Preparation method and application of an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor

Abstract

The application belongs to the field of electrochemical sensing and detection, and particularly relates to a preparation method of an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor and application thereof. First, gold nanocages (AuNGs) with external porosity and internal hollow are prepared by galvanic replacement, and the special cage structure is conducive to electron transmission. The AuNGs are self-assembled with amino-reduced graphene oxide under the action of electrostatic force. Under the synergistic action, the composite material has a large specific surface area, excellent conductivity and high electrocatalytic activity, which is conducive to the improvement of sensitivity. Then, o-phenylenediamine is used as a functional monomer, and diuron (DU) is used as a template molecule. A polymer film is formed on the surface of the modified electrode by electro-polymerization. Finally, a large number of imprinted cavities are exposed in the polymer film by eluting the template, and the cavities are used for specific binding of DU. The molecularly imprinted electrochemical sensor has high sensitivity and good selectivity, and can realize the detection of DU in actual samples.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrochemical sensing, and particularly relates to a preparation method of an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor and application thereof BACKGROUND

[0002] Diuron (DU) is an effective component in plant protection and fungicide formulations, belongs to the benzene urea herbicide, and is widely used for preventing and treating broadleaf weeds after the emergence of crops such as cotton, fruits and cereals. In addition, DU has a long half-life (> 300 days) and high migration, and its residues will continuously accumulate in the soil and enter the groundwater, causing environmental pollution. At the same time, it is found that DU has carcinogenic and neurotoxic effects on mammals, which can seriously affect the respiratory, endocrine and cardiovascular systems.

[0003] Electrochemical detection has attracted widespread attention due to its low cost, simple operation, fast response and other advantages, and is one of the most potential and convenient methods for detecting DU at present. It is reported that DU is an electroactive substance, which is usually oxidized to form dimers on the surface of a glassy carbon electrode (GCE) to generate an electrical signal, and the detection is realized by establishing a linear relationship between the concentration and the electrical signal. Traditional electrochemistry based on this phenomenon has developed new types of nanomaterial modified electrodes, focusing on improving the sensitivity of detection, but the selectivity of various interferences in practical application needs to be improved. In order to overcome the above problems, molecularly imprinted polymers (MIP) with specific recognition ability can be used as recognition elements to improve the selectivity of the sensor. As a kind of surface imprinting method, the electro-polymerization molecular imprinting technology not only can improve the number and integrity of the imprinting cavities, but also can control the morphology and thickness of the MIP, so as to complete the preparation and modification of the MIP on the surface of the GCE in one step. The electro-polymerization method solves the defects of the currently reported DU-MIP, such as complex preparation, difficult template elution and uncontrollable film morphology. Moreover, the molecularly imprinted electrochemical sensors constructed at present generally have poor conductivity and weak electrochemical signal of MIP, so it is urgent to develop a new type of sensor to overcome the current technical problems. SUMMARY

[0004] In view of the problems of insufficient selectivity of most electrochemical sensors for detecting DU and complex preparation and low imprinting efficiency of a few prepared imprinted electrochemical sensors at present, the application constructs a molecularly imprinted electrochemical sensor based on a high-performance graphene-based composite material by using an electro-polymerization imprinting technology, so as to realize sensitive and specific detection of DU.

[0005] The application prepares a composite material of high-conductivity amino-reduced graphene oxide loaded gold nanocage (NH2-rGO@AuNGs), which is used as a substrate to improve the signal response of a sensor; wherein, the AuNGs have an interesting cage structure with outer wall multi-cavity and inner cavity, have a large specific surface area and a large number of electroactive sites, and are beneficial to the transfer of electrons at the interface. In addition, the NH2-rGO not only has more excellent conductive performance than the rGO, but also can prepare the NH2-rGO@AuNGs through electrostatic adsorption. As for the NH2-rGO@AuNGs as an electrode material, there is no report on the high-affinity o-phenylenediamine (o-PD) as a DU-MIP functional monomer. Based on this, the application adopts an electro-polymerization method to construct a molecular imprinting electrochemical sensor based on the NH2-rGO@AuNGs, has the advantages of simple production, strong selectivity, high reusability and good stability, and realizes sensitive and specific analysis of the DU in an actual sample. The method can be used for large-scale production and commercial application, and fills the blank of the existing DU detection technology.

[0006] The application provides a high-conductivity graphene-based nanocomposite and a preparation method thereof.

