Dye-derived red fluorescent carbon dots as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of carbon-based nano luminescent materials, and provides a dye-derived red fluorescent carbon dot as well as a preparation method and application thereof, and the dye-derived red fluorescent carbon dot can be obtained by taking azure A dye and ethylenediamine tetraacetic acid as reaction precursors and carrying out hydrothermal reaction at 18-220 DEG C. And the emission wavelength of the carbon dots is expanded to 684 nm. The prepared carbon dots do not need surface passivation or complex modification, the process is simple and convenient, and excellent optical performance and good stability are shown at the same time. The invention develops a high-sensitivity fluorescence sensing method for amaranth, realizes efficient and specific detection of amaranth, and has excellent selectivity and sensitivity. Based on the reversible change of the solution from azure to red in the process that the carbon dots respond to the amaranth, an intelligent mobile phone recognition application is constructed, and the convenience and practicability of the detection process are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon-based nanoluminescent materials, and specifically relates to a dye-derived red fluorescent carbon dot and a preparation method and application thereof. More specifically, the fluorescent carbon dot is used for smart phones to identify and detect amaranth. Background Art

[0002] Amaranth is a synthetic food colorant and a water-soluble azo dye, which is widely used in the coloring of food, flavoring, pharmaceutical formulations and cosmetics. Its excellent stability under various processing conditions such as high temperature and strong light makes it a highly respected and reliable colorant in the food industry. However, studies have shown that amaranth may pose a potential threat to human health and is known to cause health problems such as allergic reactions and hyperactivity in children. Although amaranth can effectively enhance the visual appeal of food, its health risks and corresponding regulatory restrictions cannot be ignored. In recent years, research on the intake of synthetic pigments has gradually increased at home and abroad. Currently reported methods for detecting food pigments include high-performance liquid chromatography, electrochemical method, ultraviolet-visible absorption spectroscopy, microcolumn method and polarography. Among them, fluorescence method has become an important supplementary detection method due to its advantages such as simple operation, high sensitivity, fast detection speed and convenient analysis. However, at present, research on the development of amaranth fluorescence sensors is still limited, and high-quality fluorescence detection methods for amaranth are still scarce.

[0003] Carbon dots have become a research hotspot in the field of nanomaterials due to their excellent optical properties, especially in environmental monitoring and food safety testing. Although significant progress has been made in the use of carbon dots for trace detection of food pigments, the existing carbon dot fluorescence emission is mainly concentrated in the short-wavelength region, which is easily interfered by the spontaneous fluorescence of biological tissues and environmental background. In the process of extending the emission wavelength of carbon dots to the required long-wavelength range, the formation of photoluminescence is usually related to the generation of multi-heterocyclic molecular domains in the synthesis, resulting in low emission efficiency and difficulty in accurately controlling optical properties. Considering the importance of red light in biological imaging and sensing applications, it is urgent to develop suitable fluorophores as precursors to achieve the extension of the emission wavelength of carbon dots to the long-wavelength region, especially around 700 nm. Summary of the invention

[0004] The present invention provides dye-derived red fluorescent carbon dots, and a preparation method and application thereof. The present invention uses azure A dye and ethylenediaminetetraacetic acid as reaction precursors for the first time, successfully prepares red fluorescent carbon dots, and constructs a highly sensitive fluorescence sensing method for amaranth red. Through the reversible change of the solution between azure and red during the response of the fluorescent carbon dots to amaranth red, simple identification based on a smartphone is achieved.

[0005] The present invention also provides a method for preparing red fluorescent carbon dots, which is simple to operate, has a wide range of raw material sources and low cost, and has good promotion potential. In addition, based on the synthesized carbon dots, the present invention further constructs a highly specific fluorescence sensing method for amaranth.

[0006] The present invention is realized by the following technical scheme: a dye-derived red fluorescent carbon dot, which uses azure A dye and ethylenediaminetetraacetic acid as reaction precursors, and can obtain the dye-derived red fluorescent carbon dot through a hydrothermal reaction at 18-220°C.

