Construction method and application of molecularly imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe

Abstract

The present invention discloses a method for constructing a molecularly imprinted CuMOFs electrochemical sensor based on a copper ferrocyanide signal probe. The method uses a glassy carbon electrode modified with reduced graphene oxide as a sensing platform, a magnetic molecularly imprinted copper MOF material (MMIP‑CuMOFs) as a recognition element, and copper ferrocyanide (CuCHF) as a signal probe. The electrochemical sensor preparation steps are as follows: (1) using bisphenol A as a template molecule, preparing MMIP‑CuMOFs by an in-situ self-assembly method; (2) preparing a reduced graphene oxide modified electrode by an electrodeposition method; (3) dripping the prepared MMIP‑CuMOFs onto the reduced graphene oxide modified electrode, and using CuCHF generated by the reaction of Cu2+ in MMIP‑CuMOFs with potassium ferrocyanide as a signal probe to achieve quantitative determination of bisphenol A. The sensor of the present invention has the advantages of high sensitivity and good selectivity, and has broad application prospects in the detection of harmful substances in food.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical analysis and detection, and in particular to a method for constructing a molecular imprinted CuMOFs electrochemical sensor based on a copper ferrocyanide signal probe. Background Art

[0002] With the rapid development of science and technology, human living standards have been greatly improved. At the same time, food safety issues have received more and more attention. Illegal food additives frequently occur, and it is of great significance to develop simple, sensitive, rapid and highly selective methods for detecting harmful substances in food. At present, many traditional methods, such as high performance liquid chromatography-mass spectrometry, ultraviolet spectrophotometry, gas chromatography-mass spectrometry, etc., have been developed for the detection of harmful substances in food. Although these methods have excellent repeatability and accuracy, they all have the disadvantages of complex operation, high cost, environmental pollution and complex sample pretreatment. In recent years, electrochemical methods have been widely used in the detection of harmful substances in food due to their advantages of low cost, simple operation, high sensitivity, rapid response and easy miniaturization. However, electrochemical methods are easily affected by matrix effects, making it difficult to achieve high selectivity detection of targets. Therefore, when using electrochemical sensors to detect harmful substances in complex samples, it is necessary to introduce materials with excellent specific properties to improve the selectivity of the sensor. Molecular imprinting electrochemical sensors can solve the above problems well because they combine molecular imprinting polymers with high selectivity and high chemical stability.

[0003] Traditional molecular imprinting polymers usually have low adsorption capacity, slow mass transfer rate, and separation from sample solutions requires centrifugation and filtration, which is time-consuming and cumbersome. The magnetic molecular imprinting material prepared by combining molecular imprinting polymers with magnetic nanoparticles can overcome the above shortcomings. In addition, Fe3O4 nanoparticles have high conductivity and can amplify electrochemical signals. Therefore, the construction of electrochemical sensors using magnetic Fe3O4 molecular imprinting materials as recognition elements can effectively improve the sensitivity of the sensor. Although magnetic molecular imprinting polymers can be quickly separated from the matrix, they are limited by their own adsorption capacity and cannot quickly and effectively enrich the target molecules. Metal organic framework materials (MOFs) have a large surface area and adjustable components and structures, which can effectively make up for the defects of the above magnetic molecular imprinting polymers.

[0004] In addition, transition metal ferrocyanide has been widely used in electrochemical sensors due to its unique redox properties. 3- / 4-) as a signal probe to construct electrochemical sensors is widely studied. It is reported that copper ferrocyanide also has a set of good redox signal peaks near 0.7V, which can also be used as a signal probe for the construction of electrochemical sensors. Copper ferrocyanide can be [Fe(CN)6] 3- / 4- With Cu 2+ Therefore, the Cu in the magnetic molecular imprinted CuMOFs material (MMIP-CuMOFs) 2+ It is expected to be combined with [Fe(CN)6] 3- / 4- The reaction generates copper ferrocyanide signal probe, which is used to construct an electrochemical sensor.

