Preparation and application of fluorescent carbon quantum dots from grape leaves

Abstract

The invention discloses a preparation method of grape leaf fluorescent carbon quantum dots and its application. Firstly, natural biomass grape leaves are used as raw materials, and low eutectic ionic liquid is used to modify them to prepare blue fluorescent carbon quantum dots through a hydrothermal method. The blue fluorescent carbon quantum dots are used as probe materials for the detection of gallic acid in wine samples. The preparation method of the detection material disclosed by the invention is simple, and the process is easy to control. The obtained carbon quantum dots have good stability and high fluorescence intensity. The detection of gallic acid to be detected has high sensitivity, wide linear range and low detection limit. The linear range and detection limit are 1×10 ‑7 ~1×10 ‑3 mol / L and 38nmol / L, which can realize trace detection of gallic acid.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation and application of fluorescent carbon nanomaterials, and relates to the preparation of grape leaf fluorescent carbon quantum dots and the application of the same in gallic acid detection. Background Art

[0002] Gallic acid, also known as gallic acid, is a polyphenolic organic compound widely found in animals and plants. As a natural organic compound, gallic acid plays an important role in food preservation and storage. The detection of gallic acid is an important indicator for monitoring the nutritional quality of food. Therefore, it is very necessary to establish a sensitive gallic acid detection method.

[0003] In recent years, researchers at home and abroad have developed many methods for detecting gallic acid. These methods quantitatively or qualitatively detect the content of gallic acid by analyzing the interaction between gallic acid and other compounds in the sample or specific physical properties. These methods have their own characteristics in terms of sensitivity and stability, including ultraviolet spectrophotometry, high performance liquid chromatography, liquid chromatography-mass spectrometry, etc. However, the analysis cost, process, and analysis speed are issues that need further improvement and optimization. In recent years, new zero-dimensional nano carbon quantum dots with stable luminescence performance and good biocompatibility have attracted the attention of researchers. More and more researchers use carbon quantum dots as fluorescent probes to detect target analytes, and the gradual increase in literature reports just confirms this trend. Therefore, how to obtain carbon quantum dots with good detection effects through suitable biomass raw materials and preparation processes has become one of the hot topics for many researchers.

[0004] Grape leaves are byproducts of grape cultivation. They are rich in carbohydrates, crude fiber and other organic substances, and are considered to have certain potential for resource utilization. For example, there have been reports in the literature that grape leaves are used as animal feed, fertilizer, etc. to achieve resource utilization. Therefore, how to utilize them as resources, use grape leaves as precursors to prepare carbon quantum dots, and use the interaction between the analyte and the carbon quantum dots to weaken the fluorescence, thereby achieving efficient and accurate detection of the analyte, has become a research direction. Summary of the invention

[0005] The present invention aims to prepare a grape leaf fluorescent carbon quantum and its application. Natural biomass grape leaves are used as precursors, natural low eutectic ionic liquids are used as modifiers, and a simple hydrothermal synthesis method is used to prepare carbon quantum dots with high fluorescence intensity, good stability, good specificity and high sensitivity for gallic acid detection. The carbon quantum dots have a strong fluorescence quenching effect on gallic acid, with a quenching efficiency of up to 96%, and have a wider detection range and a lower detection limit, which are 1×10 -7 ~1×10 -3mol / L and 38nmol / L, which can realize trace detection of gallic acid, has low cost, simple operation and good application prospects.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing fluorescent carbon quantum dots from grape leaves is carried out in the following order:

[0008] S1. Collect natural biomass raw material grape leaves, dry them and crush them to less than 100 mesh, weigh grape leaf powder and natural low eutectic ionic liquid, put them in a beaker, and add ultrapure water to form solution A;

[0009] S2. Place solution A in a magnetic suspension stirrer at room temperature and stir for 1 hour. Filter to remove the residue to obtain solution B.

[0010] S3, take 10mL of solution B and put it into a 25mL volumetric flask, dilute to the mark with ultrapure water, transfer to a reactor, and react at 180-240°C for 6-12h to obtain a brown carbon quantum dot solution C;

[0011] S4. Transfer solution C to a centrifuge tube, centrifuge, and filter with a 0.22 μm microporous filter membrane to obtain a grape leaf fluorescent carbon quantum dot solution.

[0012] As a limitation of the present invention, in step S1, the mass volume ratio of the grape leaf powder to ultrapure water is 1:300 g / mL, and the mass ratio of the grape leaf powder to the natural low eutectic ionic liquid is 1:10.

