Preparation method of La-coated ZrMOF fluorescent material and application of La-coated ZrMOF fluorescent material in detection of ethephon residues

Abstract

The invention provides a preparation method of a La-coated ZrMOF fluorescent material and application of the La-coated ZrMOF fluorescent material in detection of ethephon residues. The preparation method comprises the following steps: adding zirconium tetrachloride, lanthanum acetate and 2-aminoterephthalic acid into N, N-dimethylformamide, dissolving, stirring and mixing to obtain a mixture; and after heating reaction, centrifuging, washing the precipitate, and drying to obtain the La-ZrMOF fluorescent material. The La-coated ZrMOF fluorescent material can be used for detecting ethephon, a strong fluorescence signal is generated after the La-coated ZrMOF fluorescent material and ethephon are incubated, and a standard curve can be drawn according to different ethephon concentrations and corresponding fluorescence intensities, so that rapid fluorescence detection of ethephon residues is realized, and the detection efficiency is effectively improved; the method can be used for preparing a paper-based sensor for quickly identifying whether ethephon residues exist or not by naked eyes, and the method gets rid of the limitation of instrument use and realizes on-site preliminary detection and judgment of ethephon.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical sensors, and particularly relates to a preparation method of a La@ZrMOF fluorescent material and an application thereof in detecting ethephon residues. Background Art

[0002] Ethephon (ETH), a 2-chloroethylphosphonic acid, is one of the most popular plant growth control agents in the world and a pre- and post-harvest ripening enhancer for fruits, vegetables, and grains. Excessive use of artificial ripening has been questioned due to various health issues. Long-term intake of foods containing ETH can cause gastrointestinal irritation and erosion of the digestive system, and large intakes may be harmful to the kidneys and brain. Therefore, there is a great need to monitor the ETH content in plant foods, especially in fruits and vegetables, as the use of these foods is common. Traditional detection methods mainly include gas chromatography (GC), high-performance liquid chromatography (HPLC), and ion chromatography (IC). Although the above techniques are extremely responsive and accurate for pesticide detection, they are cumbersome, labor-intensive, and heavily equipment-dependent, and are both laborious and time-consuming. This still poses a huge challenge for simple, rapid, and sensitive analyte detection.

[0003] At present, new rapid detection technologies for ethephon have also made great progress. For example, the detection of ethephon by gold nanoparticle-loaded molecular imprinting switch sensors has made up for the shortcomings of instrumental analysis methods to a certain extent, but it also has its shortcomings. For example, the reaction conditions of the gold nanoparticle-loaded molecular imprinting switch sensors in the preparation process need to be precisely controlled, which greatly increases the difficulty and cost. The shedding, deformation and aging of the membrane layer will affect the reliability of the sensor. Due to the large interface resistance between the gold nanoparticles and the molecular imprinting polymer or the poor electron transfer path, the sensor response speed slows down or the signal attenuates, thus affecting the detection effect. Summary of the invention

[0004] The present invention aims to provide a method for preparing a paper-based fluorescent sensor based on a metal organic framework and a method for fluorescent detection of ethephon residues. The metal organic framework is used as a fluorescent probe and is attached to the surface of a paper-based sensor through the high porosity, high adsorption, high specific surface area and fluorescence characteristics of the metal organic framework. The specific fluorescence recognition response to ethephon is used to achieve efficient, rapid and accurate detection of ethephon.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a La@ZrMOF fluorescent material comprises the following steps:

[0007] S1. Add zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid to N,N-dimethylformamide, dissolve and stir to mix to obtain a mixture.

[0008] S2. After heating and reacting the above mixture, centrifuge it, then wash the precipitate and dry it to obtain the La@ZrMOF fluorescent material.

[0009] For the preparation method as described above, preferably, in step S1, the zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid are added in a molar ratio of 20 - 30:3 - 8:20 - 28, and the amount of N,N-dimethylformamide is added according to the volume-mass ratio of N,N-dimethylformamide to zirconium tetrachloride of 1 L:8 g.

[0010] For the preparation method as described above, preferably, in step S1, the stirring and mixing is carried out by stirring at 25 °C for 0.2 - 1 h.

