Preparation method and application of polygonatum cyrtonema carbon quantum dots

Abstract

The invention provides a preparation method and application of polygonatum cyrtonema carbon quantum dots, and belongs to the technical field of preparation of nano luminescent materials. The carbon quantum dots are prepared by taking stems and leaves of polygonatum cyrtonema as a carbon source and adopting a hydrothermal method. The carbon quantum dot provided by the invention has a very strong inhibition effect on pectobacterium carotovorum. According to the invention, biological resources are effectively utilized, a foundation is laid for prevention and treatment of plant bacterial diseases, and the application prospect is wide.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of nano-luminescent materials, and particularly relates to a polygonatum sibiricum carbon quantum dot and a preparation method thereof, as well as an application of the polygonatum sibiricum carbon quantum dot in preventing and treating the bacterial soft rot pathogen of Polygonatum sibiricum. Background Art

[0002] Discovered in 2004, carbon quantum dots (CQDs) are carbon-based nanomaterials less than 10 nm in size. They possess excellent optical properties, good water solubility and stability, low cytotoxicity, environmental friendliness, and a wide range of raw material sources. They are widely used in various fields, including agricultural control, microbial inhibition, bioimaging, sensors, drug delivery, water purification, photoelectric conversion, and healthcare. The synthesis of CQDs can be accomplished through two methods: top-down and bottom-up. The hydrothermal method, part of the bottom-up approach, allows for the structure and function of CQDs to be altered by adjusting the carbon source, material-liquid ratio, and temperature during the synthesis process. CQDs can also be modified by adding modifiers to further optimize their functionality. The hydrothermal method offers advantages such as simple equipment, low cost, mild reaction conditions, and stable CQD particle size.

[0003] In the field of agricultural biocontrol, carbon quantum dots can destroy microbial membrane structures through covalent and non-covalent interactions; enter the cytoplasm to assist in the production of large amounts of reactive oxygen species; and inhibit microbial activity through various means, such as releasing heat energy through the photothermal effect. Using natural biomass as precursors not only improves the utilization of biomass materials, but also produces carbon quantum dots with inhibitory effects on bacteria. For example, carbon quantum dots prepared from banana peels and tea byproducts can inhibit Bacillus subtilis; carbon quantum dots synthesized from bamboo fungus caps and lactobacilli have inhibitory effects on Ralstonia solanacearum and Xanthomonas campestris; and carbon quantum dots synthesized from Impatiens balsamina can inhibit the growth of Penicillium italicum.

[0004] Bacterial soft rot is one of the most important bacterial diseases worldwide, causing the rhizomes of many plants, including Chinese medicinal materials, crucifers, leguminous families, umbelliferae, and cucurbitaceae, to rot. The incidence of root rot in Paris polyphylla ranges from 50% to 87.7%; outbreaks of root rot in the rare herb Anoectochilus roxburghii can lead to yield reductions of up to 70% to 80%. The Chinese medicinal material Parsley is one of the two Paris polyphylla-derived medicinal plant elements listed in the Chinese Pharmacopoeia. It has excellent anti-tumor and anti-inflammatory effects and plays a significant role in traditional Chinese medicine. However, Parsley is prone to diseases such as soft rot, leaf spot, and root rot during artificial cultivation, which seriously affect yield and quality. Zheng Meixia and colleagues isolated and identified for the first time the pathogen causing soft rot in seven-leaf clover as Pectobacterium carotovorum. This pathogen causes soft rot in seven-leaf clover, with an incidence rate as high as 45% in the seven-leaf clover cultivation areas of Fujian. Traditional chemical pesticides can easily lead to resistance and environmental pollution. The development of a green antibacterial agent based on biomass carbon quantum dots is of great significance for promoting the sustainable cultivation of seven-leaf clover, a traditional Chinese medicinal herb. Summary of the Invention

[0005] In order to solve the problem of preventing and controlling bacterial diseases of Polygonatum sibiricum and the problem of utilizing waste biomass resources, the present invention provides a method for preparing Polygonatum sibiricum carbon quantum dots (PC-CQDs) by using a hydrothermal method with a by-product of Polygonatum sibiricum as a precursor.

[0006] To achieve the above objectives, the inventors provide the following technical solutions:

[0007] A method for preparing carbon quantum dots from polygonatum sibiricum is disclosed, which uses the stem and leaf parts of polygonatum sibiricum as a byproduct as a carbon source and adopts a hydrothermal method to prepare the carbon quantum dots.

[0008] The preparation method comprises the following steps: weighing powder of polygonatum sibiricum stems and leaves, uniformly dispersing the powder with ultrapure water, placing the sample into a polyfluoroethylene reactor, and performing a hydrothermal reaction at 170-190° C. for 6-10 hours; after natural cooling, filtering with filter paper 2-3 times, filtering with a 0.22 μm nylon filter head, dialyzing with a 100-500 Da dialysis bag for 18-24 hours, and changing the water every 6-8 hours; and taking the solution in the dialysis bag and freeze-drying it.

[0009] Furthermore, there are hydroxyl groups, amino groups, carboxyl groups, ether groups, sulfonic acid groups and amide groups on the surface of the polygonatum sibiricum carbon quantum dots.

