A method for fluorescent detection of methylthioacetaldoxime

Abstract

The method for detecting methylthioacetaldehyde oxime by fluorescence provided by the present disclosure utilizes the active groups such as phenylboronic acid contained on the surface of the phenylboronic acid functionalized carbon quantum dots, so that the phenylboronic acid functionalized carbon quantum dots can produce complexation with copper ions, and the fluorescence of the phenylboronic acid functionalized carbon quantum dots is quenched through a static quenching mechanism. The complexation of methylthioacetaldehyde oxime with copper ions is stronger than the complexation of the phenylboronic acid functionalized carbon dots with copper ions, and when methylthioacetaldehyde oxime exists, it can prevent the combination of copper ions and the phenylboronic acid functionalized carbon dots, and then the fluorescence of the phenylboronic acid functionalized carbon quantum dots quenched by fluorescence is recovered. This process constructs an "OFF-ON" sensing system, so that the phenylboronic acid functionalized carbon quantum dots can be used as a fluorescence sensor to realize high-sensitivity detection of methylthioacetaldehyde oxime. The method provided by the present disclosure has high sensitivity, good selectivity, low cost and is easy to operate.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of methylthioacetaldoxime detection, in particular to a fluorescence detection method of methylthioacetaldoxime and application thereof in pesticide residue detection. BACKGROUND

[0002] Developing a rapid detection method for environmental pollutants has an important role in maintaining ecological environment safety and protecting human health.

[0003] Methylthioacetaldoxime is an intermediate for producing pesticide methomyl and other carbamate pesticides with similar structures, and is also one of the hydrolysis products of the above pesticides. Methylthioacetaldoxime has a foul odor and certain neurotoxicity. Methomyl is a highly toxic carbamate pesticide, which can cause insects to die by excessive excitement through inhibiting the activity of acetylcholinesterase in the body of the insects. Since methomyl is toxic to human body and frequently causes pesticide poisoning, the use of methomyl on vegetables has been prohibited. Therefore, the detection of methylthioacetaldoxime and methomyl has a great application demand in poisoning treatment and safety evaluation of agricultural products.

[0004] At present, the conventional detection method for methylthioacetaldoxime and methomyl mainly relies on chromatographic techniques, including GC-MS (gas chromatography-mass spectrometry) and HPLC-MS (liquid chromatography-mass spectrometry), the principle of which is that the sample is extracted with acetonitrile, the extract is purified by solid phase extraction or dispersive solid phase extraction, and then detected by high performance liquid chromatography with a fluorescence detector and a post-column derivatization system. Although this method has high sensitivity, it is expensive and requires large instruments and special operation, which cannot meet the demand of real-time detection on site. In addition, the rapid detection method for organophosphorus and carbamate pesticides based on enzyme inhibition method is also widely used, which is cheap and intuitive, but the specificity of this method is not strong, and it is easily interfered by the matrix, especially it cannot distinguish different toxicities of carbamate pesticides.

[0005] Methomyl is hydrolyzed under alkaline conditions to generate methylthioacetaldoxime, and oxime compounds can be used as industrial extractants for copper ions, which is mainly because the hydrogen atom in the oxime structure can be replaced by metals, and the nitrogen atom with unpaired electrons can also form a certain chelate ring structure with copper ions. Copper ions can also form a complex with boronic acid groups.

[0006] The "OFF-ON" sensing system is a kind of sensor designed by the principle of recovery of probe molecule fluorescence after the target molecule is combined with the quencher. Compared with the target molecule directly as a quencher, it has the advantages of high sensitivity and strong anti-interference ability. As a new type of carbon nanomaterial with good biocompatibility, low toxicity and rich surface functional groups, carbon quantum dots have the ability to functionalize and construct such sensors. At present, there is no method for detecting methylthioacetaldoxime based on copper ion-phenylboronic acid functionalized carbon quantum dots probe. SUMMARY

[0007] The present disclosure aims to at least solve one of the technical problems existing in the prior art.

