Electrochemical sensor for detecting penicillin as well as preparation method and application of electrochemical sensor

Abstract

The embodiment of the invention provides an electrochemical sensor for detecting penicillin as well as a preparation method and application of the electrochemical sensor. The electrochemical sensor comprises a base electrode, a first solid film and a second solid film, wherein the first solid film and the second solid film are sequentially stacked on the base electrode; the first solid film is a multi-walled carbon nanotube, and the second solid film is an MIL-101-NH2 (Cr) composite material; the MIL-101-NH2 (Cr) composite material is a metal organic framework material formed by copolymerization of trivalent chromium salt and 2-aminoterephthalic acid. According to the electrochemical sensor for detecting penicillin as well as the preparation method and the application of the electrochemical sensor, penicillin molecules can be detected, and the detection limit can reach 2.071 mu mol / L; the method can be widely applied to detection of penicillin in foods such as dairy products.

Description

Technical Field

[0001] The present invention relates to the technical field of penicillin detection, in particular to an electrochemical sensor for detecting penicillin and a preparation method and application thereof. Background Art

[0002] Penicillin, the first β-lactam antibiotic to be widely used in clinical practice, exhibits significant antimicrobial activity against Gram-positive bacteria (such as Streptococcus and Streptococcus pneumoniae) by irreversibly inhibiting transpeptidase activity during bacterial cell wall peptidoglycan synthesis, thereby interfering with cell wall synthesis. The main risks associated with its clinical use include: 1) triggering allergic reactions, including type I immediate hypersensitivity reactions and severe anaphylactic shock; and 2) long-term abuse, which can induce bacterial resistance mechanisms such as β-lactamases, exacerbating the problem of antimicrobial resistance in public health. my country's current pharmacopoeia standards strictly define the purity, potency, and impurity limits for penicillins. In the food safety field, GB 31650-2019, the National Food Safety Standard, clearly stipulates the maximum penicillin residue limit in animal-derived foods (for example, a limit of 4 μg / kg in milk). However, excessive antibiotic residues in dairy products and other products remain a significant concern, requiring highly sensitive and specific analytical techniques for accurate detection and risk management.

[0003] Currently, the main methods for detecting penicillin residues are microbiological assays, high-performance liquid chromatography (HPLC), and enzyme-linked immunosorbent assays (ELISA). Microbiological assays, based on the inhibition of sensitive bacteria by penicillin, quantify the size of the inhibition zone. However, they have low sensitivity (detection limit approximately 50 μg / kg) and are time-consuming. HPLC, using chromatographic separation coupled with ultraviolet / fluorescence detection, can accurately determine residual levels of monomers such as penicillin G. It has high sensitivity (quantification limit can reach below 1 μg / kg), but the equipment cost is high and the operation is complex. Furthermore, rapid ELISA assays, based on antigen-antibody binding, offer the advantages of ease of use and batch testing, with a detection limit typically between 3 and 10 μg / kg. However, they are susceptible to matrix interference, leading to false positives.

[0004] Currently, while antibody-based electrochemical sensors offer high detection sensitivity (reaching the ng / mL level), their practical application is hampered by poor antibody stability (susceptibility to inactivation due to temperature and pH) and high preparation costs. On the other hand, metal-organic framework (MOF) materials have demonstrated excellent adsorption and enrichment capabilities in the field of mycotoxin detection, but their application in the specific recognition of penicillins is limited by the difficulty in accurately elucidating the synergistic mechanisms of the various components in their composite materials. Therefore, the development of an antibody-free electrochemical sensor based on the synergistic action of a single functionalized MOF and conductive materials (such as graphene and carbon nanotubes) to achieve high sensitivity (LOD < 0.1 μg / kg) and highly selective detection of penicillins has become an urgent research need. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide an antibody-free electrochemical sensor based on a single functionalized MOF and its preparation method and application, so as to achieve high-sensitivity and high-selectivity detection of penicillin.

[0006] In a first aspect, the present invention provides an electrochemical sensor for detecting penicillin, comprising: a base electrode and a first solid film and a second solid film sequentially stacked on the base electrode; the first solid film is a multi-walled carbon nanotube, and the second solid film is a MIL-101-NH2(Cr) composite material; the MIL-101-NH2(Cr) composite material is a metal-organic framework material formed by copolymerization of trivalent chromium salt and 2-aminoterephthalic acid.

[0007] Preferably, the trivalent chromium salt is one or more of chromium nitrate and chromium chloride; and the molar ratio of the trivalent chromium salt to the 2-aminoterephthalic acid is 1:(1-2).