[0010] Furthermore, the polygonatum sibiricum carbon quantum dots are nearly spherical nanoparticles with a diameter of 2.508±0.940 nm, a distinct graphene lattice structure, a crystallinity of 17-18%, and fluorescence maximum excitation wavelength / emission wavelength of 380 nm / 460 nm, respectively.

[0011] Furthermore, the application of the carbon quantum dots of Polygonatum sibiricum in preventing and treating soft rot of Parsley septempunctata is described. Specifically, the carbon quantum dots of Polygonatum sibiricum are prepared into a 9.4-18.8 mg / mL solution and sprayed on the roots, stems, or leaves of Parsley septempunctata to inhibit Pectobacterium carotovora, thereby preventing and treating the soft rot caused by the bacteria.

[0012] The beneficial effects of the present invention are:

[0013] (1) The preparation method of the present invention has simple process, low preparation cost, and is green and environmentally friendly.

[0014] (2) Compared with carbon quantum dots prepared using tea processing byproducts, gelatin, etc. as precursors, the carbon quantum dots of the present invention have stronger thermal stability.

[0015] (3) Polygonatum multiflorum carbon quantum dots have good chemical stability and photostability, which prolongs the prevention and control cycle; multiple antibacterial mechanisms ensure their strong antibacterial activity; and good fluorescence properties make them more suitable for detection by modern equipment, which can prevent and control crop diseases in a timely manner.

[0016] (4) The use of by-products of Polygonatum sibiricum as a source for the preparation of carbon quantum dots not only improves the utilization rate of biological resources, but also obtains renewable biological control materials with good properties, broadens the application range of Polygonatum sibiricum, and lays a theoretical foundation for the application of green biomass-derived carbon quantum dots in the prevention and control of bacterial diseases. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 100,000x transmission electron microscopy image (a), particle size distribution (b), 1500,000x transmission electron microscopy image (c) and X-ray crystal diffraction pattern (d) of PC-CQDs described in a specific embodiment.

[0018] Figure 2 Fourier transform infrared spectrum (a), X-ray photoelectron spectrum (b), C spectrum (c), N spectrum (d), O spectrum (e), S spectrum (f), hydrated particle size distribution (g) and Zeta potential distribution (h) of PC-CQDs described in the specific implementation method.

[0019] Figure 3 This is the thermogravimetric change curve of PC-CQDs described in the specific implementation method.

[0020] Figure 4 UV-visible light spectrum (a), fluorescence color development (b), excitation and emission spectra (c), and wavelength dependence of fluorescence emission spectrum (d) of PC-CQDs described in a specific embodiment.

[0021] Figure 5Figure 3 shows the inhibition zone test results of PC-CQDs on FJAT-49333 (a), the turbidity degree of FJAT-49333 by the doubling dilution method (b), the OD change curve of the MIC experiment (c), and the growth status of FJAT-49333 by the poisonous plate method (d).

[0022] Figure 6 The preparation process of PC-CQDs and the inhibition mechanism diagram of FJAT-49333 described in the specific implementation method. DETAILED DESCRIPTION

[0023] In order to explain the technical content, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0024] Example 1

[0025] 1 Materials and Methods

[0026] 1.1 Materials and Reagents

[0027] The pathogenic bacteria strain of soft rot of seven-leaf gentian: Pectobacterium carotovorum FJAT-49333, stored in glycerol at -80°C, is currently deposited at the Institute of Crop Science, Fujian Academy of Agricultural Sciences (Zheng Meixia, Su Hailan, Xiao Rongfeng, He Guiqiang, Zhu Yujing*. Identification of the pathogen of bacterial soft rot of seven-leaf gentian in Fujian Province, Journal of Fujian Agricultural Sciences, 2021, 36(3): 332-336.). The stems and leaves of Polygonatum cyrtonema were collected from the Polygonatum cyrtonema planting base of Jiahe Planting Professional Cooperative in Guangze County, Nanping City, Fujian Province in November 2023, dried at 65°C, crushed, and passed through a 60-mesh sieve. They were then dried at room temperature and stored for later use.

[0028] Streptomycin sulfate (STR, analytical grade) was purchased from Sinopharm Chemical Reagent Co., Ltd.; TSB medium (trypticase 17.0 g / L, soy papain hydrolyzate 3.0 g / L, sodium chloride 5.0 g / L, glucose 2.5 g / L, potassium dihydrogen phosphate 2.5 g / L, pH 7.3 ± 0.2) was purchased from BD Biosciences (USA); agar powder (analytical grade) was purchased from Beijing Bio-Technology Co., Ltd. For TSB liquid medium, 35 g of TSB powder was dissolved in 1 L of water; for TSB semi-solid medium, 9 g of agar was added to TSB liquid medium; and for TSB solid medium, 18 g of agar was added to TSB liquid medium.

