A method for detecting carbofuran based on aminated CdSe / ZnS quantum dots

Abstract

The application discloses a method for detecting carbofuran based on aminoated CdSe / ZnS quantum dots, and belongs to the technical field of pesticide residue detection. The application provides amino-modified CdSe / ZnS quantum dots, establishes a fluorescence detection method for rapidly determining carbofuran based on good water solubility and the quenching effect of carbofuran on the fluorescence of the aminoated CdSe / ZnS quantum dots. The method realizes high-sensitivity detection of carbofuran, and the accuracy can be comparable to that of LC-MS method, and the detection limit is lower.

Description

Technical Field

[0001] This invention relates to the field of pesticide residue detection technology, specifically to a method for detecting carbofuran based on aminated CdSe / ZnS quantum dots. Background Technology

[0002] Carbofuran (also known as Furadan, chemical formula C) 12 H 15 NO3 (carbamate) is a class of carbamate pesticides, a broad-spectrum and highly effective insecticide widely used for pest control in vegetables and other crops. However, carbofuran can react with nitrites to form nitrosamines, which have potential carcinogenic, teratogenic, and mutagenic effects; its binding with cholinesterase is irreversible, thus resulting in high toxicity. Carbofuran residues on vegetables and other crops can be absorbed by the human body through the digestive tract, respiratory tract, and skin. After absorption, it is mainly distributed in the liver, kidneys, fat, and muscles, causing neurotoxicity and easily producing reactions such as salivation, tearing, and pupil constriction. In severe cases, it can lead to symptoms such as decreased blood pressure and loss of consciousness. Long-term consumption of food containing excessive levels of carbofuran poses a significant health risk. In addition, carbofuran has a half-life of 30 to 60 days in soil, is not easily degraded, has high mobility, and is prone to causing environmental pollution (Wang Zerong et al., Anhui Agricultural Sciences, 2011, 39(18):10942-10943.; Wan Kai et al., Tropical Agricultural Sciences, 2015, 35(7):57-62.).

[0003] The main detection methods for carbofuran include high performance liquid chromatography (HPLC) (Yu Chaoxu et al., Zhejiang Agricultural Sciences, 2018, 59(11):2086-2088.), gas chromatography (Wang Jielian et al., Food Research and Development, 2015, 36(19):155-157.), liquid chromatography-tandem mass spectrometry (He Huali et al., Journal of Analytical Testing, 2014, 33(2):197-202.), gas chromatography-mass spectrometry (GB / T5009.104-2003), and enzyme inhibition method (Cheng Jing, Agriculture and Technology, 2015, 4(35):3.). These methods have advantages such as low detection limits and good accuracy, but they also have the characteristics of complicated pretreatment, expensive instruments, and the need for specialized personnel to operate, which limits the rapid and convenient detection.

[0004] Therefore, establishing a sensitive, simple, and low-cost rapid detection method for carbofuran pesticide residues is of great significance to environmental monitoring and food safety.

[0005] Fluorescence spectroscopy, with its advantages of high sensitivity, ease of operation, and speed, has received widespread attention and application in the detection of toxic and harmful substances. Quantum dots are highly efficient fluorescent materials, and due to their tunable size and unique optical and electrical properties, they are highly sought after by researchers. CdSe quantum dots have a high energy bandwidth and are a mature semiconductor quantum dot. Due to their certain toxicity, covering their surface with a high-energy-bandwidth ZnS shell to form a core-shell structure can effectively reduce toxicity and improve the luminescence efficiency and stability of quantum dots (Cheng Yang et al., Journal of Analytical Science, 2021, 37(5):606-610). Currently, there are no reports on using CdSe / ZnS quantum dots as fluorescent probes for the determination of carbofuran pesticide residues.