[0011] For the preparation method as described above, preferably, in step S2, the temperature of the heating reaction is 110 - 130 °C, and the reaction is carried out for 20 - 28 h.

[0012] For the preparation method as described above, preferably, in step S2, the centrifugation conditions are 6000 - 8000 rpm for 5 - 10 min; when washing, first use N,N-dimethylformamide, and then use ethanol for washing; the drying conditions are drying in a vacuum drying oven at 80 - 120 °C for 10 - 12 h.

[0013] Application of the La@ZrMOF fluorescent material obtained by the preparation method as described above in the preparation of ethephon detection reagents.

[0014] Application of the La@ZrMOF fluorescent material obtained by the preparation method as described above in the detection of ethephon.

[0015] For the application as described above, specifically, dissolve the La@ZrMOF fluorescent material in water to obtain a fluorescent probe, incubate the fluorescent probe with the test solution and standard solutions with different gradient concentrations of ethephon respectively; measure the fluorescence intensity of each incubated solution at an excitation wavelength of 365 nm and an emission wavelength of 450 nm; draw a standard curve based on the different gradient concentrations of the ethephon standard solution and their corresponding fluorescence intensities, and substitute the measured fluorescence intensity of the test solution into the standard curve to obtain the concentration of ethephon in the test solution.

[0016] Application of the La@ZrMOF fluorescent material obtained by the preparation method as described above in the preparation of a paper-based sensor for detecting ethephon.

[0017] For the application described above, preferably, the preparation method of the paper-based sensor is to soak a filter paper strip in an aqueous solution of La@ZrMOF fluorescent material with a mass concentration of 1.5 - 2 mg / ml for 24 - 50 h, and then dry it to obtain.

[0018] A detection kit for detecting ethephon, which includes the La@ZrMOF fluorescent material obtained by the preparation method described above.

[0019] A method for detecting ethephon residues, which includes the following steps:

[0020] A. Dissolve the La@ZrMOF fluorescent material obtained by the above preparation method in water to make an aqueous solution of the fluorescent probe. Add the aqueous solution of the fluorescent probe into standard solutions and test solutions containing different gradient concentrations of ethephon respectively, and incubate.

[0021] B. Measure the fluorescence intensity of each incubated solution at an excitation wavelength of 365 nm and an emission wavelength of 450 nm; draw a standard curve according to the standard solutions with different gradient concentrations of ethephon and their corresponding fluorescence intensities, and substitute the measured fluorescence intensity of the solution into the standard curve to obtain the concentration of ethephon in the measured solution.

[0022] For the method for detecting ethephon residues described above, preferably, the mass concentration of the aqueous solution of the fluorescent probe is 0.5 - 2.0 mg / ml, the volume ratio of the aqueous solution of the fluorescent material to the standard solution or the test solution is 1:1, and the reaction time is 20 - 30 min.

[0023] Furthermore, the mass concentration of the aqueous solution of the fluorescent probe is 0.6 mg / ml; the incubation time is 30 min.

[0024] The beneficial effects of the present invention are as follows:

[0025] The present invention provides a preparation method of a La@ZrMOF fluorescent material. The MOF material obtained by this method can be used as a fluorescent probe, which has the advantages of high pore rate, high adsorption and high specific surface area. The introduction of amino groups in the material enables La@ZrMOF to have a fluorescence response to ethephon and exhibits excellent fluorescence performance. It can realize the rapid fluorescence detection of ethephon residues through the specific fluorescence recognition of ethephon, thus effectively improving the detection efficiency.

[0026] The present invention also provides a method for fluorescence detection of pesticide residues. A strong fluorescence signal can be generated through the specific fluorescence recognition of ethephon by the La@ZrMOF fluorescence material. Based on the positive correlation between the concentration of ethephon residues and the fluorescence signal generated by La@ZrMOF, a standard curve can be plotted by the ethephon concentration and fluorescence intensity, and a rapid fluorescence detection method for ethephon residues based on La@ZrMOF can be constructed, so as to realize the rapid fluorescence detection of ethephon residues and effectively improve the detection efficiency. This detection method can be effectively used for the detection of ethephon residues in ripe fruits, vegetables and grains.