[0008] To this end, the present disclosure provides a fluorescence detection method for methylthioacetaldoxime, which uses phenylboronic acid functionalized carbon quantum dots as a probe to detect methylthioacetaldoxime. The method has high sensitivity, good selectivity, low cost and is easy to operate.

[0009] The fluorescence detection method for methylthioacetaldoxime provided by the present disclosure comprises:

[0010] Mixing phenylboronic acid functionalized carbon quantum dots, an aqueous solution containing copper ions and a standard solution containing methylthioacetaldoxime with different concentrations, and obtaining a plurality of homogeneous solutions A after reaction; performing fluorescence excitation on each homogeneous solution A to determine the functional relationship between the concentration of methylthioacetaldoxime and the fluorescence intensity;

[0011] Mixing the phenylboronic acid functionalized carbon quantum dots, the aqueous solution containing copper ions and the test extract containing methylthioacetaldoxime, and obtaining a homogeneous solution B after reaction; performing fluorescence excitation on the homogeneous solution B, and using the functional relationship between the concentration of methylthioacetaldoxime and the fluorescence intensity to obtain the concentration of methylthioacetaldoxime contained in the test extract;

[0012] The phenylboronic acid functionalized carbon quantum dots are prepared according to the following steps:

[0013] Dissolving citric acid and thioethanolamine in a low eutectic solvent prepared from urea and choline chloride at a molar ratio of 1:1, and performing ultrasonic treatment to form a homogeneous solution A; performing pyrolysis reaction on the solution A to obtain a solution B; performing dialysis and drying on the solution B to obtain sulfur and nitrogen co-doped carbon quantum dots;

[0014] Mixing the sulfur and nitrogen co-doped carbon quantum dots with deionized water, and performing amidation reaction under the action of a catalyst and 4-aminobenzeneboronic acid; and performing dialysis and drying on the product obtained by the amidation reaction to obtain the phenylboronic acid functionalized carbon quantum dots.

[0015] In some embodiments, the solute in the copper ion-containing aqueous solution is selected from a mixture of any one or more of copper chloride, copper sulfate, copper nitrate, and copper acetate.

[0016] In some embodiments, the concentration of the copper ion-containing aqueous solution is 10 mg / mL to 20 mg / mL.

[0017] In some embodiments, the test sample extract is selected from a water sample of apple, cucumber, rice, or river water.

[0018] In some embodiments, the mass ratio of the phenylboronic acid functionalized carbon quantum dots, the copper ion-containing aqueous solution, and the standard solution is 1:500-1000:5000-10000.

[0019] In some embodiments, the mass ratio of the phenylboronic acid functionalized carbon quantum dots, the copper ion-containing aqueous solution, and the test sample extract is 1:500-1000:5000-10000.

[0020] In some embodiments, the excitation wavelength is 357 nm.

[0021] In some embodiments, the mass ratio of the sulfur and nitrogen co-doped carbon quantum dots, the deionized water, the catalyst, and the 4-aminophenylboronic acid is 1:30000:50:100.

[0022] In some embodiments, the sulfur and nitrogen co-doped carbon quantum dots are mixed with deionized water, and an amidation reaction is performed in the presence of a catalyst and 4-aminophenylboronic acid, including:

[0023] The sulfur and nitrogen co-doped carbon quantum dots, the deionized water, and the catalyst are mixed to activate the catalyst, and the activation is performed for 15 min to obtain an activated product.

[0024] The activated product is mixed with 4-aminophenylboronic acid, and an amidation reaction is performed at room temperature for 12 h.

[0025] In some embodiments, the dialysis of the product obtained by the amidation reaction is performed for 48 h.

[0026] Further, the product obtained by the amidation reaction is dialyzed, and the deionized water is periodically replaced during the dialysis process to obtain a phenylboronic acid functionalized carbon quantum dot solution.

[0027] Further, the phenylboronic acid functionalized carbon quantum dot solution is subjected to freeze-drying after removing most of the solvent by rotary evaporation to obtain the phenylboronic acid functionalized carbon quantum dots.

