Nitrogen-doped glucosyl fluorescent carbon quantum dot as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped glucosyl fluorescent carbon quantum dot as well as a preparation method and application thereof, and the carbon quantum dot is prepared by taking D-(+) anhydrous dextrose, polyethyleneimine and curcumin as raw materials through hydrothermal reaction. The carbon quantum dot has an excellent effect in an antioxidant capacity test of representative free radicals (DPPH and ABTS), has high electropositivity (+ 39.8 mV), and can react with cell membranes of typical bacteria (staphylococcus aureus and escherichia coli), so that a good sterilization purpose is achieved. The preparation method of the carbon quantum dots is simple and easy to implement, raw materials are economical, and the carbon quantum dots have good economic benefits when applied to production.

Description

Technical Field

[0001] The present invention relates to fluorescent carbon quantum dots and a preparation method and application thereof, in particular to fluorescent carbon quantum dots with a large Stokes shift (>100 nm) having high antioxidant capacity and antibacterial potential and a preparation method and application thereof, belonging to the technical field of fluorescent probes. Background Art

[0002] Various reactive oxygen species (ROS) frequently appear in various areas of society and play an important role. In biology, wounds are often accompanied by inflammatory reactions, which induce the production of ROS. Excessive ROS can lead to strong oxidative stress, damage proteins, and cause cell damage, often manifesting as delayed wound healing and, in severe cases, life-threatening. In food, because foods such as fruits and seafood are easily oxidized, the cost of low-temperature storage is relatively high, especially during transportation and sales, and the preservation effect is still limited. Therefore, the antioxidant preservation of food at room temperature remains a major challenge. In the field of cosmetics, as people's attention to facial health continues to increase, antioxidants can effectively prevent skin aging and the formation of pigmentation. Antioxidants that can scavenge free radicals, inhibit lipid peroxidation, and protect the skin from ultraviolet damage are gaining increasing attention.

[0003] Bacterial infections occur frequently and seriously endanger people's health. Antibiotics are widely used to inhibit bacterial diseases, but the abuse of antibiotics can lead to the emergence of drug-resistant bacteria. In addition to antibiotics, precious metal nanoparticles (NPs) (gold, silver, palladium, ruthenium, platinum) and metal oxide nanoparticles (ZnO, TiO2 and CuO) have been used as antibacterial alternatives because of their broad-spectrum antibacterial ability and high antibacterial properties. However, these nanobactericides are hindered in clinical application due to their high cytotoxicity, high cost, and long-term retention in the body. Therefore, it is crucial to develop non-toxic and environmentally friendly antibacterial agents to effectively kill bacteria.

[0004] Traditional Chinese Medicine (TCM), a treasure of ancient Chinese science, demonstrates significant advantages in disease prevention and treatment. Chinese herbal medicines, as essential components of TCM and clinical practice, hold significant value. Curcumin (Cur), a diketone compound extracted from the rhizomes of plants in the Zingiberaceae and Araceae families, can enhance the body's immune system and exhibit antioxidant, anti-inflammatory, lipid-lowering, and anti-cancer properties. However, due to its low bioavailability and hydrophobicity, curcumin has not been widely used in practical medical applications.

[0005] Polyethyleneimine (PEI) is an amphiphilic cationic polymer. Due to its abundant primary, secondary, and tertiary amines in its molecular structure, PEI has excellent solubility in water. Its abundant surface amino groups provide the basis for its high positive charge. This high positive charge is generally exploited as an antibacterial agent against both Gram-negative and Gram-positive bacteria, interacting with and disrupting the negatively charged bacterial cell membranes to achieve antibacterial effects. Furthermore, the abundance of amino groups provides numerous reactive sites for reactions in which PEI participates as a raw material.

[0006] Carbon dots (CDs) have excellent properties such as small size, easy surface functionalization, high stability, strong hydrophilicity, good biocompatibility and low toxicity. The interaction between the hydrophobic groups and the hydrophobic layer on their surface, as well as the hydrophilic layer exposed to the outside, protect the internal structure of CDs, improve their water solubility and stability, while retaining the stable and unique optical properties of CDs. They have been widely studied in various fields.

