Method for visually detecting dicamba based on fluorescence-enhanced molecularly imprinted ratiometric fluorescent probe

Abstract

The invention provides a method for visually detecting dicamba based on a fluorescence-enhanced molecularly imprinted ratiometric fluorescent probe, relates to the technical field of visual detection methods, and comprises the method for visually detecting dicamba based on the fluorescence-enhanced molecularly imprinted ratiometric fluorescent probe. A visual detection technology based on a fluorescence-enhanced molecular imprinting ratio fluorescent probe shows subversive potential, and the method not only simplifies a sample pretreatment process and greatly shortens the detection time, but also has the advantages of remarkable cost benefit, simplicity and convenience in operation and no need of complicated laboratory equipment, and more importantly, the method has a good application prospect. Through the accurate recognition characteristic of the molecular imprinting technology, the specificity of fluorescence sensing analysis is greatly improved, non-specific interference can be effectively overcome, and a target compound can be accurately locked even in a complex matrix.

Description

Technical Field

[0001] The invention relates to the technical field of visual detection methods, and in particular to a method for visually detecting dicamba using a molecular imprinting ratio fluorescent probe based on fluorescence enhancement. Background Art

[0002] Dicamba (DIC) is a phenylcarboxylic acid herbicide with a mechanism of action similar to that of plant growth hormones, which controls weeds by simulating the effects of growth hormones. The herbicide is widely used in the cultivation of cereals such as wheat, corn, rice, and sorghum to effectively manage weeds. DIC has the properties of good water solubility, low soil adsorption, high mobility, and long residual effect. Toxicological studies have shown that DIC has a series of adverse effects. It can disrupt the normal function of the endocrine system, severely damage the liver and kidneys, and may cause changes in the structure of the uterus and breast. In addition, DIC also exhibits potential developmental toxicity, which may cause embryonic malformations and produce genetic toxicity to fish, rodents, and plants. Epidemiological studies have pointed out that there is a correlation between DIC and a variety of human cancers, including lung cancer, colon cancer, liver cancer, and bile duct cancer, which has further aroused widespread public concern about the problem of DIC residues. The International Food Codex has established clear standards for the residue limits of DIC. Specifically, the maximum residue limit of DIC in soybeans is set at 10 mg / kg, while the maximum residue limit in wheat is 2 mg / kg. These regulations are intended to ensure food safety. Therefore, it is very meaningful to establish a fast and convenient method for detecting DIC residue content.

[0003] Currently, the quantitative analysis of DIC generally relies on high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). These two technologies have indeed performed well in ensuring measurement accuracy and high sensitivity, providing a reliable quantitative basis for scientific research and regulatory fields. However, the application of these traditional methods is accompanied by significant limitations. Not only do they require expensive professional equipment support, but the analysis cycle is long and the initial sample processing steps are complicated and cumbersome, which undoubtedly poses a severe challenge to on-site testing and large-scale screening work that urgently requires rapid response. In particular, the high cost of testing and maintenance, coupled with the reliance on professional technicians, limits its popularization and application in resource-limited or remote areas, making it difficult to meet the urgent needs of modern agriculture for efficient and low-cost pesticide residue monitoring.

[0004] Therefore, it is necessary to provide a new method for visual detection of dicamba based on fluorescence enhancement molecular imprinting ratio fluorescence probe to solve the above technical problems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for visually detecting dicamba based on a fluorescence-enhanced molecular imprinting ratio fluorescent probe.

[0006] The method for visually detecting dicamba using a molecular imprinting ratiometric fluorescent probe based on fluorescence enhancement provided by the present invention comprises the following steps:

[0007] S1. Synthesis of CdTe quantum dots and Eu metal organic frameworks:

[0008] (1) Preparation of cadmium telluride quantum dots:

[0009] 74.0 μL MPA, 91.7 mg hydrated cadmium chloride and 20.0 mg sodium citrate were dissolved in 40.0 mL double distilled water, and the pH of the solution was adjusted to 11.2 with 1.0 M sodium hydroxide. Then, 4.4 mg potassium tellurite and 20.0 mg sodium borohydride were added to the solution and stirred until completely dissolved. The solution was then placed in an oil bath at 90° C. and refluxed for 6 h. After the reaction was completed, the solution was cooled naturally to room temperature, and 40.0 mL of anhydrous ethanol was added to precipitate cadmium telluride quantum dots. Finally, the solution was centrifuged for 5 min and dried at 60° C. to obtain cadmium telluride quantum dot powder.