[0006] Typically, quantum dots in solution tend to aggregate and precipitate or oxidize during storage, leading to a decrease in fluorescence performance. Certain modifications can help maintain the original fluorescence efficiency and stability of the quantum dots. Furthermore, fluorescence intensity is affected not only by the type and structure of the fluorescent substance but also by factors such as the type of solvent, solution pH, and ions. Given the water solubility of carbofuran, using water as a solvent to construct the detection system offers advantages such as being environmentally friendly and having fewer toxic side effects. Therefore, developing a rapid and effective fluorescence analysis method for carbofuran residues is a problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a fluorescence analysis method that can rapidly detect carbofuran pesticide residues with high sensitivity and accuracy.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides the application of aminated CdSe / ZnS quantum dots as fluorescent probes in the preparation of carbofuran detection kits.

[0010] This invention modifies CdSe / ZnS quantum dots with amino groups to enhance their water solubility. Further research revealed that the carbamate pesticide carbofuran exhibits good compatibility with aminated CdSe / ZnS quantum dots in aqueous solvents, without any heterogeneous conditions such as layering or crystallization. Fluorescence measurements showed that carbofuran quenches the fluorescence response signal of aminated CdSe / ZnS quantum dots, and the fluorescence signal shows a linear relationship with the logarithm of the carbofuran concentration. Therefore, by measuring the fluorescence intensity of the quantum dots after the reaction with carbofuran, the concentration of carbofuran can be calculated.

[0011] Furthermore, the aminated CdSe / ZnS quantum dots are prepared by a hydrothermal method. Preferably, the preparation method of the aminated CdSe / ZnS quantum dots includes: adding zinc acetate and thioacetamide solution dropwise alternately to a CdSe quantum dot solution under an oxygen-free atmosphere, reacting at 60-100℃ for 0.5-2 h to obtain amino-modified CdSe / ZnS core-shell structured quantum dots.

[0012] The method for preparing CdSe quantum dots includes: dispersing cadmium acetate dihydrate and sodium oleate in ethanol to obtain an ethanol dispersion, dispersing oleic acid and selenium powder in water to obtain an aqueous dispersion, mixing the two and heating at 40-100℃ for 0.5-3h in a non-oxygen atmosphere, and then reacting at 100-300℃ for 0.5-3h to obtain CdSe quantum dots.

[0013] More preferably, the preparation method of the aminated CdSe / ZnS quantum dots includes: mixing an ethanol dispersion and an aqueous dispersion, heating at 40°C for 2 hours under nitrogen protection, transferring the mixture to a reaction vessel, and reacting at 180°C for 3 hours to obtain CdSe quantum dots; then, under a nitrogen atmosphere, alternately adding 1 mmol of zinc acetate and 1 mmol of thioacetamide solution to the CdSe quantum dot solution while stirring vigorously, and reacting at 100°C for 2 hours to obtain aminated CdSe / ZnS quantum dots.

[0014] The aminated CdSe / ZnS quantum dots prepared in this invention have a maximum excitation wavelength of 260 nm and a maximum emission wavelength of 543 nm.

[0015] Specifically, the present invention provides a method for rapid detection of carbofuran based on the aminated CdSe / ZnS quantum dots. The method includes: adding the sample to be tested into an aminated CdSe / ZnS quantum dot solution, measuring the fluorescence intensity value of the quantum dots after the reaction, and then substituting the fluorescence intensity value into a standard curve to calculate the content of carbofuran in the sample to be tested.

[0016] In the above method, a mixed aqueous solution containing 0.05-0.2 mol / L sodium hydroxide and 0.05-0.2 mol / L phosphate was used as the reaction solvent. Studies have shown that the aminated CdSe / ZnS quantum dots exhibit the strongest fluorescence response in this solvent system.

[0017] Preferably, the solvent is a mixed aqueous solution containing 0.1 mol / L sodium hydroxide and 0.1 mol / L phosphate. The phosphate comprises equal amounts of disodium hydrogen phosphate and sodium dihydrogen phosphate.

[0018] Preferably, the concentration of aminated CdSe / ZnS quantum dots in the reaction system is 0.01-1.0 mg / mL. More preferably, the concentration of aminated CdSe / ZnS quantum dots in the reaction system is 0.1 mg / mL.