[0007] The method for preparing the dye-derived red fluorescent carbon dots is as follows: (1) Grinding Azure A and EDTA evenly, then dissolving them in secondary water, and ultrasonicating to obtain a uniform mixed solution; wherein the mass ratio of Azure A, secondary water and EDTA is 1-4:400-1000:1-10; (2) Hydrothermal reaction: The above solution was transferred to a hydrothermal reactor and reacted at 180-220°C for 6-10 hours. After the reaction was completed, it was allowed to stand and cool to room temperature. The insoluble matter was filtered out and centrifuged at 10,000 rpm to collect the supernatant. Subsequently, the supernatant was dialyzed using a 500-1000 Da dialysis bag for 1-3 days to obtain a pure carbon dot aqueous solution. After the dialysis was completed, freeze drying was performed. The freeze drying conditions were set as follows: initial temperature: -80°C, heating rate: 0.5°C / min, to ensure that the water in the solution sublimated slowly to avoid damage to the carbon dot structure. The freeze drying process lasted for 24-48 hours until a completely dry carbon dot solid powder was obtained.

[0008] Furthermore, the mass ratio of the azure A, secondary water and ethylenediaminetetraacetic acid is 1:400:1; the temperature of the hydrothermal reaction is 200° C. for 8 hours; and the dialysis condition is dialysis treatment in a 500 Da dialysis bag for 3 days.

[0009] The present invention also provides the use of the dye-derived red fluorescent carbon dots or the dye-derived red fluorescent carbon dots prepared by the method in the simple identification of amaranth based on a smart phone.

[0010] Further, the specific application method is: (1) Preparation of R-CDs dispersion: The prepared dye-derived red fluorescent carbon dot R-CDs powder was dissolved in ultrapure water to obtain an R-CDs aqueous solution with a concentration of 3.0 mg / ml; then 100 ul of the R-CDs aqueous solution was mixed with 2.0 ml of PBS buffer with a pH of 7.4, and 0-150 uM amaranth was gradually added in different concentration gradients to obtain an R-CDs dispersion; (2) Observe the color change of the solution: expose the mixed sample to a light source and use a smartphone camera to capture the color change of the solution. As the concentration of amaranth increases, the color of the carbon dot solution gradually changes from azure to red, which is recorded by image capture. (3) Image acquisition and color analysis: Through the smartphone application, the captured images are converted into RGB color values ​​and the RGB data corresponding to each image is recorded; the application automatically extracts the R, G, and B values ​​of the main colors in the image and then calculates the R / (G+B) ratio; (4) Linear fitting and detection limit calculation: The relationship between the R / (G+B) ratio and the amaranth concentration was fitted by linear regression, and the regression equation was obtained as R / (G+B)=-0.0121 C + 0.4319, R²=0.9964. The detection limit of this method was calculated to be 1.31 μM.

[0011] The present invention uses Azure A dye and ethylenediaminetetraacetic acid as precursors for the first time to successfully prepare red fluorescent carbon dots, and extend the emission wavelength of the carbon dots to 684 nm. The prepared carbon dots do not require surface passivation or complex modification, the process is simple, and they exhibit excellent optical properties and good stability. A highly sensitive fluorescence sensing method for amaranth red was developed to achieve efficient and specific detection of amaranth red with excellent selectivity and sensitivity. Based on the reversible change of the solution from azure to red during the response of carbon dots to amaranth red, a smartphone recognition application was constructed, which greatly improved the convenience and practicality of the detection process. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a transmission electron microscope image of carbon dots prepared in Example 1 of the present invention; Figure 2 This is an infrared spectrum of the carbon dots prepared in Example 1 of the present invention, where the abscissa represents the detection wavelength and the ordinate represents the transmittance; Figure 3 This is the XPS spectrum of the carbon dots prepared in Example 1 of the present invention; Figure 4 The ultraviolet absorption spectrum and fluorescence excitation-emission spectrum of the carbon dots prepared in Example 1 of the present invention; Figure 5 The excitation-emission fluorescence matrix spectrum of the carbon dots prepared in Example 1 of the present invention; Figure 6 The results of the study on the ion selectivity of the carbon dots prepared in Example 1 of the present invention at a fluorescence intensity of 684 nm; Figure 7 The fluorescence change and related linear relationship diagram of the carbon dots prepared in Example 1 of the present invention under different concentrations of amaranth; Figure 8 This is a diagram of the application of amaranth imaging recognition with the assistance of a smartphone based on the carbon dots prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0014] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosure and materials cited therein are hereby incorporated by reference.

