Green emission carbonized polymer dot, preparation method and nitrite ion detection method based on green emission carbonized polymer dot

Abstract

The invention relates to the technical field of ion detection, and discloses a green emission carbonized polymer dot, a preparation method and a nitrite ion detection method based on the green emission carbonized polymer dot. The detection method comprises the following steps: taking a g-CPDs working solution, adding solutions containing nitrite ions with different concentrations, incubating and observing the fluorescence color change of the solutions, determining the fluorescence intensity F of the solution after the reaction, and simultaneously determining the fluorescence intensity F0 of a blank working solution; establishing a standard curve for detecting the nitrite ions according to the relationship between the fluorescence intensity of the g-CPDs before and after the reaction and the change value of the concentration of the nitrite ions; the method comprises the following steps: taking a g-CPDs working solution, adding a to-be-detected solution containing nitrite ions, incubating, observing the fluorescence color change of the solution, and measuring the fluorescence intensity of the solution; and calculating the concentration of the nitrite ions in the to-be-detected liquid according to the linear relationship between F0 / F and the concentration of the nitrite ions. The detection method is sensitive and anti-interference, and is suitable for food and environmental water sample detection.

Description

Technical Field

[0001] This invention relates to the field of ion detection technology, and in particular to a method for preparing green emission carbonized polymer dots and a method for detecting nitrite ions based on green emission carbonized polymer dots. Background Technology

[0002] Nitrite ions are common harmful pollutants in the environment and food. In the environment, agricultural nitrogen fertilizer loss and industrial wastewater discharge can lead to excessive nitrite ion levels in water bodies, causing algae growth and oxygen deficiency in aquatic organisms. In food, nitrite ions are used as color-protecting agents and preservatives in meat products (ham, bacon), but excessive intake can lead to methemoglobinemia in humans. They can also react with amines to form highly carcinogenic nitrosamines. The World Health Organization (WHO) stipulates that the maximum pollution level of nitrite ions in drinking water is ≤3.0 mg / kg, and the Chinese national standard GB5009.33-2016 stipulates that the residual nitrite ions in meat products is ≤30 mg / kg.

[0003] Traditional methods for nitrite ion detection have significant limitations: spectrophotometry is cumbersome and slow in color development; ion chromatography requires expensive instruments and relies on specialized personnel; and electrochemical methods suffer from poor stability and are susceptible to interference. In recent years, fluorescent carbon dots have become ideal probes for nitrite ion detection due to their good water solubility, low toxicity, and excellent photostability. However, existing carbon dots have the following shortcomings: ① complex preparation process requiring multiple modification steps; ② low fluorescence quantum yield and insufficient detection sensitivity; ③ weak anti-interference ability, resulting in large detection errors in complex samples (such as high-salt pickled vegetable juice). Therefore, developing fluorescent carbon dots that are simple to prepare, highly stable, sensitive, and resistant to interference is of great significance for the rapid detection of nitrite ions. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in the aforementioned technologies. To this end, it proposes a one-step hydrothermal method for preparing highly stable g-CPDs, and a fluorescence detection method based on these g-CPDs, enabling sensitive and accurate detection in food and environmental samples, including: m-phenylenediamine and ethylenediaminetetraacetic acid were dissolved in deionized water at a mass ratio of 1:0.5 to 1:1.5 to obtain a mixed solution; The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and heated in an oven at 200-220°C for 7-12 hours. After the high-temperature reaction was completed, the mixed solution was naturally cooled to room temperature. The resulting dispersion was filtered through a 0.22 μm ultrafiltration membrane to remove insoluble matter. The filtrate was dialyzed for 22-48 hours using a dialysis bag with a molecular weight cutoff of 1000 Da. The dialysis liquid was freeze-dried for 24 hours to obtain g-CPDs powder.