[0007] Existing methods include using quaternary ammonium salt curcumin to prepare carbon quantum dots (CN114106823A), which achieved effective bactericidal performance but failed to demonstrate antioxidant capacity; using curcumin alone as the sole carbon source and functional substance to prepare carbon dots (CN110891557A), which only studied antiviral activity but lost its antibacterial and antioxidant properties; using polyethyleneimine alone as a carbon source to synthesize carbon dots (CN115159506A), which only explored the nitrogen-doped multicolor fluorescence of polyethyleneimine. The research found that the carbon dots had no antibacterial and antioxidant properties; related researchers used polyethyleneimine as an independent carbon source to synthesize carbon dots (CN106829922A), and also only explored the optimal preparation method and the effect of different pH values on fluorescence intensity, without involving the exploration of antibacterial and antioxidant properties; related personnel used polyethyleneimine and curcumin to prepare carbon dots (CN118165724A), and used the traditional Chinese medicine properties of curcumin to study the anticancer effect and promote the tumor inhibition process, but also did not reflect the antibacterial and antioxidant properties.

[0008] Existing PEI-based carbon dots or curcumin-based carbon dots are mostly based on a single carbon source and lack synergistic effects with small molecule monosaccharides (such as glucose). This results in limited carbon dot carbonization ability and antioxidant performance, and difficulty balancing charge density and biosafety. Therefore, the use of D-(+) anhydrous glucose as a common carbon source increases the carbon dot formation ability, overcoming the problem of low carbon dot yield. At the same time, the Stokes shift of the carbon dots prepared is small (<100nm), and the distance between the fluorescence excitation spectrum position and the fluorescence emission spectrum position is close, resulting in the disadvantage of fluorescence excitation self-absorption during the fluorescence emission process, which greatly limits its application in fluorescence. Therefore, the preparation of fluorescent carbon dots with large Stokes shifts that have both efficient antioxidant ability and antibacterial potential has important application and research significance, and there has been no report on the antibacterial and antioxidant effects of glucose-based CDs based on large Stokes shifts. Summary of the Invention

[0009] Purpose of the invention: One purpose of the present invention is to provide a nitrogen-doped glucose-based fluorescent carbon quantum dots. Another purpose of the present invention is to provide a method for preparing the nitrogen-doped glucose-based fluorescent carbon quantum dots. The last purpose of the present invention is to provide the application of the nitrogen-doped glucose-based fluorescent carbon quantum dots in antibacterial and antioxidant applications.

[0010] Technical solution: The nitrogen-doped glucose-based fluorescent carbon quantum dots described in the present invention are prepared by hydrothermal reaction using D-(+) anhydrous glucose, polyethyleneimine, and turmeric as raw materials.

[0011] The method for preparing nitrogen-doped glucose-based fluorescent carbon quantum dots of the present invention comprises the following preparation steps:

[0012] D-(+) anhydrous glucose, polyethyleneimine and curcumin were dissolved in water, ultrasonically treated, hydrothermally reacted, cooled, ultrasonically treated again, and the supernatant was filtered, dialyzed, and freeze-dried.

[0013] Furthermore, the mass ratio of D-(+) anhydrous glucose, polyethyleneimine and curcumin is 1:(3-9):(3-9), and the ultrasonic treatment time is more than 30 minutes. The temperature of the hydrothermal reaction is 160-200°C, and the hydrothermal reaction time is 6-14 hours. The ultrasonic treatment is again carried out for more than 30 minutes. The supernatant is centrifuged at 10,000 rpm for 40 minutes and then filtered with a 0.22 μm membrane. Dialysis is performed in a dialysis bag with a molecular cutoff of 1,000 for more than 24 hours.

[0014] The present invention also includes the use of the nitrogen-doped glucose-based fluorescent carbon quantum dots in antibacterial and / or antioxidant applications.