[0008] In a second aspect, the present invention further provides a method for preparing the electrochemical sensor for detecting penicillin as described above, comprising the following steps: preparing a multi-walled carbon nanotube suspension; The trivalent chromium salt and 2-aminoterephthalic acid are dissolved in a solvent to form a mixed solution, and the mixed solution is heated to cause a copolymerization reaction to prepare a MIL-101-NH2(Cr) composite material; The multi-walled carbon nanotube suspension is drop-coated on the surface of the base electrode to form a first solid film, and then the MIL-101-NH2(Cr) composite material is drop-coated on the surface of the first solid film to form a second solid film, thereby obtaining a finished product.

[0009] Preferably, in the step of preparing the multi-walled carbon nanotube suspension, the method for preparing the multi-walled carbon nanotube suspension comprises: An acidic solution is added to the multi-walled carbon nanotubes for acidification, and ultrasonic treatment is performed to prepare a multi-walled carbon nanotube suspension.

[0010] Preferably, the mass-to-volume ratio of the multi-walled carbon nanotubes to the acidic solution is 1-10 g / mL; and the ultrasonic treatment conditions are: ultrasonic power of 200-400 W, and ultrasonic time of 4-6 h.

[0011] Preferably, the heating temperature for the copolymerization reaction of the mixed solution is 100-150°C.

[0012] Preferably, before the step of applying the multi-walled carbon nanotube suspension droplets to the surface of the base electrode to form the first solid film, the method further comprises: performing an activation treatment on the base electrode; The method for activating the basic electrode comprises placing the basic electrode in an acidic solution and scanning the basic electrode by cyclic voltammetry at a potential range of -0.6 to 1.0 V and a scanning frequency of 50 to 100 mV / s for 20 to 50 cycles.

[0013] In a third aspect, the present invention further provides a use of the electrochemical sensor described above in detecting penicillin.

[0014] Preferably, the application method comprises: Placing a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode in an electrolytic cell containing an electrolyte; the working electrode is the electrochemical sensor described above; Prepare penicillin standard solutions with different concentration gradients; The redox peak current values of penicillin standard solutions with different concentration gradients were detected by linear voltammetry, and a linear regression equation of I=kC+b was obtained by performing a linear regression between the redox peak current value I and the concentration C. A certain amount of sample was placed in the electrolytic cell, and the redox peak current value of the sample was detected by linear voltammetry. The concentration of penicillin in the sample was calculated by the following formula (1): C=(Ib) / k(1) Preferably, the electrolyte in the electrolytic cell comprises a PBS buffer solution with a volume ratio of (4-5):1 and a potassium ferricyanide solution with a molar concentration of 3-5 mmol / L.

[0015] The beneficial effects of the present invention are: The present invention provides an electrochemical sensor for detecting penicillin, a preparation method thereof, and an application thereof. The metal organic framework material MIL-101-NH2(Cr) with amino functional groups is synthesized by a solvent thermal method. The surface of the material is rich in amino functional groups (-NH2) and open metal sites (Cr 3+), the amino group is partially protonated to form -NH3 in aqueous solution + , endowing the material with a positive surface charge. Multi-walled carbon nanotubes (MWCNTs), through their hydrophobic surface and π-electron system, generate strong π-π stacking interactions and coordination bonds with MIL-101-NH2(Cr), thereby constructing a stable three-dimensional conductive composite structure. The mesoporous structure of the MIL-101-NH2(Cr) composite provides abundant adsorption sites. Its surface amino groups selectively recognize penicillin molecules through hydrogen bonding and electrostatic interactions with the β-lactam ring of the penicillin molecule. Furthermore, the open metal sites form stable coordination bonds with the carboxyl groups of penicillin, significantly improving the enrichment efficiency. Furthermore, the high conductivity of the MWCNTs effectively promotes electron transport, creating a synergistic effect with the adsorption-catalytic properties of MIL-101-NH2(Cr), resulting in the sensor exhibiting high sensitivity and excellent anti-interference performance for penicillin detection.

