A rapid detection method for dimethoate based on ratiometric fluorescent probe of carbon quantum dots

Abstract

The present invention discloses a method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots, and belongs to the technical field of pesticide detection. The method uses fluorescent carbon quantum dots as the only fluorophore, establishes a standard curve based on the linear relationship between the excitation peak intensity ratio and the concentration of dimethoate, and realizes rapid detection of dimethoate. The specific steps include: (1) synthesis of fluorescent carbon quantum dots; (2) establishment of a standard curve; (3) pretreatment of fruit and vegetable samples; (4) determination of the content of dimethoate in fruit and vegetable samples. The present invention utilizes the dual excitation characteristics of carbon quantum dots to construct a rapid detection ratiometric fluorescent probe of dimethoate, which can quickly, sensitively and accurately detect the concentration of dimethoate in fruit and vegetable samples, does not require enzyme labeling, does not require external fluorophores, is simple to operate, is green and environmentally friendly, has a quick response, good selectivity, good reproducibility, high sensitivity, and low detection cost, and provides a new strategy for the construction of ratiometric fluorescent probes for other types of pesticides.

Description

Technical Field

[0001] The invention belongs to the technical field of pesticide detection, and in particular relates to a dimethoate rapid detection method based on a ratiometric fluorescent probe of carbon quantum dots. Background Art

[0002] Dimethoate is a moderately toxic systemic organophosphorus insecticide and acaricide. With its easy use, long-lasting efficacy and easy degradation, it is widely used to control piercing-sucking mouthparts pests on various crops, such as aphids, leafhoppers, whiteflies, leaf miners and some scale pests, and has made great contributions to ensuring food production safety and promoting agricultural economic development. However, the long-term, large-scale or irregular use of dimethoate has not only seriously damaged the ecosystem, but also posed a huge threat to human health. Therefore, the development of new technologies and methods for rapid and sensitive detection of dimethoate pesticide residues and strengthening the monitoring of pesticide residues in agricultural products and environmental samples are of great theoretical and practical significance for ensuring food safety and protecting the ecological environment.

[0003] Since chromatography has its own separation function and has significant advantages in high detection flux, especially chromatographic technology coupled with modern detectors, it is the mainstream technology for detecting dimethoate at present. However, chromatographic technology is not only expensive in instruments and time-consuming in detection, but also has relatively high requirements for operators, and cannot achieve instant detection, and instant detection means are particularly important in the handling of emergency events. And the existing rapid detection methods based on biotechnology construction require imported test kits, and there are problems such as difficulty in obtaining raw materials. Although the economic cost of most rapid detection methods is low, the research is time-consuming, and most rapid detection methods can only achieve qualitative or semi-quantitative detection, which cannot be promoted and used in a short time. Therefore, it is still necessary to develop a simple, fast, cheap and sensitive method for the detection of pesticides in agricultural products.

[0004] Fluorescence detection technology can respond to the target detection object quickly and sensitively, and it is simple to operate and low in price. Especially in recent years, with the rapid development of nanotechnology, fluorescence detection technology has attracted the attention of more and more scholars. At present, in the fluorescence detection of organophosphorus pesticides such as dimethoate, the inhibitory effect of organophosphorus pesticides on cholinesterase, tyrosinase, etc. is mostly used to construct fluorescent sensors. For example, CN107607507A discloses a fluorescence detection method for organophosphorus pesticide residues. The method is based on urease inhibition system and uses polymer quantum dots as fluorescent probes to detect organophosphorus pesticides in fruits and vegetables. However, biospecific enzymes are expensive, and the conditions for storage and use are harsh. They are easily inactivated in actual use and cause false positive signals. CN110412005A discloses a dimethoate pesticide detection method based on aptamer regulation of carbon dot fluorescence. The carbon dots used in the method are used as signal molecules, nanosilver is used as a quencher, and combined with aptamer technology, dimethoate can be specifically detected in many interfering substances such as bromopropylphosphine and acetamiprid. However, the detection system of this method is complex, and the aptamers used are biologically active substances that are easily inactivated and have high prices, making the detection cost high.

