Fluorescent carbon quantum dot, preparation method thereof and application of fluorescent carbon quantum dot in atrazine detection

Abstract

The invention discloses a fluorescent carbon quantum dot, a preparation method thereof and application of the fluorescent carbon quantum dot in atrazine detection, and belongs to the technical field of pesticide residue detection. The carbon quantum dots are obtained by taking citric acid and o-phenylenediamine as raw materials and a mixed solution of ethanol and water as a solvent through the steps of hydrothermal reaction, centrifugation, dialysis, nitrogen blowing, freeze drying and the like. The preparation method provided by the invention has low requirements on equipment, and is simple to operate and low in cost. The fluorescent carbon quantum dots prepared by the method have the characteristics of good fluorescence stability, good water solubility, good selectivity to atrazine, high sensitivity and the like. The detection method shows that the fluorescence enhancement degree of the fluorescent carbon quantum dots and the atrazine concentration are in a linear correlation trend, the detection limit of the detection method is as low as 20ng / L, and the detection result is rapid and accurate. Therefore, the method can be used for rapidly, accurately and sensitively detecting the atrazine in an actual sample and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of pesticide residue detection, and in particular relates to a fluorescent carbon quantum dot and a preparation method thereof and an application of the fluorescent carbon quantum dot in atrazine detection. Background Art

[0002] Atrazine is a common triazine herbicide. Its aliases are also called atrazine, grass-deionized, and sub-deionized. It is widely used for growth regulation and weed control of field crops. The residual hazards of atrazine are mainly reflected in the potential impact on the environment and human health. Although this herbicide plays an important role in agriculture, its residues may cause soil and water pollution, thereby affecting the balance of the ecosystem. In addition, long-term exposure to agricultural products containing atrazine residues may pose risks to human health, such as causing neurological problems or endocrine disruption. Therefore, when applying atrazine, it is necessary to strictly follow the usage specifications to ensure reasonable application and regular detection of residues to ensure food safety and environmental protection. In addition, in the preliminary compilation reference of the list of carcinogens published by the World Health Organization's International Agency for Research on Cancer on October 27, 2017, atrazine was included in the list of Class 3 carcinogens. Therefore, the research on atrazine detection methods is of great significance. Traditional atrazine detection methods include: liquid chromatography, gas chromatography, mass spectrometry, etc. However, these traditional detection methods all have a common problem: the instruments are expensive, the operation steps are cumbersome and time-consuming, the sensitivity is low, and the requirements for operators are high.

[0003] Carbon quantum dot fluorescent probe is a new type of fluorescent material with narrow fluorescence emission peak, high fluorescence intensity, good chemical stability and various preparation methods. These characteristics make carbon quantum dots have broad application prospects in the field of fluorescent probes. First, the fluorescence properties of carbon quantum dots are stable and not easily affected by environmental factors such as pH value and temperature. This enables carbon quantum dot fluorescent probes to provide stable fluorescence signals in complex biological environments. Secondly, carbon quantum dots have good biocompatibility and low toxicity, making them ideal fluorescent probes in the biomedical field. Through surface modification, the water solubility, dispersibility and stability of carbon quantum dots can be further improved, and their fluorescence properties and biocompatibility can also be regulated. In addition, the preparation methods of carbon quantum dot fluorescent probes are diverse, and carbon quantum dots with different morphologies, sizes and optical properties can be obtained by different preparation methods. This provides more possibilities for the research and development of carbon quantum dot fluorescent probes with excellent performance.