[0016] The electrochemical sensor can detect penicillin molecules within 10 -10.3 ~10 -5 The method has a wide linear range of 1.5 μmol / L and a detection limit of 2.071 μmol / L. It can be widely used in the detection of penicillin in foods such as dairy products, with sample recoveries ranging from 75.5% to 131.82%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0018] Figure 1 This is a flow chart for the preparation of an electrochemical sensor for detecting penicillin; Figure 2a It is the detection linearity plot of cyclic voltammetry; Figure 2b is the electrochemical impedance spectroscopy; Figure 3a The concentration gradient is 10 -10.3 ~10 -5 Linear voltammetry curve in the mol / L range; Figure 3b The concentration gradient is 10 -10.3 ~10 -5 Linear voltammetric detection linearity plot in the mol / L range. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0020] An embodiment of the present invention provides an electrochemical sensor for detecting penicillin, comprising: a base electrode and a first solid film and a second solid film sequentially stacked on the base electrode; the first solid film is a multi-walled carbon nanotube, and the second solid film is a MIL-101-NH2(Cr) composite material; the MIL-101-NH2(Cr) composite material is a metal-organic framework material formed by copolymerization of trivalent chromium salt and 2-aminoterephthalic acid.

[0021] Specifically, the trivalent chromium salt is one or more of chromium nitrate and chromium chloride; and the molar ratio of the trivalent chromium salt to the 2-aminoterephthalic acid is 1:(1-2).

[0022] An embodiment of the present invention provides a method for preparing an electrochemical sensor for detecting penicillin, comprising the following steps: S1: Preparation of multi-walled carbon nanotube suspension; S2: dissolving trivalent chromium salt and 2-aminoterephthalic acid in a solvent to form a mixed solution, and copolymerizing the mixture at a temperature of 100-150° C. to obtain a MIL-101-NH2(Cr) composite material; S3: drop-coating the multi-walled carbon nanotube suspension on the surface of the base electrode to form a first solid film, and then drop-coating the MIL-101-NH2(Cr) composite material on the surface of the first solid film to form a second solid film, thereby obtaining a finished product.

[0023] In the above step S1, the method for preparing the multi-walled carbon nanotube suspension comprises the following steps: S11: adding an acidic solution to the multi-walled carbon nanotubes for acidification, and performing ultrasonic treatment to obtain a multi-walled carbon nanotube suspension.

[0024] The solvent is a mixed solution of butanol and 1,4-dioxane in a volume ratio of (1-3):1; the catalyst can be acetic acid. The mass-to-volume ratio of the multi-walled carbon nanotubes to the acidic solution is 1-10 g / mL; and the ultrasonic treatment conditions are: an ultrasonic power of 200-400 W and a sonication time of 4-6 hours.

[0025] In the above step S3, before the step of applying the multi-walled carbon nanotube suspension droplets to the surface of the base electrode to form the first solid film, the step further includes: activating the base electrode; The step of activating the basic electrode comprises placing the basic electrode in an acidic solution and scanning the basic electrode by cyclic voltammetry at a potential range of -0.6 to 1.0 V and a scanning frequency of 50 to 100 mV / s for 20 to 50 cycles.

[0026] An embodiment of the present invention provides an application of an electrochemical sensor in detecting penicillin.

[0027] The above application method comprises: placing a three-electrode system consisting of a working electrode, a counter electrode and a reference electrode in an electrolytic cell containing an electrolyte; the working electrode is the electrochemical sensor described above; Prepare penicillin standard solutions with different concentration gradients; The redox peak current values of penicillin standard solutions with different concentration gradients were detected by linear voltammetry, and a linear regression equation of I=kC+b was obtained by performing a linear regression between the redox peak current value I and the concentration C. A certain amount of sample was placed in the electrolytic cell, and the redox peak current value of the sample was detected by linear voltammetry. The concentration of penicillin in the sample was calculated by the following formula (1): C=(Ib) / k(1) Specifically, the electrochemical sensor uses a glassy carbon electrode as the base electrode, constructing a MWCNTs-MIL-101-NH2(Cr) / GCE electrochemical sensor. A platinum wire electrode is used as the counter electrode, and a saturated calomel electrode is used as the reference electrode. The electrolyte in the electrolytic cell consists of a PBS buffer solution with a volume ratio of (4-5):1 and a potassium ferricyanide solution with a molar concentration of 3-5 mmol / L.

[0028] The following is further described with reference to specific examples.

[0029] Example 1 An electrochemical sensor for detecting penicillin provided by an embodiment of the present invention is a MWCNTs-MIL-101-NH2(Cr) / GCE electrochemical sensor, wherein the molar ratio of trivalent chromium salt and 2-aminoterephthalic acid, which are copolymerized to form the MIL-101-NH2(Cr) composite material, is 1:1.