[0007] In order to realize the above technical purposes, the application specifically includes the following steps:

[0008] (1) Preparation of AuNGs:

[0009] (a) Firstly, ethylene glycol is heated in an oil bath, and under stirring conditions, sodium sulfide (Na2S) solution, polyvinylpyrrolidone (PVP) solution and silver nitrate (AgNO3) solution are added, and reflux is carried out, and after the reflux is completed, the precipitate is collected and washed by centrifugation with acetone and water, and the product after washing is silver nanocube (AgNCs), which is dispersed in an aqueous solution again to obtain an AgNCs suspension;

[0010] (b) The prepared AgNCs suspension and PVP aqueous solution are mixed to obtain a mixed solution, which is heated and refluxed in an oil bath; then HAuCl4 solution is slowly added to the mixed solution until a stable light blue color is presented, and then the precipitate is collected by centrifugation, and then washed by centrifugation with saturated sodium chloride solution and ultrapure water, and the product after washing is gold nanocage (AuNGs) solid, which is dispersed in an aqueous solution again to obtain an AuNGs suspension;

[0011] (2) Preparation of NH2-rGO:

[0012] The reduced graphene oxide (rGO) is added into an ethanol-water solution, ultrasonic dispersion is performed, then the aminopropyl triethoxysilane (APTES), ethylenediamine and hydrochloric acid (HCl) are sequentially added, the mixture is stirred uniformly, the precipitate is taken out after centrifugation, then the precipitate is washed with ethanol and water in sequence to remove the residual APTES, and finally the aminated reduced graphene oxide solid is dried to obtain an NH2-rGO solid;

[0013] (3) Preparation of the NH2-rGO@AuNGs:

[0014] The NH2-rGO solid prepared in the step (2) is added into the AuNGs suspension prepared in the step (1) to perform mixing and stirring, a mixed solution is obtained, then the NH2-rGO@AuNGs composite material is obtained after centrifugation and drying;

[0015] Preferably, in the step (1), the amount ratio of the ethylene glycol, the Na2S solution, the PVP solution and the AgNO3 solution in the (a) is 50 mL: 750 μL: 12.5 mL: 4.2 mL, wherein the concentration of the Na2S solution is 3 mmol / L, the concentration of the PVP solution is 1 mg / mL, and the concentration of the AgNO3 solution is 0.2 mmol / L; the heating temperature is 150°C, the reflux time is 15 min, and the stirring speed is 200 rpm; and the concentration of the AgNCs suspension is 6-8 nmol / L.

[0016] Preferably, in the step (1), the amount ratio of the AgNCs suspension, the PVP aqueous solution and the HAuCl4 solution in the (b) is 2 mL: 50 mL: 10-15 mL, wherein the concentration of the PVP aqueous solution is 1 mg / mL, the heating reflux temperature is 100°C, and the reflux time is 10 min; the concentration of the HAuCl4 solution is 0.5 mmol / L; and the concentration of the AuNGs suspension is 0.75 mg / mL.

[0017] Preferably, in the step (2), the amount ratio of the rGO, the ethanol-water solution, the APTES, the ethylenediamine and the HCl is 5 mg: 15 mL: 1 g: 10 μL: 20 μL; wherein the ethanol-water solution is a solution obtained by mixing ethanol and water in a volume ratio of 2:1; the ultrasonic dispersion time is 1 h, and the stirring time is 7 h; and the drying temperature is 60°C, and the drying time is 24 h.

[0018] Preferably, in the step (3), the amount ratio of the NH2-rGO and the AuNGs suspension is 1.0 mg: 1 mL, the mixing and stirring time is 12 h, the drying temperature is 60°C, and the drying time is 24 h.

[0019] The NH2-rGO@AuNGs composite material prepared by the above method is in the shape of a wrinkled two-dimensional nanosheet, the loaded AuNGs solid particle size is 30-50 nm, and the composite material has a special structure of external porosity and internal hollow, and the pore size is about 2.0-5.0 nm, which is beneficial to electron transmission.

