involving multiple disciplinary technologies such as chemistry, materials science, information technology, and microelectronics. This sensing method can construct corresponding detection electrodes according to different detection substances, and the equipment and materials used have advantages such as being portable, capable of real-time detection, short response time, and low preparation cost compared with conventional detection methods, and are widely used in fields such as food safety, environmental monitoring, medical diagnosis, and industrial process control.

[0003] Graphene oxide (GO), a graphene derivative obtained by oxidizing graphene materials, has a two-dimensional structure similar to that of graphene, enabling it to have a large specific surface area and good electrical conductivity. At the same time, its surface also has many oxygen-containing groups such as hydroxyl groups and alkoxy groups. These oxygen-containing groups not only enable GO to have excellent dispersibility in water and polar solvents but also provide it with rich active sites, thereby improving the chemical catalytic performance of GO. This makes GO widely used as a modification material on the electrode surface. Layered double hydroxides (LDHs) are special compounds with a layer-columnar structure, composed of positively charged layers and anions intercalated between the layers. This special-structured substance has characteristics such as interlayer anion exchangeability, thermal stability, artificial enzyme mimicking activity, large specific surface area, and two-dimensional nanostructure. Combining this excellent material with an electrochemical sensor can improve the sensitivity of the sensor, reduce its detection limit, and also use its catalytic characteristics as an electrocatalyst to amplify electrochemical signals. Moreover, this material is simple to prepare and low in cost, and is suitable for preparing electrochemical sensors with high sensitivity and low price. Therefore, using the electrochemical and structural characteristics of double metal hydroxides or graphene oxide to prepare composite materials for modifying the electrode surface can construct an accurate and low-cost electrochemical detector. Summary of the Invention

[0004] The purpose of the present invention is to provide a GO / Mg-Fe-LDH modified electrode and an electrochemical sensor to solve the following technical problems: The working electrode of the existing electrochemical sensor has low sensitivity.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A GO / Mg-Fe-LDH modified electrode, which is composed of a working electrode and a layer of magnesium-iron double metal hydroxide and a layer of graphene oxide wrapped around the surface of the working electrode from the inside out.

[0006] As a further solution of the present invention: coat a magnesium-iron layered double metal hydroxide solution on the surface of the working electrode and dry it to obtain a layer of magnesium-iron double metal hydroxide.

[0007] As a further solution of the present invention: the working electrode is any one of a glassy carbon electrode, a platinum electrode, a gold electrode, and a copper electrode.

[0008] As a further solution of the present invention: the magnesium-iron layered double metal hydroxide solution uses water as a solvent, and each milliliter of the solution contains 0.5-3 mg of magnesium-iron layered double metal hydroxide (Mg-Fe-LDH).

[0009] As a further solution of the present invention: the working electrode is pretreated before coating the magnesium-iron layered double metal hydroxide solution; the pretreatment step includes grinding the working electrode in a slurry containing polishing powder; the voltage difference between the two peaks of the working electrode obtained after pretreatment is less than 0.1 V.

[0010] As a further solution of the present invention: coat a graphene oxide solution on the surface of the working electrode wrapped with a layer of magnesium-iron double metal hydroxide and dry it to obtain a modified electrode wrapped with a layer of magnesium-iron double metal hydroxide and a layer of graphene oxide from the inside out.

[0011] As a further solution of the present invention: the graphene oxide solution uses water as a solvent, and each milliliter of the solution contains 0.5-3 mg of graphene oxide.

[0012] An electrochemical sensor uses the GO / Mg-Fe-LDH modified electrode of any one of the above as the working electrode of the electrochemical sensor.

[0013] As a further solution of the present invention: the electrochemical sensor is used for the detection of the content of mycophenolic acid.