[0030] Figure 1 This is a flow chart for the preparation of an electrochemical sensor for detecting penicillin. Figure 1 The preparation method of the electrochemical sensor comprises the following steps: 1) Weigh a certain amount of multi-walled carbon nanotubes, add a nitric acid solution with a mass volume ratio of 1g / mL, ultrasonically disperse and acidify for 6 hours; after acidification, wash until neutral, dry, grind, and store at room temperature for later use; weigh 5mg of the treated multi-walled carbon nanotubes, place them in 5mL of ultrapure water, and ultrasonically treat them at an ultrasonic power of 200W for 6 hours to form a 1mg / mL multi-walled carbon nanotube suspension; 2) Dissolve 2 mmol of chromium nitrate, 2 mmol of 2-aminoterephthalic acid, and 5 mmol of NaOH in 15 mL of deionized water and stir for 5 min to obtain solution A. Transfer solution A to a 20 mL polytetrafluoroethylene-lined autoclave and heat at 150°C for 12 h to obtain solution B. Cool solution B to room temperature, centrifuge to remove the supernatant, and collect the product. Wash the product with N,N-dimethylformamide and methanol, and reflux the product in a methanol solution at 70°C for 48 h, replacing the methanol every 12 h. Finally, dry the product in a vacuum oven at 80°C for 12 h to obtain the MIL-101-NH2(Cr) composite material, which is then collected for later use.

[0031] 3) Polish a glassy carbon electrode with 0.02 μm diameter alumina powder; rinse the polished glassy carbon electrode with deionized water, ultrasonically clean it in deionized water for 3 minutes, ultrasonically clean it in anhydrous ethanol for 3 minutes, and ultrasonically clean it again in deionized water for 3 minutes; place the cleaned glassy carbon electrode in 0.5 M (mol / L) sulfuric acid solution and activate it by cyclic voltammetry over a potential range of -0.6 to 1.0 V for 50 cycles; rinse it with deionized water after activation and place it in deionized water for later use; 4) Take 3 μL of multi-walled carbon nanotube suspension and drop-coat it on the surface of the activated glassy carbon electrode. Refrigerate and dry it for 4 hours until the surface of the glassy carbon electrode becomes a thin film, forming a layer of MWCNTs film. Then, drop-coat the MIL-101-NH2(Cr) composite material on the surface of the MWCNTs film to prepare the MWCNTs-MIL-101-NH2(Cr) / GCE electrochemical sensor.

[0032] Example 2 An electrochemical sensor for penicillin detection provided in this embodiment is a MWCNTs-MIL-101-NH2(Cr) / GCE electrochemical sensor. The molar ratio of trivalent chromium salt and 2-aminoterephthalic acid, which are copolymerized to form the MIL-101-NH2(Cr) composite material, is 1:2. Its preparation method is the same as in Example 1.

[0033] Example 3 The electrochemical sensor for detecting penicillin and the preparation method provided in this embodiment of the present invention are the same as those in Example 1, except that the mass-to-volume ratio of the multi-walled carbon nanotubes to the acidic solution is 5 g / mL.

[0034] Example 4 The electrochemical sensor for detecting penicillin and the preparation method provided in this embodiment of the present invention are the same as those in Example 1, except that the mass-to-volume ratio of the multi-walled carbon nanotubes to the acidic solution is 10 g / mL.

[0035] Example 5 The electrochemical sensor for detecting penicillin and the preparation method provided in this embodiment of the present invention are the same as those in Example 1, except that the ultrasonic power is 300 W and the ultrasonic time is 6 h.

[0036] Example 6 The electrochemical sensor for detecting penicillin and the preparation method provided in this embodiment of the present invention are the same as those in Example 1, except that the ultrasonic power is 400 W and the ultrasonic time is 4 h.

[0037] Example 7 An electrochemical sensor for detecting penicillin and a preparation method provided in this embodiment of the present invention are the same as those in Example 1.

[0038] The application method of the electrochemical sensor comprises the following steps: 1) Prepare PBS buffer solution with pH = 7.5; 2) Weigh a certain amount of penicillin and dissolve it in ultrapure water to make a volume of 10 -10.3 ~10 -5 Penicillin standard solution with M (mol / L) concentration gradient; 3) Weigh a certain amount of potassium ferrocyanide and dissolve it in ultrapure water to prepare a 5 mM (mmol / L) potassium ferrocyanide solution; 4) Construction of a three-electrode system: 5 mL of PBS buffer solution was transferred to the electrolytic cell, and 1 mL of potassium ferricyanide solution was added to form the electrolyte. The MWCNTs-MIL-101-NH2(Cr) / GCE electrochemical sensor was used as the working electrode, the platinum wire electrode as the counter electrode, and the saturated calomel electrode as the reference electrode. The working conditions were set as follows: potential range of -1 to 1 V, scan rate of 0.05 V / s, and sensitivity of 10 -5 A / V, pulse width 50ms.