[0020] In a second aspect, the application provides a preparation method of a molecular imprinting electrochemical sensor, comprising providing a composite material, coating the composite material on the outer surface of an electrode substrate and drying to obtain a sensitive material layer, wherein the sensitive material layer is a composite material of metal nanoparticles and carbon nanomaterials; arranging a MIP layer on the side of the sensitive material layer away from the electrode substrate, polymerizing a functional monomer by an electro-polymerization method to form a polymer layer, and the polymer layer contains a template molecule; removing the template molecule in the polymer layer to form an imprint cavity in the polymer layer. The construction process of the molecular imprinting electrochemical sensor comprises the following steps:

[0021] (4) The glassy carbon electrode (GCE) is polished and polished with aluminum oxide powder, and then ultrasonically cleaned in ethanol and ultrapure water, and then cyclic voltammetry scanning is performed in an aqueous solution containing potassium chloride and potassium ferricyanide until the peak potential difference is less than 90 mV, proving that the GCE pretreatment is completed; and a pretreated glassy carbon electrode is obtained;

[0022] (5) The NH2-rGO@AuNGs composite material prepared in step (3) is ultrasonically dispersed in ultrapure water to prepare a dispersion liquid; the NH2-rGO@AuNGs dispersion liquid is uniformly coated on the surface of the pretreated GCE, and dried to obtain an NH2-rGO@AuNGs / GCE;

[0023] (6) The NH2-rGO@AuNGs / GCE obtained in step (5) is subjected to continuous cyclic voltammetry scanning in an acetate buffer solution containing o-phenylenediamine (o-PD, a functional monomer) and diuron (DU, a template molecule) in a certain voltage range; after scanning, the electrode is taken out and dried at room temperature (a layer of copper brown film appears on the surface of the electrode), and the obtained modified electrode is denoted as o-PD / NH2-rGO@AuNGs / GCE;

[0024] (7) The modified electrode (o-PD / NH2-rGO@AuNGs / GCE) obtained in step (6) is immersed in an elution solution and soaked under stirring at a certain speed, and then rinsed with ultrapure water and dried to obtain an amino-functionalized graphene-based diuron molecular imprinting electrochemical sensor, denoted as MIP / NH2-rGO@AuNGs / GCE.

[0025] Preferably, in step (4), the diameter of the glassy carbon electrode (GCE) is 2 mm; the particle size of the aluminum oxide powder used is 0.05 μm; the concentrations of potassium chloride (KCl) and potassium ferricyanide in the aqueous solution are 0.1 mol / L and 5 mmol / L, respectively.

[0026] Preferably, in step (5), the concentration of the NH2-rGO@AuNGs dispersion liquid is 1 mg / mL; the amount of NH2-rGO@AuNGs dispersion liquid used for modification is 3.5 μL; the drying temperature is 24℃, and the drying time is 10 h.

[0027] Preferably, in step (6), the ratio of the amounts of o-phenylenediamine (o-PD, functional monomer), DU (template molecule) and acetate buffer solution is 2.2 mg:0.93 mg:4 mL, the concentration of the acetate buffer solution is 0.1 mol / L, and the pH value is 5.0; the potential range of the cyclic voltammetry scan is 0.2-1.2 V, the scan speed is 50 mV / s, and the number of cycles is 20.

[0028] Preferably, in step (7), the elution solution is a mixed solution of ethanol and acetic acid mixed at a volume ratio of 9:1, the speed is 50 rpm, and the stirring soaking time is 60 s.

[0029] The detection steps are as follows:

[0030] (1) The MIP / NH2-rGO@AuNGs / GCE sensor prepared in the above steps is immersed in a standard solution containing different concentrations of diuron (DU), and after incubation with stirring, the electrode is taken out and washed with ultrapure water to remove unbound DU, to obtain the incubated MIP / NH2-rGO@AuNGs / GCE; wherein the sensor MIP / NH2-rGO@AuNGs / GCE and the diuron standard solution are in one-to-one correspondence, i.e., one sensor corresponds to one diuron standard solution;

[0031] (2) The incubated MIP / NH2-rGO@AuNGs / GCE in step (1) is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the platinum wire electrode is used as the counter electrode for electrochemical detection, and the standard curve is established by detecting the current signals generated by different concentrations of DU, with the concentration of the DU standard solution as the abscissa and the generated current signal as the ordinate.

[0032] (3) Actual sample DU detection: first prepare the test solution, place the sensor MIP / NH2-rGO@AuNGs / GCE in the test solution, incubate at room temperature, then take out, wash the sensor with ultrapure water, then detect to obtain the current signal generated by diuron; then the current signal is brought into the standard curve constructed in step (2), so that the concentration of diuron in the actual sample can be obtained, and the detection of diuron in the actual sample can be realized.

[0033] Preferably, the concentration of the DU standard solution in step (1) is 10 ng / mL-10 μg / mL.

[0034] Preferably, the incubation time in steps (1) and (3) is 5-30 min, and the stirring speed is 50 rpm.