[0014] The beneficial effects of the present invention: The present invention modifies the working electrode with graphene oxide and magnesium-iron double metal hydroxide to obtain a GO / Mg-Fe-LDH modified electrode. In this application, the electrode is first surface-modified with Mg-Fe-LDH, which has better conductivity, so that the sensing performance is more stable. Secondly, GO is further used to modify the electrode with a magnesium-iron double metal hydroxide layer, providing a large effective specific surface area, which is conducive to the adsorption of the analyte and improves the sensitivity of the sensor. Using it as the working electrode of an electrochemical sensor is suitable for detecting mycophenolic acid (MPA) in feed. The modified electrode prepared in this application has a large specific surface area, which can provide more active sites for the reaction, thus significantly improving the sensitivity of the sensor to the target molecule. The good catalytic performance of the material can significantly increase the charge transfer rate; the specific groups on the surface of graphene oxide enhance the specific catalysis of the target molecule, significantly improving the specificity of the sensor. Compared with traditional MPA detection methods such as tandem chromatography-mass spectrometry, high-performance liquid chromatography, and gas chromatography, the sensor of the present invention has the advantages of low cost, simple operation, and fast response speed. Brief Description of the Drawings

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] Figure 1 It is a graph of the detection data of the mycophenolic acid concentration by the modified electrode prepared in Example 1 of this application; Figure 2 It is a graph of the detection data of the effective specific surface area of the modified electrodes prepared in Example 1 and Comparative Examples 1-2 of this application; Figure 3 It is a cyclic stability detection curve graph of the modified electrode prepared in this application Figure 4 It is a detection graph of the repeatability and reproducibility of the modified electrode prepared in this application; Figure 5 It is a specific detection curve graph of the modified electrode prepared in this application. Detailed Description of the Invention

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1 A preparation method of a GO / Mg-Fe-LDH modified electrode includes the following steps: S1: Prepare a 4 mmol / L potassium ferricyanide solution (containing 0.1 mol / L potassium chloride): Weigh 1.055 g of potassium ferrocyanide trihydrate, 0.823 g of potassium ferricyanide and 3.727 g of potassium chloride in a 100 mL beaker, dissolve them with ultrapure water, then transfer to a 500 mL volumetric flask and make up to the mark with ultrapure water to obtain a 5 mmol / L potassium ferricyanide solution; S2: Pretreatment: Sprinkle polishing powder (Al2O3) on the suede, then add ultrapure water and stir well to form a homogeneous slurry. Polish the glassy carbon electrode (GCE) in a circular motion perpendicular to the suede on the slurry. Then, ultrasonically treat it in ultrapure water, absolute ethanol, and ultrapure water for 30 s each. Note that the electrode should be leaned against the inner wall of the beaker, and then dry it for standby; Test the pretreated glassy carbon electrode in the potassium ferricyanide solution prepared in S1 under cyclic voltammetry (CV) mode. If the voltage difference between the two peaks is less than 0.1 V, the grinding is qualified; otherwise, repeat the above steps until the peak difference is less than 0.1 V (CV parameter settings: potential range -0.2 - 0.6 V, scan rate 50 mV / s, initial scan polarity: forward, scan rate 0.05 V / s, number of scan segments 2, sampling interval 0.001 V, rest time 2 s, sensitivity 1.e-004 A / V); S3: Weigh 1.0 mg of Mg-Fe-LDH (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat it until there are no obvious particles at the bottom of the centrifuge tube to obtain a Mg-Fe-LDH solution; Weigh 1.5 mg of GO (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat it until there are no obvious particles at the bottom of the centrifuge tube to obtain a GO solution; Accurately pipette 5 μL of the above-prepared Mg-Fe-LDH solution and drop it onto the electrode surface, then place it in an oven to dry to obtain an electrode with a magnesium-iron double metal hydroxide layer on the surface; Drop 5 μL of the above-prepared GO solution onto the surface of the electrode with a magnesium-iron double metal hydroxide layer and dry it again to obtain a GO / Mg-Fe-LDH modified electrode.