[0004] In short, carbon quantum dot fluorescent probes have good application prospects and development potential. With the in-depth research on their preparation, modification, properties and applications, they are expected to play a more important role in biomedicine, anti-counterfeiting imaging, analytical detection and other fields in the future. Summary of the invention

[0005] To solve the above technical problems, the present invention provides a kind of fluorescent carbon quantum dots and its preparation method and application in atrazine detection. The carbon quantum dots in the present invention are obtained by hydrothermal reaction, centrifugation, dialysis, nitrogen blowing and freeze drying with citric acid and o-phenylenediamine as raw materials and a mixed solution of ethanol and water as solvent. The preparation method in the present invention has low requirements on equipment, simple operation and low cost. The fluorescent carbon quantum dots prepared by the method in the present invention have the characteristics of good fluorescence stability, good water solubility, good selectivity for atrazine and high sensitivity. The detection method in the present invention shows that the fluorescence enhancement degree of the fluorescent carbon quantum dots is linearly correlated with the atrazine concentration, and the detection limit of the detection method is as low as 20ng / L, and the detection result is fast and accurate. Therefore, the present invention can be used for fast, accurate and sensitive detection of atrazine in actual samples.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] One of the purposes of the present invention is to provide a method for preparing carbon quantum dots. The preparation method uses citric acid, o-phenylenediamine, ethanol and ultrapure water as raw materials and is carried out by a high-temperature hydrothermal method. The specific steps include: firstly fully dissolving citric acid and o-phenylenediamine in a mixed solution of ethanol and ultrapure water, then heating at 150-200°C in a high-temperature and high-pressure reactor for 6-16 hours, cooling to room temperature and successively removing large particle impurities and small molecular substances, and finally blowing with nitrogen and freeze-drying to obtain a solid powder, which is the carbon quantum dots.

[0008] Preferably, the volume ratio of the ethanol to the ultrapure water is 1:(0.5-1.5), the dissolved concentration of the citric acid in the mixed solution is 2-6 g / L, and the dissolved concentration of the o-phenylenediamine in the mixed solution is 2-18 g / L.

[0009] More preferably, the usage ratio of the citric acid to the o-phenylenediamine is 1:(1-3).

[0010] More preferably, the amounts of the citric acid and the o-phenylenediamine are 0.2 g and 0.4 g respectively, and the amounts of the ethanol and the ultrapure water are 20 ml respectively.

[0011] Preferably, the large particle impurities are removed by filtration, and the small molecular substances are removed by dialysis, and the filtration and dialysis are filtering the solution after the heating reaction with a 0.22 μm organic membrane and dialyzing it with a 1000 Da dialysis bag for 48 hours.

[0012] The second object of the present invention is to provide a carbon quantum dot, which is prepared by using the preparation method.

[0013] The third object of the present invention is to provide a rapid detection method for atrazine based on a carbon quantum dot fluorescent probe, wherein the rapid detection method for atrazine comprises using the carbon quantum dots, and specifically comprises the following steps:

[0014] (1) Preparation of synthetic carbon quantum dots: The preparation method comprises using the above-mentioned carbon quantum dot preparation method;

[0015] (2) Establishing a linear standard curve: Take several centrifuge tubes, first add the carbon quantum dot solution prepared in step (1), then add different concentrations of atrazine solution, then add buffer solution and mix well, heat at 38-42°C for 8-12 minutes, then fix the excitation wavelength to 320-420nm to obtain the fluorescence intensity, and finally use the fluorescence intensity ratio before and after adding atrazine as the ordinate and the concentration of atrazine added as the abscissa to establish a linear relationship, and calculate the corresponding regression equation;

[0016] (3) Eliminate possible interference: Take possible coexisting substances of atrazine and proceed according to step (2);

[0017] (4) Sample pretreatment;

[0018] (5) Determination of atrazine content: Take the carbon quantum dots in step (1) and add buffer solution, then add the pretreatment solution obtained by sample pretreatment in step (4), and then heat at a constant temperature of 38-42°C for 8-12 minutes, fix the excitation wavelength to 320-420nm, the excitation slit to 5nm, and the emission slit to 10nm, and obtain the fluorescence intensity. The fluorescence intensity after adding atrazine at an emission wavelength of 490nm is compared with the fluorescence intensity before adding atrazine and substituted into the equation constructed in step (2) for calculation to obtain the atrazine content in the sample.

[0019] Preferably, the concentration of the carbon quantum dot solution in step (2) is 0.5-1.5×10 -6 g / mL, the amount added to each centrifuge tube is 3-5mL.