[0028] Further, the catalyst is selected from N,N'-diisopropylcarbodiimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

[0029] In some embodiments, the temperature of the pyrolysis reaction is 160℃, and the reaction time is 2h.

[0030] In some embodiments, the dialysis of the solution B is performed for 96h.

[0031] In some embodiments, the deionized water is periodically replaced during the dialysis of the solution B, and a sulfur and nitrogen co-doped carbon quantum dot solution is obtained after dialysis.

[0032] Further, the sulfur and nitrogen co-doped carbon quantum dot solution is freeze-dried after most of the solvent is removed by rotary evaporation to obtain the sulfur and nitrogen co-doped carbon quantum dots.

[0033] In some embodiments, the mass ratio of the citric acid, the thioethanolamine, and the deep eutectic solvent is 1:1:20.

[0034] In some embodiments, the detection product extraction solution containing methanethiol acetaldoxime is a solution containing methanethiol acetaldoxime generated by hydrolysis of methomyl under alkaline conditions.

[0035] Further, the solution containing methanethiol acetaldoxime generated by hydrolysis of methomyl under alkaline conditions comprises: mixing a methomyl solution with a lye, adding an acid solution to terminate the reaction after 2min-10min of reaction, and obtaining a solution containing methanethiol acetaldoxime.

[0036] Further, the lye is selected from a mixture of any one or more of sodium hydroxide solution, potassium hydroxide solution, and lithium hydroxide solution.

[0037] Further, the acid solution is selected from a mixture of any one or more of hydrochloric acid, nitric acid, and sulfuric acid.

[0038] Further, the mass ratio of the methomyl solution to the lye is 1:0.01-0.1.

[0039] Further, the amount of substance of the lye and the acid solution is equal.

[0040] The present disclosure provides a fluorescence detection method for methanethiol acetaldoxime, which has the following characteristics and beneficial effects:

[0041] The active groups contained in the surface of the phenylboronic acid functionalized carbon quantum dots make the carbon quantum dots capable of producing complexation with copper ions, and the fluorescence of the carbon quantum dots is quenched by a static quenching mechanism. The complexation between the methylthioacetaldoxime and the copper ions is stronger than that between the carbon quantum dots and the copper ions, and when the methylthioacetaldoxime exists, the methylthioacetaldoxime can prevent the copper ions from combining with the carbon quantum dots, so that the fluorescence of the carbon quantum dots quenched by the methylthioacetaldoxime is recovered. This process constructs an "OFF-ON" sensing system, so that the phenylboronic acid functionalized carbon quantum dots can be used as a fluorescence sensor to realize high-sensitivity detection of the methylthioacetaldoxime.

[0042] In addition, when the phenylboronic acid functionalized carbon quantum dots are prepared, the eutectic solvent effectively disperses and dissolves the solute through hydrogen bond interaction, so that the reaction for forming the carbon quantum dots can be carried out at normal pressure, and the dangerous hydrothermal reaction is avoided. Meanwhile, the eutectic solvent also effectively reduces the synthesis temperature and the reaction time of the carbon quantum dots, and can save the energy and time required in the synthesis process. The eutectic solvent can also participate in the formation of the carbon quantum dots, modify the surface of the carbon quantum dots, and improve the dispersity and stability. The amide reaction further covalently links the recognition element 4-aminophenylboronic acid and the carbon quantum dots, and the reaction is carried out at room temperature, which is green and friendly, and the reaction is complete.

[0043] The fluorescence detection method provided by the present disclosure can be used for residual detection of the pesticide methomyl. The method is convenient, sensitive and low in cost. Specifically, the present disclosure utilizes the hydrolysis of methomyl under alkaline conditions to generate methylthioacetaldoxime, and then quantitatively detects the methomyl by the above-mentioned fluorescence detection method. The method is easy to implement, can be applied to various substrates, and can detect the pesticide at a concentration below the residual limit according to the national standard, and has application potential as a rapid pesticide residue detection method. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The working curve of the methylthioacetaldoxime detected by the phenylboronic acid functionalized carbon quantum dots in the present disclosure embodiment 1.