[0005] Ratiometric fluorescent probes have the advantages of high sensitivity, simple operation, and short response time to the target. In addition, the method focuses on the signal changes of two different fluorophores at the same time, normalizes the two signals or uses their ratio as the output signal, which is equivalent to introducing an internal standard. Therefore, it can eliminate the interference of instrument noise and environment to a certain extent and improve the accuracy of the method. It has attracted much attention in the detection of pesticide residues. Since the ratiometric fluorescent probe needs to focus on the changes of more than two fluorescence signals at the same time, the conventional practice is to introduce two different fluorophores at the same time. This strategy is feasible, but the introduction of different fluorophores will undoubtedly increase the experimental operation, and the different fluorophores introduced may antagonize each other and affect each other's fluorescence effect. Therefore, the ratiometric fluorescent probe targeting a single fluorophore will have more advantages. Although there are reports on the construction of ratiometric sensors based on a single fluorophore with dual emission properties, the reported fluorescent sensors are almost all concentrated on the emission spectrum, and there are few reports on fluorescent sensors based on excitation spectra, let alone ratiometric fluorescent sensors based on excitation spectra.

[0006] The rapid, sensitive and accurate detection of the target organophosphorus pesticide dimethoate is the development direction of modern pesticide residue analysis. In view of the above-mentioned existing problems, the present invention provides a single fluorophore-based enzyme-free ratiometer fluorescent probe for rapid detection of the organophosphorus pesticide dimethoate. It does not require enzyme labeling, is simple to operate, is green and environmentally friendly, has a quick response, good selectivity, good reproducibility and high sensitivity, and provides a new reference for the development of other new detection technologies for organophosphorus pesticides. Summary of the invention

[0007] In view of the above problems, the present invention provides a method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots. The method can rapidly, sensitively and accurately detect the concentration of dimethoate in fruit and vegetable samples, does not require enzyme labeling, does not require external fluorophores, is simple to operate, is green and environmentally friendly, has a quick response, good selectivity, good reproducibility and high sensitivity.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots, using fluorescent carbon quantum dots as the only fluorophore, establishing a standard curve based on the linear relationship between the excitation peak intensity ratio and the concentration of dimethoate, and realizing rapid detection of dimethoate; the specific steps are as follows:

[0010] (1) Synthesis of fluorescent carbon quantum dots: xylose was used as a carbon source and ammonium bicarbonate was used as a nitrogen source to synthesize fluorescent carbon quantum dots by a hydrothermal method. Xylose and ammonium bicarbonate were mixed and dissolved in deionized water, ultrasonically stirred at room temperature, and then transferred to a tetrafluoroethylene autoclave for reaction. After the reaction was completed, the mixture was cooled to room temperature, filtered and dialyzed to obtain fluorescent carbon quantum dots, which were then stored in a low temperature environment away from light for later use;

[0011] (2) Establishment of standard curve: Take 15 clean colorimetric tubes, add 30 μL of the fluorescent carbon quantum dots prepared in step (1) and a certain amount of surfactant to each colorimetric tube, then add 0, 10, 20, 30, 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900 μL of 1 μg / mL dimethoate solution to the above 15 colorimetric tubes, fix the volume, and shake well; fix the emission wavelength to 400-430 nm, scan the fluorescence excitation spectrum with a fluorescence spectrophotometer and record the corresponding fluorescence intensity; take the difference between the ratio of the fluorescence excitation intensity at 330 nm and 238 nm before and after the addition of dimethoate [(I 330 / I 238 )-(I 330 / I 238 )0] as the ordinate, the concentration of dimethoate as the abscissa, establish a standard curve, and find the regression equation of the standard curve; [(I 330 / I 238 )-(I 330 / I 238 )0], (I 330 / I 238 )0 is the ratio of the fluorescence excitation peaks at 330 nm and 238 nm before adding dimethoate, (I 330 / I 238 ) is the ratio of the fluorescence excitation peaks at 330 nm and 238 nm after adding dimethoate;

[0012] (3) Pretreatment of fruit and vegetable samples: extracting juice from fruit and vegetable samples, adding acetonitrile, stirring thoroughly and filtering, collecting the filtrate, adding sodium chloride to the filtrate, shaking vigorously, and standing at room temperature to separate water and acetonitrile to obtain an acetonitrile mixed solution; heating the acetonitrile mixed solution and evaporating it to near dryness, adding methanol for washing, collecting the washing liquid, filtering, obtaining a fruit and vegetable sample pretreatment liquid, and refrigerating it in a low temperature environment for later use;