[0035] Preferably, the electrochemical detection instrument in steps (2) and (3) is a CHI852D (Shanghai Chenhua) electrochemical workstation, and the scanning voltage range during detection is 1.0-1.4 V.

[0036] The beneficial effects of the present application are:

[0037] (1) The present application adopts an electro-polymerization molecular imprinting technology to prepare a MIP with controllable morphology, selects o-PD with excellent affinity as a functional monomer, and the prepared imprinting cavity is specifically combined with DU through hydrogen bonding and π-π conjugation, thereby improving the selectivity of the sensor, and the imprinting factor is 6.91.

[0038] (2) The present application combines NH2-rGO and AuNGs through electrostatic adsorption, and the special structure of the porous outer part and the hollow inner part of AuNGs is conducive to electron transfer, thereby improving the sensitivity of the sensor.

[0039] (3) The electrochemical sensor constructed based on the electro-polymerization molecular imprinting technology is used for the detection of DU, has a wide linear range (10 ng / mL-10 μg / mL), and has a low detection limit of 4.3 ng / mL. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a schematic diagram of the construction process of the molecular imprinting electrochemical sensor of the present application; the inserted diagram (A) is a preparation process schematic diagram of NH2-rGO@AuNGs, the inserted diagram (B) is a current response schematic diagram of the sensor without adding DU, and the inserted diagram (C) is a current response schematic diagram of the sensor after adding DU.

[0041] Figure 2 (A) is a TEM diagram of AuNGs; and (B) is a TEM diagram of NH2-rGO@AuNGs.

[0042] Figure 3 Figure 9 shows SEM images of MIP / NH2-rGO@AuNGs / GCE, where (A) is the SEM image of NIP / NH2-rGO@AuNGs / GCE, and the inset (B) is the SEM image of MIP / NH2-rGO@AuNGs / GCE.

[0043] Figure 4 Figure 10 shows the linear relationship between different concentrations of DU standard solution and electrochemical signals (A), and the selectivity of the molecularly imprinted electrochemical sensor (B).

[0044] Figure 5 Figure 11 shows the reusability of the molecularly imprinted electrochemical sensor (A), and the 8-day stability of the molecularly imprinted electrochemical sensor (B). DETAILED DESCRIPTION

[0045] The technical solutions of the present application are described in detail below through specific examples.

[0046] Example 1

[0047] This example provides a preparation method of a molecularly imprinted electrochemical sensor, according to the material preparation and sensor construction diagram shown in Figure 8, the specific steps are as follows: Figure 1

[0048] (1) 50 mL of ethylene glycol was heated to 150℃ in an oil bath, and the stirring speed was 200 rpm. 750 μL of 3 mmol / L sodium sulfide (Na2S) solution, 12.5 mL of 1 mg / mL polyvinylpyrrolidone (PVP) solution and 4.2 mL of 0.2 mmol / L silver nitrate (AgNO3) solution were successively added to the above solution, and refluxed for 15 min; after the reflux was completed, the precipitate was collected and centrifuged, washed with acetone and water for 3 times, to obtain silver nanocubes (AgNCs), which were redispersed in an aqueous solution to obtain an AgNCs suspension, the concentration of the AgNCs suspension was 8 nmol / L, and the AgNCs suspension was stored in a refrigerator at 4℃ in the dark.

[0049] (2) 2 mL of the prepared AgNCs suspension and 50 mL of 1 mg / mL PVP aqueous solution were heated to 100℃ in an oil bath, and refluxed for 10 min. Then 10 mL of 0.5 mmol / L tetrachloroauric acid (HAuCl4) solution was slowly added until a stable light blue color appeared, and then the precipitate was collected by centrifugation, and washed with saturated sodium chloride solution and ultrapure water for three times, to obtain gold nanocage (AuNGs) solid, which was redispersed in an aqueous solution to obtain an AuNGs suspension, wherein the concentration of the AuNGs suspension was 0.75 mg / mL.

[0050] ​(3) 5 mg of reduced graphene oxide (rGO) was dispersed in 15 mL of ethanol-water mixed solution with a volume ratio of 2:1, and ultrasonic dispersion was performed for 1 h; then 1 g of aminopropyltriethoxysilane (APTES), 10 μL of ethylenediamine and 20 μL of hydrochloric acid (HCl) were added in sequence, stirring was performed for 7 h, the precipitate was taken out after centrifugation, and the precipitate was washed with ethanol and water in sequence to remove residual APTES, and finally dried at 60°C for 24 h to obtain NH2-rGO solid.