[0010] (2) Preparation of Europium Metal Organic Framework:

[0011] Weigh 0.2 g of europium nitrate hexahydrate and 0.2 g of 2-aminoterephthalic acid, dissolve in 20.0 mL of dimethylformamide, then transfer the solution to a 50 mL polytetrafluoroethylene reactor, react at 120 ° C for 4 hours, after the reaction is completed, wait for the solution to cool to room temperature, centrifuge at 4000 r / min for 5 minutes, collect the precipitate, and wash it alternately with dimethylformamide and anhydrous methanol several times to remove impurities, and finally dry it at 60 ° C to obtain yellow europium metal organic framework powder;

[0012] S2. Preparation of molecularly imprinted polymer / non-molecularly imprinted polymer probes:

[0013] (1) Preparation of core-shell quantum dots:

[0014] 4.0 mg of cadmium telluride quantum dot powder was uniformly dispersed in a mixed solution consisting of 80.0 mL of anhydrous ethanol and 20.0 mL of water, and then 0.4 mL of tetraethyl orthosilicate and 0.4 mL of ammonia water were added to the mixed solution. The mixture was stirred for 12 h. After the reaction was completed, the mixture was centrifuged and washed several times with anhydrous ethanol, and finally dried at 60 ° C to obtain core-shell quantum dot powder.

[0015] (2) Preparation of molecularly imprinted polymers:

[0016] 1.0-5.0 mg of europium metal organic framework, 5.0 mg of DIC, and 3.5-17.5 mg of acrylamide were weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 90.0-270.0 mg of ethylene glycol dimethyl acrylate and 5.0-25.0 mg of azobisisobutyronitrile were added, and stirring was continued for 2 hours to complete the pre-assembly. Then, high-purity nitrogen was ventilated for 10 minutes, and then the mixture was reacted in a water bath at 70° C. for 15 hours. After the reaction was completed, the mixture was centrifuged at 4000 r / min for 5 minutes to obtain a precipitate, and then washed alternately with anhydrous methanol and double distilled water for several times until the ultraviolet-visible absorption spectrum of the last washing liquid had no absorption peak of DIC, and finally dried at 60° C. to obtain a molecularly imprinted polymer powder. The non-molecularly imprinted polymer was synthesized under the same preparation conditions as the molecularly imprinted polymer, but the template molecule DIC was not added during the preparation process.

[0017] (3) Configuration of molecular imprinting polymer and non-molecular imprinting polymer probe solution:

[0018] Accurately weigh 4.0 mg of molecularly imprinted polymer or non-molecularly imprinted polymer and 1.0 mg of core-shell quantum dots, disperse them in 10.0 mL of double distilled water to obtain a molecularly imprinted polymer or non-molecularly imprinted polymer probe solution with a concentration of 0.5 mg / mL;

[0019] S3. Fluorescence detection and visual detection of dicamba:

[0020] Dissolve DIC and its structural analogs in dimethylformamide to obtain a 2.0 mM standard stock solution. Take 1.0 mL of the probe solution and 1.0-80.0 μL of the DIC stock solution into a 5 mL centrifuge tube, then dilute to 2.0 mL with dimethylformamide. After the probe reacts with DIC for 15 minutes, transfer the solution to a cuvette to scan the fluorescence spectrum.

[0021] The steps of visual detection are as follows: place the above-mentioned test solutions in a dark environment, irradiate each test solution with ultraviolet light, then record the fluorescence color through a smartphone, convert it into RGB numerical information, and fit and calculate the linear relationship between the RGB value and the DIC concentration.

[0022] Furthermore, in S3, the specific conditions of fluorescence detection are set as follows: the excitation wavelength is set to 365 nm, the excitation slit width is adjusted to 3 nm, the emission slit width is adjusted to 5 nm, and the emission spectrum scanning range is set to 350-650 nm.

[0023] Furthermore, the amount of europium metal organic framework used was 1.0 mg, the amount of acrylamide used was 3.5 mg, the amount of ethylene glycol dimethyl acrylate used was 90.0 mg, and the amount of azobisisobutyronitrile used was 5.0 mg.

[0024] Furthermore, the amount of europium metal organic framework used was 2.0 mg, the amount of acrylamide used was 7.0 mg, the amount of ethylene glycol dimethyl acrylate used was 135.0 mg, and the amount of azobisisobutyronitrile used was 10.0 mg.

[0025] Furthermore, the amount of europium metal organic framework used was 3.0 mg, the amount of acrylamide used was 10.5 mg, the amount of ethylene glycol dimethyl acrylate used was 180.0 mg, and the amount of azobisisobutyronitrile used was 15.0 mg.

[0026] Furthermore, the amount of europium metal organic framework used was 4.0 mg, the amount of acrylamide used was 14.0 mg, the amount of ethylene glycol dimethyl acrylate used was 225.0 mg, and the amount of azobisisobutyronitrile used was 20.0 mg.