[0015] Furthermore, the antioxidant is anti-DPPH free radical and / or ABTS free radical. The bacteria are Staphylococcus aureus and / or Escherichia coli.

[0016] The present invention uses polyethyleneimine, D-(+) anhydrous glucose and curcumin as composite precursors, and prepares carbon dots with high positive charge and high antioxidant capacity through a one-step hydrothermal method. This design combines the positive charge characteristics of PEI's amino groups, the carbon skeleton construction ability of glucose and the natural antioxidant activity of curcumin. Through the synergistic carbonization of PEI and glucose, a positively charged carbon core rich in amino groups on the surface is formed, which enhances electrostatic adsorption with microbial membranes; curcumin is embedded in the carbon dot structure through π-π stacking or hydrogen bonding, avoiding photodegradation and improving antioxidant stability and water solubility, solving the problem of low utilization due to its poor solubility; abandoning metal catalysts and adopting a green synthesis process, it meets the safety requirements of food and biomedical applications. Compared with the existing technology, the method of the present invention has significant advantages in charge regulation, antioxidant efficacy and process compatibility, providing a new strategy for the efficient delivery and functional application of natural active ingredients. At the same time, the rich functional groups and double bonds provide a good foundation for the surface modification of CDs. The carbon dots prepared in the present invention using D-(+) anhydrous glucose, curcumin and polyethyleneimine as precursors have excellent antibacterial and antioxidant properties and can be used in a wider range of application scenarios. The lack of any one of the precursors cannot achieve similar excellent antibacterial and antioxidant effects as those of the present application.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The nitrogen-doped glucose-based fluorescent carbon quantum dots of the present invention utilize polyethyleneimine as a nitrogen source and a source of positive charge, curcumin as a carbon source and antioxidant, and D-(+) anhydrous glucose as a synergistic carbon source to prepare a nitrogen-doped glucose-based fluorescent carbon quantum dot (GCP-CDs) with high positive charge and high antioxidant capacity. The optimal fluorescence excitation peak position of the GCP-CDs is at 340nm, the optimal fluorescence emission peak position is at 467nm, and its Stokes shift is 127nm. The large shift greatly avoids the disadvantages of fluorescence excitation self-absorption in fluorescence test-related applications. The GCP-CDs prepared by the present invention have excellent results in the antioxidant capacity test of representative free radicals (DPPH and ABTS), and the invention has high positive charge (+39.8mV), which can interact with the cell membranes of typical bacteria (Staphylococcus aureus and Escherichia coli), thereby achieving a good bactericidal purpose. The preparation method of the carbon quantum dots of the present invention is simple and easy, the raw materials are economical, and application in production will have good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the synthesis and antioxidant capacity determination of carbon quantum dots of the present invention;

[0019] Figure 2 The transmission electron microscope image and particle size distribution diagram of the carbon quantum dots prepared in Example 1;

[0020] Figure 3 The Fourier transform infrared spectra of polyethyleneimine, curcumin, D-(+) anhydrous glucose and the carbon quantum dots prepared in Example 1 are shown;

[0021] Figure 4 This is the X-ray photoelectron spectrum of the carbon quantum dots prepared in Example 1;

[0022] Figure 5 The UV-visible absorption spectrum, fluorescence excitation and fluorescence emission spectra of the carbon quantum dots prepared in Example 1; the fluorescence emission spectra at different fluorescence excitation wavelengths and the fluorescence chromaticity diagram;

[0023] Figure 6 This is a graph showing the fluorescence stability of the carbon quantum dots prepared in Example 1 under different pH conditions;

[0024] Figure 7 The fluorescence intensity change diagram of carbon quantum dots prepared with different raw material ratios in Example 1 and Example 2;

[0025] Figure 8 The DPPH free radical scavenging rate and Zeta potential of carbon quantum dots prepared with different raw material ratios in Example 1 and Example 2 are shown;

[0026] Figure 9 The fluorescence intensity change diagram of carbon quantum dots prepared at different hydrothermal temperatures in Example 1 and Example 3