[0051] (4) The NH2-rGO solid of step (3) was mixed with the AuNGs suspension of step (2) according to a usage ratio of 1.0 mg: 1 mL, stirring was performed for 12 h to obtain a mixed solution, and the two were combined through electrostatic adsorption; finally, the mixed solution was centrifuged to take the precipitate, and after drying at 60°C for 24 h, an aminated reduced graphene oxide loaded gold nanocage composite material was obtained, denoted as NH2-rGO@AuNGs.

[0052] Figure 2 Figure (A) is a TEM image of AuNGs, the particle size is 30 nm-50 nm, the morphology is a cage-like structure with a hollow interior and a porous exterior, the surface has a plurality of holes penetrating into the interior, and the pore size is about 2.0-5.0 nm; Figure (B) is a TEM image of NH2-rGO@AuNGs, the AuNGs on the wrinkled two-dimensional nanosheet are uniformly distributed, and the morphology of the AuNGs has not changed.

[0053] (5) A glassy carbon electrode (GCE, Φ = 2 mm) was polished and polished with 0.05 μm aluminum oxide powder, and then ultrasonic cleaned in ultrapure water, ethanol and ultrapure water in sequence and dried. Then cyclic voltammetry scanning was performed in a 5 mmol / L potassium ferricyanide solution containing 0.1 mol / L potassium chloride, until the peak potential difference was less than 90 mV, proving that the GCE pretreatment was completed, and a pretreated GCE was obtained.

[0054] (6) The NH2-rGO@AuNGs composite material prepared in step (4) was ultrasonically dispersed in ultrapure water to prepare a 1 mg / mL NH2-rGO@AuNGs dispersion; 3.5 μL of the NH2-rGO@AuNGs dispersion was taken with a pipette gun and uniformly coated on the surface of the pretreated GCE, and dried to obtain a NH2-rGO@AuNGs / GCE.

[0055] (7) 2.2 mg of o-phenylenediamine (o-PD, functional monomer) and 0.93 mg of diuron (DU, template molecule) were added into 4 mL of 0.1 mol / L acetate buffer solution (pH 5.0), and 20 continuous cyclic voltammetry scans were performed in the range of 0.2-1.2 V at a scan rate of 50 mV / s by electro-polymerization. After drying at room temperature, a layer of copper-brown film appeared on the surface of the electrode, and the modified electrode was denoted as o-PD / NH2-rGO@AuNGs / GCE.

[0056] (8) The modified electrode prepared in step (7) was immersed in a mixed solution of ethanol and acetic acid with a volume ratio of 9:1, and stirred at a speed of 50 rpm for 60 s to remove the DU molecules. Then, the electrode was rinsed with ultrapure water and dried to obtain an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor, denoted as MIP / NH2-rGO@AuNGs / GCE.

[0057] Comparative Example 1:

[0058] A non-imprinted polymer (NIP) was prepared according to the same procedure as in Example 1, except that no template molecule diuron was added during the polymerization process in step (7), and the obtained sensor was denoted as NIP / NH2-rGO@AuNGs / GCE.

[0059] (1) The MIP / NH2-rGO@AuNGs / GCE sensor provided in Example 1 and the NIP / NH2-rGO@AuNGs / GCE in Comparative Example 1 were immersed in an aqueous solution containing 5 mmol / L potassium ferricyanide and 0.1 mol / L potassium chloride, and the electrochemical properties of the sensors were investigated by cyclic voltammetry and alternating current impedance.

[0060] Due to the lack of effective imprinting sites, the NIP / NH2-rGO@AuNGs / GCE showed lower oxidation peak current and larger impedance value than the MIP / NH2-rGO@AuNGs / GCE.

[0061] Figure 3 The SEM images of the molecularly imprinted electrochemical sensors provided in Comparative Example 1 and Example 1, respectively, can be seen from the figures. As shown in the figures, due to the swelling and shrinking of the polymer film, the non-imprinted film of Figure (A) exhibits a rough and uniform surface, and the surface is covered with small o-phenylenediamine nanoparticles. The surface of the imprinted film of Figure (B) is more rough, which is mainly due to the swelling of the polymer during the elution process, causing the diuron molecules to fall off and exposing a large number of imprinting cavities.