[0045] Figure 2 The infrared spectrum of the phenylboronic acid functionalized carbon quantum dots prepared in the present disclosure embodiment 1. The absorption at 1599 cm -1 and 1509 cm -1 corresponds to amide I peak and amide II peak, which indicates that the formation of the amide bond covalently combines the phenylboronic acid and the carbon quantum dots. The characteristic absorption peak at 1328 cm -1 is the asymmetric stretching vibration of the boron-oxygen bond of the phenylboronic acid group, which also indicates that the surface of the carbon quantum dots has the boronic acid group.

[0046] Figure 3The transmission electron microscope image of the phenylboronic acid functionalized carbon quantum dots prepared in Embodiment 1 of the present disclosure can show the morphology and size of the carbon quantum dots.

[0047] Figure 4 The working curve for detecting methomyl by the phenylboronic acid functionalized carbon quantum dots in Embodiment 2 of the present disclosure.

[0048] Figure 5 The mass spectrum for judging the degree of hydrolysis of the method for detecting methomyl by the phenylboronic acid functionalized carbon quantum dots in Embodiment 2 of the present disclosure. DETAILED DESCRIPTION

[0049] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. In addition, if not specifically stated, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also readily available to those skilled in the art.

[0050] The technical solutions of the present application are not limited to the specific embodiments listed below, and should also include various applications of the phenylboronic acid structure for methanesulfoncarboxaldehyde oxime recognition.

[0051] Embodiment 1:

[0052] Embodiment 1 of the present application is a method for quantitatively detecting the concentration of methanesulfoncarboxaldehyde oxime using phenylboronic acid functionalized carbon quantum dots, which is completed according to the following steps:

[0053] I. Preparation of phenylboronic acid functionalized carbon quantum dots, specifically including:

[0054] 1) Preparation of a eutectic solvent: mix 13.96 g of choline chloride and 6.00 g of urea, heat at 80°C for 30 min, until the system is clear and transparent, and cool to room temperature to obtain a eutectic solvent for preparing sulfur-nitrogen co-doped carbon quantum dots.

[0055] 2) Preparation of sulfur-nitrogen co-doped carbon quantum dots: mix 1 g of citric acid, 1 g of thioethanolamine, and 20 g of the eutectic solvent, then add to a flask, heat in an oil bath, set the reaction time to 2 h and the temperature to 160°C; after the reaction is completed, cool to room temperature, filter the product through a microporous filter membrane to obtain a red-brown solution; dialyze through a dialysis bag (3500 Da), concentrate by rotary evaporation, and freeze-dry the dialysis liquid to obtain sulfur-nitrogen co-doped carbon quantum dots.

[0056] 3) Preparation of phenylboronic acid functionalized carbon quantum dots: 1 mg of the sulfur and nitrogen co-doped carbon quantum dots obtained in step 2) was dissolved in 30 mL of deionized water, 50 mg of each of the catalysts N,N'-diisopropylcarbodiimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide were added, and the reaction was allowed to proceed for 15 min to activate the carboxyl groups in the carbon quantum dots, then 100 mg of 4-aminophenylboronic acid was added, and the reaction was allowed to proceed at room temperature for 12 h. The product was filtered through a 0.22 μm microporous filter membrane to obtain a red-brown solution; dialysis was performed in a dialysis bag (3500 Da), and the dialysate was concentrated by rotary evaporation and freeze-dried to obtain the phenylboronic acid functionalized carbon quantum dots.