[0027] Figure 10 The DPPH free radical scavenging rate and Zeta potential of carbon quantum dots prepared at different hydrothermal temperatures in Example 1 and Example 3 are shown;

[0028] Figure 11 The fluorescence intensity change diagram of carbon quantum dots prepared under different hydrothermal times in Example 1 and Example 4

[0029] Figure 12 The DPPH free radical scavenging rate and Zeta potential of the carbon quantum dots prepared at different hydrothermal times in Example 1 and Example 4 are shown;

[0030] Figure 13 This is a test chart of the DPPH free radical scavenging ability of carbon quantum dots in Example 5;

[0031] Figure 14 This is a test chart of the ability of carbon quantum dots to scavenge ABTS free radicals (antioxidant performance) in Example 5;

[0032] Figure 15 This is a comparison chart of the antibacterial ability of carbon quantum dots at different concentrations against Escherichia coli and Staphylococcus aureus in Example 6. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0034] Example 1

[0035] 0.1g of D-(+)-glucose (D-(+)-glucose), 0.3g of polyethyleneimine, and 0.9g of curcumin were added to a beaker, followed by 35mL of ultrapure water. The mixture was stirred thoroughly and sonicated for 40 minutes. The fully dispersed solution was transferred to a polytetrafluoroethylene-lined high-pressure hydrothermal reactor and placed in a preheated 180°C oven for 10 hours. After the reaction, the reactor was removed and cooled to room temperature. The reaction solution was removed and sonicated again for 30 minutes. The supernatant was collected and the resulting aqueous dispersion was centrifuged at 10,000 rpm for 40 minutes and filtered through a 0.22μm membrane filter. After filtration, the solution was dialyzed for 24 hours in a dialysis bag with a molecular weight cutoff of 1000 to obtain a blue-green fluorescent carbon quantum dot solution. Finally, the dialyzed solution was freeze-dried in a freeze dryer to obtain a dark brown nitrogen-doped glucose-based fluorescent carbon quantum dot powder (GCP-CDs).

[0036] The carbon quantum dot solution prepared in this example was dripped onto a copper mesh and placed in a constant temperature incubator for 12 hours for transmission electron microscopy analysis and particle size analysis. The results are as follows: Figure 2 As shown, Figure 2 The transmission electron microscope image and particle size distribution diagram of the carbon quantum dots prepared in Example 1 are shown in Figures a and b. Figure 2 As can be seen in a, the carbon quantum dots are evenly distributed and Figure 2 As can be seen from the upper right illustration in middle a, GCP-CDs have a clear lattice structure with a lattice spacing of 0.21 nm, which matches the (100) crystal plane of graphite. Figure 2 From Figure b, we can see that the average size of the GCP-CDs is 2 to 4 nm.

[0037] Infrared spectroscopy analysis was performed on polyethyleneimine, curcumin, D-(+) anhydrous glucose and the carbon quantum dots prepared in this example. The results are as follows: Figure 3 shown. Figure 3 The infrared spectra of polyethyleneimine, curcumin, D-(+) anhydrous glucose and carbon dots prepared in Example 1 are shown in Figure 1, where the horizontal axis is the wavelength and the vertical axis is the transmittance. Figure 3 As shown, at 3420cm -1 There is a stretching vibration peak of OH at 3210 cm -1 The stretching vibration peaks of C=O and C=C are at 1630 cm -1 and 1512cm -11120cm -1 The absorption peak of CN is at 755cm, and the bending vibration peak of CH in the benzene ring is at 755cm -1 In summary, infrared spectroscopy proved that polyethyleneimine and curcumin were successfully doped into the carbon quantum dots to form corresponding chemical bonds.

[0038] The carbon quantum dots prepared in this example were subjected to X-ray diffraction analysis, and the results were as follows: Figure 4 shown. Figure 4 The X-ray diffraction (XRD) pattern of the carbon dots prepared in Example 1 is shown in FIG. Figure 4 It can be seen that the XRD spectrum of GCP-CDs shows a diffraction bun peak centered at 2θ=23°. The interlayer spacing is This may be related to the (002) lattice space of graphitic carbon, which is a typical characteristic of graphitic carbon materials. Therefore, the above results further prove that GCP-CDs have a graphite-like structure.