[0020] Preferably, the concentration of the atrazine solution in step (2) is set to 0, 10, 20, 50, 80, 100, 150, 200, 300, 400, 500, 600, 800, 1000, 1200 ng / L, and the amount added to each centrifuge tube is 280-320 μL.

[0021] Preferably, the buffer in step (2) is acetate buffer, the pH value is 4-7, and the amount added is 4-6 mL.

[0022] When the concentration range of atrazine is 15-800 ng / L, the corresponding linear regression equation is y=0.0085x+1.2827, where x is the concentration of atrazine and the linear regression coefficient R2 =0.9883, detection limit is 20ng / L.

[0023] Preferably, the possible coexisting substances of atrazine in step (3) are imidacloprid, chlorpyrifos, cypermethrin, melamine, triadimenol, pyraclostrobin, Cu 2+ , Fe 3+ and K + Any one or more of .

[0024] Preferably, when the sample in step (4) is a fruit or vegetable sample, the pretreatment method is: first squeeze the juice, then add a suitable amount of acetonitrile and water mixed solution for filtration extraction, and store in a low-temperature refrigerator. The filtration is to filter the extract with a 0.22 μm organic membrane.

[0025] Using the method of the present invention, the fluorescence response to atrazine is completed within 8 minutes and can remain stable for a long time.

[0026] A fourth object of the present invention is to provide an application of the preparation method, the carbon quantum dots or the atrazine rapid detection method in atrazine detection.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention utilizes the fluorescence characteristics of carbon quantum dots to detect atrazine, and can quickly and sensitively measure the concentration of atrazine in the sample without adding other fluorescent groups. It is environmentally friendly and economical, has a relatively fast response, outstanding selectivity, and low cost.

[0029] 2. The carbon quantum dots described in the present invention have good selectivity, and the common heavy metal ions Cu 2+ , Fe 3+ and K + The detection of atrazine is less affected by other types of pesticides such as imidacloprid, cypermethrin, triadimenol, etc. Therefore, selective detection of atrazine can be achieved without enzyme labeling, which can avoid data differences caused by enzyme inactivation.

[0030] 3. The method provided by the present invention can respond quickly to atrazine, and the stability time after the response is relatively long, and can be continuously stable for more than 90 minutes. This rapid detection method has good application prospects.

[0031] 4. The raw materials used in the present invention are easily available, the preparation method is simple, the prepared materials have good stability and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is an infrared spectrum of the carbon quantum dot material in Example 1 of the present invention;

[0033] Figure 2 This is an X-ray photoelectron spectrum of carbon quantum dots in Example 1 of the present invention;

[0034] Figure 3 This is the excitation and emission spectra of the carbon quantum dot material in Example 1 of the present invention;

[0035] Figure 4 is the fluorescence intensity of the carbon quantum dot material prepared under different experimental conditions in Example 1 of the present invention after combining with atrazine;

[0036] Figure 5 This is a fluorescence intensity response diagram of the carbon quantum dot material in Example 2 of the present invention to different concentrations of atrazine;

[0037] Figure 6 This is the standard curve diagram after fitting in Example 2 of the present invention;

[0038] Figure 7 The results of investigating the interaction time between atrazine and the fluorescent probe in Example 3 of the present invention are as follows;

[0039] Figure 8 The results of the investigation of atrazine and the fluorescent probe at different pH values ​​in Example 3 of the present invention are shown;

[0040] Fig. 9 This is an interference diagram of the fluorescence intensity caused by some common interfering substances in Example 4 of the present invention. DETAILED DESCRIPTION

[0041] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and essence of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention. The products, equipment, etc. used in the following examples are commercially available unless otherwise specified, and the methods used are consistent with conventional methods unless otherwise specified.

[0042] The technical solution of the present invention is further described in detail below in conjunction with embodiments.