[0057] II. Detection of the concentration of methylthioacetaldoxime in the standard solution: 800 μL of an aqueous solution of methylthioacetaldoxime at different concentrations was taken as the standard solution, 100 μL of the 150 mg / L phenylboronic acid functionalized carbon quantum dot solution prepared in step one and 100 μL of the 15 mg / L copper chloride solution were added, and the reaction was allowed to proceed at room temperature for 3 min. The fluorescence spectrum of the aqueous solution of methylthioacetaldoxime at different concentrations was recorded under excitation at 357 nm, and the fluorescence intensity at 464 nm (corresponding to the peak value of the emission spectrum) was recorded. Among them, the fluorescence intensity without the addition of methylthioacetaldoxime was denoted as F0, and the fluorescence intensity after the addition of methylthioacetaldoxime was denoted as F. According to the results measured after the interaction of methylthioacetaldoxime at different concentrations with the phenylboronic acid functionalized carbon quantum dots, a standard curve was plotted with the concentration of methylthioacetaldoxime as the horizontal axis and F0 / F (the ratio of the fluorescence intensity) as the vertical axis. The curve equation of the standard curve obtained in this example was y = 1.2069x + 1.2005, x represented the concentration of methylthioacetaldoxime, and y represented F0 / F. The linear degree R Figure 1 of the standard curve in this example was 0.9985, which was greater than 0.99, indicating good correlation. 2

[0058] ​III. Detection of the concentration of methionyl acetaldoxime in the actual sample: Take 2 g of apple (or cucumber, rice or river water sample) and add 2 mL of acetonitrile, extract using the QuEChERS method, take 800 μL of the obtained detection product extract, add 100 μL of 150 mg / L of the phenylboronic acid functionalized carbon quantum dots solution prepared in step one and 100 μL of 15 mg / L of copper chloride solution, react at room temperature for 3 min, and test the detection product extract according to the method for detecting the concentration of methionyl acetaldoxime in step two (specifically, excite at an excitation wavelength of 357 nm, and record the fluorescence spectrum of the detection product extract and the fluorescence intensity at 464 nm. Wherein, the fluorescence intensity of the blank extract without adding methionyl acetaldoxime is F0, and the fluorescence intensity of the detection product extract after adding methionyl acetaldoxime is F, and the F0 / F of the detection product extract is obtained. The concentration of methionyl acetaldoxime in the detection product extract is calculated by the standard curve method, that is, the fluorescence F0 / F of the detection product extract is brought into the standard curve obtained in step two, and the concentration of methionyl acetaldoxime in the detection product extract is obtained.

[0059] Figure 2 、 Figure 3 is the characterization result of the phenylboronic acid functionalized carbon quantum dots. Figure 2 is the infrared spectrum of the prepared phenylboronic acid functionalized carbon quantum dots. 1599 cm -1 and 1509 cm -1 Absorption peaks correspond to amide I peak and amide II peak, which indicates that the formation of amide bond covalently combines phenylboronic acid with carbon quantum dots. The characteristic absorption peak at 1328 cm -1 is the asymmetric stretching vibration of the boron-oxygen bond of the phenylboronic acid group, which also indicates that the surface of the carbon quantum dots has the boronic acid group. Figure 3 is the transmission electron microscopy of the prepared phenylboronic acid functionalized carbon quantum dots. The prepared quantum dots have a near-circular appearance, and the average size is 7 nm-10 nm.

[0060] Example 2:

[0061] This example 2 is a method for quantitatively detecting methomyl using phenylboronic acid functionalized carbon quantum dots, which is completed according to the following steps:

[0062] I. Prepare the boronic acid functionalized carbon quantum dots according to step one in example 1.