[0013] (4) Determination of the content of dimethoate in fruit and vegetable samples: Take the fluorescent carbon quantum dots prepared in step (1), add lauric acid and the fruit and vegetable sample pretreatment solution prepared in step (3), fix the emission wavelength to 400-430 nm, scan the fluorescence excitation spectrum with a fluorescence spectrophotometer and record the corresponding fluorescence intensity; calculate the difference between the fluorescence excitation intensity ratio at 330 nm and 238 nm [(I 330 / I 238 )-(I 330 / I 238 )0], and substitute it into the regression equation described in step (2) to calculate the content of dimethoate in the fruit and vegetable samples.

[0014] As a preferred technical solution, the fluorophore is a fluorescent carbon quantum dot with dual excitation characteristics. When the emission wavelength is fixed at 400-430nm, the fluorescent carbon quantum dot has an excitation peak at 220-240nm and 320-330nm respectively.

[0015] As a preferred technical solution, the response of the fluorophore to dimethoate is completed within 1 minute and remains stable within 60 minutes.

[0016] As a preferred technical solution, the fluorescent carbon quantum dots exhibit good monodispersity and sphericity, with a particle size of 1.4 to 2.6 nm and an average size of 2 nm.

[0017] As a preferred technical solution, in step (2), when the concentration range of dimethoate is 2-100 ng / mL and 100-180 ng / mL, the corresponding linear regression equations are [(I 330 / I 238 )-(I 330 / I 238 )0]=0.041ρ-0.097 and [(I 330 / I 238 )-(I 330 / I 238 )0]=0.082ρ-4.16, where ρ is the concentration of dimethoate, the linear regression coefficients R are 0.9981 and 0.9956 respectively, and the detection limit is 0.67ng / mL.

[0018] As a preferred technical solution, in step (2), the surfactant is one or more of polyvinyl alcohol, sodium dodecylbenzene sulfonate, lauric acid, and polyethylene glycol, with a concentration of 0.1 g / L and an amount of 0 to 300 μL.

[0019] As a preferred technical solution, in step (1), the masses of xylose and ammonium bicarbonate are 0.05-0.3 g and 0.5-2.5 g, respectively.

[0020] As a preferred technical solution, in step (1), the reaction is carried out at 160-210° C. for 3-16 hours.

[0021] As a preferred technical solution, in step (1), the filtration and dialysis are to filter the solution after the reaction with a 0.22 μm filter membrane, collect the filtrate, and then dialyze the supernatant with water using a 1000 Da dialysis bag for 20 to 24 hours.

[0022] As a preferred technical solution, in step (3), the filtration is to filter the washing liquid using a 0.22 μm filter membrane.

[0023] As a preferred technical solution, in step (3), the samples are fruit and vegetable samples such as pitaya, banana, apple, pear, radish, cabbage, etc.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0025] 1. The present invention utilizes the dual excitation characteristics of carbon quantum dots to construct a rapid detection ratiometric fluorescent probe for dimethoate, which can rapidly, sensitively and accurately detect the concentration of dimethoate in fruit and vegetable samples, without the need for enzyme labeling or external fluorophores, and is simple to operate, green and environmentally friendly, with a quick response, good selectivity, good reproducibility, high sensitivity and low detection cost, providing a new strategy for the construction of ratiometric fluorescent probes for other types of pesticides.

[0026] 2. The ratiometric fluorescent probe based on carbon quantum dots of the present invention shows good selectivity for dimethoate, common anions and cations SO4 2- Ions, Ca 2+ Ions and other types of pesticides such as amikacin, terbufos, and alachlor have little effect on the detection of dimethoate. Therefore, the selective detection of dimethoate can be achieved without specific enzyme labeling, which not only reduces the detection cost and experimental operations, but also avoids false positive signals caused by enzyme inactivation.

[0027] 3. The rapid detection ratiometric fluorescent probe of dimethoate provided by the present invention shows a rapid response to dimethoate, can be stabilized within 1 minute, and the stabilization time can be maintained for more than 1 hour. It has a fast reaction efficiency and a long stabilization time, and has significant advantages in the rapid detection of dimethoate. This instant detection method has a good application prospect in the handling of emergency events.