[0027] The present invention also provides a method for rapid visual identification of ethephon residues through a paper-based sensor. This method uses the prepared test paper to get rid of the limitation of instrument use, and the test result can be obtained by the naked eye, realizing the on-site preliminary detection and judgment of ethephon. Moreover, the prepared test paper can be stored for a long time, with stable materials and no signal attenuation. Brief Description of the Drawings

[0028] Figure 1 It is the scanning electron microscope image of La@ZrMOF involved in the present invention;

[0029] Figure 2 It is the fluorescence response spectrum diagram of the present invention to ethephon, and the excitation wavelength is 365nm;

[0030] Figure 3 It is the fitting curve of the present invention to ethephon with different concentrations of 0 - 400mg / L, the excitation wavelength is 365nm, and the emission wavelength is 450nm;

[0031] Figure 4 It is the visible effect diagram of the paper-based sensor provided by the present invention under ultraviolet light, and the wavelength of the ultraviolet lamp is 365nm. Detailed Embodiments

[0032] The present invention first synthesized a novel fluorescent La@ZrMOF nanomaterial for the convenient and intuitive detection of ETH based on the ligand-to-metal charge transfer process. La 3+ ions are used in the MOF material to improve the detection sensitivity of the fluorescence resonance energy transfer process. As the concentration of ETH increases, the fluorescence signal gradually enhances, and the color changes from colorless to blue simultaneously. Meanwhile, a paper-based method was designed to rapidly and visually determine ETH for on-site detection, enabling it to be effectively used in various actual products, taking apples, pears and tomatoes as examples. The method of the present invention makes the detection of ETH simple, rapid and easy to use, through a sensitive method using fluorescence and visual techniques with a paper-based microsensor. This provides a convenient method for the rapid on-site detection of ETH, indicating the further development potential of novel fluorescent MOF nanomaterials for pesticide detection.

[0033] A preparation method of La@ZrMOF fluorescent material provided by the present invention includes: adding zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid into N,N-dimethylformamide for dissolution, and pouring the mixed suspension into a high-temperature reaction vessel lined with polytetrafluoroethylene to prepare the fluorescent material: La@ZrMOF. It is found that after the material reacts with ethephon, there is an obvious characteristic peak at the emission wavelength of 365 nm, and the fluorescence intensity changes differently according to different concentrations of ethephon, indicating that the fluorescent material can specifically recognize ethephon by fluorescence.

[0034] The present invention also provides a fluorescence detection method for pesticide residues. The fluorescence signal generated by the specific fluorescence recognition of ethephon by this MOF can be enhanced, and based on the sensitivity curve of the concentration of ethephon residues and the fluorescence signal of La@ZrMOF, a rapid fluorescence detection method for ethephon residues based on MOF is constructed, so as to realize the rapid fluorescence detection of ethephon residues and effectively improve the detection efficiency.

[0035] Specifically, the present invention provides a preparation method of La@ZrMOF fluorescent material, which is prepared by the following method:

[0036] S1: Add zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid into N,N-dimethylformamide for dissolution;

[0037] Specifically, this step S1 specifically includes:

[0038] S11: Weigh a certain amount of zirconium tetrachloride, lanthanum acetate, and a certain amount of 2-aminoterephthalic acid and pour them into a beaker of appropriate size;

[0039] S12: Add a certain amount of N,N-dimethylformamide solution to the beaker and stir at 25 °C for 0.5 h.

[0040] It should be noted that the dosages of zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid in this step are carried out according to the molar ratio of 20-30:3-8:20-28, and the dosages of each component can be determined according to one's own needs.

[0041] S2: Pour the mixed suspension into a high-pressure reaction kettle lined with polytetrafluoroethylene, heat at high temperature, and prepare La@ZrMOF;

[0042] Specifically, this step S2 specifically includes:

[0043] S21: Pour the N,N-dimethylformamide solution of zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid into a high-pressure reaction kettle of appropriate size;

[0044] S22: Screw on the lid of the high-pressure reactor and place it in the oven. React at 110 - 130 °C for 20 - 28 h;

[0045] After centrifugation, wash three times with N,N-dimethylformamide and four times with ethanol. After drying at 80 °C in a vacuum drying oven for 12 h, collect the brown powder product La@ZrMOF.