[0019] Preferably, the reaction conditions are 10-20 min at room temperature. After the reaction system is maintained for 10 min, the fluorescence signal remains essentially unchanged.

[0020] After the reaction was completed, the fluorescence response signal was measured. The excitation wavelength was set to 260 nm, and the fluorescence intensity value at a wavelength of 543 nm was recorded.

[0021] Preferred fluorescence measurement conditions: slit width of excitation spectrum: 5 nm, PMT voltage: 500 V, scan rate: 1200 nm / min, response time: 0.002 s.

[0022] The method for constructing the standard curve includes: using aminated CdSe / ZnS quantum dots as fluorescent labels to detect a series of carbofuran solutions with concentration gradients ranging from 0.1 to 100.0 μg / L, with an excitation wavelength of 260 nm, recording the fluorescence intensity value at a wavelength of 543 nm, and linearly fitting the fluorescence intensity value with the logarithm of the carbofuran concentration to obtain the standard curve.

[0023] The above method allows for rapid and accurate quantification of the sample to be tested. Furthermore, the sample to be tested can be agricultural crops such as spinach, bok choy, tomatoes, cucumbers, or environmental water bodies such as lakes and rivers.

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

[0025] This invention provides an amino-modified CdSe / ZnS quantum dot. Based on its good water solubility and the quenching effect of carbofuran on the fluorescence of amino-modified CdSe / ZnS quantum dots, a rapid fluorescence detection method for determining carbofuran is established. Carbofuran quenches the fluorescence signal of amino-modified CdSe / ZnS quantum dots, and the fluorescence intensity shows a linear relationship with the logarithm of the carbofuran concentration. The detection limit reaches 0.06 μg / L. This method achieves highly sensitive detection of carbofuran, with accuracy comparable to LC-MS, but with a lower detection limit. Attached Figure Description

[0026] Figure 1 Transmission electron microscopy image of 0.1 mg / mL aminated CdSe / ZnS quantum dots.

[0027] Figure 2 Energy dispersive spectroscopy elemental analysis of aminated CdSe / ZnS quantum dots.

[0028] Figure 3 The fluorescence response diagrams of aminated CdSe / ZnS quantum dots in different solvents (water, 0.1 mol / L sodium hydroxide, 0.1 mol / L hydrochloric acid, 0.1 mol / L phosphate buffer solution, ethanol) are shown.

[0029] Figure 4 The fluorescence response of 0.1 mg / mL aminated CdSe / ZnS quantum dots in NaOH and PBS solutions of different concentrations (0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1.0 mol / L) was studied.

[0030] Figure 5 The fluorescence response was measured for 10.0 mg / L carbofuran and 0.1 mg / mL amino-modified CdSe / ZnS quantum dots.

[0031] Figure 6 The fluorescence quenching time of carbofuran on aminated CdSe / ZnS quantum dots is denoted as .

[0032] Figure 7 This experiment demonstrates the specificity of aminated CdSe / ZnS quantum dots for carbofuran fluorescence determination.

[0033] Figure 8 The graph shows the linear relationship between the fluorescence of aminated CdSe / ZnS quantum dots and carbofuran, where A represents the fluorescence measurement under various concentration conditions; and B represents the fitted curve.

[0034] Figure 9 The spectrum of carbofuran was detected by LC-MS. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0037] The instruments and reagents used in the following examples:

[0038] Ultra-high performance liquid chromatography-triple quadrupole mass spectrometry (AB5500), fluorescence spectrometer (Hitachi F-7000); 200kV field emission transmission electron microscope (Thermo Fisher Talos F200X); drying oven (Hangzhou Biaodun), ultrapure water system (Millipore), circular oscillator (IKA VORTEX 1); constant temperature water bath (Shanghai Jinghong DK-S28), vortex oscillator (IKA), centrifuge (Shanghai Anting), etc.

