Quaternary ammonium salt functionalized licorice carbon quantum dots antibacterial material, and preparation method and application thereof

Abstract

The application belongs to the technical field of bacteriostatic material preparation, and discloses a quaternary ammonium salt functionalized licorice carbon quantum dot bacteriostatic material, a preparation method thereof and an application thereof. The preparation method comprises the following steps: mixing licorice, water and a quaternary ammonium salt solution, and performing hydrothermal reaction to obtain the quaternary ammonium salt functionalized licorice carbon quantum dot bacteriostatic material. The obtained bacteriostatic material has strong bacteriostatic activity on common foodborne disease pathogenic bacteria, gram-positive staphylococcus aureus and gram-negative escherichia coli, and lays a foundation for further application in the field of food safety.

Description

Technical Field

[0001] The present invention relates to the technical field of antibacterial material preparation, and in particular to a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, a preparation method and application thereof. Background Art

[0002] Foodborne illnesses and other related diseases caused by bacterial infections affect millions of people each year. Currently, antibiotics are the most common treatment for bacterial infections. However, the widespread use and even overuse of antibiotics of varying levels can easily lead to bacterial resistance, even leading to the emergence of superbugs. This makes treatment more difficult and increases the threat to food safety and human health.

[0003] Currently, antimicrobial technologies are commonly used in the food industry to inhibit microbial growth and extend food shelf life. Common food antimicrobial technologies include traditional thermal sterilization, novel thermal sterilization, non-thermal physical sterilization, and chemical sterilization. Traditional and novel thermal sterilization technologies are commonly used to sterilize heat-resistant foods. However, the high temperatures required by traditional thermal sterilization can cause thermochemical reactions such as color changes, destruction of nutrients, flavor changes, and loss of uniformity in the food system. Lower temperatures can result in incomplete sterilization. Furthermore, novel thermal sterilization technologies often require inadequate temperature and time process parameters. Low temperatures lead to poor sterilization effectiveness, while high temperatures can easily damage heat-sensitive proteins in food, causing nutrient loss and consuming excessive amounts of energy. Non-thermal physical sterilization technologies are used to sterilize heat-sensitive foods. However, these technologies can lead to decreased sensory quality, poor sterilization penetration, and incomplete sterilization. This can make it easier for food contaminated with nuclear radiation to be consumed, increasing the risk of illness. Chemical sterilization technologies are often used to sterilize packaging materials, equipment, and production plants. However, the dosage of additives used in chemical sterilization technologies is difficult to control, and inadequate supervision and control can easily lead to excessive dosages during production. Irregular operations, such as improper use of additives during production, can also leave chemical residues, increasing risks to human health and safety. As can be seen, different sterilization technologies have different mechanisms of action, influencing factors, applicable conditions, limitations, and potential safety hazards, necessitating careful and rational selection of sterilization technologies. Furthermore, due to the complexity and high cost of the equipment used, sterilization technologies have not been widely adopted in the food industry.

[0004] Therefore, sterilization also requires the selection of new antibacterial materials with stronger biosafety to reduce the risk of bacterial exposure. Summary of the Invention

[0005] The purpose of the present invention is to provide a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material and its preparation method and application, so as to solve many problems existing in existing sterilization technology.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, comprising the following steps:

[0008] Licorice, water and quaternary ammonium salt solution are mixed and subjected to hydrothermal reaction to obtain quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material.

[0009] Preferably, in the method for preparing the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, the quaternary ammonium salt contained in the quaternary ammonium salt solution is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride.

[0010] Preferably, in the method for preparing the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, the mass volume ratio of the licorice to the quaternary ammonium salt solution is 0.05-1.5 g: 0.05-1.5 mL.

[0011] Preferably, in the method for preparing the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, the mass fraction of the quaternary ammonium salt contained in the quaternary ammonium salt solution is 40-50%.

[0012] Preferably, in the method for preparing the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, the temperature of the hydrothermal reaction is 180-200° C., and the time of the hydrothermal reaction is 12-14 hours.

[0013] Preferably, in the method for preparing the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, the following post-treatments are further performed after the hydrothermal reaction: centrifugation and concentration.