[0046] It should be noted that the dosages of zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid in this step are carried out according to a molar ratio of 20 - 30:3 - 8:20 - 28 respectively, and the dosage of N,N-dimethylformamide is carried out according to a volume-mass ratio of N,N-dimethylformamide to zirconium tetrachloride of 1 mL:8 mg. If the above ratios are not followed, the blue fluorescence property is poor and the detection effect sensitivity decreases. In other embodiments, the dosages of each component can be determined according to one's own needs. Further, it is preferred that the dosages of zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid are carried out according to a molar ratio of 25:6:25, and react at 120 °C for 24 h to obtain a product with better blue fluorescence property and high detection effect sensitivity.

[0047] The embodiments of the present invention also provide a fluorescence detection method for ethephon residues, which is based on the above La@ZrMOF fluorescent material for rapid detection, and specifically includes the following steps:

[0048] S1: Incubate the aqueous solution of the La@ZrMOF fluorescent material prepared by the above preparation method with the test solution and standard solutions containing different concentrations of ethephon respectively:

[0049] S2: After shaking and mixing evenly, measure the fluorescence intensity of the test solution at an excitation wavelength of 365 nm and an emission wavelength of 450 nm, and the slit width is 5 nm;

[0050] S3: Perform non-linear fitting with the absolute value of the fluorescence intensity corresponding to different concentrations of ethephon to construct a new rapid detection method for ethephon. Among them, the test solution can be a fruit and vegetable extract containing ethephon residues, and the fruit and vegetable extract uses water.

[0051] It should be noted that in the above implementation method, the concentration of the La@ZrMOF fluorescent material is 0.5 - 2.0 mg / ml, the volume ratio of the aqueous solution of the fluorescent material to the fruit and vegetable extract is 1:1, and the incubation time is 20 - 30 min.

[0052] Of course, in other embodiments, the dosages of each component can be determined according to one's own needs, and the embodiments of the present invention do not make any limitations.

[0053] Specifically, the present invention provides a method for fluorescence detection of pesticide residues. The fluorescence signal enhanced by the specific fluorescence recognition of ethephon by the prepared La@ZrMOF fluorescence material can be used. Based on the positive correlation between the concentration of ethephon residues and the fluorescence signal of La@ZrMOF, a sensitivity curve can be plotted by detecting the concentration and fluorescence intensity of different ethephon standard solutions, and a rapid fluorescence detection method for ethephon residues based on the La@ZrMOF fluorescence material can be constructed, thereby realizing the rapid fluorescence detection of ethephon residues and effectively improving the detection efficiency.

[0054] The present invention also provides a paper-based sensor that can preliminarily judge the ethephon content with the naked eye under ultraviolet light. By observing whether the color of the test strip changes under ultraviolet light, the residual amount of ethephon can be roughly analyzed.

[0055] The following examples are used to further illustrate the present invention, but should not be construed as limiting the present invention. Modifications or substitutions made to the present invention without departing from the spirit and essence of the present invention all fall within the scope of the present invention.

[0056] Unless otherwise specified, the technical means used in the examples are conventional means well-known to those skilled in the art. Unless otherwise specified, the reagents used in the examples are of analytical grade or above. For reagents or instruments without indicating the manufacturer, conventional products available on the market can be used.

[0057] Example 1

[0058] This example provides a preparation method for the La@ZrMOF fluorescence material, which specifically includes the following steps:

[0059] S1: Weigh 240 mg of zirconium tetrachloride, 76 mg of lanthanum acetate, and 181 mg of 2-aminoterephthalic acid and add them to a 100 ml beaker. Then add 30 ml of N,N-dimethylformamide solution to the beaker and stir at room temperature for 30 min to fully dissolve.