[0028] 4. The fluorescent carbon quantum dots of the present invention use xylose as a carbon source and ammonium bicarbonate as a nitrogen source and are prepared by a simple one-step hydrothermal method. The synthesis method is simple, green and environmentally friendly, has good stability and high fluorescence efficiency. The xylose raw material used is widely present in plants, especially in the waste parts of agricultural products such as corn cobs and straw, which are rich in resources and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a transmission electron microscopy (TEM) image of fluorescent carbon quantum dots.

[0030] Figure 2 This is the particle size distribution diagram of fluorescent carbon quantum dots.

[0031] Figure 3 This is the excitation and emission spectra of fluorescent carbon quantum dots.

[0032] Figure 4 Schematic diagram of the detection principle of dimethoate pesticide.

[0033] Figure 5 This is the fluorescence response diagram of the fluorescence excitation spectrum of fluorescent carbon quantum dots at 238nm and 330nm to different concentrations of dimethoate.

[0034] Figure 6 This is the standard curve for detecting dimethoate pesticide.

[0035] Figure 7 This is the fluorescence response diagram of the fluorescent probe to dimethoate and other interfering substances. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below by way of examples. These examples are only used to illustrate the present invention and do not limit the protection scope of the present invention.

[0037] Example 1 Preparation of dual-excitation fluorescent carbon quantum dots

[0038] The carbon quantum dot solution was synthesized by a one-step hydrothermal method. 0.2g xylose and 1.5g ammonium bicarbonate were dissolved in 10mL deionized water, ultrasonically stirred at room temperature, and then transferred to a 100mL tetrafluoroethylene high-pressure reactor and reacted in an oven at 180°C for 4h. After the reaction was completed, the reactor was cooled to room temperature and filtered with a 0.22μm filter membrane. After the filtrate was collected, the supernatant was dialyzed with water for 24h with a dialysis bag (1000Da) to obtain dual-excitation fluorescent carbon quantum dots. The prepared fluorescent carbon quantum dot solution was stored at 4°C for later use.

[0039] The carbon quantum dots obtained in Example 1 were characterized by transmission electron microscopy. Figure 1 As shown, Figure 1 This is a transmission electron microscope image of fluorescent carbon quantum dots. Figure 1 It can be seen that the nitrogen-doped fluorescent carbon quantum dots of the present invention exhibit good monodispersity and sphericity. Figure 2 To count the particle sizes of 100 carbon quantum dots, the particle size distribution diagram of N-CQDs was obtained, and it was found that they were mainly distributed in the range of 1.4 to 2.6 nm, with an average size of 2 nm.

[0040] Figure 3 is the excitation and emission spectra of fluorescent carbon quantum dots. Figure 3 It can be seen that when the emission wavelength is fixed at 420nm, the dual-excitation fluorescent carbon quantum dots of the present invention have two excitation peaks at around 235nm and 327nm, corresponding to sp 2 The π-π* transition of the graphite carbon core and the n-π* transition of functional groups such as C=O and N=O. Whether under 238nm or 330nm excitation, only one emission peak is detected at around 420nm in the emission spectrum. This double excitation single emission phenomenon is attributed to the hyperconjugation of the two fluorescent centers. When the excitation wavelength is fixed at 238nm, the maximum emission wavelength is around 420nm, and the Stokes shift is 182nm. This double excitation phenomenon provides a new strategy for the construction of fluorescence ratio sensors.

[0041] Example 2 Construction of ratiometric fluorescent probe for dimethoate pesticide

[0042] Take 15 clean colorimetric tubes, add 30 μL of the fluorescent carbon quantum dots prepared in Example 1, 150 μL of lauric acid and 0, 10, 20, 30, 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900 μL of dimethoate standard solution (1 μg / mL) into a series of colorimetric tubes, dilute to 5 mL with a pH 6 aqueous solution, and shake well. Fix the emission wavelength at 400-430 nm, scan the excitation spectrum in the range of 220-400 nm with a Shimadzu RF5301 PC fluorescence photometer, and record the fluorescence intensity I around 238 nm and 330 nm. 238 and I 330 The ratio of the excitation peak intensity at 330 nm to the excitation peak intensity at 238 nm after adding dimethoate (I 330 / I 238 ) and the ratio of the excitation peak intensity at 330 nm to the excitation peak intensity at 238 nm before adding dimethoate (I 330 / I 238 )0 difference [(I 330 / I 238 )-(I 330 / I 238 )0] as the ordinate and the concentration of dimethoate as the abscissa, a standard curve was established to obtain the regression equation and linear correlation coefficient.