[0005] However, there are disadvantages such as limited imprinting sites and insensitive electrical signal response when modifying MCMMIPs directly on glassy carbon electrodes. Therefore, conductive materials can be used to modify the electrode surface to increase the specific surface area and conductivity of the electrode, thereby improving the sensitivity of the sensor. Reduced graphene oxide (RGO) is a two-dimensional film structure arranged in a honeycomb shape obtained by reduction on the basis of graphene oxide (GO), with properties similar to GO, but it loses some functional groups, so the properties are more stable, and the electrical conductivity is also better than GO, which can effectively improve the sensitivity of the sensor. Therefore, the present invention uses a glassy carbon electrode modified with reduced graphene oxide as a sensing platform, MMIP-CuMOFs as a recognition element, and copper ferrocyanide as a signal probe to construct an electrochemical sensor for detecting harmful substances bisphenol A in food. Summary of the invention

[0006] The present invention aims to solve the problems of low selectivity and sensitivity of existing analytical methods in detecting harmful substances in food, and combines the high selectivity of MMIP-CuMOFs with the advantages of high sensitivity and simple and fast operation of electrochemical sensors. 2+ Copper ferrocyanide generated by reaction with potassium ferrocyanide was used as a signal probe to construct a molecularly imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe and applied it to the detection of bisphenol A in food.

[0007] Compared with existing detection methods, the electrochemical sensor method has the advantages of good selectivity, high sensitivity, less time consumption, simple operation and rapid response.

[0008] The technical scheme of the present invention is: the present invention introduces MMIP-CuMOFs as a recognition element to improve the specific recognition ability of the sensor to the object to be detected, and modifies it on the electrode modified with reduced graphene oxide by a dripping method, that is, the constructed sensor. The sensor is placed in a solution containing bisphenol A for adsorption, and the change of the copper ferrocyanide electrical signal after adsorbing different concentrations of bisphenol A molecules is used to achieve high sensitivity and high selectivity detection of bisphenol A.

[0009] The specific steps of the method for constructing the molecularly imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe are as follows:

[0010] (1) 1.08 g FeCl3·6H2O and 6.5 g 1,6-hexanediamine were dissolved in 70 mL ethylene glycol, 0.5 g trisodium citrate was added, 1 g polyethylene glycol was added after ultrasonic dissolution, and after sufficient dissolution, the mixture was poured into a reaction kettle and placed in an oven at 215°C for reaction for 6.5 h. The black product was taken out, washed alternately with water and anhydrous ethanol three times, and dried at 60°C for 3 h to obtain Fe3O4-NH2;

[0011] (2) Take 0.03-0.1g of dried Fe3O4-NH2, 0.34g of copper acetate, 0.2g of benzene trimecchymic acid and 30-50mg of bisphenol A in a mortar and grind for half an hour until the mixture is evenly mixed. Then add 5mL of water and 5mL of N,N-methyleneformamide to the reactor, place the resulting mixture on the reactor platform, and react at 125°C for 12-24h to obtain a green product. After that, use 5mL of a mixture of acetonitrile and acetic acid with a volume ratio of 99:1 to wash repeatedly to remove the template molecule bisphenol, and finally wash with anhydrous ethanol 3 times and dry at 110°C for 1h to obtain MMIP-CuMOFs;

[0012] (3) Using graphite powder as raw material, graphene oxide was prepared by Hummers' modified method. 0.2 g of graphene oxide was ultrasonically dispersed in 20 mL of PBS buffer solution with pH = 8 to obtain a graphene oxide suspension; a glassy carbon electrode was placed in the above graphene oxide suspension, a platinum sheet electrode was used as an auxiliary electrode, and an Ag / AgCl electrode was used as a reference electrode. Cyclic voltammetry was used with a scan rate of 50 mV / s, a voltage range of -1.4 V to 0 V, and 5 to 25 scans to obtain a reduced graphene oxide modified glassy carbon electrode;

[0013] (4) 5 mg of MMIP-CuMOFs was dispersed in 5 mL of water, and 5 μL of the MMIP-CuMOFs dispersion was dripped onto the reduced graphene oxide modified electrode and dried at 60°C to obtain a MMIP-CuMOFs / reduced graphene oxide modified electrode, which is a sensor for detecting bisphenol A.