[0060] S2: Pour the N,N-dimethylformamide solution of zirconium tetrachloride, lanthanum acetate, and 2-aminoterephthalic acid into a 100 ml polytetrafluoroethylene-lined autoclave, seal the autoclave lid, and react at 120 °C for 24 h.

[0061] S3: After centrifuging the reaction product at 6000 rpm for 10 min, wash the precipitate three times with N,N-dimethylformamide and four times with ethanol, and dry it in a vacuum drying oven at 80 °C for 12 h to collect the brown fluorescent material La@ZrMOF.

[0062] The material prepared above was detected by scanning electron microscopy, and the obtained scanning electron micrograph is as Figure 1As shown, the results indicate that the obtained La@ZrMOF is an irregular spherical shape with an average particle size of about 200 nm.

[0063] Example 2

[0064] Dissolve the La@ZrMOF fluorescent material prepared in Example 1 in water to prepare an aqueous solution of a fluorescent probe at 0.6 mg / ml. Add 1 ml of the aqueous solution of the fluorescent probe to solutions containing different concentrations of ethephon (0 mg / L, 25 mg / L, 50 mg / L, 100 mg / L, 500 mg / L), and incubate for 30 min. At the same time, for the ethephon solution with a concentration of 200 mg / L and the incubated solution, respectively, use a fluorescence spectrophotometer to read the emission spectra. The results are as Figure 2 shown. It can be seen from the results that the fluorescent La@ZrMOF material has an obvious characteristic peak at an emission wavelength of 365 nm, and the fluorescence intensity changes differently according to different concentrations of ethephon, indicating that the material can perform specific fluorescence recognition of ethephon.

[0065] Example 3

[0066] A method for detecting ethephon residues, which comprises the following steps:

[0067] S1: Add the fluorescent La@ZrMOF material prepared in Example 1 to water to prepare an aqueous solution of a fluorescent probe at a concentration of 0.6 mg / ml. Add 1 ml of the aqueous solution of the fluorescent probe to 1 ml of standard solutions containing different concentrations of ethephon in fruit and vegetable extracts (i.e., water) (the concentrations of ethephon are 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.4 mg / L, 0.8 mg / L, 1 mg / L, 2 mg / L, 4 mg / L, 8 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, 80 mg / L, 100 mg / L, 200 mg / L, 400 mg / L), and incubate for 30 min.

[0068] S2: After shaking and mixing evenly, measure the fluorescence intensity of the test solution with a fluorescence spectrophotometer at an excitation wavelength of 365 nm and an emission wavelength of 450 nm, with a slit width of 5 nm; measure the fluorescence intensity of the test solution.

[0069] Perform curve fitting on the absolute value of the fluorescence intensity measured for the standard solutions with the above different gradient concentrations of ethephon (the fluorescence intensity of the test solution - the fluorescence intensity of the blank solution) and the concentration of ethephon. The results are as Figure 3 shown. The abscissa is the standard gradient concentration of ethephon, and the ordinate is the fluorescence value. The obtained R 2 is 0.998, and the fitting equation is Y = (140 + 105.7x) / (1 + 0.06x - 2.4x 2), where X represents the concentration of ethephon in the solution, with the unit of mg / L, and Y is the fluorescence intensity. The detection limit of this method is 30 μg / L. Thus, the absolute value result obtained by subtracting the fluorescence intensity of the blank solution from the measured fluorescence intensity of the test solution can be substituted into the standard curve to determine the residual concentration of ethephon, thereby achieving the rapid detection of the residual concentration of ethephon.

[0070] Example 4

[0071] Preparation and detection of the ethephon detection paper: The La@ZrMOF prepared in Example 1 was made into a La@ZrMOF suspension with a concentration of 2 g / L in water and used to soak the filter paper for 48 h. After that, the test paper strip was air-dried naturally. Then, 1.0 mL of fruit and vegetable extract containing ethephon was dropped onto the test paper strip. Here, the fruit and vegetable extract was prepared by chopping 5 - 10 g of fruit samples and transferring them to 4 - 6 mL of water, shaking for 15 - 30 minutes, centrifuging at 5000 - 8000 rpm for 20 minutes, and taking the supernatant. Detection was carried out on plows, apples, and tomatoes respectively, with the added ethephon concentrations being 0 mg / L, 5 mg / L, 10 mg / L, and 20 mg / L; under ultraviolet light, the fluorescence was observed with the naked eye. The results are as Figure 4 shown. It can be observed with the naked eye that under ultraviolet light, ethephon at different concentrations has different intensities of blue fluorescence. The results indicate that it can be determined whether ethephon is present by the presence or absence of blue fluorescence. It shows that the prepared paper-based sensor can be used for the on-site rapid detection of ethephon residues in fruits and vegetables, without the need for precision instruments, professional testers, and with low costs.