[0027] Furthermore, the amount of europium metal organic framework used was 5.0 mg, the amount of acrylamide used was 17.5 mg, the amount of ethylene glycol dimethyl acrylate used was 270.0 mg, and the amount of azobisisobutyronitrile used was 25.0 mg.

[0028] Compared with the related art, the method for visual detection of dicamba by using a molecular imprinting ratio fluorescence probe based on fluorescence enhancement provided by the present invention has the following beneficial effects:

[0029] The method for visually detecting dicamba based on fluorescence-enhanced molecular imprinting ratio fluorescent probes uses a visual detection technology based on fluorescence-enhanced molecular imprinting ratio fluorescent probes, which shows disruptive potential. This method not only simplifies the sample pretreatment process and greatly shortens the detection time, but also is cost-effective, easy to operate, and does not require complex laboratory equipment. More importantly, through the precise recognition characteristics of molecular imprinting technology, the specificity of fluorescence sensing analysis is greatly improved, which can effectively overcome nonspecific interference and accurately lock the target compound even in a complex matrix. Therefore, the combination of fluorescence analysis and molecular imprinting technology has opened up a new way to overcome the limitations of current HPLC and LC-MS technologies, and has a certain degree of value in promoting environmental protection and ensuring food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the amount of europium metal organic framework provided for the invention;

[0031] Figure 2 A schematic diagram of the amount of acrylamide provided for the invention;

[0032] Figure 3 A schematic diagram of the dosage of ethylene glycol dimethyl acrylate provided for the invention;

[0033] Figure 4A schematic diagram of the dosage of azobisisobutyronitrile provided for the invention;

[0034] Figure 5 A schematic diagram of the molecular imprinting polymer concentration provided for the invention;

[0035] Figure 6 Schematic diagram of fluorescence detection and visual detection DIC provided by the invention;

[0036] Figure 7 The synthetic flow chart of the dicamba molecular imprinting ratio fluorescent probe provided in the invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Embodiment 1

[0039] The method for visually detecting dicamba using a molecular imprinting ratiometric fluorescent probe based on fluorescence enhancement provided by the present invention comprises the following steps:

[0040] S1. Synthesis of CdTe quantum dots and Eu metal organic frameworks:

[0041] (1) Preparation of cadmium telluride quantum dots:

[0042] 74.0 μL MPA, 91.7 mg hydrated cadmium chloride and 20.0 mg sodium citrate were dissolved in 40.0 mL double distilled water, and the pH of the solution was adjusted to 11.2 with 1.0 M sodium hydroxide. Then, 4.4 mg potassium tellurite and 20.0 mg sodium borohydride were added to the solution and stirred until completely dissolved. The solution was then placed in an oil bath at 90° C. and refluxed for 6 h. After the reaction was completed, the solution was cooled naturally to room temperature, and 40.0 mL ethanol was added to precipitate cadmium telluride quantum dots. Finally, the solution was centrifuged for 5 min and dried at 60° C. to obtain cadmium telluride quantum dot powder.

[0043] (2) Preparation of Europium Metal Organic Framework:

[0044] Weigh 0.2 g of europium nitrate hexahydrate and 0.2 g of 2-aminoterephthalic acid, dissolve in 20.0 mL of dimethylformamide, then transfer the solution to a 50 mL polytetrafluoroethylene reactor, react at 120 ° C for 4 hours, after the reaction is completed, wait for the solution to cool to room temperature, centrifuge at 4000 r / min for 5 minutes, collect the precipitate, and wash it alternately with dimethylformamide and anhydrous methanol several times to remove impurities, and finally dry it at 60 ° C to obtain yellow europium metal organic framework powder;

[0045] S2. Preparation of molecularly imprinted polymer / non-molecularly imprinted polymer probes:

[0046] (1) Synthesis of core-shell quantum dots:

[0047] 4.0 mg of cadmium telluride quantum dot powder was uniformly dispersed in a mixed solution consisting of 80.0 mL of anhydrous ethanol and 20.0 mL of water, and then 0.4 mL of tetraethyl orthosilicate and 0.4 mL of ammonia water were added to the mixed solution. The mixture was stirred for 12 h. After the reaction was completed, the mixture was centrifuged and washed several times with anhydrous ethanol, and finally dried at 60 ° C to obtain core-shell quantum dot powder.

