Working electrode for detecting molecular imprinting ratio of BPA as well as preparation method and application of working electrode

Abstract

The invention discloses a working electrode for detecting the molecular imprinting ratio of BPA as well as a preparation method and application of the working electrode, and belongs to the field of analysis and detection. The invention aims to simply and accurately detect the content of BPA. The method comprises the following steps: 1, dispersing a nickel salt and an organic ligand in N, N-dimethylformamide and absolute ethyl alcohol respectively, uniformly mixing the nickel salt and the organic ligand, carrying out solvothermal reaction, washing, and carrying out vacuum drying; dispersing the mixed solution and multi-walled carbon nanotubes in a solvent, and carrying out an ultrasonic reaction; then adding a fixing agent, dripping on a glassy carbon electrode, drying, dripping [APMIm] Br, and naturally drying to obtain a modified electrode; and placing the modified electrode in a phosphate buffer solution containing thionine and BPA, performing electrochemical polymerization to form a film, performing natural drying, placing the film in a sulfuric acid solution, performing elution, and performing drying to obtain the working electrode. The electrode has high sensitivity and good selectivity, and after the reference probe is introduced, the test precision is greatly improved. The method is applied to detection of BPA content in water samples and plastic products.

Description

Technical Field

[0001] The invention belongs to the field of analysis and detection, and in particular relates to a method for preparing a molecular imprinting ratio working electrode for detecting BPA. Background Art

[0002] Bisphenol A (BPA), also known as 2,2-bis(4-hydroxyphenyl)-propane, is a class of harmful chemicals with estrogen characteristics, and has the characteristics of heat resistance, light weight, acid resistance, and impact resistance. When BPA is used in baby bottles, water bottles, or other food packaging, it may migrate into the food and be absorbed by the human body under the influence of oil, acid or other external environment, causing a variety of adverse effects on humans, such as decreased fertility, decreased immune function, and even the occurrence of cancer. Therefore, rapid and accurate detection of the content of BPA in the environment is an important technical means to ensure human health and environmental safety, and has important practical significance.

[0003] At present, many BPA detection methods have been developed and are becoming more and more perfect. Among the methods that have been reported, chromatography and its combination technology are the most commonly used analytical detection methods due to their high sensitivity and good selectivity, but they have problems such as expensive equipment, complex operation, and long analysis time. Summary of the invention

[0004] In order to detect the content of BPA simply and accurately, the present invention provides a method for preparing a molecular imprinting ratio working electrode for detecting BPA, which is used as an electrochemical sensor working electrode for electrochemical detection of BPA content, and is particularly suitable for electrochemical detection of BPA content in tap water samples and plastic products.

[0005] The present invention uses a nickel-based metal organic framework / multi-walled carbon nanotube composite material as an electrode modification material to improve the conductivity and electroactive area of ​​a bare glassy carbon electrode, and uses thionine as both a functional monomer for preparing a molecular imprinting membrane and a reference probe for electrochemical detection to construct a molecular imprinting ratio electrochemical sensor that specifically responds to BPA. The electrode prepared by the method of the present invention not only has high sensitivity and good selectivity, but also greatly improves the test accuracy after the reference probe is introduced.

[0006] The present invention adopts solvent thermal reaction to prepare nickel-based metal organic framework material, ultrasonic reaction to prepare nickel-based metal organic framework / multi-walled carbon nanotube composite material, nickel-based metal organic framework / multi-walled carbon nanotube composite material as modification material of electrochemical sensing interface, thionine as functional monomer for preparing molecular imprinting membrane and reference probe for electrochemical detection, and prepares molecular imprinting ratio electrochemical sensor with specific recognition response to template molecule BPA on the surface of modified electrode by electrochemical polymerization. The present invention introduces ratio detection strategy, takes electrochemical response of polythionine and potassium ferrocyanide as reference probe signal and detection signal respectively, combines molecular imprinting technology, prepares molecular imprinting ratio electrochemical sensor with specific recognition response to BPA molecule, and applies it to detection of BPA content, which has simple operation, low cost, high sensitivity and good selectivity.