[0043] Figure 4 This is a schematic diagram of the detection principle of the pesticide dimethoate. Figure 5 The fluorescence response diagram of the fluorescence excitation spectrum of fluorescent carbon quantum dots at 238nm and 330nm to different concentrations of dimethoate. Figure 4 and Figure 5 , fluorescent carbon quantum dots were prepared by a one-step hydrothermal method using xylan and ammonium bicarbonate as raw materials. The prepared fluorescent carbon quantum dots have dual excitation characteristics, that is, when the emission wavelength is fixed at 400-430nm, the two excitation peaks are located at 238nm and 330nm respectively. After the addition of dimethoate, the excitation peak at 238nm was effectively quenched within 1min, while the excitation peak at 330nm did not change much. The difference between the ratio of the excitation peak intensity at 330nm to the excitation peak intensity at 238nm before and after the addition of dimethoate [(I 330 / I 238 )-(I 330 / I 238 )0] showed a good linear relationship with the concentration of dimethoate, based on which a new method for detecting dimethoate can be established.

[0044] Figure 6 This is the standard curve for detecting dimethoate pesticide. Figure 6It can be seen that the concentration range of dimethoate detected by the established ratiometric fluorescent probe is 2-100 ng / mL and 100-180 ng / mL, and the corresponding linear regression equations are [(I 330 / I 238 )-(I 330 / I 238 )0]=0.041ρ-0.097 and [(I 330 / I 238 )-(I 330 / I 238 )0]=0.082ρ-4.16, where ρ is the concentration of dimethoate; the linear regression coefficients R were 0.9981 and 0.9956 respectively, and the detection limit was 0.67ng / mL.

[0045] Example 3: Investigation of the response time and stability of the ratiometric fluorescent probe for rapid detection of dimethoate

[0046] Take a clean colorimetric tube, add 30 μL of the fluorescent carbon quantum dots prepared in Example 1, 150 μL of 0.1 g / L lauric acid and 200 μL of 1 μg / mL dimethoate standard solution to the colorimetric tube, dilute to 5 mL, and shake well. Fix the excitation wavelength at 400-430 nm, scan the excitation spectrum of the carbon quantum dots with a Shimadzu RF5301 PC fluorescence photometer within 0, 0.5, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 60 min, and calculate (I 330 / I 238 )value.

[0047] The experimental results show that the reaction between dimethoate and carbon quantum dots is basically completed within 1 minute and remains basically stable within 60 minutes, indicating that the dimethoate ratiometer fluorescent probe provided by the present invention has fast reaction efficiency and long stability time, and has significant advantages in the rapid detection of dimethoate.

[0048] Example 4 Investigation of the Selectivity of the Fluorescent Probe for Rapid Detection of Dimethoate Ratiometer

[0049] In order to verify the selectivity of the ratiometric fluorescent probe constructed by the present invention, this example investigates the effects of common anions and cations and their pesticides on it. Take 21 clean colorimetric tubes, add 30 μL of the fluorescent carbon quantum dots prepared in Example 1, 150 μL of 0.1 g / L lauric acid, control the final concentration of dimethoate to 40 ng / mL, and then add 100 times of Ca 2 + 、SO4 2- Mg 2+ , K + , Cl - 、Na + 、CO3 2- 、NO3 -、Al 3+ NH4 + 、HCO3 - ions, 50 times the amount of amoxicillin, terbuthion, alachlor, methyl thiocyclic phosphorus, clothianidin, methyl naphthalene, acephate, methyl parathion, trichlorfon, phosalone, dilute to 5 mL, shake well. Fix the emission wavelength at 400-430 nm, scan the excitation spectrum in the range of 220-400 nm with Shimadzu RF5301 PC fluorescence photometer, and record the excitation wavelength 238 nm (I 238 ) and 330nm(I 330 ) and calculate the fluorescence intensity [(I 330 / I 238 )-(I 330 / I 238 )0] value.