[0062] Example 2:

[0063] The MIP / NH2-rGO@AuNGs / GCE sensor provided by Example 1 and the sensor NIP / NH2-rGO@AuNGs / GCE of Comparative Example 1 were immersed in a solution containing different concentrations of DU standard solution and stirred for incubation for 15 min, so that the DU molecules were recombined with the cavities; then the sensor was washed with ultrapure water to remove the unbound DU, and the resulting product was labeled as DU / MIP / NH2-rGO@AuNGs / GCE; the DU standard solution was 0.01, 0.025, 0.07, 0.2, 0.4, 0.7, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 μg / mL, respectively.

[0064] The above product (DU / MIP / NH2-rGO@AuNGs / GCE) was used as a working electrode, an Ag / AgCl (saturated KCl) electrode was used as a reference electrode, and a platinum wire electrode was used as a counter electrode. The electrochemical signals were detected and recorded by an electrochemical luminescence instrument workstation with a model number of CHI852D (Shanghai Chenhua). Differential voltammetry pulse method was used to collect the electrical signals, and the scanning potential was set from 1.0 V to 1.4 V with a scanning rate of 50 mV / s. The current signal of DU was used as the vertical coordinate, and the corresponding DU concentration was used as the horizontal coordinate, and a standard curve was established for the detection of the DU concentration in the actual sample.

[0065] From Figure 4 (A) can be seen, with the increase of DU concentration, the peak current signal gradually increases, and in the concentration range of 10 ng / mL to 10 μg / mL, it shows a good linear relationship, and the standard curve is I = 0.51C DU + 0.026 (R 2 = 0.996), and the detection limit is 4.3 ng / mL.

[0066] Example 3:

[0067] Performance analysis of molecularly imprinted electrochemical sensor:

[0068] Figure 5 (A) Taking the MIP sensor as an example, the reusability of the sensor was investigated: the same MIP sensor was tested and eluted for five consecutive cycles, and the change of the current response was observed. The experiment was carried out in triplicate, and the sensing response of DU was detected for 5 times in succession. Due to the slight degradation of the imprinted cavity, the peak current after the fifth regeneration was only 8.7% lower than the initial response, showing good reusability.

[0069] Figure 5 (B) The stability test was carried out for 8 consecutive days, and the current response on the 8th day still retained 93.5% of the initial value, indicating that the MIP / NH2-rGO@AuNGs / GCE had excellent stability.

[0070] Example 4:

[0071] The constructed amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor was used to analyze the actual sample, and the steps were as follows:

[0072] (1) A cotton defoliant product, i.e. thiabendazole · diuron 540 g / L suspension concentrate, was purchased from an agricultural supply store in Midong District, Urumqi City, Xinjiang Uygur Autonomous Region, wherein the concentration of DU was 180 g / L; then different volumes of methanol were used for dissolution and ultrasonic treatment, and the solution was filtered through a 0.22 μm organic filter membrane, and after cooling, the defoliant solution was obtained.

[0073] (2) The defoliant solution containing DU at a concentration of 0.1 μg / mL, 0.5 μg / mL and 1 μg / mL was prepared, and the actual sample was analyzed, and it was calculated that the original concentration of DU in the cotton defoliant was 175-176 g / L, which was basically consistent with the actual label value (180 g / L), and the recovery rate was in the range of 97.1% to 98.0%, and the relative standard deviation (RSD) was less than 3.84%, which indicated that the sensor could be used for actual sample detection.

[0074] (3) The detection results of the constructed sensor were further verified by high performance liquid chromatography-mass spectrometry (HPLC-MS) method, and the actual concentration of DU in the defoliant ripening agent detected by HPLC-MS method was 176-198 g / L, which was basically consistent with the detection results of the constructed sensor, and the experimental results of the two methods were close to the theoretical label value 180 g / L, which verified that the MIP / NH2-rGO@AuNGs / GCE sensor had good feasibility in actual sample analysis.

[0075] The related test results are shown in Table 1.

[0076] Table 1.

[0077]

[0078]

[0079] Comparative Example 2:

[0080] The selectivity test of the molecular imprinting electrochemical sensor: wherein blank refers to the absence of target, defined as a blank sample; interfering substances are structural analogues and other actual sample coexisting substances, including thiamethoxam (TO), carbendazim (CBZ), benomyl (BM), imidacloprid (IMC), thiamethoxam (TMX), ethephon (ETH), thiabendazole (TDZ), monuron (MU), isoproturon (ISO), and the corresponding concentration of each is 1 μg / mL; Mix is a mixture of the above interfering substances, and the corresponding concentration is 1 μg / mL; DU is the target, and the corresponding concentration is 1 μg / mL; Mix+DU is a mixture of interfering substances and DU, and the concentration of Mix and DU in the mixture is 1 μg / mL.