[0019] Example 2 A method for preparing a GO / Mg-Fe-LDH modified electrode includes the following steps: S1: Prepare a 4 mmol / L potassium ferricyanide solution (containing 0.1 mol / L potassium chloride): Weigh 1.055 g of potassium ferrocyanide trihydrate, 0.823 g of potassium ferricyanide and 3.727 g of potassium chloride in a 100 mL beaker, dissolve them with ultrapure water, then transfer to a 500 mL volumetric flask and make up to the mark with ultrapure water to obtain a 5 mmol / L potassium ferricyanide solution; S2: Pretreatment: Sprinkle polishing powder (Al2O3) on the suede, then add ultrapure water and stir well to form a homogeneous slurry. Rub the glassy carbon electrode (GCE) in a circular motion perpendicular to the suede on the slurry, and then ultrasonically treat it in ultrapure water, absolute ethanol, and ultrapure water for 30 s each. Note that the electrode should lean against the inner wall of the beaker, and then dry it for standby; Test the pretreated glassy carbon electrode in the potassium ferricyanide solution prepared in S1 in cyclic voltammetry (CV) mode. If the voltage difference between the two peaks is less than 0.1 V, the grinding is qualified; otherwise, repeat the above steps until the peak difference is less than 0.1 V (CV parameter settings: potential range -0.2 - 0.6 V, scan rate 50 mV / s, initial scan polarity: forward, scan rate 0.05 V / s, number of scan segments 2, sampling interval 0.001 V, standing time 2 s, sensitivity 1.e-004 A / V); S3: Weigh 0.5 mg of Mg-Fe-LDH (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat it until there are no obvious particles at the bottom of the centrifuge tube to obtain a Mg-Fe-LDH solution; Weigh 0.5 mg of GO (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat it until there are no obvious particles at the bottom of the centrifuge tube to obtain a GO solution; Accurately pipette 5 μL of the above-prepared Mg-Fe-LDH solution and drop it onto the electrode surface, then place it in an oven to dry to obtain an electrode with a magnesium-iron double metal hydroxide layer on the surface. Drop 5 μL of the above-prepared GO solution onto the surface of the electrode with a magnesium-iron double metal hydroxide layer and dry it again to obtain a GO / Mg-Fe-LDH modified electrode.

[0020] Example 3 A method for preparing a GO / Mg-Fe-LDH modified electrode includes the following steps: S1: Prepare a 4 mmol / L potassium ferricyanide solution (containing 0.1 mol / L potassium chloride): Weigh 1.055 g of potassium ferrocyanide trihydrate, 0.823 g of potassium ferricyanide, and 3.727 g of potassium chloride in a 100 mL beaker, dissolve them with ultrapure water, and then transfer them to a 500 ml volumetric flask and make up to the mark with ultrapure water to obtain a 5 mmol / L potassium ferricyanide solution; S2: Pretreatment: Sprinkle polishing powder (Al2O3) on the suede, then add ultrapure water and stir well to form a homogeneous slurry. Rub the glassy carbon electrode (GCE) in a circular motion perpendicular to the suede on the slurry, and then ultrasonically treat it in ultrapure water, absolute ethanol, and ultrapure water for 30 s each. Note that the electrode should lean against the inner wall of the beaker, and then dry it for standby; The pretreated glassy carbon electrode was tested in the potassium ferricyanide solution prepared in S1 under cyclic voltammetry (CV) mode. If the voltage difference between the two peaks is less than 0.1 V, the grinding is qualified; otherwise, repeat the above steps until the difference between the two peak values is less than 0.1 V (CV parameters are set as: potential range -0.2 - 0.6 V, scan rate 50 mV / s, initial scan polarity: forward, scan rate 0.05 V / s, number of scan segments 2, sampling interval 0.001 V, rest time 2 s, sensitivity 1.e-004 A / V); S3: Weigh 3 mg of Mg-Fe-LDH (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat until there are no obvious particles at the bottom of the centrifuge tube to obtain a Mg-Fe-LDH solution; Weigh 3 mg of GO (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat until there are no obvious particles at the bottom of the centrifuge tube to obtain a GO solution; Accurately pipette 5 μL of the above-prepared Mg-Fe-LDH solution and drop it onto the electrode surface, then place it in an oven to dry, obtaining an electrode with a magnesium-iron double metal hydroxide layer on the surface; Drop 5 μL of the above-prepared GO solution onto the surface of the electrode with a magnesium-iron double metal hydroxide layer and dry it again to obtain a GO / Mg-Fe-LDH modified electrode.