[0014] The molecular imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe of the present invention is used for the detection method of bisphenol A in food as follows:

[0015] a. Prepare bisphenol A aqueous solutions of different concentrations using deionized water;

[0016] b. The MMIP-CuMOFs / reduced graphene oxide modified electrode was placed in a bisphenol A aqueous solution for adsorption for 20 min;

[0017] c. The above-mentioned adsorbed electrode was used as the working electrode, the platinum electrode was used as the auxiliary electrode, and the Ag / AgCl electrode was used as the reference electrode to form a three-electrode system, and the system was placed in a 2.5 mmol / L potassium ferrocyanide solution;

[0018] d. Potassium ferrocyanide reacts with Cu in MMIP-CuMOFs 2+ The copper ferrocyanide generated by the reaction was used as a redox probe, and the current values ​​corresponding to the adsorption of different concentrations of bisphenol A were obtained by differential pulse voltammetry. A standard curve was drawn with the peak current difference as the ordinate and the logarithm of the concentration as the abscissa.

[0019] e. The MMIP-CuMOFs / reduced graphene oxide modified electrode was placed in an aqueous solution of bisphenol A of unknown concentration for adsorption, and then a three-electrode system was formed and placed in a potassium ferrocyanide solution to detect the corresponding current value, and the concentration of bisphenol A was obtained according to the standard curve.

[0020] Furthermore, the electrochemical parameters of the differential pulse voltammetry are: scanning potential range: 0.3V~1.1V, scanning rate: 100mV / s.

[0021] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses a glassy carbon electrode modified with reduced graphene oxide as a sensing platform, MMIP-CuMOFs as a recognition element, and utilizes potassium ferrocyanide to react with Cu in MMIP-CuMOFs. 2+ The copper ferrocyanide generated by the reaction is used as a signal probe to construct a molecular imprinted CuMOFs electrochemical sensor based on the copper ferrocyanide signal probe, and is applied to the detection of bisphenol A in food. The sensor prepared by the present invention is used for the detection of harmful substances in food. Compared with other methods for detecting harmful substances in food, the sensor has simple equipment, convenient operation, good selectivity, high sensitivity, and has significant potential for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The flowchart of the preparation of MMIP-CuMOFs / reduced graphene oxide modified electrode;

[0023] Figure 2 Cyclic voltammograms of different modified electrodes: (a) bare glassy carbon electrode, (b) reduced graphene oxide modified electrode, (c) MMIP-CuMOFs / reduced graphene oxide modified electrode, (d) MMIP-CuMOFs / reduced graphene oxide modified electrode (after adsorption of 50 nmol / L bisphenol A);

[0024] Figure 3Differential pulse voltammograms of different modified electrodes: (a) bare glassy carbon electrode, (b) reduced graphene oxide modified electrode, (c) MMIP-CuMOFs / reduced graphene oxide modified electrode, (d) MMIP-CuMOFs / reduced graphene oxide modified electrode (after adsorption of 50 nmol / L bisphenol A);

[0025] Figure 4 is a graph showing the change of the current signal of the sensor with the concentration of bisphenol A;

[0026] Figure 5 The standard curve of the sensor response signal corresponding to the concentration of bisphenol A. DETAILED DESCRIPTION

[0027] The present invention is further described below by means of specific examples. The following examples are helpful for those skilled in the art to understand the present invention in detail, but in no way limit the scope of protection of the present invention.

[0028] Example 1

[0029] The construction method of molecularly imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe, the steps are as follows Figure 1 shown.