[0005] The carbon dots prepared by the above method proposed in this invention are green emitting carbonized polymer dots, spherical in shape, with an average particle size of 2.27±0.47nm and a lattice spacing of 0.19nm; the optimal excitation wavelength in aqueous solution is 450nm, the optimal emission wavelength is 513nm, and the fluorescence quantum yield is 36.42%; under the conditions of pH 3-11, NaCl concentration 0-1000μM, and xenon lamp irradiation for 60min, the fluorescence intensity fluctuation is ≤5%.

[0006] This invention provides a method for detecting nitrite ions using a prepared green-emitting carbonized polymer spot fluorescence method, comprising: 1) Dissolve the prepared g-CPDs in ultrapure water to prepare a working solution with a concentration of 0.3-0.5 mg / mL; 2) Add 2 mL of nitrite solution of different concentrations to g-CPDs; incubate at 30℃ for 25-35 min, and measure the fluorescence intensity F at 513 nm with 450 nm as the excitation wavelength. At the same time, measure the fluorescence intensity F0 of the blank working solution (2 mL working solution + 2 mL ultrapure water). 3) Establish a standard curve for detecting nitrite ions based on the relationship between the fluorescence intensity before and after the reaction of g-CPDs and the change in nitrite ion concentration; 4) Take 2 mL of the working solution and add 2 mL of the test solution containing nitrite ions. Calculate the concentration of nitrite ions in the test solution based on the linear relationship between F0 / F and the concentration of nitrite ions.

[0007] Compared with the prior art, the beneficial effects of the present invention are: This g-CPDs are prepared by a one-step hydrothermal method using m-phenylenediamine and ethylenediaminetetraacetic acid as raw materials. No complex subsequent modification process is required. The raw materials are inexpensive and readily available. The operation is simple and can be mass-produced in the laboratory, which greatly reduces the preparation cost. The prepared g-CPDs are spherical and uniformly dispersed, with excellent water solubility. Under a wide acid-base range of pH 3-11, a high-salt environment of 0-1000μM, and a long-term light irradiation of xenon lamp for 60 min, the fluorescence intensity fluctuation is ≤5%. They have excellent photostability and salt resistance, and can be used for the detection of complex matrix samples such as food and environment. The fluorescence detection system for nitrite ions constructed based on these g-CPDs has a detection limit as low as 0.109 μM and a linear range of 0.5-260 μM (R²=0.999). It exhibits high detection sensitivity and good quantitative accuracy. It is unresponsive to 15 common amino acids, 27 cations and anions, and only nitrite ions can cause fluorescence quenching through diazotization with amino groups on the carbon dot surface. It also has strong anti-interference ability. When used in actual testing of food samples such as ham, bacon, and kimchi, as well as environmental water samples such as drinking water and tap water, the recovery rate can reach 96.7%-102.5%, with a relative standard deviation (RSD) of <5.14%. The test results are in high agreement with those of ion chromatography, which fully verifies the reliability of the method. It can widely meet the needs of rapid, sensitive, and accurate detection of nitrite ions in food safety supervision and environmental water sample monitoring.

[0008] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. The technical solutions of the invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0009] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The image shows a physical sample of the g-CPDs prepared as given in the examples. Figure 2 The TEM image and particle size distribution histogram of g-CPDs given in the example show that the g-CPDs have a particle size range of 1.15-3.75 nm and an average particle size of 2.27 ± 0.47 nm. Figure 3 The XRD pattern given in the example shows that it has a broad diffraction peak at 2θ = 22°, corresponding to an interlayer spacing of 0.40 nm, which is significantly larger than the 0.34 nm of the graphite (002) crystal plane, indicating that g-CPDs are a polymer-carbon hybrid structure with an amorphous structure as the main component. Figure 4 The optical performance characterization results given in the examples show a broad absorption band in the 275-320 nm range in the left figure, which is attributed to the aromatic n-π* transition of the C=O group. The maximum emission center is located at 513 nm when the excitation wavelength is 445 nm. The g-CPDs probe solution is transparent and light green under sunlight, and exhibits bright green fluorescence under 445 nm excitation light. Figure 4 (Illustration). As shown in the right figure, as the excitation wavelength increases from 390 nm to 465 nm, the emission peak remains at 513 nm. This typical excitation-independent photoluminescence behavior indicates that g-CPDs have a uniform surface state emission mechanism. Figure 5 The fluorescence intensity at 513 nm is given in the examples for different nitrite ion concentrations. Figure 6The linear relationship between F0 / F and nitrite ion concentration is given in the examples; Figure 7 The fluorescence intensity at 513 nm for different amino acids is given in the examples; Figure 8 The examples illustrate the effect of different amino acids on the fluorescence intensity of g-CPDs; Figure 9 The fluorescence intensity at 513 nm for different cations is given in the examples; Figure 10 The examples illustrate the effect of different cations on the fluorescence intensity of g-CPDs; Figure 11 The fluorescence intensity at 513 nm for different anions is given in the examples; Figure 12 The examples illustrate the effect of different anions on the fluorescence intensity of g-CPDs. Detailed Implementation