[0014] Preferably, in the method for preparing the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, the mass volume ratio of the licorice to the water is 0.05-1.5 g:1-3 mL.

[0015] The present invention also provides a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material prepared by the preparation method of the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material.

[0016] The present invention also provides an application of the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material in the food field.

[0017] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention selects licorice, a traditional Chinese medicine with a wide distribution, easy collection, biosafety and medicinal and edible properties, as a carbon source, and uses dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (Si-QAC) to modify the carbon source to prepare a new quaternary ammonium salt-functionalized licorice carbon quantum dot antibacterial material (abbreviated as QG-CDs). The material intervenes with selected typical foodborne disease pathogens, Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The antibacterial activity of quaternary ammonium salt-functionalized licorice carbon quantum dots at different concentrations is investigated, and its antibacterial mechanism is preliminarily explored. The antibacterial activity of quaternary ammonium salt-functionalized licorice carbon quantum dots is comprehensively evaluated. It is found that the antibacterial material obtained by the present invention has strong antibacterial activity against common foodborne disease pathogens, Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, laying the foundation for its further application in the field of food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0020] Figure 1 This is a transmission electron microscope image of the licorice carbon quantum dot material obtained in Comparative Example 1;

[0021] Figure 2 This is a transmission electron microscope image of the licorice carbon quantum dot material obtained in Comparative Example 2;

[0022] Figure 3 This is a transmission electron microscope image of the licorice carbon quantum dot material obtained in Example 1;

[0023] Figure 4 This is a transmission electron microscope image of the licorice carbon quantum dot material obtained in Example 2;

[0024] Figure 5 The analysis results of the constituent elements of the licorice carbon quantum dot material obtained in Comparative Example 1 are as follows;

[0025] Figure 6 The analysis results of the constituent elements of the licorice carbon quantum dot material obtained in Comparative Example 2 are as follows;

[0026] Figure 7 The composition element analysis results of the licorice carbon quantum dot material obtained in Example 1;

[0027] Figure 8 The composition element analysis results of the licorice carbon quantum dot material obtained in Example 2;

[0028] Figure 9 FT-IR spectra of the licorice carbon quantum dot materials obtained in Comparative Examples 1 and 2 and Examples 1 and 2;

[0029] Figure 10The XRD analysis diagram of the licorice carbon quantum dot materials obtained in Comparative Examples 1-2 and Examples 1-2;

[0030] Figure 11 The UV spectra of the licorice carbon quantum dot materials obtained in Comparative Examples 1-2 and Examples 1-2 are shown;

[0031] Figure 12 The fluorescence spectra of the licorice carbon quantum dot materials obtained in Comparative Examples 1 and 2 and Examples 1 and 2 are shown, wherein (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Example 1, and (d) is Example 2;

[0032] Figure 13 The comprehensive evaluation results of the antibacterial activity of four licorice carbon quantum dot materials are shown in Figure 1. Among them, a is the culture result of Staphylococcus aureus with 0 mg / mL G-CDs, b is the culture result of Staphylococcus aureus with 17 mg / mL G-CDs 180 The culture results of Staphylococcus aureus and 17 mg / mL G-CDs are shown in Figure 2. 200 d is the culture results of Staphylococcus aureus and 50μg / mL QG-CDs 200 The culture results of Staphylococcus aureus and 20μg / mL QG-CDs are shown in Figure 5. 200 The culture results of Staphylococcus aureus and 0 μg / mL QG-CDs are shown in Figure 2. 200 The culture results of Staphylococcus aureus and 1μg / mL QG-CDs 200 The culture results of E. coli and 50 μg / mL QG-CDs are shown in Figure 2. 200 The culture results of E. coli and 20 μg / mL QG-CDs are shown in Figure 2. 200 The culture results of E. coli and 0 μg / mL QG-CDs are shown in Figure 2. 200 The culture results of E. coli and 1 μg / mL QG-CDs are shown in Figure 2. 200 The culture results of E. coli, l is the culture results of E. coli with 0 mg / mL G-CDs, m is the culture results of E. coli with 17 mg / mL G-CDs 180 The culture results of E. coli and 17 mg / mL G-CDs 200 The culture results of o are Staphylococcus aureus and 50μg / mL QG-CDs 180 The culture results of Staphylococcus aureus and 20 μg / mL QG-CDs 180 The culture results of Staphylococcus aureus and 0 μg / mL QG-CDs 180 The culture results of Staphylococcus aureus and 1 μg / mL QG-CDs 180The culture results of E. coli and 50 μg / mL QG-CDs 180 The culture results of E. coli and 20 μg / mL QG-CDs 180 The culture results of E. coli and 0 μg / mL QG-CDs 180 The culture results of E. coli and 1 μg / mL QG-CDs 180 The culture results;