[0048] (2) Preparation of molecularly imprinted polymers:

[0049] 1.0 mg of europium metal organic framework, 5.0 mg of DIC, and 3.5 mg of acrylamide were weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 90.0 mg of ethylene glycol dimethyl acrylate and 5.0 mg of azobisisobutyronitrile were added, and stirring was continued for 2 hours to complete the pre-assembly. Then, high-purity nitrogen was ventilated for 10 minutes, and then the mixture was reacted in a water bath at 70°C for 15 hours. After the reaction was completed, the mixture was centrifuged at 4000 r / min for 5 minutes to obtain a precipitate, and then the precipitate was washed alternately with anhydrous methanol and double distilled water for several times until the UV-visible absorption spectrum of the last washing liquid had no absorption peak of DIC. Finally, the precipitate was dried at 60°C to obtain a molecularly imprinted polymer powder. The non-molecularly imprinted polymer was synthesized under the same preparation conditions as the molecularly imprinted polymer. The template molecule DIC was added to the molecularly imprinted polymer during the preparation process, while the template molecule DIC was not added to the non-molecularly imprinted polymer during the preparation process.

[0050] (3) Configuration of molecular imprinting polymer and non-molecular imprinting polymer probe solution:

[0051] Accurately weigh 4.0 mg of molecularly imprinted polymer or non-molecularly imprinted polymer and 1.0 mg of core-shell quantum dots, disperse them in 10.0 mL of double distilled water to obtain a molecularly imprinted polymer or non-molecularly imprinted polymer probe solution with a concentration of 0.5 mg / mL;

[0052] S3. Fluorescence detection and visual detection of dicamba:

[0053] Dissolve DIC and its structural analogs in dimethylformamide to obtain a 2.0 mM standard stock solution. Take 1.0 mL of the probe solution and 1.0-80.0 μL of the DIC stock solution into a 5 mL centrifuge tube, then dilute to 2.0 mL with dimethylformamide. After the probe reacts with DIC for 15 minutes, transfer the solution to a cuvette to scan the fluorescence spectrum.

[0054] The specific conditions for fluorescence detection were set as follows: the excitation wavelength was set to 365 nm, the excitation slit width was adjusted to 3 nm, the emission slit width was adjusted to 5 nm, and the emission spectrum scanning range was set to 350-650 nm;

[0055] The steps of visual detection are as follows: place each of the above test solutions in a dark environment, irradiate each test solution with an ultraviolet lamp (λex=365nm), then record the fluorescence color through a smartphone, convert it into RGB numerical information, and fit and calculate the linear relationship between the RGB value and the DIC concentration.

[0056] Embodiment 2

[0057] The same method as described in Example 1 is followed, except that:

[0058] 2.0 mg of europium metal organic framework, 5.0 mg of DIC, and 7.0 mg of acrylamide were weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 135.0 mg of ethylene glycol dimethyl acrylate and 10.0 mg of azobisisobutyronitrile were added, and stirring was continued for 2 hours to complete the pre-assembly. Then, high-purity nitrogen was ventilated for 10 minutes, and then reacted in a 70°C water bath for 15 hours. After the reaction was completed, centrifuged at 4000 r / min for 5 minutes to obtain a precipitate, and then washed alternately with anhydrous methanol and double distilled water several times until the UV-visible absorption spectrum of the last washing liquid had no absorption peak of DIC, and finally dried at 60°C to obtain a molecular imprinting polymer powder.

[0059] Embodiment 3

[0060] The same method as described in Example 1 is followed, except that:

[0061] 3.0 mg of europium metal organic framework, 5.0 mg of DIC, and 10.5 mg of acrylamide were weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 180.0 mg of ethylene glycol dimethyl acrylate and 5.0-25.0 mg of azobisisobutyronitrile were added, and stirring was continued for 2 hours to complete the pre-assembly. Then, high-purity nitrogen was ventilated for 10 minutes, and then reacted in a 70°C water bath for 15 hours. After the reaction was completed, centrifuged at 4000 r / min for 5 minutes to obtain a precipitate, and then washed alternately with anhydrous methanol and double distilled water for several times until the UV-visible absorption spectrum of the last washing liquid had no absorption peak of DIC, and finally dried at 60°C to obtain a molecular imprinting polymer powder.

[0062] Embodiment 4

[0063] The same method as described in Example 1 is followed, except that:

[0064] 4.0 mg of europium metal organic framework, 5.0 mg of DIC, and 14.0 mg of acrylamide were weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 225.0 mg of ethylene glycol dimethyl acrylate and 20.0 mg of azobisisobutyronitrile were added, and stirring was continued for 2 hours to complete the pre-assembly. Then, high-purity nitrogen was ventilated for 10 minutes, and then reacted in a 70°C water bath for 15 hours. After the reaction was completed, centrifuged at 4000 r / min for 5 minutes to obtain a precipitate, and then washed alternately with anhydrous methanol and double distilled water several times until the UV-visible absorption spectrum of the last washing liquid had no absorption peak of DIC, and finally dried at 60°C to obtain a molecular imprinting polymer powder.