[0043] Example 1 Preparation process of fluorescent carbon quantum dots

[0044] Carbon quantum dots were prepared by hydrothermal synthesis. 0.2g citric acid and 0.4g o-phenylenediamine were dissolved in a mixed solution of 20ml ethanol + 20ml ultrapure water, and then fully dissolved by ultrasound. Then, it was placed in a 100ml high-temperature and high-pressure reactor and heated at 180°C for 12h. After cooling to room temperature, it was filtered with a 0.22μm organic filter membrane to remove large particle impurities, and the filtered filtrate was dialyzed with a 1000Da dialysis bag to remove small molecules. Finally, carbon quantum dot solid powder was obtained after nitrogen blowing and freeze-drying, and it was placed in a 4°C refrigerator for storage.

[0045] The carbon quantum dot material prepared in Example 1 was characterized by infrared spectroscopy. Figure 1 is the infrared spectrum of carbon quantum dot materials, Figure 1 It can be seen that there is also a benzene ring structure in the structure, which contains amino and hydroxyl functional groups, CO, and NH groups. Figure 2 This is the X-ray photoelectron spectrum of the prepared carbon quantum dot material. From the peaks at 284.8, 400.4 and 531.7 eV, it can be determined that the material contains C, N, O elements and their approximate content ratios. Figure 3 This is the excitation emission spectrum of carbon quantum dot materials. Figure 4 In order to compare the fluorescence intensity of the materials after combining with atrazine under different experimental conditions during the preparation process, taking the addition of atrazine concentration of 500 ng / L as an example, it was found that the fluorescence intensity ratio was optimal when the reaction temperature was 180°C and the reaction time was 12h.

[0046] Example 2 Construction of fluorescent probe for atrazine pesticide

[0047] Figure 5 This is the fluorescence response diagram after adding different pesticides. Figure 6 is the standard curve fitted according to the fluorescence response spectrum. Figure 6 It can be seen that the concentration range of atrazine detected by the established fluorescent probe is 20-1000 ng / L, and the corresponding linear regression equation is y=0.0085x+1.2827, and the linear regression coefficient R 2 For R 2 =0.9883.

[0048] Example 3 Response time and stability study of atrazine rapid detection method

[0049] In a clean centrifuge tube, add 4 mL of the prepared carbon quantum dot material solution (10 -6 g / mL), 5mL sodium acetate buffer (pH=6) and 300μL of 200ng / L atrazine standard solution, fixed the excitation wavelength at 380nm, and tested its fluorescence intensity with a fluorescence spectrophotometer at 0, 2, 4, 6, 8, 10, and 12min.

[0050] Figure 7 This is the result of investigating the interaction time between atrazine and the material. It can be seen that after adding atrazine, the fluorescence intensity of the material remains stable after 10 minutes. Figure 8 The figure is a comparison of the fluorescence intensity after atrazine is combined with the material at different pH values ​​when the atrazine concentration is 500 ng / L. It can be seen that the fluorescence intensity ratio is at the optimal value when the pH is 6.

[0051] Example 4: Selectivity of atrazine detection

[0052] In order to reflect the selectivity of the fluorescent probe constructed by the present invention, this embodiment selects some common metal ions and other pesticides to affect the fluorescence intensity, and adds 4 mL of the prepared fluorescent material solution and 5 mL of sodium acetate buffer solution to each centrifuge tube, and then adds imidacloprid, cypermethrin, chlorpyrifos, melamine, triadimenol, sulfone pyraclostrobin, Cu 2+ , Fe 3+ , K + , heated at 40℃ for 10min, tested the fluorescence intensity, fixed the excitation wavelength at 380nm, recorded the fluorescence intensity at the emission wavelength of 490nm, and calculated F / F0.

[0053] Fig. 9 It is a fluorescence response diagram of some common metal ions and other pesticides, wherein the horizontal axis represents the interfering substance, and the vertical axis represents the ratio of the fluorescence intensity after adding the interfering substance to the fluorescence intensity without adding the interfering substance. It can be seen from the figure that some common ions and other pesticides have little effect on atrazine pesticide, and the invention has a high selectivity for atrazine.

[0054] Comparative Example 1

[0055] This comparative example is the method in patent CN 109781685 A.