[0033] Figure 14 The Zeta potential analysis results of a series of licorice carbon quantum dot materials and Staphylococcus aureus, Escherichia coli and the combination of the two, among which (a) is the Zeta potential of the four licorice carbon quantum dot materials at 50 μg / mL, and (b) is the OD 600 =0.2, (c) is the Zeta potential of the four licorice carbon quantum dot materials mixed with Staphylococcus aureus, and (d) is the Zeta potential of the four licorice carbon quantum dot materials mixed with Escherichia coli. DETAILED DESCRIPTION

[0034] The present invention provides a method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, comprising the following steps:

[0035] Licorice, water and quaternary ammonium salt solution are mixed and subjected to hydrothermal reaction to obtain quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material.

[0036] In the present invention, the mass volume ratio of the licorice to the water is preferably 0.05-1.5 g:1-3 mL, more preferably 0.1-0.8 g:1-2 mL, and even more preferably 0.1 g:2 mL.

[0037] In the present invention, the quaternary ammonium salt solution is preferably a mixture of a quaternary ammonium salt and an organic solvent.

[0038] In the present invention, the quaternary ammonium salt contained in the quaternary ammonium salt solution is preferably dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride.

[0039] In the present invention, the organic solvent is preferably methanol.

[0040] In the present invention, the mass volume ratio of the licorice to the quaternary ammonium salt solution is preferably 0.05-1.5 g:0.05-1.5 mL, more preferably 0.1-0.5 g:1-1.5 mL, and more preferably 0.1 g:1 mL.

[0041] In the present invention, the mass fraction of the quaternary ammonium salt contained in the quaternary ammonium salt solution is preferably 40 to 50%, more preferably 42 to 46%, and even more preferably 42%.

[0042] In the present invention, the hydrothermal reaction is preferably carried out in a high-pressure reactor.

[0043] In the present invention, the high-pressure reactor is preferably purged with a protective atmosphere before use.

[0044] In the present invention, the protective atmosphere is preferably nitrogen.

[0045] The present invention does not limit the purging time, which is based on the actual volume of the high-pressure reactor.

[0046] Specifically in the embodiment of the present invention, the purging time is preferably 5 to 10 minutes, more preferably 5 to 8 minutes, and more preferably 5 minutes.

[0047] In the present invention, the temperature of the hydrothermal reaction is preferably 180-200°C, more preferably 180-185°C or 195-200°C, more preferably 180°C or 200°C; the time of the hydrothermal reaction is preferably 12-14h, more preferably 12-13h, more preferably 12h.

[0048] In the present invention, the following post-treatments are preferably performed after the hydrothermal reaction: centrifugation and concentration.

[0049] In the present invention, the specific operation of the centrifugation is preferably: adding water to the product of the hydrothermal reaction, mixing and centrifuging.

[0050] The present invention does not limit the volume of water added to the product of the hydrothermal reaction, and a solution familiar to those skilled in the art can be used.

[0051] In the present invention, the centrifugal speed is preferably 500-3000 rpm, more preferably 2000-3000 rpm, and more preferably 3000 rpm; the centrifugal time is preferably 20-40 min, more preferably 30-40 min, and more preferably 30 min.

[0052] In the present invention, the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material is preferably stored at 4 to 20°C, more preferably 4 to 10°C, and even more preferably 4°C.

[0053] The present invention also provides a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material prepared by the preparation method of the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material.

[0054] The present invention also provides an application of the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material in the food field.