[0065] Embodiment 5

[0066] The same method as described in Example 1 is followed, except that:

[0067] 5.0 mg of europium metal organic framework, 5.0 mg of DIC, and 17.5 mg of acrylamide were weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 270.0 mg of ethylene glycol dimethyl acrylate and 25.0 mg of azobisisobutyronitrile were added, and stirring was continued for 2 hours to complete the pre-assembly. Then, high-purity nitrogen was ventilated for 10 minutes, and then reacted in a 70°C water bath for 15 hours. After the reaction was completed, centrifuged at 4000 r / min for 5 minutes to obtain a precipitate, and then washed alternately with anhydrous methanol and double distilled water several times until the UV-visible absorption spectrum of the last washing liquid had no absorption peak of DIC, and finally dried at 60°C to obtain a molecular imprinting polymer powder.

[0068] 1. Optimization of the amount of response material Europium metal organic framework:

[0069] The amount of Eu-MOF can directly affect the number of effective imprinting sites of molecular imprinting polymers. Therefore, the amount of Eu-MOF was investigated. As the amount of Eu-MOF increased, the fluorescence enhancement factor (I' 440 / I 440 ) gradually increased, and the amount of Eu-MOF became stable after it exceeded 4.0 mg. This is because when the amount of Eu-MOF was greater than 4.0 mg, the excess Eu-MOF in the reaction system could not be embedded in the polymer microspheres and was eluted. Therefore, 4.0 mg of Eu-MOF was selected for subsequent experiments. The results are shown in Figure 1 As shown;

[0070] 2. Optimization of the dosage of functional monomer acrylamide:

[0071] The amount of functional monomer used will affect the selective recognition performance of molecular imprinting polymers. Therefore, the amount of acrylamide was investigated. When the amount of acrylamide was 10.5 mg, the fluorescence enhancement factor (I' 440 / I 440 ) is the largest. When the amount of acrylamide is less than 10.5 mg, the functional monomers in the reaction system are less, and DIC is not completely anchored in the polymer, resulting in fewer binding sites in the molecularly imprinted polymer. 440 / I 440 When the amount of acrylamide is greater than 10.5 mg, there are too many functional monomers in the reaction system, which reduces the interaction between DIC and the europium metal organic framework, resulting in a decrease in the number of effective imprinting sites. 440 / I 440 Therefore, the dosage of acrylamide was selected as 10.5 mg for subsequent experiments; the results are as follows Figure 2 As shown;

[0072] 3. Optimization of the amount of crosslinking agent ethylene glycol dimethyl acrylate:

[0073] The amount of cross-linking agent used will affect the yield of molecular imprinting polymer and its selective recognition performance. Therefore, the amount of ethylene glycol dimethyl acrylate used needs to be investigated. When the amount of ethylene glycol dimethyl acrylate is 180.0 mg, the fluorescence enhancement factor at 440 nm (I' 440 / I 440 ) is the largest. When the amount of ethylene glycol dimethyl acrylate is less than 180.0 mg, there are too many exposed binding sites, and the DIC molecules in the probe solution are insufficient to fully bind to the europium metal organic framework, resulting in I' 440 / I 440 When the amount of ethylene glycol dimethyl acrylate is greater than 180.0 mg, the Europium metal organic framework is embedded deeper, the binding sites are reduced, and I' 440 / I440 The value decreased, therefore, the amount of ethylene glycol dimethyl acrylate was selected as 180.0 mg for subsequent experiments; the results are as follows Figure 3 As shown;

[0074] 4. Optimization of the dosage of initiator azobisisobutyronitrile:

[0075] The amount of initiator used will affect the speed of the polymerization reaction, and thus affect the density and performance of the molecularly imprinted polymer. Therefore, this experiment investigated the amount of azobisisobutyronitrile used. The fluorescence enhancement factor (I') at 440 nm was 440 / I 440 ) did not change significantly, but in the subsequent scale-up experiment, when 5.0 mg of azobisisobutyronitrile was used, 50% of the groups failed to synthesize. Finally, 10.0 mg of azobisisobutyronitrile was selected for subsequent experiments; the results are shown in Figure 4 shown.