[0063] II. Detection of the concentration of methomyl in standard solution: 1 mL of methomyl aqueous solution with different concentrations was taken, 0.1 mL of 2 mol / L sodium hydroxide solution was added, and after five minutes of reaction, 0.1 mL of 2 mol / L hydrochloric acid solution was added to terminate the reaction, 800 μL of hydrolyzate was taken, 100 μL of 150 mg / L of phenylboronic acid functionalized carbon quantum dot solution prepared in step one and 100 μL of 15 mg / L of copper chloride solution were added, and the reaction was carried out at room temperature for 3 min, irradiation was carried out at an excitation wavelength of 357 nm, and the fluorescence spectrum of methomyl with different concentrations and the fluorescence intensity at 464 nm were recorded. Among them, the fluorescence intensity without adding methomyl is recorded as F0, and the fluorescence intensity after adding methomyl is F. According to the results measured after the interaction of methomyl with different concentrations and carbon dots, the concentration of methomyl is taken as the horizontal axis, and F0 / F (the ratio of fluorescence intensity) is taken as the vertical axis to plot a standard curve ( Figure 4 Figure 4 ), the curve equation of the standard curve obtained in this example is y = 0.7114x + 1.1461, x is the concentration of methomyl, and y is F0 / F. The linear degree of the curve in this example is R2 = 0.9986, which is greater than 0.99. Figure 5 is the mass spectrum before and after hydrolysis, (a) is the mass spectrum of methomyl before hydrolysis, and the molecular ion peak of methomyl ([M+H] + , m / z = 162.9) can be observed, (b) is the mass spectrum of methomyl after hydrolysis, and the molecular ion peak of methomyl has disappeared, while the molecular ion peak of methylthioacetaldoxime ([M+H] + , m / z = 105.9) appears, indicating that the hydrolysis of the standard solution is complete.

[0064] III. Detection of the concentration of methomyl in actual samples: 2 g of apples (which can also be replaced with cucumbers, rice, or water samples of river water) was taken, 2 mL of acetonitrile was added, and the QuEChERS method was used for extraction, 1 mL of methomyl extract was obtained, 0.1 mL of 2 mol / L sodium hydroxide solution was added, and after five minutes of reaction, 0.1 mL of 2 mol / L hydrochloric acid solution was added to terminate the reaction, 800 μL of methomyl hydrolyzate was taken, 100 μL of 150 mg / L of phenylboronic acid functionalized carbon quantum dot solution prepared in step one and 100 μL of 15 mg / L of copper chloride solution were added, and the reaction was carried out at room temperature for 3 min, irradiation was carried out at an excitation wavelength of 357 nm, and the fluorescence spectrum of methomyl hydrolyzate and the fluorescence intensity at 464 nm were recorded. Among them, the fluorescence intensity of the blank sample without adding methomyl hydrolyzate is recorded as F0, and the fluorescence intensity of the methomyl hydrolyzate is F. F0 / F of the methomyl hydrolyzate is brought into the standard curve obtained in step two to obtain the concentration of methomyl in the actual sample.

[0065] In summary, the method for detecting methylthioacetaldehyde oxime by fluorescence provided by the present disclosure is a method for detecting methylthioacetaldehyde oxime by using phenylboric acid functionalized carbon quantum dots. Specifically, the present disclosure utilizes the active groups such as phenylboric acid contained on the surface of the phenylboric acid functionalized carbon quantum dots, so that the phenylboric acid functionalized carbon quantum dots can produce complexation with copper ions, and through the static quenching mechanism, the fluorescence of the phenylboric acid functionalized carbon quantum dots is quenched. The complexation of methylthioacetaldehyde oxime with copper ions is stronger than the complexation of the phenylboric acid functionalized carbon dots with copper ions, and when methylthioacetaldehyde oxime exists, it can prevent the combination of copper ions and the phenylboric acid functionalized carbon dots, and thus the fluorescence recovery of the phenylboric acid functionalized carbon quantum dots after fluorescence quenching occurs. This process constructs an “OFF-ON” sensing system, so as to realize the high-sensitivity detection of methylthioacetaldehyde oxime by the phenylboric acid functionalized carbon quantum dots as a fluorescence sensor. Further, since methylthioacetaldehyde oxime is one of the hydrolysis products of the pesticide methomyl, the above-mentioned fluorescence detection method can be used for determining the methomyl residue, and contributes to the pesticide poisoning rescue, agricultural product safety evaluation and the like.