[0010] The present invention will be described below with reference to the accompanying drawings. The preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0011] Example 1 Preparation of g-CPDs: 1) Raw material preparation: Accurately weigh 1g of m-phenylenediamine and 1g of ethylenediaminetetraacetic acid, dissolve them in 40mL of deionized water to obtain a mixed solution; 2) Hydrothermal reaction: Transfer the solution to a 100mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in a 180℃ oven for constant heating for 8 hours; 3) Purification: After the reaction is complete, cool to room temperature and filter with a 0.22 μm aqueous ultrafiltration membrane. The filtrate is placed in a 1000 Da dialysis bag and dialyzed in deionized water for 24 h (changing the water every 6 h). 4) Drying: The dialysis liquid was transferred to a freeze dryer and dried at low temperature for 12 hours to obtain a yellowish-brown g-CPDs powder, which was then sealed and stored in a refrigerator at 4°C for later use. Figure 1 ).

[0012] Example 2 Characterization of g-CPDs 1) A 0.1 mg / mL carbon dot solution was dropped onto a copper grid, allowed to dry naturally, and observed using a JEM-2100F transmission electron microscope. The particle size was 2.27 ± 0.47 nm, and the particles were uniformly dispersed. Figure 2 ); 2) X-ray diffraction (XRD, XRD-6100, Shimadzu, Japan) was used to analyze the phase composition, with a 2θ scanning range of 5°–80°. Figure 3 ); 3) Excitation / emission spectra measured with an F-320 fluorescence spectrophotometer (450nm / 513nm) Figure 4 The relative quantum yield is 36.42% (based on Rhodamine B, φ=89%).

[0013] Example 3 Performance testing of g-CPDs for detecting nitrite ions 1) Dissolve the g-CPDs prepared in Example 1 in ultrapure water to prepare a working solution of 0.4 mg / mL; 2) Prepare standard solutions with nitrite ion concentrations of 0.5, 1, 2, 4, 6, 8, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, and 260 μM; 3) Take 2 mL of working solution + 2 mL of standard solution, incubate at 30℃ for 30 min, and measure the fluorescence intensity F at 513 nm. For the blank group (2 mL of working solution + 2 mL of ultrapure water), measure F0. 4) Plotting nitrite ion concentration on the x-axis and F0 / F on the y-axis, the linear equation is obtained: F0 / F = 0.01109c + 0.99407 (R 2 =0.999), detection limit 0.109μM (S / N=3) Figure 5 , Figure 6 ).

[0014] Example 4: Anti-interference experiment 1) Prepare 0.01M of 15 kinds of amino acids ( Figure 7 , Figure 8 (glycine, L-histidine, etc.), 16 kinds of cations ( Figure 9 , Figure 10 (Na) + K + Cu 2+ etc.), 13 kinds of anions (etc.) Figure 11 , Figure 12 (SO4) 2- NO3 - etc.) solution; 2) Take 2 mL of carbon dot working solution, add 20 μL of interfering solution, and measure the fluorescence intensity F1; then add 10 μL of 0.01 M nitrite ion solution and measure the fluorescence intensity F2. 3) The effect of all interfering substances on F1 is less than 3%. After the addition of nitrite ions, F2 is reduced by more than 80% compared with F1, which is consistent with the quenching effect of adding nitrite ions alone, confirming strong anti-interference.