[0076] Optimization of Molecularly Imprinted Polymer Concentration:

[0077] The ratiometric fluorescence analysis method is performed by comparing the fluorescence intensity of the dual emission wavelengths. Therefore, it is necessary to examine the dosage of core-shell quantum dots and molecularly imprinted polymers. When the concentration of molecularly imprinted polymers is 0.1 mg / mL, I 440 / I 565 When the concentration of molecular imprinting polymer was 0.2 mg / mL, I 440 / I 565 When the concentration of molecular imprinting polymer was 0.3 mg / mL, I 440 / I 565 From 1.3 to 4.3, the fluorescence color changed from light yellow to blue-purple, and the color change was obvious. Considering the detection sensitivity and visualization effect of the method, 0.2 mg / mL of molecular imprinting polymer was selected for subsequent experiments. Therefore, the concentrations of core-shell quantum dots and molecular imprinting polymer were set to 0.05 mg / mL and 0.2 mg / mL, respectively. The results are shown in Figure 5 shown.

[0078] S4. Actual sample analysis:

[0079] Corn and soil were selected as actual samples, and a recovery experiment was designed. First, 2.2 mg, 4.4 mg and 6.6 mg of DIC were weighed and added to 1.0 g of corn or soil samples, respectively. After the samples were evenly dispersed in 10 mL of anhydrous methanol, ultrasonic extraction was performed for 1 h to promote the release of the target substance. The extract was then filtered to remove insoluble matter. Then 2.0 mL of the filtrate was taken, dried with nitrogen to remove the solvent, and then re-dissolved with 2.0 mL of dimethylformamide to obtain a sample solution. Finally, 40.0 μL of the sample solution was added to 1.0 mL of the molecular imprinting ratio fluorescent probe solution and supplemented to 2.0 mL with dimethylformamide. After the molecular imprinting ratio fluorescent probe reacted with DIC for 15 min, the solution was transferred to a cuvette for fluorescence measurement.

[0080] In order to determine the optimal detection time, DIC was mixed with the molecular imprinting ratio fluorescent probe solution and the fluorescence intensity ratio (I 440 / I 565 ) changes, I 440 / I 565 It increases continuously with the passage of time and remains basically unchanged after 15 minutes, so 15 minutes is set as the detection time;

[0081] By observing the freeze-dried Eu-MOF and Eu-MOF-DIC powders under a microscope, the Eu-MOF-DIC showed a dendritic network structure, indicating that the enhancement phenomenon belongs to the CEE effect. The Eu-MOF and DIC are connected by hydrogen bonds to form a dendritic cross-linked network structure, which inhibits the luminescence center. The non-radiative transition of the organic ligand 2-aminoterephthalic acid in the Eu-MOF improves its charge transfer efficiency and enhances fluorescence.

[0082] S5. Fluorescence detection and visual detection DIC:

[0083] Under the optimal conditions, we tested the response behaviors of molecular imprinting ratio fluorescent probe and non-molecular imprinting polymer probe to DIC. With the increase of DIC concentration, the fluorescence intensity of molecular imprinting ratio fluorescent probe at 440nm gradually increased, while the fluorescence intensity at 565nm remained basically unchanged. 440 / I 565 ) and DIC concentration showed two linear relationships between 1.0-80.0 μM, and the linear equations obtained by fitting were:

[0084] (I 440 / I 565 )1=0.01373CDIC+0.78026(R=0.9993),(1.0-35.0μM)

[0085] (I440 / I 565 )2=0.04875CDIC-0.52448(R=0.9975),(35.0-80.0μM)

[0086] The detection limits (3σ / k) were LOD1=0.57μM and LOD2=0.16μM, respectively (where k is the slope of the calibration line, σ is the standard deviation of the blank measurement, and n=6). In addition, with the change of concentration, the fluorescence color of the molecularly imprinted ratio fluorescence probe solution changed from yellow to blue, indicating that it has the potential for visual detection. The fluorescence response spectrum of the non-molecularly imprinted polymer probe mixed with different concentrations of DIC shows that the quenching efficiency of DIC on the non-molecularly imprinted polymer probe is relatively low. At the same time, the fluorescence color change of the non-molecularly imprinted polymer probe solution is not significant because the non-molecularly imprinted polymer probe lacks the molecularly imprinted cavity that can specifically recognize DIC. The results are shown in FIG. Figure 6 shown.

[0087] Next, the fluorescence color of each probe solution was converted into RGB value using the digital processing software of the smartphone. In the concentration range of 1.0-80.0 μM, (B+G) / R and DIC concentration showed two linear relationships, and the linear equations were:

[0088] y1=0.00934CDIC+1.36121(R=0.9983),(1.0-40.0μM)

[0089] y2=0.01632CDIC+1.08072(R=0.9985),(40.0-80.0μM)

[0090] The detection limits (3σ / k) were: LOD1 = 0.96μM and, LOD2 = 0.55μM (where k is the slope of the calibration line, σ is the standard deviation of the blank measurement, and n = 6). In addition, as the DIC concentration increased, the chromaticity coordinates gradually moved from yellow to blue, and the CIE coordinates were linearly related to the DIC concentration. This result was consistent with the phenomenon analyzed by the smartphone, further indicating that the change in fluorescence color can be monitored by the naked eye or a smartphone to achieve semi-quantitative detection of DIC; the results are shown in Figure 6 shown.