[0039] Selenium powder (CAS No.: 7782-49-2, 99%, AR), cadmium acetate dihydrate (CAS No.: 5743-04-4, 99%, AR), sodium oleate (CAS No.: 143-19-1, 98%, AR) were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Thioacetamide (CAS No.: 62-55-5, 98%, AR), zinc acetate dihydrate (CAS No.: 5970-45-6, 99%, AR), sodium hydroxide (CAS No.: 1310-73-2, 96%, AR), sodium dihydrogen phosphate dihydrate (CAS No.: 13472-35-0, 99%, AR), disodium hydrogen phosphate dodecahydrate (CAS No.: 10039-32-4, 98%, AR), acetylene... Nitriles (CAS No.: 75-05-8, HPLC), anhydrous magnesium sulfate (CAS No.: 7487-88-9, 98%, AR), sodium chloride (CAS No.: 7647-14-5, 99.8%, AR), sodium citrate dihydrate (CAS No.: 6132-04-3, 99%, AR), and disodium citrate hemihydrate (CAS No.: 6132-05-4, 99%, AR) were purchased from China National Pharmaceutical Group Co., Ltd. Carbofuran (CAS No.: 1563-66-2, 99%, AR) and Cetirizine (Carbaryl, C 12 H 11 NO2 (CAS No.: 63-25-2), Aldicarb (C7H) 14 N2O2S, CAS No.: 116-06-3), malathion (C 10 H 19 O6PS2 (CAS No.: 121-75-5), Metrocarb (C9H) 11 O2N (CAS No.: 1129-41-5) was purchased from Tanmo Quality Inspection Standard Material Center. All reagents were used directly after purchase.

[0040] The water used in the experiment was all ultrapure water (resistivity 18.2 MΩ·cm).

[0041] Example 1: Preparation of amination-modified CdSe / ZnS quantum dots

[0042] 1. Preparation of amination-modified CdSe / ZnS quantum dots

[0043] First, 1 mM cadmium acetate dihydrate and 1.2 g sodium oleate were dispersed in 10 mL of ethanol. Then, 2 mL of oleic acid and 1 mmol of selenium powder were added to 20 mL of water. The ethanol dispersion and the water dispersion were mixed evenly and heated at 40 °C for 2 hours under N2 protection. The mixture was then transferred to a 100 mL reactor and reacted at 180 °C for 3 hours to obtain CdSe quantum dots.

[0044] Under a N2 atmosphere, 1 mmol of zinc acetate and 1 mmol of thioacetamide solution were added dropwise to a CdSe quantum dot solution while stirring vigorously. The mixture was reacted at 100 °C for 2 hours, centrifuged, washed three times with water, and then dried in a vacuum oven at 80 °C to obtain amino-modified CdSe / ZnS core-shell quantum dots.

[0045] The quantum dots were redispersed in water to obtain a quantum dot solution of 1.0 mg / mL, which was then refrigerated for later use.

[0046] 2. Characterization of amination-modified CdSe / ZnS quantum dots

[0047] 2.1 The size and morphology of the prepared quantum dots were analyzed using field emission transmission electron microscopy, such as... Figure 1 As shown, the central region of the quantum dot is darker in color, while the outer region is lighter, confirming that the prepared quantum dots are core-shell quantum dots with a size of 15-40 nm. Figure 2 As shown, mapping scans of quantum dots revealed the presence of Cd, Se, Zn, S, and N elements, with Zn, S, and N elements distributed in the outer shell region of the quantum dots, proving that amino groups have been successfully modified on the surface of the quantum dots.

[0048] 2.2 Fluorescence response analysis of the prepared quantum dots was performed using a fluorescence spectrometer.

[0049] A series of quantum dot solutions with concentrations (0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1.0 mg / mL) were prepared for the determination of fluorescence response. The fluorescence response of the prepared quantum dots was analyzed using a fluorescence spectrometer. Fluorescence testing conditions: slit width of excitation spectrum: 5 nm, PMT voltage: 500 V, scan rate: 1200 nm / min, response time: 0.002 s, maximum excitation wavelength: 260 nm, maximum emission wavelength: 543 nm.