[0039] The carbon quantum dots prepared in this example were analyzed by UV-visible absorption spectrum, fluorescence excitation spectrum and fluorescence emission spectrum. Figure 5 shown. Figure 5 The UV-visible absorption spectrum, fluorescence excitation and fluorescence emission spectrum of the carbon quantum dots prepared in Example 1 are shown in Figure 1, where a is the UV-visible absorption spectrum, where the horizontal axis is wavelength, the left vertical axis is absorbance, and the right vertical axis is fluorescence intensity; b is the fluorescence emission spectrum at different fluorescence excitation wavelengths, where the horizontal axis is wavelength and the vertical axis is fluorescence intensity; c is the fluorescence chromaticity diagram. Figure 5 As can be seen in a, the UV-visible absorption peak of GCP-CDs at 280 nm corresponds to the aromatic sp 2 The absorption peak at 348nm corresponds to the n-π transition of C=O / C-NH2. * transition, which provides the ability to emit at longer wavelengths. Figure 5 It can also be clearly seen in Figure b that the optimal fluorescence excitation peak position of GCP-CDs is at 340nm, and the optimal fluorescence emission peak position is at 467nm. Figure 5 It is not difficult to see in Figure c that the carbon dot solution (0.06 mg / mL) appears slightly yellow under visible light and exhibits bright blue-green fluorescence under 365 nm ultraviolet light.

[0040] The fluorescence stability of the carbon quantum dots prepared in this example was analyzed under different pH conditions. Figure 6 shown. Figure 6 The fluorescence stability diagram of the carbon quantum dots prepared in Example 1 under different pH conditions is shown in FIG. 1 , wherein the horizontal axis is the wavelength and the vertical axis is the fluorescence intensity; Figure 6As can be seen, the fluorescence intensity of the GCP-CDs is higher under acidic conditions (pH ≤ 3.5), stable under pH conditions between 4.5 and 10.5, and lower under alkaline conditions (pH > 10.5). This is because in a strongly acidic environment, the surface functional groups of the carbon quantum dots, such as carboxyl (-COOH) and amino (-NH2), undergo protonation, increasing the surface positive charge. This enhances the fluorescence intensity by altering electron transition pathways or reducing nonradiative recombination. Within the pH range of 4.5 to 10.5, the surface functional groups of the carbon quantum dots are in a dynamic equilibrium. When the pH approaches the pKa value of the functional groups, the surface electron cloud distribution stabilizes, the fluorescence intensity changes less, and the fluorescence is relatively stable. In a strongly alkaline environment, the carboxyl groups are completely deprotonated, and the amino groups are also completely deprotonated to -NH2, increasing the surface negative charge. This leads to enhanced dispersion of the GCP-CDs due to electrostatic repulsion. At the same time, excessive negative charge can cause changes in the surface electronic structure, forming new nonradiative recombination centers and reducing the fluorescence intensity.

[0041] Example 2

[0042] The preparation process was the same as that in Example 1, except that the mass ratios of D-(+) anhydrous glucose, polyethyleneimine, and curcumin were 1:9:3, 1:6:3, 1:3:3, and 1:3:6, respectively; the other steps and conditions were the same as those in Example 1, and four groups of nitrogen-doped glucose-based fluorescent carbon quantum dot powders were obtained.

[0043] The fluorescence emission spectra of the nitrogen-doped glucose-based carbon quantum dots obtained in Example 1 and this example were tested, and the corresponding fluorescence intensity at 467 nm was as follows: Figure 7 As shown by Figure 7 It can be seen that when the mass ratio of D-(+) anhydrous glucose, polyethyleneimine and curcumin is 1:3:9, the fluorescence intensity of the prepared carbon dots is the highest.