[0021] Comparative Example 1 A method for preparing a graphene oxide modified electrode includes the following steps: S1: Prepare a 4 mmol / L potassium ferricyanide solution (containing 0.1 mol / L potassium chloride): Weigh 1.055 g of potassium ferrocyanide trihydrate, 0.823 g of potassium ferricyanide and 3.727 g of potassium chloride in a 100 mL beaker, dissolve them with ultrapure water, and then transfer them to a 500 ml volumetric flask and make up to the mark with ultrapure water to obtain a 5 mmol / L potassium ferricyanide solution; S2: Pretreatment: Sprinkle polishing powder (Al2O3) on the suede, then add ultrapure water and stir well to form a homogeneous slurry. Grind the glassy carbon electrode (GCE) in a circular motion perpendicular to the suede on the slurry, and then ultrasonically treat it in ultrapure water, absolute ethanol, and ultrapure water for 30 s each. Note that the electrode should be leaned against the inner wall of the beaker, and then dry it for later use; The pretreated glassy carbon electrode was tested in the potassium ferricyanide solution prepared in S1 under cyclic voltammetry (CV) mode. If the voltage difference between the two peaks is less than 0.1 V, the grinding is qualified; otherwise, repeat the above steps until the difference between the two peak values is less than 0.1 V (CV parameters are set as: potential range -0.2 - 0.6 V, scan rate 50 mV / s, initial scan polarity: forward, scan rate 0.05 V / s, number of scan segments 2, sampling interval 0.001 V, rest time 2 s, sensitivity 1.e-004 A / V); S3: Weigh 1.5 mg of GO (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat it until there are no obvious particles at the bottom of the centrifuge tube to obtain a GO solution; Accurately pipette 5 μL of the above-prepared GO solution with a pipette gun and drop-coat it onto the surface of the electrode, then put it into an oven to dry, obtaining a modified electrode.

[0022] Comparative Example 2 A preparation method of a magnesium-iron double metal hydroxide modified electrode includes the following steps: S1: Prepare a 4 mmol / L potassium ferricyanide solution (containing 0.1 mol / L potassium chloride): Weigh 1.055 g of potassium ferrocyanide trihydrate, 0.823 g of potassium ferricyanide and 3.727 g of potassium chloride in a 100 mL beaker, dissolve them with ultrapure water, and then transfer them to a 500 ml volumetric flask and make up the volume to the mark with ultrapure water to obtain a 5 mmol / L potassium ferricyanide solution; S2: Pretreatment: Sprinkle polishing powder (Al2O3) on the suede, then add ultrapure water and stir well to form a homogeneous slurry. Grind the glassy carbon electrode (GCE) in a circular motion perpendicular to the suede on the slurry. Then ultrasonically treat it in ultrapure water, absolute ethanol, and ultrapure water for 30 s each. Note that the electrode should lean against the inner wall of the beaker, and then dry it for standby; Test the pretreated glassy carbon electrode in the potassium ferricyanide solution prepared in S1 under the cyclic voltammetry (CV) mode. If the voltage difference between the two peaks is less than 0.1 V, the grinding is qualified; otherwise, repeat the above steps until the difference between the two peak values is less than 0.1 V (CV parameter settings: potential range -0.2 - 0.6 V, scanning speed 50 mV / s, initial scanning polarity: forward, scanning rate 0.05 V / s, number of scanning segments 2, sampling interval 0.001 V, standing time 2 s, sensitivity 1.e-004 A / V); S3: Weigh 1.0 mg of Mg-Fe-LDH (purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.) and place it in a 2 mL centrifuge tube. Add 1 mL of ultrapure water and ultrasonically treat it until there are no obvious particles at the bottom of the centrifuge tube to obtain a Mg-Fe-LDH solution; Accurately pipette 5 μL of the above-prepared Mg-Fe-LDH solution with a pipette gun and drop-coat it onto the surface of the electrode, then put it into an oven to dry, obtaining a modification.

[0023] Performance Detection (1) Detect the concentration of mycophenolic acid a. Construct a system: Based on the modified electrode prepared in Example 1 as the working electrode of the electrochemical sensor, use a platinum wire counter electrode and Ag / AgCl as the reference electrode, and a CHI760E electrochemical workstation to form a three-electrode sensing system; b. Preparation of the detection solution: Preparation of MPA standard solution: Accurately weigh 10.0 mg of MPA standard sample into a 10 mL volumetric flask, dilute it to the mark with absolute ethanol, tighten the bottle cap and invert it up and down to shake well to dissolve it, obtaining an MPA solution with a concentration of 1 mg / ml. Store it in a refrigerator at 4 °C, and take it out when in use, dilute it to the target concentration with PBS and then use it.

[0024] Preparation of PBS buffer solution: Weigh 15.601 g of sodium dihydrogen phosphate dihydrate and 9.0 g of sodium chloride into a 500 ml beaker, dissolve them with ultrapure water, then transfer them to a 1000 mL volumetric flask and dilute to the mark with ultrapure water to obtain a 0.1 mol / L phosphate buffer stock solution. When in use, adjust the pH to 3.5 with 1 mol / mL NaOH and analytical pure phosphoric acid before use. The role of the phosphate buffer is to provide electrolytes as the electrolyte solution to reduce the solution resistance.