[0050] 3. Solvent selection for fluorescence assay of amination-modified CdSe / ZnS quantum dots

[0051] To test the effect of solvent on the fluorescence response of quantum dots, quantum dots were dissolved in different solvents (water, 0.1 mol / L sodium hydroxide solution, 0.1 mol / L hydrochloric acid solution, 0.1 mol / L phosphate buffer solution, phosphate buffer solution containing 0.1 mol / L sodium hydroxide, and ethanol), and fluorescence response analysis was performed using a fluorescence spectrometer.

[0052] like Figure 3The fluorescence signals of aminated CdSe / ZnS quantum dots showed significant differences, with higher fluorescence responses in alkaline and phosphate buffer solutions, the highest response in phosphate buffer solution containing 0.1 mol / L sodium hydroxide, and the lowest response in hydrochloric acid and ethanol.

[0053] 4. To determine the optimal solvent and concentration for aminated CdSe / ZnS quantum dots, sodium hydroxide solution and PBS buffer were selected as solvents for further fluorescence response exploration. Sodium hydroxide solutions with concentrations of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1.0 mol / L, disodium hydrogen phosphate solutions with concentrations of 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0 mol / L, and an equal volume of sodium dihydrogen phosphate (PBS) solution were used as solvents for aminated CdSe / ZnS quantum dots, and their fluorescence responses were measured.

[0054] like Figure 4 As shown, the quantum dots exhibit the strongest fluorescence response when using 0.1 mol / L sodium hydroxide solution and 0.1 mol / L PBS solution as solvents. Therefore, this experiment will use a mixed solution containing 0.1 mol / L sodium hydroxide solution and 0.1 mol / L PBS as the optimal solvent for fluorescence measurement.

[0055] Example 2: Fluorescence determination of carbofuran by aminated CdSe / ZnS quantum dots

[0056] 1. To explore the effect of carbofuran molecules on quantum dots, a 10.0 mg / L carbofuran solution (solution 1), a 0.1 mg / mL aminated CdSe / ZnS quantum dot solution (solution 2), and a mixed solution containing 10.0 mg / L carbofuran and 0.1 mg / mL aminated CdSe / ZnS quantum dots (solution 3) were prepared using a mixed solution containing 0.1 mol / L sodium hydroxide solution and 0.1 mg / mL aminated CdSe / ZnS quantum dots as solvents, and fluorescence was measured.

[0057] The fluorescence spectroscopy measurement conditions were as follows: excitation and emission slit width: 5 nm, PMT voltage: 500 V, scan rate: 1200 nm / min, and response time: 0.002 s.

[0058] The results are as follows Figure 5 As shown, solution 1 showed almost no fluorescence response, solution 2 showed a high fluorescence response, while solution 3 showed a decreased response. Therefore, it can be inferred that the addition of carbofuran molecules has a quenching effect on the fluorescence of aminated CdSe / ZnS quantum dots.

[0059] 2. Selection of fluorescence determination conditions for carbofuran from amination-modified CdSe / ZnS quantum dots

[0060] To explore the fluorescence quenching effect of carbofuran on quantum dots, 0.1 mg / mL aminated CdSe / ZnS quantum dots were used as fluorescent probes, and 10.0 mg / L carbofuran was used as a quencher. The fluorescence response of the above solutions was tested after 0 min, 2 min, 5 min, 10 min, 15 min, and 20 min.

[0061] The results are as follows Figure 6 As shown, 10 minutes is basically the optimal reaction time.

[0062] 3. Specificity experiment of aminated CdSe / ZnS quantum dots for carbofuran fluorescence determination

[0063] To verify the specificity of aminated CdSe / ZnS quantum dots for carbofuran fluorescence determination, several other carbamate pesticides were selected as comparisons and the same determination procedure was used (using 0.1 mg / mL aminated CdSe / ZnS quantum dots as fluorescent probes and 10.0 mg / L pesticides as quenchers).