[0015] Technical equivalents to the specific embodiments described that are apparent to those skilled in the art using no more than routine experimentation are intended to be encompassed by this application.

[0016] The experimental methods in the following examples are all conventional methods unless otherwise specified. The instruments and equipment used in the following examples are all conventional laboratory instruments and equipment unless otherwise specified; the experimental materials used in the following examples are all purchased from conventional biochemical reagent stores unless otherwise specified.

[0017] Example 1: Preparation of dye-derived red fluorescent carbon dots, the specific method is as follows: Step 1: Weigh 0.05 g of Azure A and 0.05 g of ethylenediaminetetraacetic acid, grind and mix in a mortar, then dissolve in 20 mL of secondary water, and ultrasonicate to obtain a uniform mixed solution. The above solution is transferred to a 50 mL hydrothermal reactor.

[0018] Step 2, placing the hydrothermal kettle in an oven, reacting at 200° C. for 8 hours to obtain a red solution.

[0019] Step 3, after filtering the insoluble matter, dialyze in a 500 Da dialysis bag in a glass container for 3 days to obtain a pure carbon dot aqueous solution.

[0020] Step 4, freeze-drying the fluorescent carbon dot aqueous solution to obtain red fluorescent carbon dots with a relative quantum yield of 14.6%.

[0021] The structural characterization of the carbon dots prepared in Example 1 is shown in Figure 1 , Figure 2 and Figure 3 . Figure 1 The transmission electron microscope (TEM) image of the carbon dots prepared in Example 1 shows that the average particle size of the carbon dots is 4.90±0.07 nm, and the high-resolution TEM shows a lattice spacing of 0.22 nm, corresponding to the (100) crystal plane of graphite carbon.

[0022] Figure 2This is the infrared spectrum (FT-IR) of the carbon dots prepared in Example 1. The carbon dots have a wavelength of 3447 cm - There is a characteristic peak at ¹, corresponding to the stretching vibration of OH / NH; 2833 cm - ¹ and 2715 cm - The peaks at ¹ are attributed to the asymmetric and symmetric stretching vibrations of CH, respectively; 1605 cm - The peak at ¹ indicates the stretching vibration of C=O; while the peak at 1365 cm - ¹ and 1124 cm - The peaks of ¹ are related to the vibrations of CN and CO, respectively.

[0023] Figure 3 This is the full X-ray photoelectron spectroscopy (XPS) spectrum of carbon dots prepared in Example 1 of the present invention, where C 1s 、N 1s and O 1s The main peaks of carbon dots appear at 59.04%, 13.00% and 27.96% atomic percentages, respectively, and the corresponding binding energies are located at 284.8eV, 400.2 eV and 531.1 eV. The comprehensive results show that the structural characteristics of carbon dots are that they contain sp² aromatic conjugated domains and are interspersed with sp³ defect sites. The surface is modified with hydrophilic functional groups such as -NH2 and -COOH. These complex structural elements together give the material unique electronic and chemical properties.

[0024] The optical properties of the carbon dots prepared in Example 1 are as follows: Figure 4 and Figure 5 shown. Figure 4 The UV absorption spectrum and fluorescence excitation-emission spectrum of the carbon dots prepared in Example 1. The UV absorption spectrum shows that the carbon dots have two obvious absorption peaks at about 200 nm and 292 nm, corresponding to the π-π transition in the aromatic structure and the n-π transition of the C=O and C=N groups, respectively. In addition, a broad absorption peak was observed at 655 nm, which is related to the low-energy surface state. The fluorescence excitation-emission spectrum shows that the optimal excitation wavelength (λex) and emission wavelength (λem) of the carbon dots are 666 nm and 684 nm, respectively. Figure 5 The excitation-emission fluorescence matrix spectrum of the carbon dots prepared in Example 1 shows that when the excitation wavelength changes from 300 nm to 680 nm, the emission peak position of the carbon dots at 684 nm remains constant, which is attributed to the uniform surface state of the carbon dots.