[0007] The present invention is based on the rapid detection of the content of BPA samples. The factors affecting the electrochemical performance mainly include: the ratio of functional monomers to template molecules, elution conditions, etc. The above conditions are optimized to construct a molecular imprinting ratio electrochemical sensor with specific recognition of BPA.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The object of the present invention is to provide a method for preparing a molecular imprinting ratio working electrode for detecting BPA, comprising the following steps:

[0010] Step 1, dispersing nickel salt in N,N-dimethylformamide to obtain solution A, dispersing organic ligand in anhydrous ethanol to obtain solution B, mixing solutions A and B, and performing a solvothermal reaction. After the reaction is completed, washing and vacuum drying are performed to obtain a nickel-based metal organic framework material;

[0011] Step 2, dispersing the nickel-based metal organic framework material and the multi-walled carbon nanotubes in a solvent, and subjecting the mixture to ultrasonic reaction;

[0012] Step 3, then add a fixing agent, drop it on the glassy carbon electrode, dry it, drop-coat 1-aminopropyl-3-methylimidazolium bromide ionic liquid ([APMIm]Br), dry it naturally, and obtain a modified electrode;

[0013] Step 4: placing the modified electrode in a phosphate buffer containing thionine and BPA, electrochemically polymerizing the modified electrode into a film, drying the film naturally, placing the modified electrode in a sulfuric acid solution for elution, and drying the modified electrode to obtain the working electrode.

[0014] In one embodiment of the present invention, in step 1, the nickel salt is Ni(NO3)2·6H2O; and the organic ligand is 1,3,5-benzenetricarboxylic acid.

[0015] In one embodiment of the present invention, in step 1, the molar ratio of the nickel salt to the organic ligand is 7:2.

[0016] In one embodiment of the present invention, in step 1, the solvent thermal reaction is carried out at 120° C. for 12 hours.

[0017] In one embodiment of the present invention, in step 1, after solid-liquid separation by centrifugation, the solid is collected, then washed three times with N,N-dimethylformamide, and then washed with anhydrous ethanol until neutral.

[0018] In one embodiment of the present invention, in step 2, the mass ratio of the nickel-based metal organic framework material to the multi-walled carbon nanotubes is 1:5.

[0019] In one embodiment of the present invention, in step 3, the fixing agent is a 1 wt.% chitosan solution, and the volume ratio of the composite material to the fixing agent is 3:1.

[0020] In one embodiment of the present invention, in step 3, the product is placed in an oven at 50° C. and dried for 10 min-20 min.

[0021] In one embodiment of the present invention, in step 3, the concentration of [APMIm]Br is 0.5 mM.

[0022] In one embodiment of the present invention, the concentration ratio of thionine to BPA in step 4 is 1:1-8:1, preferably 4:1.

[0023] In one embodiment of the present invention, the concentration of BPA in step 4 is 0.2 mM.

[0024] In one embodiment of the present invention, the concentration of thionine in step 4 is 0.2 mM-1.6 mM.

[0025] In one embodiment of the present invention, the pH value of the phosphate buffer containing thionine and BPA in step 4 is 5.5.

[0026] In one embodiment of the present invention, in step 4, the process parameters of electrochemical polymerization film formation are: scanning potential: -0.4V-0.4V, number of scanning cycles: 25 cycles, scanning rate: 0.1V·s -1 .

[0027] In one embodiment of the present invention, in step 4, the process of eluting the template molecules is to place the electrode in a 0.1MH2SO4 solution for elution.

[0028] Another object of the present invention is to provide a working electrode prepared by any of the above methods.

[0029] Another object of the present invention is to provide an electrochemical sensor comprising a working electrode prepared by any of the above methods.

[0030] Another object of the present invention is to provide the molecular imprinting ratio working electrode as a working electrode of an electrochemical sensor for electrochemical detection of BPA content; in particular, for electrochemical detection of BPA content in tap water samples.