[0091] like Figure 7 Shown is a synthetic flow chart of the dicamba molecular imprinting ratio fluorescent probe, which covers the entire operation steps.

[0092] Soil and corn were selected as actual samples to design a recovery experiment. Table 1 shows the experimental results of fluorescence analysis and smartphone analysis of DIC in actual samples. No DIC was detected in the blank sample. The fluorescence analysis results showed that the recovery range was between 97.5-116.7%, and the relative standard deviation (RSD) calculated after three parallel determinations was less than 3.6%. The smartphone analysis results showed that the recovery range was between 91.2-111.0%, and the RSD was less than 4.4%. The experimental results show that the molecular imprinting ratio fluorescence probe can accurately determine DIC in corn and soil samples, and the MIFR probe combined with the smartphone was successfully applied to the quantitative detection of DIC in actual samples.

[0093] Table 1 Recovery of DIC in soil and corn

[0094]

[0095] In summary, a new type of molecular imprinting ratiometric fluorescent probe was successfully constructed based on europium metal organic framework and cadmium telluride quantum dots, which achieved sensitive detection of DIC. The fluorescence enhancement mechanism was attributed to cross-linking fluorescence enhancement. DIC and europium metal organic framework were connected by hydrogen bonds to form a network polymer, which restricted non-radiative transitions and enhanced fluorescence emission. Under 365nm ultraviolet light, the fluorescence color of the probe solution can be changed from yellow to blue. Based on this phenomenon, a method for analyzing DIC with a smartphone was developed. Recovery experiments in corn and soil samples showed that the recovery rate of the fluorescence method was between 97.5-116.7%, and the RSD was less than 3.6%; the recovery rate of the smartphone analysis method was between 91.2-111.0%, and the RSD was less than 4.4%, which showed that the molecular imprinting ratiometric fluorescent probe had good accuracy and precision in the detection of DIC, and also showed that this method had the potential for on-site visualization detection. This work provided a new method for the fluorescence quantitative detection and on-site visualization detection of DIC in food and drugs.

[0096] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for visually detecting dicamba based on a fluorescence-enhanced molecular imprinting ratiometric fluorescent probe, characterized in that: The method comprises the following steps: S1. Preparation of cadmium telluride quantum dots and europium metal organic frameworks: (1) Preparation of cadmium telluride quantum dots: 74.0 μL MPA, 91.7 mg hydrated cadmium chloride and 20.0 mg sodium citrate were dissolved in 40.0 mL double distilled water, and the pH of the solution was adjusted to 11.2 with 1.0 M sodium hydroxide. Then, 4.4 mg potassium tellurite and 20.0 mg sodium borohydride were added to the solution and stirred until completely dissolved. The solution was then placed in an oil bath at 90° C. and refluxed for 6 h. After the reaction was completed, the solution was cooled naturally to room temperature, and 40.0 mL of anhydrous ethanol was added to precipitate cadmium telluride quantum dots. Finally, the solution was centrifuged for 5 min and dried at 60° C. to obtain cadmium telluride quantum dot powder. (2) Preparation of Europium Metal Organic Framework: Weigh 0.2 g of europium nitrate hexahydrate and 0.2 g of 2-aminoterephthalic acid, dissolve in 20.0 mL of dimethylformamide, then transfer the solution to a 50 mL polytetrafluoroethylene reactor, react at 120 ° C for 4 hours, after the reaction is completed, wait for the solution to cool to room temperature, centrifuge at 4000 r / min for 5 minutes, collect the precipitate, and wash it alternately with dimethylformamide and anhydrous methanol several times to remove impurities, and finally dry it at 60 ° C to obtain yellow europium metal organic framework powder; S2. Preparation of molecularly imprinted polymer / non-molecularly imprinted polymer probes: (1) Preparation of core-shell quantum dots: 4.0 mg of cadmium telluride quantum dot powder was uniformly dispersed in a mixed solution consisting of 80.0 mL of anhydrous ethanol and 20.0 mL of water, and then 0.4 mL of tetraethyl orthosilicate and 0.4 mL of ammonia water were added to the mixed solution. The mixture was stirred for 12 h. After the reaction was completed, the mixture was centrifuged and washed several times with anhydrous ethanol, and finally dried at 60 ° C to obtain core-shell quantum dot powder. (2) Preparation of molecularly imprinted polymers: 1.0-5.0 mg of europium metal organic framework, 5.0 mg of dicamba, and 3.5-17.5 mg of acrylamide are weighed and dispersed in a mixed solvent of 8.0 mL of anhydrous ethanol and 2.0 mL of water. After stirring for 1 hour, 90.0-270.0 mg of ethylene glycol dimethyl acrylate and 5.0-25.0 mg of azobisisobutyronitrile are added, and stirring is continued for 2 hours to complete pre-assembly, followed by ventilation with high-purity nitrogen for 10 minutes, and then reacting in a 70°C water bath for 15 hours. After the reaction is completed, centrifugation is performed at 4000 r / min for 5 minutes to obtain a precipitate, and then washed alternately with anhydrous methanol and double distilled water for several times until the ultraviolet-visible absorption spectrum of the last washing liquid has no absorption peak of dicamba, and finally dried at 60°C to obtain a molecularly imprinted polymer powder; the non-molecularly imprinted polymer is synthesized under the same preparation conditions as the molecularly imprinted polymer, but the template molecule dicamba is not added during the preparation process. (3) Configuration of molecular imprinting polymer and non-molecular imprinting polymer probe solution: Accurately weigh 4.0 mg of molecularly imprinted polymer or non-molecularly imprinted polymer and 1.0 mg of core-shell quantum dots, disperse them in 10.0 mL of double distilled water to obtain a molecularly imprinted polymer or non-molecularly imprinted polymer probe solution with a concentration of 0.5 mg / mL; S3. Fluorescence detection and visual detection of dicamba: Dissolve DIC and its structural analogs in dimethylformamide to obtain a 2.0 mM standard stock solution. Take 1.0 mL of the probe solution and 1.0-80.0 μL of the DIC stock solution into a 5 mL centrifuge tube, then dilute to 2.0 mL with dimethylformamide. After the probe reacts with DIC for 15 minutes, transfer the solution to a cuvette to scan the fluorescence spectrum. The steps of visual detection are as follows: place the above-mentioned test solutions in a dark environment, irradiate each test solution with ultraviolet light, then record the fluorescence color through a smartphone, convert it into RGB numerical information, and fit and calculate the linear relationship between the RGB value and the DIC concentration.