[0025] The results of the study on the responsiveness of the carbon dots prepared in Example 1 to amaranth are as follows: Figure 6 and Figure 7 In the standard operation, the prepared R-CDs powder was first dissolved in ultrapure water to obtain a concentration of 3.0 mg·mL- Then, 100 μL of R-CDs solution (concentration 3.0 mg mL - ¹) was mixed with 2.0 mL of PBS buffer (pH = 7.4), and different concentrations of amaranth (0-150 µM) were gradually added to prepare R-CDs dispersions. The fluorescence emission spectrum of each sample was measured at an excitation wavelength of 666 nm, and each measurement was repeated three times. In addition, the interference effects of other chemicals in the presence of R-CDs were evaluated separately, using the same experimental procedures as amaranth. Figure 6 It was shown that in the presence of different metal ions, representative biological molecules and food additives, the fluorescence intensity of R-CDs did not change significantly. Only amaranth red could significantly inhibit the fluorescence emission of carbon dots, showing obvious selectivity. Figure 7 It was further confirmed that with the increase of amaranth red concentration, the fluorescence intensity of carbon dots at 684 nm decreased significantly, and showed a good linear response in the concentration range of 0.1-2.5 µM, with a linear regression equation of ΔF=209553.5885C+11749.3502, R²=0.9917, and a detection limit (LOD) of 16.7 nM. These results show that the prepared R-CDs have excellent selectivity and sensitivity and can be used for efficient detection of amaranth red.

[0026] The application of smartphone-assisted amaranth imaging recognition based on the carbon dots prepared in Example 1 is as follows Figure 8 shown. Figure 8The detection process is demonstrated: 1) Sample preparation: First, different concentrations of amaranth solution are mixed with carbon dot solution to ensure that the two are evenly mixed and form a stable dispersion. During this process, stirring or ultrasonic treatment can be used to ensure that amaranth is completely dissolved and evenly distributed; 2) Observation of solution color change: The mixed sample is exposed to an appropriate light source, and the color change of the solution is captured using a smartphone camera. As the concentration of amaranth increases, the color of the carbon dot solution gradually changes from azure to red, and this change can be recorded by image capture. 3) Image acquisition and color analysis: Use a smartphone camera to take pictures of the solution, ensuring that factors such as the shooting angle and light source of the image have minimal impact on color recognition. The captured images are converted into RGB color values ​​through a smartphone application, and the RGB data corresponding to each image is recorded. The application automatically extracts the R, G, and B values ​​of the main colors in the image. 4) Data processing and analysis: The extracted RGB values ​​are input into the data processing software to calculate the R / (G+B) ratio. By comparing the R / (G+B) ratios at different amaranth concentrations, a linear curve between the concentration and the ratio was drawn, and the correlation was further analyzed. 5) Linear fitting and detection limit calculation: The relationship between the R / (G+B) ratio and the amaranth concentration was fitted by linear regression, and the regression equation R / (G+B)=-0.0121 C + 0.4319, R²=0.9964 was obtained, and the detection limit of this method was calculated to be 1.31μM. The results show that the smartphone-assisted imaging colorimetry still has a high detection sensitivity when the amaranth concentration is low. 6) Field application and verification: Using smartphones and their applications, rapid quantitative detection of amaranth was performed in a field environment. This convenient detection method does not rely on traditional large-scale laboratory equipment and can provide accurate detection results under real-time conditions, significantly improving the efficiency and flexibility of amaranth detection.

[0027] Example 2: Preparation of dye-derived red fluorescent carbon dots. Except that the amount of ethylenediaminetetraacetic acid was 0.02 g, the other conditions were the same as those in Example 1. The measured relative quantum yield was 11.2%.