[0031] The present invention also provides a method for electrochemically detecting BPA content, the method comprising the following process:

[0032] A series of BPA samples with known concentrations were prepared, and the above molecular imprinting ratio electrochemical sensor was used as the working electrode to detect the electrochemical signal of the BPA samples by square wave voltammetry (SWV). Fe ) and polythiophene (I Thi ) current signal; using the current ratio I Fe / I Thi A linear relationship was constructed with the corresponding BPA concentration to obtain the BPA detection model.

[0033] In the method of the present invention, the concentration of a series of BPA samples ranged from 5 nM to 400 nM.

[0034] In the method of the present invention, the content of BPA is determined by preparing a molecular imprinting ratio electrochemical sensor. In order to evaluate the electrochemical performance of the prepared nickel-based metal organic framework / multi-walled carbon nanotube composite material, the cyclic voltammetric behavior of a bare glassy carbon electrode, a nickel-based metal organic framework / multi-walled carbon nanotube composite modified electrode, an ionic liquid [APMIm]Br modified electrode, an electrode after electropolymerization of molecular imprinted polymer, and an imprinted electrode after eluting BPA molecules in potassium ferrocyanide was used to confirm (see Figure 1 ). The ratio of template molecule to functional monomer was further optimized, and it was found that when the concentration ratio of functional monomer to template molecule was 4:1, the prepared molecular imprinting ratio electrochemical sensor had better detection performance for BPA (see Figure 2 ).

[0035] The molecular imprinting ratio electrochemical sensor prepared by the present invention is based on nickel-based metal organic framework and multi-walled carbon nanotubes, and is used for highly sensitive identification of BPA. It has good sensitivity (see Figure 3 ), and better selectivity (see Figure 4 ). It can be used to detect BPA content in water samples and plastic products.

[0036] The present invention has the following beneficial effects:

[0037] The molecular imprinting ratio electrochemical sensor prepared by the present invention is used for the specific identification and analysis technology of BPA. The traditional detection method of BPA has a long cycle and a cumbersome process. Therefore, a molecular imprinting ratio electrochemical sensor is proposed for the development of highly sensitive identification and specific response to BPA in the environment. In the present invention, the material preparation of the modified electrode is simple and inexpensive. The detection method proposed is SWV, which can quickly detect the concentration of BPA and has high sensitivity (see the attached example). Figure 3 ), the current ratio is linearly related to the logarithm of BPA concentration in the concentration range of 5nM-400nM, and the calculated detection limit is 1.1nM; and it has good selectivity (see Figure 4 ).

[0038] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the attached drawings are only provided for reference and illustration and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Figure 2 is an electrochemical sensor diagram of molecular imprinting ratios of different modified electrodes; A is a bare glassy carbon electrode, B is a nickel-based metal organic framework / multi-walled carbon nanotube composite modified electrode, C is an ionic liquid [APMIm]Br / nickel-based metal organic framework / multi-walled carbon nanotube composite modified electrode, D is an electrode after electropolymerization molecular imprinting membrane, and E is a molecular imprinting electrochemical sensor after elution.

[0040] Figure 2 Comparison of the signals of molecularly imprinted ratiometric electrochemical sensors prepared with different ratios of template molecules and functional monomers.

[0041] Figure 3 (A) SWV diagram of the molecular imprinting ratio electrochemical sensor of the present invention for detecting different concentrations of BPA (the concentrations from a to e are 5, 6, 40, 80, 400 nM, respectively). (B) Linear relationship diagram of the BPA detection method of the present invention.