[0030] (1) 1.08 g FeCl3·6H2O and 6.5 g 1,6-hexanediamine were dissolved in 70 mL ethylene glycol, 0.5 g trisodium citrate was added, 1 g polyethylene glycol was added after ultrasonic dissolution, and after sufficient dissolution, the mixture was poured into a reaction kettle and placed in an oven at 215°C for reaction for 6.5 h. The black product was taken out, washed alternately with water and anhydrous ethanol three times, and dried at 60°C for 3 h to obtain Fe3O4-NH2;

[0031] (2) Take 0.05g of dried Fe3O4-NH2, 0.34g of copper acetate, 0.2g of benzene trimecchymethane and 30mg of bisphenol A in a mortar and grind for half an hour until the mixture is evenly mixed; then add 5mL of water and 5mL of N,N-methyleneformamide to the reactor, place the resulting mixture on the reactor platform, and react at 125°C for 24h to obtain a green product; then, use 5mL of a mixture of acetonitrile and acetic acid with a volume ratio of 99:1 to repeatedly wash to remove the template molecule bisphenol A. Finally, wash with anhydrous ethanol three times and dry at 110°C for 1h to obtain MMIP-CuMOFs;

[0032] (3) Using graphite powder as raw material, graphene oxide was prepared by Hummers' modified method. 0.2 g of graphene oxide was ultrasonically dispersed in 20 mL of PBS buffer solution with pH = 8 to obtain a graphene oxide suspension; a glassy carbon electrode was placed in the above graphene oxide suspension, a platinum sheet electrode was used as an auxiliary electrode, and an Ag / AgCl electrode was used as a reference electrode. Cyclic voltammetry was used with a scan rate of 50 mV / s, a voltage range of -1.4 V to 0 V, and 15 scans to obtain a reduced graphene oxide modified glassy carbon electrode;

[0033] (4) 5 mg of MMIP-CuMOFs was dispersed in 5 mL of water, and 5 μL of the MMIP-CuMOFs dispersion was dripped onto the reduced graphene oxide modified electrode and dried at 60°C to obtain the MMIP-CuMOFs / reduced graphene oxide modified electrode, which is a sensor for detecting bisphenol A.

[0034] Example 2

[0035] Construction method of molecularly imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe.

[0036] (1) 1.08 g FeCl3·6H2O and 6.5 g 1,6-hexanediamine were dissolved in 70 mL ethylene glycol, 0.5 g trisodium citrate was added, 1 g polyethylene glycol was added after ultrasonic dissolution, and after sufficient dissolution, the mixture was poured into a reaction kettle and placed in an oven at 215°C for reaction for 6.5 h. The black product was taken out, washed alternately with water and anhydrous ethanol three times, and dried at 60°C for 3 h to obtain Fe3O4-NH2;

[0037] (2) Take 0.1g of dried Fe3O4-NH2, 0.34g of copper acetate, 0.2g of benzenetricarboxylic acid and 50mg of bisphenol A in a mortar and grind for half an hour until the mixture is evenly mixed. Then add 5mL of water and 5mL of N,N-methyleneformamide to the reactor, place the resulting mixture on the reactor platform, and react at 125°C for 12h to obtain a green product. After that, use 5mL of a mixture of acetonitrile and acetic acid with a volume ratio of 99:1 to wash repeatedly to remove the template molecule bisphenol. Finally, wash with anhydrous ethanol three times and dry at 110°C for 1h to obtain MMIP-CuMOFs;

[0038] (3) Using graphite powder as raw material, graphene oxide was prepared by Hummers' modified method. 0.2 g of graphene oxide was ultrasonically dispersed in 20 mL of PBS buffer solution with pH = 8 to obtain a graphene oxide suspension; a glassy carbon electrode was placed in the above graphene oxide suspension, a platinum sheet electrode was used as an auxiliary electrode, and an Ag / AgCl electrode was used as a reference electrode. Cyclic voltammetry was used with a scan rate of 50 mV / s, a voltage range of -1.4 V to 0 V, and 25 scans to obtain a reduced graphene oxide modified glassy carbon electrode;

[0039] (4) 5 mg of MMIP-CuMOFs was dispersed in 5 mL of water, and 5 μL of the MMIP-CuMOFs dispersion was dripped onto the reduced graphene oxide modified electrode and dried at 60°C to obtain the MMIP-CuMOFs / reduced graphene oxide modified electrode, which is a sensor for detecting bisphenol A.

[0040] Example 3

[0041] Construction method of molecularly imprinted CuMOFs electrochemical sensor based on copper ferrocyanide signal probe.