[0025] c. Establishment of the standard curve linear regression equation of the mycophenolic acid electrochemical sensor: Please refer to Figure 1 as Figure 1 shown in Figure (A) in Figure 1 . Using a PBS buffer solution with pH 2.0 and 0.1 mol / L as the electrolyte, and adopting the three-electrode sensing system constructed above, perform differential pulse voltammetry (DPV) detection on MPA with different concentrations (concentrations are 4.17, 7.29, 10.42, 13.54, 19.79, 26.04, 32.29, 38.54 μmol / L) to obtain the peak currents of MPA test solutions with different concentrations; as 2 shown in Figure (B) in

[0026] . Taking the MPA concentration as the independent variable and the peak currents of MPA test solutions with different concentrations as the dependent variable, establish a standard curve, and the linear equation is y = 0.01712x - 0.06352 (R

[0027] = 0.9034), the concentration detection range is 4.1688 - 138.5438 μmol / L, and the detection limit is 0.5337 μmol / L. Add the extract of the feed sample to be tested into a 0.1 mol / L PBS solution electrolyte with pH 2.0, perform DPV measurement in the three-electrode sensing system configured above to obtain the peak current value, and obtain the MPA concentration according to the standard curve linear regression equation of the mycophenolic acid electrochemical sensor established above.

[0028] (2)Determination of the effective specific surface area of the electrochemical sensor: The modified electrodes prepared in Example 1 and Comparative Examples 1-2 were subjected to CV scanning in a 5 mmol / L potassium ferricyanide solution, and the scanning rates were set to 25, 50, 75, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500 mV / s to explore the electrochemically active area of the sensor. The results are as Figure 2 shown. Figure 2 Figure (A) shows the Ip-v 1 / 2 curve of the modified electrode prepared in Comparative Example 1 in a 5 mmol / L potassium ferricyanide solution, Figure 2 and Figure (B) shows the CV curves of the modified electrode prepared in Comparative Example 1 at different scanning rates; Figure 2 Figure (C) shows the Ip-v 1 / 2 curve of the modified electrode prepared in Comparative Example 2 in a 5 mmol / L potassium ferricyanide solution, Figure 2 and Figure (D) shows the CV curves of the modified electrode prepared in Comparative Example 2 at different scanning rates; Figure 2 Figure (E) shows the Ip-v 1 / 2 curve of the modified electrode prepared in Example 1 in a 5 mmol / L potassium ferricyanide solution, Figure 2 and Figure (F) shows the CV curves of the modified electrode prepared in Example 1 at different scanning rates. According to the Randles–Sevick equation and the Ip-v 1 / 2 curves of each electrode, the effective surface area of the electrode can be calculated. The calculated effective specific surface area of the modified electrode prepared in Example 1 is 0.068 cm 2 , the effective specific surface area of the modified electrode prepared in Comparative Example 1 is 0.015 cm 2 , and the effective specific surface area of the modified electrode prepared in Comparative Example 2 is 0.028 cm 2 ; it can be seen that compared with the electrodes modified with single materials, the modified electrode prepared in this application is co-modified with Mg-Fe-LDH and GO and has a larger effective surface area, that is, higher electrochemistry activity, which confirms that the modified electrode prepared in this application has more advantages.

[0029] (3)Cyclic stability detection: Using the three-electrode sensing system described in (1), CV scanning was performed 100 cycles in a potassium ferricyanide solution, and the current values were recorded and the relative standard deviation (RSD) of the current was calculated to test the stability of the electrode. The results are as Figure 3 shown in Figure (A). The RAD of the modified electrode is 1.92% (anodic peak) and 1.47% (cathodic peak), indicating relatively high surface stability. Figure 3 Figure (B) shows the CV curves.