[0039] 5) Take 10 -10.3 ~10 -5 M penicillin standard solution with different concentration gradients, 1 μL of each concentration was taken 10 times in sequence, with a sampling interval of 0.1 s.

[0040] 6) Detect and record the redox peak current values at different concentration gradients using linear voltammetry. Perform a linear regression between the redox peak current value I and the concentration C to obtain the linear regression equation I = kC + b (k and b are constants). 7) Add 10 μL of sample to the electrolytic cell three times. Detect and record the redox peak current values I1, I2, and I3 by linear voltammetry. Calculate the corresponding concentrations C1, C2, and C3 of I1, I2, and I3 using the linear regression equation. The average value of C1, C2, and C3 is the penicillin concentration in the sample.

[0041] The following is a further explanation of penicillin detection.

[0042] 1. Cyclic voltammetry and linear voltammetry 1.1 Experimental Subjects Experimental group: glassy carbon electrode surface modified with MWCNTs-MIL-101-NH2(Cr) (Example 1); Control group 1: glassy carbon electrode (GCE); Control group 2: glassy carbon electrode modified with MWCNTs; Control group 3: glassy carbon electrode surface modified with MIL-101-NH2(Cr); Control group 4: glassy carbon electrode with surface modified with MIL-101-NH2(Cr)-Pen (Penicillin).

[0043] 1.2 Experimental Methods 1) Prepare PBS buffer solution with pH = 7.5; 2) Weigh a certain amount of penicillin and dissolve it in ultrapure water to make a volume of 10 -10.3 ~10 -5 M concentration gradient of penicillin standard solution; 3) Weigh a certain amount of potassium ferrocyanide and dissolve it in ultrapure water to prepare a 5 mM potassium ferrocyanide solution; 4) Construct a three-electrode system: Pipette 5 mL of PBS buffer solution into the electrolytic cell and add 1 mL of potassium ferricyanide solution to form the electrolyte. Use the electrochemical sensors 1 to 4 in the experimental and control groups as the working electrodes, the platinum wire electrode as the counter electrode, and the saturated calomel electrode as the reference electrode. The working conditions are: potential range of -1 to 1 V, scan rate of 0.05 V / s, sensitivity of 10 -5 A / V, pulse width 50ms.

[0044] 5) Take 10 -10.3 ~10 -5M different concentration gradients of penicillin standard solution, each concentration was taken 1 μL 10 times, with a sampling interval of 0.001V.

[0045] 6) Detect and record the redox peak current and charge transfer resistance values of the experimental and control groups in the potential range of -1 to 1 V using cyclic voltammetry and electrochemical impedance spectroscopy; and detect and record the redox peak current values of the experimental group at different concentration gradients using linear voltammetry; 1.3 Results Analysis Figure 2a It is the detection linear diagram of cyclic voltammetry, where the horizontal axis "Potential" represents the potential and the vertical axis "Current" represents the redox peak current value; Figure 2b It is an electrochemical impedance spectrum, where the horizontal axis “Z'” represents the real part and the vertical axis “Z''” represents the imaginary part.

[0046] Depend on Figure 2a It can be seen that the current response is weak when the glassy carbon electrode is modified with single multi-walled carbon nanotubes and MIL-101-NH2(Cr). The redox peak current value of the glassy carbon electrode modified with MIL-101-NH2(Cr) is the highest. After the penicillin solution is added to the electrolytic cell, the redox peak current decreases, indicating that MWCNTs-MIL-101-NH2(Cr) / GCE has a significant response to penicillin.

[0047] Depend on Figure 2b It can be seen that the semiconducting properties of MIL-101-NH2(Cr) result in a high electrical impedance, but it is lower than that of GCE, indicating partial conductivity. The conductive network of MWCNTs partially compensates for the high electrical impedance of MIL-101-NH2(Cr), but is still limited by the MIL-101-NH2(Cr) itself. The increased slope of the line in the low-frequency region indicates that the material has improved ion diffusion capacity (possibly related to the porous structure of MOFs).

[0048] In summary, it is shown that the electrochemical sensor according to the embodiment of the present invention has good electrical sensing performance.