[0013] As a second limitation of the present invention, in step S1, the natural eutectic ionic liquid consists of isosorbide and urea in a molar ratio of 1:1.

[0014] As a third limitation of the present invention, in step S4, the centrifugal speed is 4000 r / min and the centrifugal time is 40 min.

[0015] As a fourth limitation of the present invention, in step S1, the drying temperature is 70° C. and the drying time is 4 hours.

[0016] As the fifth limitation of the present invention, in step S4, the grape leaf fluorescent carbon quantum dots are in the form of spherical nanoparticles with an average particle size of 4.0 nm.

[0017] The present invention also provides an application of grape leaf fluorescent carbon quantum dots, which is used to quickly detect gallic acid in wine samples.

[0018] As a limitation of the application of the grape leaf fluorescent carbon quantum dots of the present invention, the fluorescence response rate of the carbon quantum dots to gallic acid is as high as 96%.

[0019] The carbon quantum dots of the present invention are formed by the carbon-containing substances such as carbohydrates and crude fibers in grape leaves and natural low-melting ionic liquids reacting together at high temperature to form carbon quantum dots. The mixed solution of the two is placed in a magnetic levitation stirrer for full stirring, so that the carbon-containing substances in the grape leaves that are easily soluble in water and the substances that are decomposed under alkaline conditions and soluble in water can be fully leached out; and the natural low-melting ionic liquid is a flexible nanosphere material formed by two small molecules, and its surface functional groups are "grafted" with the small molecules of the carbon-containing substances in the biomass, thereby forming carbon quantum dots with good detection effect.

[0020] The grape leaf fluorescent carbon quantum dots of the present invention are prepared by the above method and tested by a fluorescence spectrophotometer. It can be seen that the optimal excitation wavelength is 320nm and the optimal emission wavelength is 410nm (as shown in the accompanying drawings of the specification). Figure 1 , Figure 2 ), the carbon quantum dots were mixed with gallic acid and the results showed that gallic acid has a -7 ~1×10 -3 The mol / L concentration range and the fluorescence intensity of carbon quantum dots show a good nonlinear relationship, and the nonlinear equation is y = 0.9593-0.9290 × e^(-x / 230.0295)(R 2 =0.9926), where 1×10 -7 ~1×10 -4 The concentration range of mol / L showed a good linear relationship with the fluorescence intensity of carbon quantum dots, and its linear equation was y = 0.0039x + 0.0177 (R 2 =0.9912).

[0021] The above preparation method as a whole, each step is closely related and inseparable from each other, and they jointly determine the morphology, particle size characteristics and detection performance of carbon quantum dots.

[0022] After adopting the above technical solution, the beneficial effects achieved by the present invention are as follows:

[0023] ① Compared with existing detection technologies, the raw materials of carbon quantum dots used in the fluorescence detection method are natural biomass grape leaves, which have low cost and wide sources, turning waste into treasure, and the preparation method is simple and environmentally friendly.

[0024] ② The detection method of the present invention is simple to operate and quick to detect, and has the advantages of high sensitivity, low detection limit and wide linear range. It can have a quenching effect on gallic acid at a relatively low concentration (0.1 μM).

[0025] The detection limit is as low as 38nmol / L, and its linear range is 1×10 -7 ~1×10-3 mol / L;

[0026] ③ The prepared carbon quantum dots have wide adaptability and good stability in a wide pH range (pH = 2-13), a wide temperature range (10°C to 50°C) and a long storage time (0d-35d);

[0027] ④ The prepared carbon quantum dots have high selectivity and can specifically identify gallic acid in the presence of multiple interferences (such as ascorbic acid, tartaric acid, citric acid, etc.), and can achieve accurate detection of gallic acid in wine.