[0015] Example 5 Detection of nitrite ions in actual samples 1) After homogenizing and centrifuging samples such as ham and kimchi, the supernatant was diluted and used as the test solution; 2) Take 2 mL of the test solution and measure the fluorescence intensity according to the steps in Example 3. Substitute the values ​​into the standard curve to calculate the nitrite ion concentration. The table below shows the spiked recovery results of actual samples (ham, kimchi, drinking water), which show the recovery rate and RSD at different spiked concentrations, thus verifying the reliability of the method.

[0016]

[0017] It is obvious that those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for preparing green emission carbonized polymer dots, characterized in that, Includes the following steps: (a) Dissolve m-phenylenediamine and ethylenediaminetetraacetic acid in deionized water at a mass ratio of 1:0.5 to 1:1.5 to obtain a mixed solution; (b) Transfer the mixed solution to a polytetrafluoroethylene-lined high-pressure reactor and heat it in an oven at 200-220°C for 7-12 hours; (c) After the high-temperature reaction is completed, the mixed solution is naturally cooled to room temperature. The resulting dispersion is filtered through a 0.22 μm ultrafiltration membrane to remove insoluble matter. The filtrate is dialyzed for 22-48 h using a dialysis bag with a molecular weight cutoff of 1000 Da. (d) The dialysis liquid was freeze-dried to obtain g-CPDs powder.

2. The preparation method according to claim 1, characterized in that, The mass ratio of m-phenylenediamine to ethylenediaminetetraacetic acid is 1:

1.

3. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature was 200 ℃, and the reaction time was 8 h.

4. The preparation method according to claim 1, characterized in that, The dialysis time was 24 hours, and the freeze-drying time was 24 hours.

5. A green emission carbonization polymer dot prepared according to the method of any one of claims 1 to 4, characterized in that, The green emitting carbonized polymer dots are spherical with an average particle size of 2.27±0.47 nm and a lattice spacing of 0.19 nm. The optimal excitation wavelength in aqueous solution is 450 nm, the optimal emission wavelength is 513 nm, and the fluorescence quantum yield is 36.42%.

6. The green emission carbonized polymer dot according to claim 5, characterized in that, Under conditions of pH 3-11, NaCl concentration 0-1000 μM, and xenon lamp irradiation for 60 min, the fluorescence intensity fluctuation was ≤5%.

7. A method for detecting nitrite ions at green emission carbonized polymer dots according to claim 5 or 6, characterized in that, Includes the following steps: 1) Dissolve the green emitting carbonized polymer in ultrapure water to prepare a working solution with a concentration of 0.3-0.5 mg / mL; 2) Add 2 mL of nitrite solution of different concentrations to g-CPDs; incubate at 30℃ for 25-35 min, and measure the fluorescence intensity F at 513 nm with 450 nm as the excitation wavelength. At the same time, measure the fluorescence intensity F0 of the blank working solution (2 mL working solution + 2 mL ultrapure water). 3) Establish a standard curve for detecting nitrite ions based on the relationship between the fluorescence intensity before and after the reaction of g-CPDs and the change in nitrite ion concentration; 4) Take 2 mL of the working solution and add 2 mL of the test solution containing nitrite ions. Calculate the concentration of nitrite ions in the test solution based on the linear relationship between F0 / F and the concentration of nitrite ions.

8. The detection method according to claim 7, wherein, The linear range of the standard curve is 0.5–260 μM, and the detection limit is 0.109 μM.

9. The detection method according to claim 7, wherein, The test solution is a food sample or an environmental water sample, and the 15 amino acids, 27 cations and anions present in the sample have an interference of <3% with the detection results.

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