[0056] Compared with the invention described in CN 109781685 A, the present invention does not need to use enzyme as a catalytic substrate, the pretreatment process is simple, the detection process is faster, and the requirement for rapid detection outdoors can be better met.

[0057] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing carbon quantum dots, characterized in that: The method uses citric acid, o-phenylenediamine, ethanol and ultrapure water as raw materials and is carried out through a high-temperature hydrothermal method. The specific steps include: firstly fully dissolving citric acid and o-phenylenediamine in a mixed solution of ethanol and ultrapure water, then heating at 150-200°C in a high-temperature and high-pressure reactor for 6-16 hours, and then cooling to room temperature to remove large particle impurities and small molecular substances, and finally blowing with nitrogen and freeze-drying to obtain a solid powder, which is the carbon quantum dots.

2. The preparation method according to claim 1, characterized in that: The volume ratio of the ethanol to the ultrapure water is 1:(0.5-1.5), the dissolved concentration of the citric acid in the mixed solution is 2-6 g / L, and the dissolved concentration of the o-phenylenediamine in the mixed solution is 2-18 g / L.

3. The preparation method according to claim 2, characterized in that: The usage ratio of the citric acid to the o-phenylenediamine is 1:(1-3).

4. A carbon quantum dot, characterized in that The carbon quantum dots are prepared by using the preparation method described in any one of claims 1 to 3.

5. A rapid detection method for atrazine based on carbon quantum dot fluorescent probe, characterized in that: The method comprises using the carbon quantum dots according to claim 4, and specifically comprises the following steps: (1) Preparation of synthetic carbon quantum dots: The preparation method comprises using the preparation method described in any one of claims 1 to 3; (2) Establishing a linear standard curve: Take several centrifuge tubes, first add the carbon quantum dot solution prepared in step (1), then add different concentrations of atrazine solution, then add buffer solution and mix well, heat at 38-42°C for 8-12 minutes, then fix the excitation wavelength to 320-420nm to obtain the fluorescence intensity, and finally use the fluorescence intensity ratio before and after adding atrazine as the ordinate and the concentration of atrazine added as the abscissa to establish a linear relationship, and calculate the corresponding regression equation; (3) Eliminate possible interference: Take possible coexisting substances of atrazine and proceed according to step (2); (4) Sample pretreatment; (5) Determination of atrazine content: Take the carbon quantum dots in step (1) and add buffer solution, then add the pretreatment solution obtained by sample pretreatment in step (4), and then heat at a constant temperature of 38-42°C for 8-12 minutes, fix the excitation wavelength to 320-420nm, the excitation slit to 5nm, and the emission slit to 10nm, and obtain the fluorescence intensity. The fluorescence intensity after adding atrazine at an emission wavelength of 490nm is compared with the fluorescence intensity before adding atrazine and substituted into the equation constructed in step (2) for calculation to obtain the atrazine content in the sample.

6. The atrazine rapid detection method according to claim 5, characterized in that: The concentration of the carbon quantum dot solution in step (2) is 0.5-1.5×10 -6 g / mL, the amount added to each centrifuge tube is 3-5mL.

7. The atrazine rapid detection method according to claim 6, characterized in that: The concentration of the atrazine solution in step (2) is set to 0, 10, 20, 50, 80, 100, 150, 200, 300, 400, 500, 600, 800, 1000, 1200 ng / L, and the amount added to each centrifuge tube is 280-320 μL.

8. The atrazine rapid detection method according to claim 7, characterized in that: The buffer in step (2) is acetate buffer, the pH value is 4-7, and the amount added is 4-6 mL.

9. The atrazine rapid detection method according to claim 8, characterized in that: The possible coexisting substances of atrazine in step (3) are imidacloprid, chlorpyrifos, cypermethrin, melamine, triadimenol, pyraclostrobin, Cu 2+ , Fe 3+ and K + Any one or more of .

10. Use of the preparation method according to any one of claims 1 to 3, the carbon quantum dots according to claim 4, or the atrazine rapid detection method according to any one of claims 5 to 9 in atrazine detection.

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