[0030] (4)Repeatability and reproducibility detection: Using the three-electrode sensing system described in (1), scan the 3.125 μmol / L MPA solution (pH = 2.0) 20 times in DPV mode, record the peak current values, and calculate the RSD of the current values for these 20 times. The results are as Figure 4 shown. Figure 4 The results shown in Figure (A) in [reference] are RSD = 1.74% < 5%. Additionally, prepare 6 more modified electrodes and test them under the same conditions. Calculate the RSD of the peak currents of these 6 modified electrodes. As Figure 4 shown in Figure (B) in [reference], the results are RSD = 1.77% < 5%, indicating that the sensor prepared by the present invention has good reproducibility for the detection of MPA. Good repeatability and reproducibility confirm that the electrode has good stability, proving that the electrode can be applied to the detection in the actual production process.

[0031] (5)Specificity detection: Using the GO / Mg-Fe-LDH modified electrode prepared by the present invention as the working electrode in an electrochemical sensor, the electrode detected several common substances in MPA and silage feed, such as sodium chloride, potassium chloride, L-isoleucine, L-leucine, glucose, sucrose, and citric acid. The DPV response to them is as Figure 5 shown. It can be seen that the interfering substances did not produce redox peaks and the overlapping degree of the measured redox peak of MPA with the redox peak of MPA without adding interfering substances is high. This indicates that the sensor prepared by the present invention has high anti-interference ability to other interfering substances and strong specificity.

[0032] (6)Actual sample detection: Dilute the silage feed sample extract with PBS buffer solution at pH = 2.0 and add MPA standard products to make their actual concentrations reach 5 μmol / L and 10 μmol / L respectively. Immerse the working electrode, counter electrode, and reference electrode in the solution to be measured, and obtain the peak current value by DPV method. According to the standard curve linear regression equation of the mycophenolic acid electrochemical sensor, calculate the MPA concentration, and calculate the recovery rate and RSD. The detection results are shown in Table 1; Table 1: Results of the recovery rate of spiked MPA in silage samples by the electrochemical sensor

[0033] As shown in Table 1, the recovery rate of corn silage is between 93.5% - 99.2%, and the RSD is between 0.23% - 0.82%. This proves that the GO / Mg-Fe-LDH modified electrode prepared in this application, when used as the working electrode in an electrochemical sensor, the electrochemical sensor can be used for the actual detection of MPV.

[0034] The above has described in detail an embodiment of the present invention, but the above content is only a preferred embodiment of the present invention and cannot be considered as defining the scope of implementation of the present invention. Any equivalent changes and improvements made within the scope of the application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A GO / Mg-Fe-LDH modified electrode, characterized in that, The modified electrode is composed of a working electrode, a layer of magnesium-iron bimetallic hydroxide and a layer of graphene oxide wrapped from the inside out on the surface of the working electrode.

2. The GO / Mg-Fe-LDH modified electrode according to claim 1, characterized in that, A magnesium-iron layered double hydroxide solution is coated on the surface of the working electrode and dried to obtain a layer of magnesium-iron bimetallic hydroxide.

3. The GO / Mg-Fe-LDH modified electrode according to claim 1, wherein The working electrode is any one of a glassy carbon electrode, a platinum electrode, a gold electrode, and a copper electrode.

4. The GO / Mg-Fe-LDH modified electrode according to claim 2, characterized in that, The magnesium-iron layered double hydroxide solution uses water as a solvent, and each milliliter of the solution contains 0.5 - 3 mg of magnesium-iron layered double hydroxide.

5. The GO / Mg-Fe-LDH modified electrode according to claim 2, wherein The working electrode is pretreated before coating with the magnesium-iron layered double hydroxide solution; the pretreatment steps include polishing the working electrode in a slurry containing polishing powder; the voltage difference between the two peaks of the working electrode obtained after pretreatment is less than 0.1 V.

6. The GO / Mg-Fe-LDH modified electrode according to claim 1, wherein, A graphene oxide solution is coated on the surface of the working electrode wrapped with a layer of magnesium-iron bimetallic hydroxide and dried to obtain a modified electrode wrapped with a layer of magnesium-iron bimetallic hydroxide and a layer of graphene oxide from the inside out.

7. The GO / Mg-Fe-LDH modified electrode according to claim 6, characterized in that, The graphene oxide solution uses water as a solvent, and each milliliter of the solution contains 0.5 - 3 mg of graphene oxide.

8. An electrochemical sensor, characterized in that, The GO / Mg-Fe-LDH modified electrode according to any one of claims 1 - 7 is used as the working electrode of the electrochemical sensor.

9. The electrochemical sensor according to claim 8, characterized in that, The electrochemical sensor is used for the detection of mycophenolic acid content.

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