[0050] Figure 7 The fluorescence response diagram of the fluorescent probe to dimethoate and other interfering substances. A~U represent A: dimethoate (40ng / mL), B: Ca 2+ (4μg / mL), C:SO4 2- (4μg / mL), D:Mg 2+ (4μg / mL), E:K + (4 μg / mL), F:Cl - (4μg / mL), G:Na + (4μg / mL), H:CO3 2- (4μg / mL), I:NO3 - (4 μg / mL), J:Al3 + (4μg / mL), K:NH4 + (4μg / mL), L: amoxifen (2μg / mL), M: terbuthion (2μg / mL), N: alachlor (2μg / mL), O: methyl thiocyanate (2μg / mL), P: clothianidin (2μg / mL), Q: methyl naphthalene (2μg / mL), R: acephate (2μg / mL), S: methyl parathion (2μg / mL), T: trichlorfon (2μg / mL), U: phosalone (2μg / mL). Among them, 40ng / mL of dimethoate [(I 330 / I 238 )-(I 330 / I 238 )0] value is 1.29, while 50 to 100 times the interfering substances cause [(I 330 / I 238 )-(I 330 / I 238 )0] value is between 0.01 and 0.23.

[0051] It can be seen that the presence of some common ions and other pesticides has little effect on the detection of dimethoate. The dimethoate rapid detection ratiometer fluorescent probe based on dual-excitation carbon quantum dots of the present invention still shows good selectivity for dimethoate in the absence of specific enzyme labeling.

[0052] Example 5 Detection of dimethoate content in pitaya

[0053] (1) Pretreatment of pitaya samples: Weigh 10g pitaya and put it into a homogenizer, add 20mL acetonitrile, stir thoroughly in a juicer for 2min, filter with filter paper, collect about 16-20mL filtrate and put it into a 50mL centrifuge tube, add about 2.4g sodium chloride, cover the stopper, shake vigorously for 2min, and let it stand at room temperature for 0.5h to separate water and acetonitrile. Use a pipette to transfer 10mL of acetonitrile solution into a 100mL beaker, place the beaker in an 80℃ water bath to heat, and slowly pass air into the beaker. After evaporating most of the liquid, add 2mL of methanol and transfer the liquid to a 10mL centrifuge tube. Rinse the beaker three times with about 3mL of methanol, collect the washing liquid into the centrifuge tube, and finally make the volume to 5mL, shake well, and refrigerate at 4℃ for later use. If the solution after the volume is turbid, it can be filtered with a 0.2μm filter membrane.

[0054] (2) Detection of the content of dimethoate in pitaya samples: Dimethoate was spiked into pitaya samples at concentrations of 0, 4, 20, and 100 ng / mL, respectively. After sample extraction and purification, 100 μL of the prepared pitaya sample solution was used for detection. The experimental process was carried out with reference to Example 2. Three parallel experiments were carried out for each sample spiked, and the recovery rate and relative standard deviation (RSD) were calculated.