[0028] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a 3D mapping surface diagram of carbon quantum dots prepared in Example 1 of the present invention;

[0030] Figure 2 This is a contour map of carbon quantum dots prepared in Example 1 of the present invention;

[0031] Figure 3 This is a transmission electron microscope image of carbon quantum dots prepared in Example 1 of the present invention;

[0032] Figure 4 Particle size distribution diagram of carbon quantum dots prepared in Example 1 of the present invention;

[0033] Figure 5 This is a fluorescence spectrum diagram of the fluorescence intensity of carbon quantum dots in Example 1 as a function of gallic acid concentration;

[0034] Figure 6 The fluorescence quenching effect diagram of Example 1 under different gallic acid concentrations under visible light and ultraviolet light, from left to right are carbon quantum dots, carbon quantum dots + 300 μm / L gallic acid, carbon quantum dots + 700 μm / L gallic acid;

[0035] Figure 7 The linear relationship and nonlinear relationship diagram between gallic acid concentration and carbon quantum dot fluorescence intensity in Example 1, wherein a is a linear relationship diagram and b is a nonlinear relationship diagram;

[0036] Figure 8 pH stability analysis diagram of carbon quantum dots in Example 1 of the present invention;

[0037] Fig. 9 The time stability analysis diagram and temperature stability analysis diagram of the carbon quantum dots in Example 1, wherein a is the time stability analysis diagram and b is the temperature stability analysis diagram;

[0038] Fig.10The selective detection of gallic acid by fluorescent carbon quantum dots in grape leaves in Example 1; wherein A: potassium pyrosulfite, B: tartaric acid, C: malic acid, D: citric acid, E: sodium benzoate, F: ascorbic acid, G: potassium sorbate, H: cyclamate, and I: gallic acid;

[0039] Fig.11 It is a graph of carbon quantum dot fluorescence data under different technical parameters in the comparative example. DETAILED DESCRIPTION

[0040] In the following examples, the reagents described are all commercially available unless otherwise specified, and the following experimental methods and detection methods are all based on existing experimental methods and detection methods unless otherwise specified.

[0041] Example 1 A method for preparing fluorescent carbon quantum dots from grape leaves

[0042] In this embodiment, grape leaf fluorescent carbon quantum dots are prepared by following the following steps in order:

[0043] S1. Collect the natural biomass raw material grape leaves and dry them at 70°C for 4 hours, then crush them to less than 100 meshes, weigh 0.1g of powder and 1g of low eutectic ionic liquid formed by isosorbide-urea (the molar ratio of the two is 1:1) into a beaker, and add 30mL of ultrapure water to form solution A;

[0044] S2. Place solution A in a magnetic levitation stirrer at room temperature and stir for 1 hour until the solution is uniform, and filter to remove the residue to obtain solution B;

[0045] S3, take 10mL of solution B and place it in a 25mL volumetric flask, add ultrapure water to the mark, shake well and transfer to a reactor, react at 220°C for 10h to obtain a brown carbon quantum dot solution C;

[0046] S4. Transfer solution C to a centrifuge tube and centrifuge it at a centrifugal speed of 4000 r / min for 40 minutes, and then filter it with a 0.22 μm microporous filter membrane to obtain an isosorbide-urea modified grape leaf fluorescent carbon quantum dot solution.

[0047] The carbon quantum dots prepared in this example were subjected to a series of tests. Figure 3 The TEM image of the carbon quantum dots is shown in FIG. 1 , from which it can be seen that the carbon quantum dots exhibit good dispersion and uniformity. The particle size distribution of the carbon quantum dots prepared in this example was tested, and the results are shown in FIG. Figure 4 As shown, through data statistics, it can be known that the average particle size is 4.0nm.

[0048] The performance of the carbon quantum dots prepared in this example was measured:

[0049] (I) Grape leaf fluorescent carbon quantum dots used as fluorescent probes to detect gallic acid content

[0050] Prepare gallic acid standard solutions of different concentrations (0.1, 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 300, 500, 700, 900, 1000 μmol / L, respectively), mix the gallic acid standard solution with the carbon quantum dot solution (provided in Example 1) in a ratio of 1:1, and use a fluorescence spectrophotometer to detect the fluorescence intensity of the mixed solution system at different concentrations (such as Figure 5 When the mixed system of 300 μmol / L and 700 μmol / L gallic acid standard solutions was selected, the fluorescence intensity of carbon quantum dots was observed to be significantly quenched under ultraviolet light (as shown in Figure 6 The optimal detection conditions are an excitation wavelength of 320 nm and an emission wavelength of 410 nm.