[0044] The nitrogen-doped glucose-based carbon quantum dots obtained in Example 1 and this example were tested for DPPH radical scavenging efficiency. Specifically, 0.1 mmol / L DPPH ethanol solution was first prepared, and the carbon quantum dots prepared in Example 1 and this example were diluted to 180 μg / mL. The carbon dots and DPPH ethanol solution were mixed at a volume ratio of 1:3. After incubation in the dark for 30 minutes, the absorbance at 517 nm was measured and recorded using an ultraviolet spectrophotometer. The results are as follows: Figure 8 shown. Figure 8 The DPPH free radical scavenging rate and Zeta potential diagram of carbon quantum dots prepared with different raw material ratios in Example 1 and Example 2, wherein CDs-DPPH is a DPPH scavenging rate diagram and CDs-Zeta is a potential diagram; Figure 8It was found that when the mass ratio of D-(+) anhydrous glucose, polyethyleneimine and curcumin was 1:3:9, the DPPH free radical scavenging efficiency was the highest, and the Zeta potential was the most moderate (+39.6 mV) after meeting the potential requirements for sterilization in vivo.

[0045] Example 3

[0046] The preparation process was the same as that in Example 1, except that the fully dispersed solution was transferred to the polytetrafluoroethylene liner of a high-pressure hydrothermal reactor and placed in an oven preheated to different temperatures for reaction, i.e., the hydrothermal reaction temperatures were 160°C, 170°C, 190°C, and 200°C, respectively; the other steps and conditions were the same as those in Example 1, and four groups of nitrogen-doped glucose-based fluorescent carbon quantum dot powders were obtained.

[0047] The nitrogen-doped glucose-based carbon quantum dots obtained in this example and example 1 were subjected to fluorescence emission spectrum testing. The fluorescence intensity corresponding to 467 nm was as follows: Figure 9 As shown by Figure 9 It can be seen that the fluorescence intensity of carbon dots is better when the hydrothermal reaction temperature is 160-200°C, and the fluorescence intensity increases from a low point and then gradually decreases. In Example 1, the fluorescence intensity of carbon dots prepared at a hydrothermal reaction temperature of 180°C is the highest.

[0048] The DPPH free radical scavenging experiment was the same as in Example 2, and the results were as follows: Figure 10 As shown, Figure 10 The DPPH free radical scavenging rate and Zeta potential diagrams of carbon quantum dots prepared at different hydrothermal temperatures in Example 1 and Example 3 are shown, wherein CDs-DPPH is the DPPH scavenging rate diagram and CDs-Zeta is the potential diagram. Figure 10 It can be seen that the DPPH radical scavenging efficiency and Zeta potential of carbon dots are better at the hydrothermal reaction temperature of 160-200℃. The DPPH radical scavenging efficiency of carbon dots prepared at 180℃ is also relatively moderate, and the Zeta potential is also the most moderate (+39.6mV) after meeting the potential requirements for sterilization in vivo.

[0049] Example 4

[0050] The preparation process was the same as that in Example 1, except that the hydrothermal reaction times were 6, 8, 12, and 14 h, respectively; the other steps and conditions were the same as those in Example 1, and four groups of nitrogen-doped glucose-based fluorescent carbon quantum dot powders were obtained.

[0051] Fluorescence emission spectra of nitrogen-doped glucose-based carbon quantum dots in Example 1 and this example were tested, and the corresponding fluorescence intensity at 467 nm was as follows: Figure 11 Shown by Figure 11 It can be seen that the fluorescence intensity of carbon dots prepared with a hydrothermal reaction time of 6-14 h increases from a low point and then gradually decreases, and the fluorescence intensity of carbon dots prepared with a hydrothermal reaction time of 10 h is the highest.

[0052] The DPPH free radical scavenging experiment was the same as in Example 2, and the results were as follows: Figure 12 shown. Figure 12 The DPPH free radical scavenging rate and Zeta potential diagrams of the carbon quantum dots prepared under different hydrothermal times in Example 1 and Example 4 are shown, wherein CDs-DPPH is the DPPH scavenging rate diagram and CDs-Zeta is the potential diagram. Figure 12 It can be seen that when the hydrothermal reaction time is 6-14h, the DPPH free radical scavenging efficiency increases from a low point and then gradually decreases. Among them, the DPPH free radical scavenging efficiency is the highest after the reaction for 10h, and the Zeta potential at this time is also the most moderate (+39.6mV) after meeting the potential requirements for sterilization in the organism.