[0081] The sensors of Comparative Example 1 and Example 1 were respectively placed in the above detection substances for incubation for 15 min, then removed, the electrodes were cleaned with ultrapure water, and then detection was performed to obtain the electrical signals of the corresponding substances.

[0082] From Figure 4 It was found in (B) that only when DU was present, MIP / NH2-rGO@AuNGs / GCE had a significant current signal. Due to the lack of imprint cavities that can specifically recognize DU, NIP / NH2-rGO@AuNGs / GCE did not show significant differences in diuron and other interfering substances.

[0083] The relevant current response values are shown in Table 2.

[0084] Table 2

[0085]

[0086]

[0087] In addition, the imprint factor (IF) can be used to further characterize the specificity of the proposed molecular imprinting electrochemical sensor, and the higher the value, the stronger the specificity. It was found from Table 1 that the IF value of MIP / NH2-rGO@AuNGs / GCE for diuron was as high as 6.91, which was much higher than that of other non-targets, proving that the sensor had a large number of imprint cavities that could specifically recognize diuron, had outstanding affinity for diuron and high anti-interference, and was suitable for practical application.

[0088] It is to be understood that the above description is not a limitation on the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should be within the scope of the present application.

Claims

1. A method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor, characterized in that, Includes the following steps: (1) Preparation of AuNGs: (a) First, ethylene glycol was heated in an oil bath. Under stirring, sodium sulfide solution, polyvinylpyrrolidone solution and silver nitrate solution were added and refluxed. After reflux, the precipitate was collected and washed by centrifugation with acetone and water respectively. The washed product was silver nanocubes, which were redispersed in an aqueous solution to obtain an AgNCs suspension. (b) The AgNCs suspension prepared in step (a) was mixed with the PVP aqueous solution to obtain a mixed solution, which was heated under reflux in an oil bath. Then, HAuCl4 solution was slowly added to the mixed solution until a stable light blue color was observed. The precipitate was collected by centrifugation and then washed by centrifugation with saturated sodium chloride solution and ultrapure water, respectively. The washed product was the gold nanocage solid, which was redispersed in the aqueous solution to obtain the AuNGs suspension. (2) Preparation of NH2-rGO: Reduced graphene oxide was added to an ethanol-water solution and ultrasonically dispersed. Then, aminopropyltriethoxysilane, ethylenediamine and hydrochloric acid were added in sequence and stirred until homogeneous. After centrifugation, the precipitate was removed and washed with ethanol and water in sequence to remove residual APTES. Finally, the aminated reduced graphene oxide solid was obtained by drying, denoted as NH2-rGO. (3) Preparation of NH2-rGO@AuNGs: The NH2-rGO prepared in step (2) is added to the AuNGs suspension prepared in step (1) and mixed and stirred to obtain a mixed solution. After centrifugation and drying, the NH2-rGO@AuNGs composite material is obtained. (4) The glassy carbon electrode is ground and polished with alumina powder, then ultrasonically cleaned in ethanol and ultrapure water in sequence, and then cyclic voltammetry is performed in an aqueous solution containing potassium chloride and potassium ferricyanide until the peak potential difference is less than 90mV, which proves that the glassy carbon electrode pretreatment is complete; the pretreated glassy carbon electrode is obtained. (5) Take the NH2-rGO@AuNGs composite material prepared in step (3) and ultrasonically disperse it in ultrapure water to prepare a dispersion; take the NH2-rGO@AuNGs dispersion and uniformly coat it onto the surface of the pretreated glassy carbon electrode, and dry it to obtain NH2-rGO@AuNGs / GCE. (6) The NH2-rGO@AuNGs / GCE obtained in step (5) was subjected to continuous cyclic voltammetry scanning in an acetate buffer solution containing o-phenylenediamine and diuron within a certain voltage range; after scanning, the electrode was removed and dried at room temperature, and the modified electrode was named o-PD / NH2-rGO@AuNGs / GCE. (7) The modified electrode o-PD / NH2-rGO@AuNGs / GCE obtained in step (6) is immersed in the elution solution and soaked under stirring at a certain speed. After stirring and soaking, it is rinsed with ultrapure water and dried to obtain an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor, denoted as MIP / NH2-rGO@AuNGs / GCE.

2. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (1) (a), the volume ratio of ethylene glycol, sodium sulfide solution, polyvinylpyrrolidone solution and AgNO3 solution is 50 mL: 750 μL: 12.5 mL: 4.2 mL, wherein the concentration of Na2S solution is 3 mmol / L, the concentration of PVP solution is 1 mg / mL, and the concentration of AgNO3 solution is 0.2 mmol / L; the heating temperature is 150 °C, the reflux time is 15 min, and the stirring speed is 200 rpm; The concentration of AgNCs suspension is 6–8 nmol / L.

3. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (1) (b), the ratio of AgNCs suspension, PVP aqueous solution and HAuCl4 solution is 2 mL: 50 mL: 10-15 mL, wherein the concentration of PVP aqueous solution is 1 mg / mL, the reflux temperature is 100 °C, and the reflux time is 10 min; the concentration of HAuCl4 solution is 0.5 mmol / L; and the concentration of AuNCs suspension is 0.75 mg / mL.

4. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (2), the ratio of reduced graphene oxide, ethanol-water solution, APTES, ethylenediamine, and HCl is 5 mg: 15 mL: 1 g: 10 μL: 20 μL; wherein the ethanol-water solution is a solution obtained by mixing ethanol and water in a volume ratio of 2:1; the ultrasonic dispersion time is 1 h, the stirring time is 7 h; the drying temperature is 60 °C, and the time is 24 h.

5. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (3), the ratio of NH2-rGO to AuNGs suspension is 1.0 mg: 1 mL, the mixing time is 12 h, the drying temperature is 60 °C, and the drying time is 24 h.

6. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (4), the diameter of the glassy carbon electrode is 2 mm; the particle size of the aluminum oxide powder used is 0.05 μm; and the concentrations of potassium chloride and potassium ferricyanide in the aqueous solution are 0.1 mol / L and 5 mmol / L, respectively.

7. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (5), the concentration of the NH2-rGO@AuNGs dispersion is 1 mg / mL; the amount of NH2-rGO@AuNGs dispersion used for modification is 3.5 μL; the drying temperature is 24 °C and the drying time is 10 h.

8. The method for preparing an amino-functionalized graphene-based diuron molecularly imprinted electrochemical sensor according to claim 1, characterized in that, In step (6), the ratio of o-phenylenediamine, diuron, and acetate buffer solution is 2.2 mg: 0.93 mg: 4 mL, the concentration of acetate buffer solution is 0.1 mol / L, and the pH value is 5.0; the potential range of cyclic voltammetry scan is 0.2 to 1.2 V, the scan rate is 50 mV / s, and the number of cycles is 20; in step (7), the elution solution is a mixture of ethanol and acetic acid in a volume ratio of 9:1, the certain speed is 50 rpm, and the stirring and soaking time is 60 s.

9. The use of the electrochemical sensor prepared according to any one of claims 1-8 for detecting diuron, characterized in that, The steps are as follows: (1) The MIP / NH2-rGO@AuNGs / GCE sensor prepared in the above steps is immersed in standard solutions containing different concentrations of diuron, and after incubation under stirring conditions, it is taken out and then cleaned with ultrapure water to remove unbound diuron, thus obtaining the incubated MIP / NH2-rGO@AuNGs / GCE; wherein the sensor MIP / NH2-rGO@AuNGs / GCE and the diuron standard solution have a one-to-one correspondence, that is, one sensor corresponds to one diuron standard solution; (2) Using the MIP / NH2-rGO@AuNGs / GCE incubated in step (1) as the working electrode, the Ag / AgCl electrode as the reference electrode, and the platinum wire electrode as the counter electrode, a standard curve is established by detecting the current signal generated by different concentrations of diuron. The concentration of the diuron standard solution is used as the abscissa, and the generated current signal is used as the ordinate. (3) Detection of diuron in actual samples: First, prepare the test solution, place the sensor MIP / NH2-rGO@AuNGs / GCE in the test solution and incubate at room temperature, then take it out, clean the sensor with ultrapure water, and then perform detection to obtain the corresponding current signal generated by diuron; then bring the generated current signal into the standard curve constructed in step (2) to obtain the concentration of diuron in the actual sample, and realize the detection of diuron in the actual sample.

10. The use according to claim 9, characterized in that, The concentration of the diuron standard solution in step (1) is 10 ng / mL-10 μg / mL; the incubation time in steps (1) and (3) is 5-30 min, and the stirring speed is 50 rpm; the electrochemical detection instruments in steps (2) and (3) are CHI852D electrochemical workstations, and the scanning voltage range during detection is 1.0-1.4V.

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