[0028] Example 3: Preparation of dye-derived red fluorescent carbon dots. Except that the amount of ethylenediaminetetraacetic acid was 0.08 g, the other conditions were the same as those in Example 1. The measured relative quantum yield was 8.2%.

[0029] Example 4: Preparation of dye-derived red fluorescent carbon dots. Except that the amount of ethylenediaminetetraacetic acid was 0.15 g, the other conditions were the same as those in Example 1. The measured relative quantum yield was 7.8%.

[0030] Example 5: Preparation of dye-derived red fluorescent carbon dots, controlling the mass ratio of Azure A, secondary water and EDTA to 4:800:10; the hydrothermal reaction temperature was 180°C for 10 hours; the dialysis treatment was performed with a 500Da dialysis bag for 2 days, and the rest of the method was the same as that described in Example 1.

[0031] Example 6: Preparation of dye-derived red fluorescent carbon dots, controlling the mass ratio of Azure A, secondary water and EDTA to 3:600:5; the hydrothermal reaction temperature was 220°C for 6 hours; the dialysis treatment was performed with a 1000Da dialysis bag for 1 day, and the rest of the method was the same as that described in Example 1.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dye-derived red fluorescent carbon dot, characterized in that: With Azure A dye and ethylenediaminetetraacetic acid as reaction precursors, dye-derived red fluorescent carbon dots can be obtained by hydrothermal reaction at 18-220°C.

2. The method for preparing the dye-derived red fluorescent carbon dots according to claim 1, characterized in that: The specific method is: (1) Grinding Azure A and EDTA evenly, then dissolving them in secondary water, and ultrasonicating to obtain a uniform mixed solution; wherein the mass ratio of Azure A, secondary water and EDTA is 1-4:400-1000:1-10; (2) Hydrothermal reaction: The above solution was transferred to a hydrothermal reactor and reacted at 180-220°C for 6-10 hours. After the reaction, the solution was allowed to cool to room temperature, the insoluble matter was filtered out and centrifuged at 10,000 rpm to collect the supernatant. Subsequently, the supernatant was dialyzed using a 500-1000 Da dialysis bag for 1-3 days to obtain a pure carbon dot aqueous solution. After the dialysis, the solution was freeze-dried. The freeze-drying conditions were set as follows: initial temperature: -80°C, the heating rate was controlled to be 0.5°C / min, and the freeze-drying process lasted for 24-48 hours until a completely dry carbon dot solid powder was obtained.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the azure A, secondary water and ethylenediaminetetraacetic acid is 1:400:1; the temperature of the hydrothermal reaction is 200° C. for 8 hours; and the dialysis condition is dialysis treatment in a 500 Da dialysis bag for 3 days.

4. Use of the dye-derived red fluorescent carbon dots according to claim 1 or the dye-derived red fluorescent carbon dots prepared by the method according to claim 2 in the simple identification of amaranth based on a smartphone.

5. The use according to claim 4, characterized in that: The specific application method is: (1) Preparation of R-CDs dispersion: The prepared dye-derived red fluorescent carbon dot R-CDs powder was dissolved in ultrapure water to obtain an R-CDs aqueous solution with a concentration of 3.0 mg / ml; then 100 ul of the R-CDs aqueous solution was mixed with 2.0 ml of PBS buffer with a pH of 7.4, and 0-150 uM amaranth was gradually added in different concentration gradients to obtain an R-CDs dispersion; (2) Observe the color change of the solution: expose the mixed sample to a light source and use a smartphone camera to capture the color change of the solution. As the concentration of amaranth increases, the color of the carbon dot solution gradually changes from azure to red, which is recorded by image capture. (3) Image acquisition and color analysis: Through the smartphone application, the captured images are converted into RGB color values ​​and the RGB data corresponding to each image is recorded; the application automatically extracts the R, G, and B values ​​of the main colors in the image and then calculates the R / (G+B) ratio; (4) Linear fitting and detection limit calculation: The relationship between the R / (G+B) ratio and the amaranth concentration was fitted by linear regression, and the regression equation was obtained as R / (G+B)=-0.0121 C + 0.4319, R²=0.9964. The detection limit of this method was calculated to be 1.31 μM.

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