[0053] Based on Examples 2-4, it can be seen that the mass ratio of anhydrous glucose, polyethyleneimine and curcumin is 1:3:9, and the most suitable hydrothermal reaction temperature is 180°C and the reaction time is 10 hours.

[0054] Example 5 Determination of the Antioxidant (Free Radical Scavenging) Capacity of Nitrogen-Doped Glucose-Based Carbon Quantum Dots

[0055] (1) Eliminate DPPH free radicals

[0056] In order to prove the feasibility of the antioxidant experimental platform, the nitrogen-doped glucose-based carbon quantum dots prepared in Example 1 were configured with GCP-CDs solutions of different concentrations from 0 to 220 μmol / L, and 0.1 mmol / L DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) ethanol solution. The carbon dot aqueous solution and 0.1 mmol / L DPPH ethanol solution were mixed in a volume ratio of 1:3 and incubated in the dark for 30 minutes before UV-visible spectroscopy characterization. The DPPH free radical scavenging efficiency was calculated by the absorbance of the solution at 517 nm. At the same time, the carbon dot solution was replaced with pure water as a blank group for comparison. Comparing the changes in the UV-visible absorption spectrum intensity, the results are as follows: Figure 13 shown. Figure 13 The graph is a test graph of the DPPH free radical scavenging ability of carbon quantum dots in Example 5, wherein a is a UV-visible absorption curve of the DPPH free radical scavenging ability of carbon quantum dots at different concentrations, and b is a dot-line graph of the free radical scavenging ability at a UV-visible absorption wavelength of 517 nm. Figure 13 It can be seen that the carbon dots have a high ability to scavenge DPPH free radicals. When the carbon dots concentration is 220 μg / mL, the DPPH scavenging efficiency reaches the highest, which is 86.83%.

[0057] (2) Eliminate ABTS free radicals

[0058] The nitrogen-doped carbon dots prepared in Example 1 were mixed with GCP-CDs solutions of different concentrations (0-220 μmol / L) and an ABTS (2,2'-azino-di(3-ethyl-benzothiazole-6-sulfonic acid) diammonium salt) aqueous solution with an absorbance A of 0.7±0.05 at 734 nm. The carbon dot aqueous solution and the ABTS aqueous solution were mixed at a volume ratio of 1:10 and incubated in the dark for 20 minutes before UV-visible spectroscopy characterization. The ABTS free radical scavenging efficiency was calculated by the absorbance of the solution at 734 nm. At the same time, the carbon dot solution was replaced with pure water as a blank group for comparison. The changes in the UV-visible absorption spectrum intensity were compared, and the results are as follows: Figure 14 shown. Figure 14 The graph is a test graph of the ability of carbon quantum dots to scavenge ABTS free radicals (antioxidant performance) in Example 5, wherein a is a UV-visible absorption curve of the ability of carbon quantum dots to scavenge ABTS free radicals at different concentrations, and b is a dot-line graph of the free radical scavenging ability at a UV-visible absorption wavelength of 734 nm. Figure 14 It can be seen that the carbon dots have a high ability to scavenge ABTS free radicals. When the carbon dots concentration reaches 200 μg / mL, the ABTS free radical scavenging efficiency does not change much. When the concentration is 220 μg / mL, the ABTS scavenging efficiency reaches the highest, which is 98.67%.