[0072] In summary, the preparation method of the La@ZrMOF fluorescent material provided by the embodiments of the present invention, the detection method for pesticide residues, uses the La@ZrMOF material as a fluorescent probe, which has the advantages of high pore rate and high specific surface area. By the fitting curve of ethephon at different concentrations and fluorescence intensity, a rapid fluorescence detection method for ethephon based on MOF is constructed, and a paper-based sensor is designed to achieve the rapid and sensitive detection of ethephon residues, greatly improving the detection efficiency. At the same time, this method is simple and fast, and can overcome the disadvantages such as the dependence on biological enzymes for ethephon detection, poor stability, and low sensitivity.

Claims

1. A method for preparing La@ZrMOF fluorescent material, characterized in that: It includes the following steps: S1, adding zirconium tetrachloride, lanthanum acetate and 2-aminoterephthalic acid into N,N-dimethylformamide, dissolving and stirring to obtain a mixture; S2. After heating the mixture to react, centrifuge it, wash the precipitate, and dry it to obtain La@ZrMOF fluorescent material.

2. The preparation method according to claim 1, characterized in that In step S1, the zirconium tetrachloride, lanthanum acetate and 2-aminoterephthalic acid are added in a molar ratio of 20-30:3-8:20-28, and the amount of N,N-dimethylformamide is added according to the volume mass ratio of N,N-dimethylformamide to zirconium tetrachloride of 1L:8g.

3. The preparation method according to claim 1, characterized in that: In step S2, the heating reaction temperature is 110-130°C, and the reaction time is 20-28 hours.

4. The preparation method according to claim 1, characterized in that: In step S2, the centrifugal condition is 6000-8000 rpm, and the centrifugal condition is 5-10 min; the washing is firstly done with N,N-dimethylformamide, and then with ethanol; the drying condition is done in a vacuum drying oven at 80-120° C. for 10-12 h.

5. Use of the La@ZrMOF fluorescent material obtained by the preparation method as described in any one of claims 1 to 4 in the preparation of ethephon detection reagents.

6. Application of the La@ZrMOF fluorescent material obtained by the preparation method according to any one of claims 1 to 4 in the detection of ethephon.

7. Use of the La@ZrMOF fluorescent material obtained by the preparation method according to any one of claims 1 to 4 in the preparation of a paper-based sensor for detecting ethephon.

8. The use according to claim 8, characterized in that The preparation method of the paper-based sensor is to soak a filter paper strip in an aqueous solution with a mass concentration of La@ZrMOF fluorescent material of 1.5 to 2 mg / ml for 24 to 50 hours and then dry it.

9. A detection kit for detecting ethephon, comprising the La@ZrMOF fluorescent material obtained by the preparation method according to any one of claims 1 to 4.

10. A method for detecting ethephon residues, characterized in that: It includes the following steps: A. dissolving the La@ZrMOF fluorescent material obtained by the preparation method according to any one of claims 1 to 4 in water to prepare a fluorescent probe aqueous solution, and adding the fluorescent probe aqueous solution to a standard solution and a test solution containing different gradient concentrations of ethephon, respectively, for incubation; B. Measure the fluorescence intensity of each incubated solution at an excitation wavelength of 365 nm and an emission wavelength of 450 nm; draw a standard curve based on the fluorescence intensity corresponding to the standard solutions of different gradient concentrations of ethephon, and substitute the fluorescence intensity of the measured solution into the standard curve to obtain the concentration of ethephon in the measured solution.

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