[0051] The test results show that the fluorescence intensity of carbon quantum dots decreases gradually with the increase of gallic acid concentration. -7 ~1×10 -3 The fluorescence intensity showed a good nonlinear relationship with the gallic acid concentration in the mol / L range, such as Figure 7 As shown, the obtained nonlinear equation is y = 0.9593-0.9290×e^(-x / 230.0295)(R 2 =0.9926), where 1×10 -7 ~1×10 -4 In the range of mol / L, the fluorescence intensity showed a good linear relationship with the gallic acid concentration, and the linear equation was y=0.0039x+0.0177(R 2 =0.9912), and according to the detection limit (LOD) calculation principle (i.e., LOD=3S / K), the detection limit was calculated to be 38nmol / L.

[0052] (II) pH stability analysis of fluorescent carbon quantum dots in grape leaves

[0053] The pH stability of the carbon quantum dots prepared in Example 1 was analyzed. A series of pH stock solutions were obtained by adjusting with 0.1 mol / L HCL and 0.1 mol / L NaOH, so that the pH of the stock solutions were 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13, respectively. The stock solutions of different pH were mixed with the carbon quantum dot solution in a ratio of 1:2, and the fluorescence intensity of the solution system at different concentrations was detected by a fluorescence spectrophotometer. Among them, the optimal detection conditions were an excitation wavelength of 320 nm and an emission wavelength of 410 nm.

[0054] Effect of different pH conditions on the fluorescence intensity of carbon quantum dots Figure 8As shown in the figure, it can be seen that the fluorescence intensity of carbon quantum dots does not change drastically in a wide pH range, and the fluorescence intensity decreases by no more than 5% under strong acid and strong base conditions, indicating that the performance of the prepared carbon quantum dots is stable and will not be affected by the test environment.

[0055] (III) Analysis of the temporal stability of fluorescent carbon quantum dots in grape leaves

[0056] The temporal stability of the carbon quantum dots prepared in Example 1 was analyzed. The carbon quantum dots prepared under the specified conditions were placed for 0d, 7d, 14d, 21d, 28d, and 35d to measure their fluorescence intensity, wherein the best detection conditions were an excitation wavelength of 320nm and an emission wavelength of 410nm.

[0057] like Fig. 9 As shown in (a), the fluorescence intensity of the prepared carbon quantum dots is relatively stable from 0 to four weeks, with an irregular quenching trend. In the fifth week, the fluorescence intensity decreases by about 8%, indicating that the prepared carbon quantum dots have good stability over a long period of time.

[0058] (IV) Analysis of temperature stability of fluorescent carbon quantum dots in grape leaves

[0059] The temperature stability of the carbon quantum dots prepared in Example 1 was analyzed. The carbon quantum dots prepared under the specified conditions were placed at constant temperatures of 10°C, 20°C, 30°C, 40°C, and 50°C for 10 minutes and then their fluorescence intensity was measured. Among them, the best detection conditions were an excitation wavelength of 320nm and an emission wavelength of 410nm.

[0060] The results of the test are as follows Fig. 9 As shown in (b), the fluorescence intensity quenching of the prepared carbon quantum dots is not obvious at 10℃~50℃, and the overall situation is relatively stable.

[0061] (V) Specific response analysis of fluorescent carbon quantum dots in grape leaves

[0062] The specificity and responsiveness of the carbon quantum dots prepared in Example 1 were analyzed. 0.1mmol / L of potassium pyrosulfite, tartaric acid, malic acid, citric acid, sodium benzoate, ascorbic acid, potassium sorbate, and sodium cyclamate were prepared respectively, and mixed with the carbon quantum dot solution in a volume ratio of 1:1. Fluorescence measurement was performed. The results showed that the grape leaf fluorescent carbon quantum dots only responded significantly to gallic acid, and its fluorescence quenching rate was as high as 96%. The fluorescence quenching effect of different substances on gallic acid is compared as follows: Fig.10 shown.

[0063] Example 2-4 Preparation method of grape leaf fluorescent carbon quantum dots

[0064] In this embodiment, grape leaf fluorescent carbon quantum dots are prepared respectively. The preparation process is similar to that in Example 1, except that the parameters in the preparation process are different, as shown in the following table.

[0065] Table 1 Preparation process parameters

[0066]

[0067] Example 5 Study on supernatant, reaction temperature and reaction time during the preparation of grape leaf fluorescent carbon quantum dots

[0068] In this embodiment, a grape leaf fluorescent carbon quantum dot is prepared to select the optimal conditions. The preparation process is similar to that of Example 1, except that the corresponding technical parameters in the preparation process (i.e., step S3) are different, as shown in the following table. Example 2 is intended to select the optimal supernatant volume, Example 3 is intended to select the optimal temperature, and Example 4 is intended to select the optimal time. The fluorescence intensity of the prepared carbon quantum dots is tested and comprehensively compared to select the optimal conditions, such as Fig.11 As shown, considering the equipment and energy consumption issues, the preferred conditions are supernatant volume 10 mL, reaction time 10 h, and reaction temperature 220°C.