[0055] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0056] Example 1

[0057] This embodiment provides a method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, comprising the following steps:

[0058] Raw licorice slices produced in Zhangye, Gansu Province were dried and ground into powder for later use; 0.1 g of licorice powder was added to 2 mL of deionized water and mixed with 1 mL of dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride methanol solution (dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride with a mass fraction of 42%); the above mixture was transferred to a high-pressure reactor that had been purged with nitrogen for 5 minutes and hydrothermally reacted at 180°C for 12 hours; after the reactor was cooled to room temperature, 15 mL of deionized water was added to the reaction product, and the resulting mixture was centrifuged at 3000 rpm for 30 minutes and then concentrated to anhydrous powder to obtain a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, recorded as QG-CDs. 180 , and stored at 4°C for future use.

[0059] Example 2

[0060] This embodiment provides a method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material. The difference from Example 1 is that the temperature of the hydrothermal reaction is changed to 200°C, and the other parameters are the same as those in Example 1. It is recorded as QG-CDs 200 .

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing a licorice carbon quantum dot material, comprising the following steps:

[0063] Raw licorice root slices from Zhangye, Gansu Province were dried and ground into powder for later use; 1 g of licorice powder was dispersed in 60 mL of deionized water, magnetically stirred for 10 min, and then placed in an ultrasonic cleaner for 30 min to disperse evenly; the thoroughly mixed solution was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 180°C for 12 h; after the reaction was completed, it was cooled to room temperature, and the product solution in the reactor was centrifuged at 20,000 rpm for 30 min. The supernatant was filtered through a 0.24 μm filter membrane to obtain licorice carbon quantum dot material, which was recorded as G-CDs. 180 , and store at 4°C for future use.

[0064] Comparative Example 2

[0065] This comparative example provides a method for preparing licorice carbon quantum dot materials. The difference from comparative example 1 is that the temperature of the hydrothermal reaction is changed to 200°C, and the other parameter conditions are the same as those in comparative example 1, which is recorded as G-CDs 200 .

[0066] The morphology of the prepared licorice carbon quantum dot materials of Comparative Examples 1-2 and Examples 1-2 was examined using a transmission electron microscope. The results are as follows: Figures 1 to 4 As shown. Figures 1 to 4 It can be seen that the obtained G-CDs and QG-CDs are both spherical or quasi-spherical. The QG-CDs prepared at 200°C have the largest particle size, about 10 nm. The particle sizes of other licorice carbon quantum dot materials are all below 10 nm and are relatively uniform with good dispersion.

[0067] Subsequently, the elemental composition of G-CDs and QG-CDs was qualitatively and semi-quantitatively analyzed by X-ray energy dispersive X-ray spectroscopy (EDX). Figures 5 to 8 shown. Figures 5 to 8 The results show absorption peaks corresponding to the elements C, N, and O in the energy spectrum. The more prominent Cu absorption peak is due to the copper mesh support used in the characterization. The figure shows that both the obtained G-CDs and QG-CDs contain C, N, and O. This is due to the natural plant (licorice) carbon source and the hydrothermal reaction during the preparation process.

[0068] In order to further study the surface composition of the four kinds of licorice carbon quantum dot materials, the licorice carbon quantum dot materials obtained in Comparative Examples 1 to 2 and Examples 1 to 2 were characterized using Fourier transform infrared (FT-IR) spectroscopy. Figure 9 As shown. Figure 9 It can be seen that different licorice carbon quantum dot materials all appear at 3390 cm -1The absorption peak near 2920cm can be attributed to the intermolecular hydrogen bond OH stretching vibration peak, which is due to the fact that the sample is not completely dried; -1 The absorption peak near 1650cm can be attributed to the stretching vibration peak of CH. -1 The absorption peaks near the C=C stretching vibration peak can be attributed to the C=C stretching vibration peak, which shows that different licorice carbon quantum dot materials have similar basic structures. 200 With G-CDs 180 In comparison, G-CDs 200 Located at 1518cm -1 The weaker absorption peak nearby comes from the asymmetric stretching vibration of R-NO2, G-CDs 180 Located at 1155cm -1 The weaker absorption peak near the lipophilic acid is derived from CO stretching vibration, which indicates that a higher hydrothermal temperature can produce a nitro-like structure in the licorice carbon quantum dot material. Compared with the unmodified licorice carbon quantum dot material, QG-CDs 200 With QG-CDs 180 Both at 2851 and 1467 cm -1 A new absorption peak appears near 1117 cm, which is derived from the CH stretching vibration and CH bending vibration. -1 The CN stretching vibrations appearing near 914 cm -1 The NH deformation vibration absorption peak appeared near the surface of the licorice carbon quantum dot material, indicating that dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride has been successfully modified, and the resulting QG-CDs were successfully synthesized. 200 and QG-CDs 180 The infrared spectra of the samples were not much different, which indicated that the hydrothermal temperatures of 200℃ and 180℃ had little effect on the surface groups of the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial materials.