[0064] The results are as follows Figure 7 As shown, aminated CdSe / ZnS quantum dots exhibit significant specificity for the determination of carbofuran, with a fluorescence quenching efficiency of 47.2%. Sevin, which has a similar structure to carbofuran, also has a certain quenching effect on the fluorescence of quantum dots, but the effect is not as good as carbofuran (fluorescence quenching efficiency of 23.3%); the quenching efficiencies of several other pesticides are all below 7%. Therefore, the prepared aminated CdSe / ZnS quantum dots have good specificity for the determination of carbofuran.

[0065] Example 3: Detection of carbofuran in real samples using amination-modified CdSe / ZnS quantum dots

[0066] 1. Standard curve and detection limit

[0067] Prepare 10 mL of each of the following concentrations of carbofuran (0, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0, 50.0, 100.0 μg / L) and 0.1 mg / mL aminated CdSe / ZnS quantum dot mixed standard working solutions. Let stand at room temperature for 10 min, and then take 300 μL of each solution into a quartz cuvette for fluorescence measurement.

[0068] The fluorescence spectroscopy measurement conditions were as follows: excitation and emission slit width: 5 nm, PMT voltage: 500 V, scan rate: 1200 nm / min, and response time: 0.002 s.

[0069] The result is as follows Figure 8The results showed that the fluorescence intensity was linearly related to the logarithm of the carbofuran concentration in the range of 0.1-100.0 μg / L, with the linear equation being I = -340.8lgC + 21720.0 and the correlation coefficient being R. 2 =0.99, and the detection limit is 0.06 μg / L (S / N = 3).

[0070] 2. Actual sample testing

[0071] 2.1 Sample Pretreatment

[0072] Fluorescence analysis: Weigh 10g of vegetables, crush them, and place them in a 50mL centrifuge tube. Add 10mL of a mixture of 0.1mol / L sodium hydroxide and PBS solution, shake for 1min, and centrifuge at 8000r / min for 5min. Collect the supernatant, add another 10mL of the mixture of 0.1mol / L sodium hydroxide and PBS solution to the lower precipitate, shake, and centrifuge. Repeat the above operation three times. Combine the supernatants into one centrifuge tube for analysis.

[0073] Liquid chromatography-mass spectrometry (LC-MS): According to GB 23200.121-2021 standard, weigh 10g of vegetable sample into a 50ml centrifuge tube, add 10mL of acetonitrile, shake vigorously for 1min, add 4g of anhydrous magnesium sulfate, 1g of sodium chloride, 1g of sodium citrate dihydrate, and 0.5g of disodium citrate sesquihydrate, shake vigorously for 1min, and centrifuge at 4200r / min for 5min. Transfer the supernatant to a plastic centrifuge tube containing dehydrating agent and purification material, centrifuge at 4200r / min for 5min, and filter the supernatant through a 0.45μm microporous membrane for analysis.

[0074] 2.2 Measurement conditions

[0075] The fluorescence spectroscopy measurement conditions were as follows: excitation and emission slit width: 5 nm, PMT voltage: 500 V, scan rate: 1200 nm / min, and response time: 0.002 s.

[0076] Liquid chromatography-mass spectrometry (LC-MS) test conditions (refer to GB 23200.121-2021 standard):

[0077] Liquid chromatography: C18, 2.1 mm (inner diameter), 100 mm in length, 1.8 μm in particle size, or equivalent; mobile phase: phase A is ammonium formate-formic acid aqueous solution (4:4:2), phase B is ammonium formate-formic acid methanol solution (4:4:3), gradient elution; flow rate: 0.3 mL / min.

[0078] Mass spectrometry testing conditions: Ion source type: electrospray ion source; Scanning mode: simultaneous scanning of positive ions and fluorine negative ions; Electrospray voltage: 5500V for positive ions, -4500V for negative ions; Ion source temperature: 350℃; Nebulizing gas: 0.345Mpa; Auxiliary heating gas: 0.345Mpa.