[0069] Table 2 Preparation process parameters

[0070]

[0071] Application Example 1: Grape leaf fluorescent carbon quantum dots for the detection of gallic acid in wine

[0072] The carbon quantum dots prepared in Example 1 of the present invention are used to detect gallic acid in an actual sample (pear wine), and the specific detection steps include:

[0073] A1. Dissolve gallic acid in 100 mL ultrapure water and prepare 1×10 -5 mol / L、1×10 -4 mol / L、7×10 -4 mol / L gallic acid solution;

[0074] A2. Take 1 mL of pear wine with a known concentration (the concentration is 218.8 mg / L, the detection method is UV spectrophotometry, and the source is the School of Food and Biology, Hebei University of Science and Technology) and put it into a 100 mL volumetric flask, and dilute to the mark with ultrapure water;

[0075] A3. Take 1 mL of the wine sample to be tested, add 1 mL of the carbon quantum dot solution, mix well, pour into a cuvette, and detect using a fluorescence spectrophotometer;

[0076] A4. Take 1 mL of the wine sample to be tested, add 1 mL of carbon quantum dot solution, and add 1 mL of gallic acid standard solution of different concentrations, mix well, pour into a cuvette, and detect using a fluorescence spectrophotometer.

[0077] The results are shown in Table 3. The recovery results in the pear wine matrix were between 90% and 100%, which showed good detection and recovery effects.

[0078] Table 3 Detection and recovery results of gallic acid in actual wine samples

[0079]

[0080] From the above tests, it can be seen that the carbon quantum dots prepared by the present invention have the advantages of high selectivity, high stability, and high sensitivity. At the same time, they also have relatively considerable detection effect and recovery rate in actual samples. The relative deviation between the measurement result by fluorescence detection method and the known concentration is 5.4%, and the recovery rate is measured by adding standard solution and its range is 90%-100%. It can be seen that this carbon quantum dot can realize the accurate detection of gallic acid in wine samples.

[0081] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. An application of grape leaf fluorescent carbon quantum dots, characterized in that: The grape leaf fluorescent carbon quantum dots are used to quickly detect gallic acid in wine samples; The grape leaf fluorescent carbon quantum dots are prepared according to the following steps: S1. Collecting natural biomass raw material grape leaves, drying and crushing to less than 100 meshes, weighing grape leaf powder and natural low eutectic ionic liquid into a beaker, adding ultrapure water to form solution A, wherein the natural low eutectic ionic liquid is composed of isosorbide and urea in a molar ratio of 1:1; S2. Place solution A in a magnetic levitation stirrer at room temperature and stir for 1 h. Filter to remove the residue to obtain solution B. S3, take 10 mL of solution B and put it into a 25 mL volumetric flask, dilute to the mark with ultrapure water, transfer to a reactor, and react at 180-240°C for 6-12 h to obtain a brown carbon quantum dot solution C; S4. Transfer solution C to a centrifuge tube, centrifuge, and filter with a 0.22 µm microporous filter membrane to obtain a grape leaf fluorescent carbon quantum dot solution.

2. The use of grape leaf fluorescent carbon quantum dots according to claim 1, characterized in that: In step S1, the mass volume ratio of the grape leaf powder to ultrapure water is 1:300 g / mL, and the mass ratio of the grape leaf powder to the natural low eutectic ionic liquid is 1:

10.

3. The use of grape leaf fluorescent carbon quantum dots according to claim 1, characterized in that: In step S4, the centrifugal speed is 4000 r / min and the centrifugal time is 40 min.

4. The use of grape leaf fluorescent carbon quantum dots according to claim 1, characterized in that: In step S1, the drying temperature is 70°C and the drying time is 4 hours.

5. The use of grape leaf fluorescent carbon quantum dots according to claim 1, characterized in that: In step S4, the grape leaf fluorescent carbon quantum dots are spherical nanoparticles with an average particle size of 4.0 nm.

6. The use of grape leaf fluorescent carbon quantum dots according to claim 1, characterized in that: The fluorescence response rate of the carbon quantum dots to gallic acid is as high as 96%.

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