[0049] Figure 3a The concentration gradient is 10 -10.3 ~10 -5 Linear sweep voltammetry curve in the mol / L range, where the horizontal axis "Potential" represents the potential and the vertical axis "Current" represents the redox peak current value; Figure 3b The concentration gradient is 10 -10.3 ~10 -5Linear voltammetry detection linearity graph in the mol / L range. The horizontal axis "Concentration" represents the concentration, and the vertical axis "Current" represents the redox peak current value; Depend on Figure 3a It can be seen that the greater the penicillin concentration, the greater the current.

[0050] Depend on Figure 3b It can be seen that at a penicillin concentration of 10 -10.3 ~10 -5 In the range of mol / L, the electrochemical sensor of the embodiment of the present invention has a good linear response. The redox peak current value is linearly related to the concentration, and its regression curve y=9.41519E -6 +4.76435E -7 x, correlation coefficient R 2 =0.99021, the detection limit (S / N=3) of the electrochemical sensor of the embodiment of the present invention is 2.071 μmol / L, and the quantification limit (S / N=10) is 2.238 μmol / L.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An electrochemical sensor for detecting penicillin, characterized in that: include: A base electrode and a first solid film and a second solid film sequentially stacked on the base electrode; the first solid film is a multi-walled carbon nanotube, and the second solid film is a MIL-101-NH2(Cr) composite material; the MIL-101-NH2(Cr) composite material is a metal organic framework material formed by copolymerization of trivalent chromium salt and 2-aminoterephthalic acid.

2. The electrochemical sensor according to claim 1, characterized in that The trivalent chromium salt is one or more of chromium nitrate and chromium chloride; the molar ratio of the trivalent chromium salt to the 2-aminoterephthalic acid is 1:(1-2).

3. A method for preparing an electrochemical sensor for detecting penicillin according to claims 1 and 2, characterized in that: include: preparing a multi-walled carbon nanotube suspension; The trivalent chromium salt and 2-aminoterephthalic acid are dissolved in a solvent to form a mixed solution, and the mixed solution is heated to cause a copolymerization reaction to prepare a MIL-101-NH2(Cr) composite material; The multi-walled carbon nanotube suspension is drop-coated on the surface of the base electrode to form a first solid film, and then the MIL-101-NH2(Cr) composite material is drop-coated on the surface of the first solid film to form a second solid film, thereby obtaining a finished product.

4. The preparation method according to claim 3, wherein: In the step of preparing the multi-walled carbon nanotube suspension, the preparation method of the multi-walled carbon nanotube suspension includes: An acidic solution is added to the multi-walled carbon nanotubes for acidification, and ultrasonic treatment is performed to prepare a multi-walled carbon nanotube suspension.

5. The preparation method according to claim 4, characterized in that: The mass volume ratio of the multi-walled carbon nanotubes to the acidic solution is 1-10 g / mL; the conditions of the ultrasonic treatment are: ultrasonic power of 200-400 W, and ultrasonic time of 4-6 hours.

6. The preparation method according to claim 3, characterized in that The heating temperature for the copolymerization reaction of the mixed solution is 100-150°C.

7. The preparation method according to claim 3, characterized in that Before the step of applying the multi-walled carbon nanotube suspension droplets to the surface of the base electrode to form a first solid film, the step further includes: activating the base electrode; The step of activating the basic electrode comprises placing the basic electrode in an acidic solution and scanning the basic electrode by cyclic voltammetry at a potential range of -0.6 to 1.0 V and a scanning frequency of 50 to 100 mV / s for 20 to 50 cycles.

8. Use of the electrochemical sensor according to any one of claims 1 to 7 in detecting penicillin.

9. The use according to claim 8, characterized in that The application method includes: Placing a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode in an electrolytic cell containing an electrolyte; the working electrode is the electrochemical sensor according to any one of claims 1 to 7; Prepare penicillin standard solutions with different concentration gradients; The redox peak current values of penicillin standard solutions with different concentration gradients were detected by linear voltammetry, and a linear regression equation of I=kC+b was obtained by performing a linear regression between the redox peak current value I and the concentration C. A certain amount of sample was placed in the electrolytic cell, and the redox peak current value of the sample was detected by linear voltammetry. The concentration of penicillin in the sample was calculated by the following formula (1): C=(Ib) / k(1).

10. The use according to claim 9, characterized in that The electrolyte in the electrolytic cell includes a PBS buffer solution with a volume ratio of (4-5):1 and a potassium ferricyanide solution with a molar concentration of 3-5 mmol / L.

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