[0042] Figure 4 Comparison of the selectivity performance of molecular imprinting ratiometric electrochemical sensors for BPA (10 nM). (a) BPA, (b) BPA + bisphenol E (BPE, 10 nM), (c) BPA + bisphenol S (BPS, 10 nM), (d) BPA + bisphenol P (BPP, 10 nM), (e) BPA + bisphenol M (BPM, 10 nM). DETAILED DESCRIPTION

[0043] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0044] Example 1: The preparation method of the working electrode for detecting the molecular imprinting ratio of BPA in this example is prepared according to the following steps:

[0045] Step 1, preparation of nickel-based metal organic framework material: 0.7mmol Ni(NO3)2·6H2O is dispersed in 18mLN,N-dimethylformamide (DMF) to obtain solution A, 0.2mmol 1,3,5-benzenetricarboxylic acid is dispersed in 18mL anhydrous ethanol to obtain solution B, then solutions A and B are mixed, and placed in a 100mL polytetrafluoroethylene high-pressure reactor for solvothermal reaction. The solvothermal reaction time is 12h, and the solvothermal reaction temperature is 120°C. After the solvothermal reaction is completed, solid-liquid separation is performed by centrifugation, and the solid is collected. The collected solid is washed three times with N,N-dimethylformamide (DMF), then washed with anhydrous ethanol until neutral, placed in a vacuum drying oven, and dried at 60°C for 10h to obtain a nickel-based metal organic framework material.

[0046] Step 2, preparation of nickel-based metal organic framework / multi-walled carbon nanotube composite material: 2 mg of nickel-based metal organic framework material and 10 mg of multi-walled carbon nanotubes are placed in 10 mL of N,N-dimethylformamide, and ultrasonic reaction is carried out in an ultrasonic cleaner with an operating frequency of 40 KHz and an ultrasonic power of 600 W. The reaction time is 30 min and the reaction temperature is room temperature. After the ultrasonic reaction, a nickel-based metal organic framework / multi-walled carbon nanotube composite material is obtained.

[0047] Step 3, preparation of modified electrode: use the nickel-based metal organic framework / multi-walled carbon nanotube composite material obtained in step 2 to prepare a modified electrode: the above nickel-based metal organic framework / multi-walled carbon nanotube composite material and 1wt.% chitosan solution (fixative) are dispersed uniformly, the volume ratio of the composite material to the fixative is 3:1, 10μL is taken and dropped on the polished glassy carbon electrode, placed in an oven at 50℃ and dried for 12min, and then 4μL of 0.5mM 1-aminopropyl-3-methylimidazolium bromide is dropped on the electrode surface after the above treatment, and naturally dried to obtain the modified electrode.

[0048] Step 4, preparation of molecular imprinting ratio electrode: The modified electrode obtained in step 3 above was placed in a phosphate buffer containing thionine and BPA (the concentration ratio of thionine to BPA was 1:1, the concentration of thionine was 0.2 mM, and the pH of the buffer was 5.5), and electrochemical polymerization was performed to form a film (electropolymerization conditions: scanning potential: -0.4 V-0.4 V, scanning number: 25 cycles, scanning rate: 0.1 V·s -1 ), and then the polymerized electrode was naturally dried and then placed in a 0.1M H2SO4 solution for elution to obtain a molecular imprinting ratio working electrode, which was used as an electrochemical sensor working electrode for electrochemical detection of BPA content.

[0049] Example 2: Preparation of molecular imprinting ratio working electrode in this example:

[0050] The modified electrode obtained in step 3 of Example 1 was placed in a phosphate buffer containing thionine and BPA (the concentration ratio of thionine to BPA was 2:1, the concentration of thionine was 0.4 mM, and the pH of the buffer was 5.5), and electrochemical polymerization was performed to form a film (electropolymerization conditions: scanning potential: -0.4 V-0.4 V, scanning number: 25 cycles, scanning rate: 0.1 V·s -1 ), and then the polymerized electrode was naturally dried and then placed in a 0.1M H2SO4 solution for elution to obtain a molecular imprinting ratio working electrode, which was used as an electrochemical sensor working electrode for electrochemical detection of BPA content.