[0042] (1) 1.08 g FeCl3·6H2O and 6.5 g 1,6-hexanediamine were dissolved in 70 mL ethylene glycol, 0.5 g trisodium citrate was added, 1 g polyethylene glycol was added after ultrasonic dissolution, and after sufficient dissolution, the mixture was poured into a reaction kettle and placed in an oven at 215°C for reaction for 6.5 h. The black product was taken out, washed alternately with water and anhydrous ethanol three times, and dried at 60°C for 3 h to obtain Fe3O4-NH2;

[0043] (2) Take 0.1g of dried Fe3O4-NH2, 0.34g of copper acetate, 0.2g of benzenetricarboxylic acid and 30mg of bisphenol A in a mortar and grind for half an hour until the mixture is evenly mixed. Then add 5mL of water and 5mL of N,N-methyleneformamide to the reactor, place the resulting mixture on the reactor platform, and react at 125°C for 24h to obtain a green product. After that, use 5mL of a mixture of acetonitrile and acetic acid with a volume ratio of 99:1 to wash repeatedly to remove the template molecule bisphenol A. Finally, wash with anhydrous ethanol three times and dry at 110°C for 1h to obtain MMIP-CuMOFs;

[0044] (3) Using graphite powder as raw material, graphene oxide was prepared by Hummers' modified method. 0.2 g of graphene oxide was ultrasonically dispersed in 20 mL of PBS buffer solution with pH = 8 to obtain a graphene oxide suspension; a glassy carbon electrode was placed in the above graphene oxide suspension, a platinum sheet electrode was used as an auxiliary electrode, and an Ag / AgCl electrode was used as a reference electrode. Cyclic voltammetry was used with a scan rate of 50 mV / s and a voltage range of -1.4 V to 0 V. Scanning for 20 cycles, a reduced graphene oxide modified glassy carbon electrode was obtained;

[0045] (4) 5 mg of MMIP-CuMOFs was dispersed in 5 mL of water, and 5 μL of the MMIP-CuMOFs dispersion was dripped onto the reduced graphene oxide modified electrode and dried at 60°C to obtain the MMIP-CuMOFs / reduced graphene oxide modified electrode, which is a sensor for detecting bisphenol A.

[0046] Example 4

[0047] The sensor obtained in Example 3 was used for the determination of bisphenol A:

[0048] (1) Cyclic voltammetry test of the sensor.

[0049] A bare glassy carbon electrode, a reduced graphene oxide modified electrode, a MMIP-CuMOFs / reduced graphene oxide modified electrode, and a MMIP-CuMOFs / reduced graphene oxide modified electrode after adsorption of 50 nmol / L bisphenol A were used as working electrodes, a platinum electrode was used as an auxiliary electrode, and an Ag / AgCl electrode was used as a reference electrode to form a three-electrode system. The system was placed in a 2.5 mmol / L potassium ferrocyanide solution for cyclic voltammetry scanning (scanning parameters: voltage range of -0.2 V to 1.0 V, scan rate of 50 mV / s). The cyclic voltammetry characterization results are shown in Figure 2 As shown in the figure, the bare glassy carbon electrode shows a pair of clear redox peaks, and the peak current value of the reduced graphene oxide modified electrode increases significantly, which indicates that the reduced graphene oxide deposited on the surface of the glassy carbon electrode has good electron conductivity, which can amplify the electrochemical signal and improve the sensitivity of the detection method. After the modification of MMIP-CuMOFs, two pairs of signal peaks appeared on the electrode, among which the peak current of potassium ferrocyanide was significantly reduced. This is because MMIP-CuMOFs are modified on the electrode, part of the effective area of ​​the electrode is covered, and the conductivity of the MOF material is poor, resulting in the obstruction of electron transfer. At this time, the Cu in MMIP-CuMOFs 2+ It will react with potassium ferrocyanide to form copper ferrocyanide, so another pair of redox peaks appears near 0.7 V. When the MMIP-CuMOFs / reduced graphene oxide modified electrode is placed in the test solution, the imprinted pores can selectively adsorb bisphenol A in the test solution, which leads to the blockage of the electron transfer channel and the decrease of both sets of peak currents.

[0050] (2) Differential pulse voltammetry test of the sensor.