[0069] XRD spectrum is generally used to analyze the crystal structure of a substance. The XRD analysis results of the four kinds of licorice carbon quantum dot materials obtained in the present invention are as follows: Figure 10 shown. Figure 10 The results show that the carbon quantum dots at different temperatures all have obvious diffraction peaks at 2θ angles of 15 to 25°, indicating that the obtained G-CDs and QG-CDs are amorphous structures, which is manifested by highly disordered carbon particles. Compared with G-CDs, the diffraction peaks of QG-CDs obtained at different temperatures have changed and become sharper, indicating that their crystallinity is higher than that of G-CDs, which is related to the changes in the structure after modification with quaternary ammonium salts. 200 and QG-CDs 180 In comparison, QG-CDs 200The higher the peak, the higher the crystallinity of the licorice carbon quantum dot material.

[0070] The present invention also carried out ultraviolet spectrum analysis on the four kinds of licorice carbon quantum dot materials obtained, and the results are as follows Figure 11 As shown. Because the carbon quantum dots after treatment at different temperatures overlap, Figure 11 Only the UV absorption curves of unmodified and functionalized licorice carbon quantum dots are shown. Figure 11 As can be seen, the two curves are quite different, which can prove that the preparation of the present invention is relatively successful. The strong absorption peak of G-CDs at 200-250nm is caused by the π-π* transition of C=C. G-CDs and QG-CDs both have absorption peaks around 270-350nm, which are caused by the n-π* transition of C=O, but the intensity varies significantly, indicating that the obtained licorice carbon quantum dot materials contain oxygen-containing groups, which is consistent with the characterization results of FT-IR and EDX.

[0071] The present invention measured the emission fluorescence spectra of G-CDs and QG-CDs obtained under different hydrothermal reaction conditions at an excitation wavelength of 360 to 400 nm. Figure 12 shown. Figure 12 The results show that compared with the fluorescence emission intensity at 180°C, the G-CDs and QG-CDs obtained at 200°C both showed stronger fluorescence properties, with the maximum excitation wavelengths located near 360nm. As the hydrothermal reaction temperature rises, the fluorescence intensity of G-CDs and QG-CDs gradually increases. Compared with different licorice carbon quantum dot materials at the same temperature, the unmodified G-CDs carbon quantum dots have better fluorescence properties than the quaternary ammonium salt functionalized QG-CDs. The obtained QG-CDs 200 The emission peak appears broadened under 360nm excitation.

[0072] The present invention selected common typical foodborne pathogens: Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) as research objects and carried out subsequent antibacterial experiments.

[0073] Preparation of bacterial suspension

[0074] (1) Preparation of Staphylococcus aureus suspension

[0075] Prepare 0.15 g of tryptone soy broth, add it to 5 mL of deionized water, stir evenly with an automatic stirrer, and sterilize under high pressure at 121°C for 15 min; after cooling to room temperature, add 0.01 mL of Staphylococcus aureus liquid (purchased from Guangdong Huankai Microbiological Technology Co., Ltd.) to the sterilized mixed solution, and culture it in a constant temperature incubator at 37°C and 160 rpm for 10 h to obtain a Staphylococcus aureus suspension, which is stored at 4°C for later use.