[0059] Example 6 Determination of the antibacterial ability of nitrogen-doped glucose-based carbon quantum dots

[0060] In order to demonstrate the antibacterial feasibility of the GCP-CDs antibacterial platform, the GCP-CDs prepared in Example 1 were subjected to Gram-negative bacteria (Escherichia coli: Figure 15 a) and Gram-positive bacteria (Staphylococcus aureus: Figure 15 c) Antibacterial ability test. The inhibitory activity of GCP-CDs against Escherichia coli and Staphylococcus aureus was determined by the plate method. First, the frozen Escherichia coli (ATCC 8739) and Staphylococcus aureus (ATCC 25923) strains (both purchased from Putian Tongchuang Biotechnology Co., Ltd.) were taken out of the -80°C refrigerator, thawed at room temperature, inoculated in solid culture medium, and incubated in an ultra-clean workbench for 16 hours. Then, some bacteria were picked, and single colonies of bacteria were obtained using the streak plate method. Take a colony and culture it in LB medium overnight. GCP-CDs solutions of different concentrations (0, 100 μg / mL) were incubated with bacteria (106 CFU / mL) and stored at 37°C for 3 hours. Then, 100 μL of bacterial suspension was spread on the solid culture medium, incubated at 37°C overnight, and the colony count was determined. The results are as shown in the figure. Figure 15 shown.

[0061] Figure 15The graph is a comparison of the antibacterial ability of carbon quantum dots at different concentrations against Escherichia coli and Staphylococcus aureus in Example 6, wherein a is a graph showing the sterilization of Escherichia coli at a concentration of 0 μg / mL, b is a graph showing the sterilization of Escherichia coli at a concentration of 100 μg / mL, c is a graph showing the sterilization of Staphylococcus aureus at a concentration of 0 μg / mL, and d is a graph showing the sterilization of Staphylococcus aureus at a concentration of 100 μg / mL. Figure 15 The results showed that the sterilization rate of Escherichia coli could reach 87% at a concentration of 100 μg / mL of GCP-CDs. Figure 15 b), the sterilization rate against Staphylococcus aureus can be as high as 99% ( Figure 15 According to the results of zeta potential measurement ( Figure 8 、 Figure 10 、 Figure 12 The GCP-CDs prepared were positively charged, while Staphylococcus aureus was negatively charged. The antibacterial mechanism of GCP-CDs may be that the positive surface charge generates strong static electricity with the negatively charged bacterial membrane, leading to membrane damage and bacterial death. Furthermore, the small particle size of the carbon dots allows them to more easily penetrate bacterial cells, leading to bacterial death.

Claims

1. A nitrogen-doped glucose-based fluorescent carbon quantum dot, characterized in that: The nitrogen-doped glucose-based fluorescent carbon quantum dots are prepared by hydrothermal reaction using D-(+) anhydrous glucose, polyethyleneimine and curcumin as raw materials.

2. The method for preparing nitrogen-doped glucose-based fluorescent carbon quantum dots according to claim 1, wherein: The method comprises the following preparation steps: D-(+) anhydrous glucose, polyethyleneimine and curcumin were dissolved in water, ultrasonically treated, hydrothermally reacted, cooled, ultrasonically treated again, and the supernatant was filtered, dialyzed, and freeze-dried.

3. The preparation method according to claim 2, characterized in that The mass ratio of D-(+) anhydrous glucose, polyethyleneimine and curcumin is 1:(3-9):(3-9), and the ultrasonic treatment time is more than 30 minutes.

4. The preparation method according to claim 2, characterized in that The temperature of the hydrothermal reaction is 160-200° C., and the time of the hydrothermal reaction is 6-14 hours.

5. The preparation method according to claim 2, characterized in that Ultrasonic treatment was performed again for more than 30 min.

6. The preparation method according to claim 2, characterized in that The supernatant was centrifuged at 10,000 rpm for 40 min and then filtered through a 0.22 μm membrane.

7. The preparation method according to claim 2, characterized in that Dialysis was performed in a dialysis bag with a molecular cut-off of 1000 for more than 24 hours.

8. Use of the nitrogen-doped glucose-based fluorescent carbon quantum dots according to claim 1 in antibacterial and / or antioxidant applications.

9. The application according to claim 8, characterized in that: Antioxidant is anti-DPPH free radical and / or ABTS free radical.

10. The application according to claim 8, characterized in that: The bacteria are Staphylococcus aureus and / or Escherichia coli.

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