[0055] The results showed that no dimethoate residues were detected in pitaya. In three parallel experiments, the average recoveries of the spiked levels of 4, 20, and 100 ng / mL were 102.24%, 93.15%, and 92.55%, respectively, and the RSDs were 3.62, 2.20, and 2.28, respectively. It can be seen that the established ratiometric fluorescent probe is not only enzyme-free, convenient, and fast in the detection of dimethoate, but also has good accuracy and precision, and has shown a wide range of application scenarios in the detection of dimethoate residues in agricultural products and environmental samples.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots, characterized in that: Fluorescent carbon quantum dots are used as the only fluorophore, and a standard curve is established according to the linear relationship between the excitation peak intensity ratio and the concentration of dimethoate to achieve rapid detection of dimethoate; the fluorophore is a fluorescent carbon quantum dot with dual excitation characteristics, and when the emission wavelength is fixed at 400-430 nm, the fluorescent carbon quantum dot has an excitation peak at 220-240 nm and 320-330 nm respectively; the specific steps are as follows: (1) Synthesis of fluorescent carbon quantum dots: xylose was used as the carbon source and ammonium bicarbonate was used as the nitrogen source. The fluorescent carbon quantum dots were synthesized by a hydrothermal method. Xylose and ammonium bicarbonate were mixed and dissolved in deionized water. The mixture was ultrasonically stirred at room temperature and then transferred to a tetrafluoroethylene autoclave for reaction. After the reaction was completed, the mixture was cooled to room temperature, filtered and dialyzed to obtain fluorescent carbon quantum dots. The dots were then stored in a low temperature environment away from light for later use. (2) Establishment of standard curve: Take 15 clean colorimetric tubes, add 30 μL of the fluorescent carbon quantum dots prepared in step (1) and a certain amount of surfactant to each colorimetric tube, then add 0, 10, 20, 30, 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900 μL of 1 μg / mL dimethoate solution to the above 15 colorimetric tubes, make up to volume, and shake well; fix the emission wavelength to 400-430 nm, scan the fluorescence excitation spectrum with a fluorescence spectrophotometer and record the corresponding fluorescence intensity; take the difference between the ratio of the fluorescence excitation intensity at 330 nm and 238 nm before and after the addition of dimethoate [(I 330 / I 238 )-(I 330 / I 238 )0] as the ordinate, the concentration of dimethoate as the abscissa, establish a standard curve, and find the regression equation of the standard curve; (3) Pretreatment of fruit and vegetable samples: Take fruit and vegetable samples to squeeze juice, add acetonitrile, stir thoroughly and filter, collect the filtrate, add sodium chloride to the filtrate, shake vigorously, let stand at room temperature to separate water and acetonitrile, and obtain an acetonitrile mixed solution; take the acetonitrile mixed solution, heat it, evaporate it to near dryness, add methanol to wash, collect the washing liquid, filter it, obtain the fruit and vegetable sample pretreatment liquid, and refrigerate it in a low temperature environment for later use; (4) Determination of dimethoate content in fruit and vegetable samples: Take the fluorescent carbon quantum dots prepared in step (1), add lauric acid and the fruit and vegetable sample pretreatment solution prepared in step (3), fix the emission wavelength to 400-430 nm, scan the fluorescence excitation spectrum with a fluorescence spectrophotometer and record the corresponding fluorescence intensity; calculate the difference between the fluorescence excitation intensity ratio at 330 nm and 238 nm [(I 330 / I 238 )-(I 330 / I 238 )0], and substitute it into the regression equation described in step (2) to calculate the content of dimethoate in the fruit and vegetable samples.

2. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: The response of the fluorophore to dimethoate was completed within 1 min and remained stable within 60 min.

3. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: The fluorescent carbon quantum dots exhibit good monodispersity and sphericity, with a particle size of 1.4-2.6 nm and an average size of 2 nm.

4. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: In step (2), when the concentration range of dimethoate is 2-100 ng / mL and 100-180 ng / mL, the corresponding linear regression equations are [(I 330 / I 238 )-(I 330 / I 238 )0]=0.041 ρ - 0.097 and [(I 330 / I 238 )-(I 330 / I 238 )0]=0.082 ρ - 4.16, where ρ is the concentration of dimethoate. The linear regression coefficients R were 0.9981 and 0.9956, respectively, and the detection limit was 0.67 ng / mL.

5. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: In step (2), the surfactant is one or more of polyvinyl alcohol, sodium dodecylbenzene sulfonate, lauric acid, and polyethylene glycol, with a concentration of 0.1 g / L and an amount of 0 to 300 μL.

6. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: In step (1), the masses of xylose and ammonium bicarbonate are 0.05-0.3 g and 0.5-2.5 g, respectively.

7. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: In step (1), the reaction is carried out at 160-210° C. for 3-16 h.

8. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: In step (1), the filtration and dialysis are to filter the solution after the reaction with a 0.22 μm filter membrane, collect the filtrate, and then dialyze the supernatant with water using a 1000 Da dialysis bag for 20 to 24 hours.

9. The method for rapid detection of dimethoate based on a ratiometric fluorescent probe of carbon quantum dots according to claim 1, characterized in that: In step (3), the filtration is to filter the washing liquid using a 0.22 μm filter membrane.

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