[0076] (2) Preparation of Escherichia coli suspension

[0077] Prepare 0.09 g of nutrient broth, add it to 5 mL of deionized water and stir evenly, and sterilize it at high pressure at 121°C for 15 min; cool to room temperature, add 0.01 mL of Escherichia coli liquid (purchased from Guangdong Huankai Microbiology Technology Co., Ltd.) to the sterilized mixed solution, and culture it at a constant temperature of 160 rpm in a constant temperature incubator at 37°C for 10 h to obtain an Escherichia coli suspension, which is stored at 4°C for later use.

[0078] Preparation of 4 kinds of liquorice carbon quantum dot material solutions. Staphylococcus aureus or Escherichia coli suspension was diluted with tryptone soy broth or nutrient broth at a ratio of 1:9 to OD 600 =0.2 for later use. 15 mL of nutrient agar or Baird-Parker agar basal medium was added to the culture dish. After the culture medium completely solidified, the licorice carbon quantum dot material solution was added. The diluted Staphylococcus aureus suspension was inoculated into the Baird-Parker medium using the spreading inoculation method, and the Escherichia coli suspension was inoculated into the nutrient agar medium. After the inoculation, the culture dish was transferred to a constant temperature and humidity incubator and incubated at 37°C for 30 hours. The results were compared and the antibacterial activity was comprehensively evaluated. The results are as follows: Figure 13 shown.

[0079] First, a bacterial culture experiment was conducted using 17 mg / mL unmodified G-CDs as the main intervention agent. Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli were inoculated in the presence of G-CDs. 180 and G-CDs 200 In the culture medium with the presence of 5% β-lactamase, a blank control was set up at the same time. After static culture at 37℃ for 30h, the growth and reproduction of the target bacteria were compared. The results were as follows: Figure 13 a~c, Figure 13 l~n in the figure. Different concentrations of G-CDs 180 and G-CDs 200 No inhibitory effect was shown on Staphylococcus aureus and Escherichia coli, which indicates that G-CDs have no inhibitory effect on the two selected pathogens.

[0080] Subsequently, Staphylococcus aureus and Escherichia coli were treated similarly using quaternary ammonium salt-functionalized QG-CDs as the main intervention agent. The two bacterial suspensions were inoculated with QG-CDs at concentrations of 0 (blank control), 1, 20, and 50 μg / mL, respectively. 180 or QG-CDs 200 The culture medium was kept at 37℃ for 30h. Figure 13 Middle d~g, Figure 13 h~k, Figure 13 o~r, Figure 13 In general, for the selected pathogens, QG-CDs 180 and QG-CDs 200 All of them showed a certain antibacterial effect, and for different concentrations of QG-CDs, the lowest concentration of QG-CDs was 1 μg / mL, which showed an inhibitory effect on Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, indicating that its antibacterial ability was positively proportional to the intervention concentration of QG-CDs. The higher the intervention concentration, the stronger the antibacterial ability.

[0081] For Gram-positive Staphylococcus aureus, QG-CDs 180 The antibacterial effect of QG-CDs 200 More obviously, it shows that the inhibitory effects of QG-CDs prepared at different hydrothermal reaction temperatures on Gram-positive Staphylococcus aureus are different. The lower the hydrothermal reaction temperature of QG-CDs, the stronger its antibacterial activity. However, for Escherichia coli, QG-CDs prepared at relatively high temperature have a stronger inhibitory effect on Gram-positive Staphylococcus aureus. 200 The inhibitory effect is more obvious. It can be seen that the QG-CDs obtained in the present invention exhibit different antibacterial activities against Gram-positive and Gram-negative pathogens. Therefore, the present invention further explores the antibacterial mechanism of QG-CDs to facilitate its application in the field of antibacterial in the future.

[0082] In order to preliminarily explore the antibacterial mechanism of a series of licorice carbon quantum dot materials, the present invention uses Zeta potential analysis to investigate the surface charge changes of the obtained series of licorice carbon quantum dot materials and Staphylococcus aureus, Escherichia coli and the combination of the two. The Zeta potential of the four licorice carbon quantum dot material solutions with a concentration of 50 μg / mL was measured. The Staphylococcus aureus suspension and the Escherichia coli suspension were diluted to OD 600 = 0.2 and filtered, and the Zeta potential of the two diluted bacterial suspensions was measured. 50 μg / mL of licorice carbon quantum dot material solution and diluted bacterial suspension were mixed in a ratio of 2:1 to prepare a mixed solution of the two, and the Zeta potential was measured. Figure 14 shown.