2. The method for visual detection of dicamba using a fluorescence-enhanced molecular imprinting ratiometric fluorescent probe according to claim 1, characterized in that: In S3, the specific conditions of fluorescence detection are set as follows: the excitation wavelength is set to 365 nm, the excitation slit width is adjusted to 3 nm, the emission slit width is adjusted to 5 nm, and the emission spectrum scanning range is set to 350-650 nm.

3. The method for visual detection of dicamba based on fluorescence enhanced molecular imprinting ratio fluorescence probe according to claim 1, characterized in that: The amount of europium metal organic framework used is 1.0 mg, the amount of acrylamide used is 3.5 mg, the amount of dicamba used is 5.0 mg, the amount of ethylene glycol dimethyl acrylate used is 90.0 mg, and the amount of azobisisobutyronitrile used is 5.0 mg.

4. The method for visual detection of dicamba based on fluorescence enhanced molecular imprinting ratiometric fluorescent probe according to claim 1, characterized in that: The amount of europium metal organic framework used was 2.0 mg, the amount of acrylamide used was 7.0 mg, the amount of ethylene glycol dimethyl acrylate used was 135.0 mg, and the amount of azobisisobutyronitrile used was 10.0 mg.

5. The method for visual detection of dicamba based on fluorescence enhanced molecular imprinting ratiometric fluorescent probe according to claim 1, characterized in that: The amount of europium metal organic framework used was 3.0 mg, the amount of acrylamide used was 10.5 mg, the amount of ethylene glycol dimethyl acrylate used was 180.0 mg, and the amount of azobisisobutyronitrile used was 15.0 mg.

6. The method for visual detection of dicamba based on fluorescence-enhanced molecular imprinting ratiometric fluorescent probe according to claim 1, characterized in that: The amount of europium metal organic framework used was 4.0 mg, the amount of acrylamide used was 14.0 mg, the amount of ethylene glycol dimethyl acrylate used was 225.0 mg, and the amount of azobisisobutyronitrile used was 20.0 mg.

7. The method for visual detection of dicamba based on fluorescence enhanced molecular imprinting ratiometric fluorescent probe according to claim 1, characterized in that: The amount of europium metal organic framework used was 5.0 mg, the amount of acrylamide used was 17.5 mg, the amount of ethylene glycol dimethyl acrylate used was 270.0 mg, and the amount of azobisisobutyronitrile used was 25.0 mg.

Images