[0051] Example 3: Preparation of molecular imprinting ratio working electrode in this example:

[0052] The modified electrode obtained in Example 2 was placed in a phosphate buffer containing thionine and BPA (the concentration ratio of thionine to BPA was 4:1, the concentration of thionine was 0.8 mM, and the pH of the buffer was 5.5), and electrochemical polymerization was performed to form a film (electropolymerization conditions: scanning potential: -0.4 V-0.4 V, scanning number: 25 cycles, scanning rate: 0.1 V·s -1 ), and then the polymerized electrode was naturally dried and then placed in a 0.1M H2SO4 solution for elution to obtain a molecular imprinting ratio working electrode, which was used as an electrochemical sensor working electrode for electrochemical detection of BPA content.

[0053] Example 6: Preparation of molecular imprinting ratio working electrode in this example:

[0054] Preparation of molecular imprinting ratio electrochemical sensor: The modified electrode obtained in Example 2 was placed in a phosphate buffer containing thionine and BPA (the concentration ratio of thionine to BPA was 8:1, the concentration of thionine was 1.6 mM, and the pH of the buffer was 5.5), and electrochemical polymerization was performed to form a film (electropolymerization conditions: scanning potential: -0.4 V-0.4 V, scanning number: 25 cycles, scanning rate: 0.1 V·s -1 ), and then the polymerized electrode was naturally dried and then placed in a 0.1M H2SO4 solution for elution to obtain a molecular imprinting ratio working electrode, which was used as an electrochemical sensor working electrode for electrochemical detection of BPA content.

[0055] Study on the detection performance of BPA by molecular imprinting ratiometric electrochemical sensor

[0056] The following experiments were used to verify the effect of the invention:

[0057] Test 1: Detection of BPA

[0058] In a mixture of 2.5 mM K3[Fe(CN)6] and 0.1 M KCl, the molecular imprinting ratio working electrode obtained in Example 3 was used as the working electrode of the electrochemical sensor, the Ag / AgCl electrode was used as the reference electrode, and the platinum wire electrode was used as the auxiliary electrode. The electrochemical signal was detected by SWV technology, and the corresponding current ratio I was measured. Fe / I Thi ; Using the current ratio I Fe / I Thi A linear detection model was constructed with the corresponding BPA concentration, such as Figure 3 It can be seen that within the concentration range of 5nM-400nM, as the BPA concentration increases, the current ratio decreases, the logarithm of the BPA concentration and the current ratio are in a linear relationship, and the detection limit is 1.1nM.

[0059] Experiment 2: Investigating the effects of different thionine and BPA concentration ratios on the constructed molecular imprinting ratio electrochemical sensor

[0060] Preparation of molecular imprinting ratio electrochemical sensor: The modified electrode obtained in step 3 of Example 1 above was placed in a phosphate buffer containing thionine and BPA (the concentration ratio of thionine to BPA was 8:1, the concentration of thionine in the buffer was 0.8 mM, and the pH of the buffer was 5.5), and electrochemical polymerization was performed to form a film (electropolymerization conditions: scanning potential: -0.4 V-0.4 V, scanning number: 25 cycles, scanning rate: 0.1 V·s -1 ), and then the polymerized electrode was left to dry naturally, and then placed in a 0.1M H2SO4 solution for elution to obtain a molecular imprinting ratio working electrode.

[0061] The molecular imprinting ratio working electrodes prepared with the concentration ratio of thionine to BPA being 1:1, 2:1, 4:1, and 8:1 were used as the working electrodes of the electrochemical sensors, the Ag / AgCl electrode was used as the reference electrode, and the platinum wire electrode was used as the auxiliary electrode to construct molecular imprinting electrochemical sensors. The molecular imprinting electrochemical sensors were then placed in a 10 nM BPA solution for adsorption for 32 min, and the electrochemical sensors were taken out to test the electrochemical response signals.

[0062] Electrochemical testing of sensors made with different thionine / BPA concentration ratios: Sensors made with different thionine / BPA concentration ratios were placed in a mixture of 2.5 mM K3[Fe(CN)6] and 0.1 M KCl, and electrochemical signal testing was performed using SWV technology. The results are shown in Figure 2. Figure 2 As shown, when the concentration ratio is 1:1, 2:1, 8:1, the current ratio I Fe / I Thi The higher the concentration, the poorer the polymerization effect, and the obtained molecular imprinting ratio electrochemical sensor cannot be used for subsequent specific content detection; when the concentration ratio is 4:1, the current ratio I Fe / I Thi The lowest, the best aggregation effect, can be constructed to obtain the high-sensitivity detection model shown in Experiment 1.