[0066] In the description of the present specification, the description referring to the terms “one embodiment”, “some embodiments”, “exemplary embodiment”, “example”, “specific example”, or “some examples” and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0067] Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A fluorescence detection method for methylthioacetaldehyde oxime, characterized in that, include: Phenylboronic acid-functionalized carbon quantum dots, an aqueous solution containing copper ions, and standard solutions containing different concentrations of methylthioacetaldehyde oxime were mixed to obtain multiple homogeneous solutions A. Fluorescence excitation was performed on each homogeneous solution A to determine the functional relationship between the concentration of methylthioacetaldehyde oxime and the fluorescence intensity. The phenylboronic acid-functionalized carbon quantum dots, an aqueous solution containing copper ions, and an extract containing methylthioacetaldehyde oxime were mixed and reacted to obtain a homogeneous solution B. The homogeneous solution B was subjected to fluorescence excitation, and the concentration of methylthioacetaldehyde oxime in the extract was obtained by using the functional relationship between the concentration of methylthioacetaldehyde oxime and the fluorescence intensity. The phenylboronic acid-functionalized carbon quantum dots were prepared according to the following steps: Citric acid and thioethanolamine were dissolved in a eutectic solvent prepared by urea and choline chloride in a molar ratio of 1:1, and the solution was ultrasonically treated to form a homogeneous solution A. Solution A was subjected to a pyrolysis reaction to obtain solution B. Solution B was dialyzed and dried to obtain sulfur-nitrogen co-doped carbon quantum dots. The sulfur-nitrogen co-doped carbon quantum dots were mixed with deionized water and subjected to an amidation reaction in the presence of a catalyst and 4-aminophenylboronic acid. The product obtained from the amidation reaction was dialyzed and dried to obtain the phenylboronic acid-functionalized carbon quantum dots.

2. The fluorescence detection method according to claim 1, characterized in that, The solute in the copper-containing aqueous solution is selected from any one or a mixture of copper chloride, copper sulfate, copper nitrate, and copper acetate; and / or The concentration of the copper ion-containing aqueous solution is 10 mg / mL to 20 mg / mL.

3. The fluorescence detection method according to claim 1, characterized in that, The extract for the test sample is selected from water samples of apples, cucumbers, rice, or river water.

4. The fluorescence detection method according to claim 1, characterized in that, The homogeneous solution A is prepared using a mass ratio of 1:500–1000:5000–10000 for the phenylboronic acid-functionalized carbon quantum dots, the copper-containing aqueous solution, and the standard solution; and / or The homogeneous solution B is prepared using a mass ratio of 1:500-1000:5000-10000 for the phenylboronic acid-functionalized carbon quantum dots, the aqueous solution containing copper ions, and the extract of the test sample.

5. The fluorescence detection method according to claim 1, characterized in that, The mass ratio of the sulfur-nitrogen co-doped carbon quantum dots, the deionized water, the catalyst, and the 4-aminophenylboronic acid is 1:30000:50:

100.

6. The fluorescence detection method according to claim 1, characterized in that, The mass ratio of the citric acid, the thioethanolamine, and the eutectic solvent is 1:1:

20.

7. The fluorescence detection method according to claim 1, characterized in that, The pyrolysis reaction was carried out at a temperature of 160℃ for 2 hours.

8. The fluorescence detection method according to any one of claims 1 to 7, characterized in that, The extract containing methylthioacetaldehyde oxime is a solution containing methylthioacetaldehyde oxime produced by hydrolyzing methomyl in the water sample to be tested under alkaline conditions.

9. The fluorescence detection method according to claim 8, characterized in that, The process of hydrolyzing methomyl under alkaline conditions to produce a solution containing methylthioacetaldehyde oxime includes: mixing the methomyl solution with an alkaline solution, reacting for 2 to 10 minutes, and then adding an acid solution to terminate the reaction, thereby obtaining a solution containing methylthioacetaldehyde oxime.

10. The fluorescence detection method according to claim 9, characterized in that, The alkaline solution is selected from any one or a mixture of sodium hydroxide solution, potassium hydroxide solution and lithium hydroxide solution; The acid solution is selected from any one or a mixture of hydrochloric acid, nitric acid, and sulfuric acid; The mass ratio of methomyl solution to alkaline solution is 1:0.01 to 0.1; The amounts of the alkaline solution and the acid solution are equal.

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