[0051] The three-electrode system was composed of MMIP-CuMOFs / reduced graphene oxide modified electrode as working electrode, platinum electrode as auxiliary electrode, and Ag / AgCl electrode as reference electrode. The system was placed in 2.5mmol / L potassium ferrocyanide solution for differential pulse voltammetry scanning (scanning parameters: scanning potential range of 0.3V~1.1V, scanning rate of 100mV / s). The MMIP-CuMOFs / reduced graphene oxide modified electrode was placed in potassium ferrocyanide solution, and the copper ferrocyanide signal was used as an indicator to scan and obtain the blank current I0; after placing the electrode in a certain concentration of bisphenol A solution to complete adsorption, the current I was scanned again, and the response current of the sensor was ΔI=I-I0. The measurement results are shown in Figure 3 and Figure 4The measured ΔI value was plotted against the logarithm of the bisphenol A concentration to obtain a standard curve for the determination of bisphenol A (see Figure 5 The linear range of bisphenol A was 0.5-500 nmol / L, and the detection limit was 0.38 nmol / L. In addition, after the sensor was placed in a 4°C environment for 10 days, its response current value was still 97.80% of the original signal, showing strong stability.

Claims

1. A method for constructing a molecularly imprinted CuMOFs electrochemical sensor based on a copper ferrocyanide signal probe, characterized in that: The method prepares magnetic molecular imprinted copper MOF materials (MMIP-CuMOFs) by in situ self-assembly, and then utilizes Cu in MMIP-CuMOFs to 2+ Copper ferrocyanide (CuCHF) generated by reaction with potassium ferrocyanide is used as a signal probe to construct an electrochemical sensor. The construction method of the sensor is as follows: (1) 1.08 g of FeCl3·6H2O and 6.5 g of 1,6-hexanediamine were dissolved in 70 mL of ethylene glycol, 0.5 g of trisodium citrate was added, and 1 g of polyethylene glycol was added after ultrasonic dissolution. After sufficient dissolution, the mixture was poured into a reaction kettle and placed in an oven at 215°C for reaction for 6.5 h. The black product was taken out, washed alternately with water and anhydrous ethanol three times, and dried at 60°C for 3 h to obtain Fe3O4-NH2; (2) Take 0.03-0.1g of dried Fe3O4-NH2, 0.34g of copper acetate, 0.2g of benzene trimecchymic acid and 30-50mg of bisphenol A in a mortar and grind for half an hour until the mixture is uniform; then add 5mL of water and 5mL of N,N-methyleneformamide to the reactor, place the resulting mixture on the reactor platform, and react at 125°C for 12-24h to obtain a green product; then, use 5mL of a mixture of acetonitrile and acetic acid with a volume ratio of 99:1 to repeatedly wash to remove the template molecule bisphenol A; finally, wash with anhydrous ethanol for 3 times and dry at 110°C for 1h to obtain MMIP-CuMOFs; (3) Using graphite powder as raw material, graphene oxide was prepared by Hummers' modified method, 0.2 g of graphene oxide was ultrasonically dispersed in 20 mL of PBS buffer solution with pH = 8 to obtain a graphene oxide suspension; a glassy carbon electrode was placed in the above graphene oxide suspension, a platinum sheet electrode was used as an auxiliary electrode, and an Ag / AgCl electrode was used as a reference electrode. Cyclic voltammetry was used at a scan rate of 50 mV / s, a voltage range of -1.4 V to 0 V, and scanned for 5 to 25 cycles to obtain a reduced graphene oxide modified glassy carbon electrode; (4) 5 mg of MMIP-CuMOFs was dispersed in 5 mL of water, and 5 μL of the MMIP-CuMOFs dispersion was dripped onto the reduced graphene oxide modified electrode and dried at 60°C to obtain the MMIP-CuMOFs / reduced graphene oxide modified electrode, which is a sensor for detecting bisphenol A.

2. An electrochemical sensor made according to the construction method of claim 1, characterized in that: Used to detect bisphenol A, the detection linear range is 0.5-500nmol / L and the detection limit is 0.38nmol / L.

Images