[0063] Experiment 3: Evaluation of the selectivity of analytical methods

[0064] In a mixed solution of 2.5 mM K3[Fe(CN)6] and 0.1 M KCl, a molecular imprinting electrochemical sensor was constructed using the molecular imprinting working electrode in Experiment 2 as the working electrode of the electrochemical sensor, the Ag / AgCl electrode as the reference electrode, and the platinum wire electrode as the auxiliary electrode.

[0065] The structural analogs of BPA, bisphenol E (BPE), bisphenol S (BPS), bisphenol P (BPP), and bisphenol M (BPM), were used as interfering substances. The electrochemical response signals of BPA (10 nM) at the same concentration with or without the addition of interfering substances were investigated, and I P / I A Value(I P Indicates the presence of interfering substances Fe / I Thi , I A I represents the absence of interfering substances Fe / I Thi ), and the selection performance of the method is evaluated by the current ratio.

[0066] The results are as follows Figure 4 As shown, I P / I AThe change value is between 98% and 101%, which is a small change, indicating that the prepared molecular imprinting ratio electrochemical sensor has a high specific recognition function for BPA. The detection method has good selectivity and can achieve specific detection of BPA.

[0067] The above describes the specific embodiments of the present invention. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essential content of the present invention.

Claims

1. A method for preparing a working electrode for detecting the molecular imprinting ratio of BPA, characterized in that: The following steps are involved: Step 1, dispersing nickel salt in N,N-dimethylformamide to obtain solution A, dispersing organic ligand in anhydrous ethanol to obtain solution B, mixing solutions A and B, and performing a solvothermal reaction. After the reaction is completed, washing and vacuum drying are performed to obtain a nickel-based metal organic framework material; Step 2, dispersing the nickel-based metal organic framework material and the multi-walled carbon nanotubes in a solvent, and subjecting the mixture to ultrasonic reaction; Step 3, then add a fixing agent, drop it on the glassy carbon electrode, dry it, drop-coat 1-aminopropyl-3-methylimidazolium bromide ionic liquid ([APMIm]Br), dry it, and obtain a modified electrode; Step 4: placing the modified electrode in a phosphate buffer containing thionine and BPA, electrochemically polymerizing the modified electrode into a film, drying the film naturally, placing the modified electrode in a sulfuric acid solution for elution, and drying the modified electrode to obtain the working electrode.

2. The method according to claim 1, characterized in that: The nickel salt is Ni(NO3)2·6H2O; the organic ligand is 1,3,5-benzenetricarboxylic acid, and the molar ratio of the nickel salt to the organic ligand is 7:

2.

3. The method according to claim 1, characterized in that: Solvothermal reaction was carried out at 120 °C for 12 h.

4. The method according to claim 1, characterized in that: The mass ratio of the nickel-based metal organic framework material to the multi-walled carbon nanotubes is 1:

5.

5. The method according to claim 1, characterized in that: The fixing agent is 1 wt.% chitosan solution, the volume ratio of the composite material to the fixing agent is 3:1; and the concentration of [APMIm]Br is 0.5 mM.

6. The method according to claim 1, characterized in that: The concentration ratio of thionine to BPA is 1:1-8:

1.

7. The method according to claim 1, characterized in that: The process parameters of electrochemical polymerization film formation are: scanning potential: -0.4V-0.4V, number of scanning cycles: 25 cycles, scanning rate: 0.1V·s -1 .

8. A working electrode prepared by the method according to any one of claims 1 to 7.

9. An electrochemical sensor comprising a working electrode prepared by the method according to any one of claims 1 to 7.

10. A working electrode prepared by the method according to any one of claims 1 to 7 for electrochemical detection of BPA content in water samples and plastic products.

Images