[0083] First, the potential of four licorice carbon quantum dot materials with a concentration of 50 μg / mL was tested. The results are as follows Figure 14 As shown in (a), the surface of G-CDs is negatively charged, with potentials of -0.53 and -9.06 mV under hydrothermal conditions of 180°C and 200°C, respectively; the surface of QG-CDs is positively charged, with potentials of +4.56 and +13.51 mV under 180°C and 200°C, respectively. This indicates that higher hydrothermal reaction temperatures will increase the absolute value of the surface charge of the resulting licorice carbon quantum dot material, i.e., the positive ones will become more positive and the negative ones will become more negative. Compared with G-CDs, the surface charge of QG-CDs modified with quaternary ammonium salts is positive, which once again shows that the functionalization of licorice carbon quantum dots by the present invention is relatively successful.

[0084] The present invention then continues to measure OD 600 = 0.2 of the surface charge of Staphylococcus aureus and Escherichia coli, such as Figure 14 As shown in (b), the results are -3.78 and -15.86 mV, respectively, both showing negative values. This indicates that the positively charged QG-CDs can electrostatically interact with Staphylococcus aureus and Escherichia coli, and that the positively charged QG-CDs interact with negatively charged Gram-positive and Gram-negative bacteria. The charge of the QG-CDs can wrap around Gram-negative bacteria, exerting good antibacterial activity. This is consistent with the antibacterial activity evaluation results mentioned above.

[0085] To support this view, the present invention selected G-CDs and QG-CDs at a concentration of 50 μg / mL as intervention agents and characterized the surface charge of Staphylococcus aureus and Escherichia coli after treatment. The results are as follows: Figure 14 (c) Figure 14 As shown in (d). G-CDs 180 and G-CDs 200 After treatment, the surface potentials of Staphylococcus aureus and Escherichia coli were negative. For example, Staphylococcus aureus was -1.03mV and -9.18mV respectively, which were closer to the surface potential of G-CDs. 180 After treatment, the surface potentials of Staphylococcus aureus and Escherichia coli were converted from -3.78 and -15.86 mV to -0.82 mV and -3.13 mV, respectively. 200 After treatment, the voltages were converted to -0.16mV and -0.51mV, and the changes were quite obvious. This indicates that the positively charged QG-CDs did have electrostatic interactions with the negatively charged pathogens, and thus showed good antibacterial activity. However, from the perspective of electrostatic interaction, compared with QG-CDs 180 , QG-CDs 200 The surface potential changes of the two pathogenic bacteria after treatment were more obvious, especially Escherichia coli, which was consistent with the200 The results were consistent with those of the previous study, which showed that the antibacterial effect on Escherichia coli was more obvious.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material, characterized in that: The following steps are involved: The licorice, water and quaternary ammonium salt solution are mixed and subjected to a hydrothermal reaction to obtain a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material; The quaternary ammonium salt contained in the quaternary ammonium salt solution is dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride; The mass volume ratio of the licorice to the quaternary ammonium salt solution is 0.05-1.5 g: 0.05-1.5 mL; The mass fraction of the quaternary ammonium salt contained in the quaternary ammonium salt solution is 40-50%.

2. The method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material according to claim 1, wherein: The temperature of the hydrothermal reaction is 180-200° C., and the time of the hydrothermal reaction is 12-14 hours.

3. The method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material according to claim 1, wherein: After the hydrothermal reaction, the following post-treatments are further performed: centrifugation and concentration.

4. The method for preparing a quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material according to claim 3, wherein: The mass volume ratio of the licorice to the water is 0.05-1.5 g:1-3 mL.

5. The quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material prepared by the preparation method of the quaternary ammonium salt functionalized licorice carbon quantum dot antibacterial material according to any one of claims 1 to 4.

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