[0079] 2.3 Actual Sample Testing

[0080] Tests on commercially available spinach samples revealed no carbofuran residue. Therefore, to verify the applicability of the constructed method, spinach samples were spiked: 100 μL of a 1.0 mg / mL carbofuran standard solution was added to every 9.9 mL of pretreated sample aqueous solution. This solution was diluted to achieve carbofuran concentrations of approximately 0.5, 5.0, and 20.0 μg / L, and fluorescence detection was performed using quantum dots as probes.

[0081] The results are shown in Table 1. The recovered rate of the spiked spinach sample solution by fluorescence determination was between 88.0% and 100.1%.

[0082] Table 1. Determination of carbofuran concentration in spinach by NH2-CdSe / ZnS QDs fluorescence method

[0083]

[0084] LC-MS is one of the commonly used methods for detecting pesticide residues such as carbofuran. The retention time for this method is 3.73 min. Figure 9 The limit of quantitation is 10.0 μg / L.

[0085] In summary, this invention provides an aminated CdSe / ZnS quantum dot, and its morphology was characterized by transmission electron microscopy. Fluorescence assays revealed that the quantum dot exhibits maximum emission at 543 nm. The quantum dot was used for carbofuran determination, and the results showed that carbofuran quenched its fluorescence signal. Under optimal conditions (0.1 mol / L sodium hydroxide and PBS mixed solution as solvent, quenching time 10 minutes), the fluorescence intensity of the quantum dot decreased linearly with increasing carbofuran concentration. The accuracy of this method is comparable to that of conventional LC-MS methods, with a lower detection limit. Experiments on spiked vegetable samples showed high recovery rates and satisfactory results.

Claims

1. A method for rapid detection of carbofuran, characterized in that, include: The sample to be tested was added to an aminated CdSe / ZnS quantum dot solution. After the reaction, the fluorescence intensity of the quantum dots was measured. The fluorescence intensity value was then substituted into the standard curve to calculate the content of carbofuran in the sample. The maximum excitation wavelength of the aminated CdSe / ZnS quantum dots was 260 nm, and the maximum emission wavelength was 543 nm. The preparation method of the aminated CdSe / ZnS quantum dots includes: alternately adding zinc acetate and thioacetamide solution to a CdSe quantum dot solution, reacting at 60-100℃ for 0.5-2 h to obtain amino-modified CdSe / ZnS core-shell structured quantum dots; carbofuran has a quenching effect on the fluorescence response signal of the aminated CdSe / ZnS quantum dots, and the fluorescence signal is linearly related to the logarithm of the carbofuran concentration; The solvent used in the aminated CdSe / ZnS quantum dot solution is a mixed aqueous solution containing 0.05-0.2 mol / L sodium hydroxide and 0.05-0.2 mol / L phosphate.

2. The method as described in claim 1, characterized in that, The solvent used is a mixed aqueous solution containing 0.1 mol / L sodium hydroxide and 0.1 mol / L phosphate.

3. The method as described in claim 1, characterized in that, The concentration of amination-modified CdSe / ZnS quantum dots in the reaction system was 0.01-1.0 mg / mL.

4. The method as described in claim 3, characterized in that, The concentration of amination-modified CdSe / ZnS quantum dots in the reaction system was 0.1 mg / mL.

5. The method as described in claim 1, characterized in that, The reaction time is 10-20 minutes.

6. The method as described in claim 1, characterized in that, The method for constructing the standard curve includes: using aminated CdSe / ZnS quantum dots as fluorescent labels to detect a series of carbofuran solutions with concentration gradients ranging from 0.1 to 100.0 μg / L, with an excitation wavelength of 260 nm, recording the fluorescence intensity value at a wavelength of 543 nm, and linearly fitting the fluorescence intensity value with the logarithm of the carbofuran concentration to obtain the standard curve.

7. The method as described in claim 1, characterized in that, The sample to be tested is either agricultural crop or environmental water.

Images