[0029] 1.2 Methods

[0030] 1.2.1 Preparation of Polygonatum multiflorum carbon quantum dots

[0031] Polygonatum cyrtonema carbon quantum dots (PC-CQDs) are prepared using a hydrothermal method. Using the stems and leaves of Polygonatum cyrtonema as a carbon source, 1g of stem and leaf powder was weighed and evenly dispersed with 15mL of ultrapure water. The sample was placed in a 25mL polyvinyl fluoride reactor and hydrothermally reacted at 180°C for 8 hours. After cooling naturally, the sample was filtered twice with filter paper and a 0.22μm nylon filter tip. The sample was then dialyzed for 24 hours using a 100-500Da filter, with the water changed every 8 hours. The solution in the dialysis bag was freeze-dried to obtain the resulting powder, which is the PC-CQDs. The powder was then dissolved in an appropriate amount of water and set aside.

[0032] 1.2.2 Structural Characterization of Carbon Quantum Dots

[0033] Characterization of PC-CQDs: Transmission electron microscopy (TEM) was used to characterize the morphology and nanometer diameter of carbon quantum dots; the operating voltage was 200 kV. X-ray diffraction analyzer (XRD) was used to characterize the lattice structure of carbon quantum dots; the test range was 5° to 90°, the scanning rate was 2° / min, Cu-Kα rays were used as the light source, the voltage was 40 kV, and the current was 50 mA. The infrared absorption of carbon quantum dots was measured on an infrared spectrometer (FT-IR) using the tablet method to analyze the surface groups of carbon quantum dots; the test wave number range was 500 to 4000 cm -1 , with a resolution of 4cm -1 , the sampling interval is 0.5cm -1 , the number of scans was 32. X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental composition of carbon quantum dots, and the functional groups corresponding to the infrared absorption peaks were verified again by measuring the fine spectra of the main elements; the test pressure was 2.0×10 -7 mbar, a spot size of 400 μm, an operating voltage of 12 kV, and a filament current of 6 mA. The full spectrum scan energy was 100 eV with a step size of 1 eV; the fine spectrum scan energy was 50 eV with a step size of 0.1 eV. The hydrated particle size and zeta potential of the carbon quantum dots were analyzed using a nanoparticle size analyzer (DLS). The thermal stability of the carbon quantum dots was analyzed using a thermogravimetric analyzer (TG) in a nitrogen-filled atmosphere. The test temperature range was 30–800°C, the heating rate was 10°C / min, and the data acquisition interval was 0.4 s.

[0034] 1.2.3 Fluorescence performance testing of carbon quantum dots

[0035] The ultraviolet absorption of the carbon quantum dots was measured using an ultraviolet-visible spectrophotometer (UV-Vis) with a wavelength range of 200 to 700 nm and a step size of 1 nm. The fluorescence of the carbon quantum dots under 365 nm ultraviolet light was observed using a darkroom UV analyzer. The fluorescence excitation and emission wavelengths of the carbon quantum dots, as well as their wavelength dependence, were analyzed using a fluorometer (FL) with a step size of 1 nm and a slit size of 2.

[0036] 1.2.4 Antibacterial properties of carbon quantum dots on FJAT-49333

[0037] FJAT-49333 was activated multiple times on TSB solid medium until the colony morphology was uniform. A single colony was picked and placed in a 250 mL conical flask containing 100 mL of TSB liquid medium and cultured in a shaker at 30°C and 170 rpm for 24 h. The concentration count was 2.625 × 10 9 CFU / mL.

[0038] The Oxford cup method was used to test the diameter of the inhibition zone of PC-CQDs against FJAT-49333. The concentration of FJAT-49333 on the double-layer plate was 5.25×10 7 Sterile water was used as the negative control, STR (300 μg / mL) was used as the positive control, the PC-CQDs concentration gradient was 50, 100, 150, 200, 250, and 300 mg / mL, the amount of liquid added to the Oxford cup was 100 μL, and the size of the inhibition zone was measured after incubation at 30°C for 48 h.

[0039] The minimum inhibitory concentration (MIC) of PC-CQDs against FJAT-49333 was measured by serial dilution method. Sterile water was used as negative control, the STR gradient concentration of positive control was 8, 4, 2, 1, 0.5, 0.25, 0.13, 0.06 mg / mL, and the concentration gradient of PC-CQDs was 150, 75, 37.5, 18.8, 9.4, 4.7, 2.3, 1.2 mg / mL. The volume of TSB in 96-well plates was 100 μL, and the bacterial concentration was 0.8×10 5 CFU / mL, culture at 30℃, measure the corresponding OD value in the measuring plate at different time periods, and observe the turbidity of the culture medium in each well.

[0040] The inhibitory effect of PC-CQDs on FJAT-49333 was tested by the poison plate method. The concentration gradient of PC-CQDs was 0, 10, 20, and 30 mg / mL, and the extract of Polygonatum cyrtonema stem and leaf (PC) with the same concentration gradient was used as the control. The specific extraction process of PC was as follows: 3g of Polygonatum cyrtonema stem and leaf powder was weighed and added to 20mL of ultrapure water. After 30min in a 100℃ water bath, the extract was centrifuged at 8000rpm for 5min, and the precipitate was discarded. The supernatant was the 150mg / mL PC solution for later use. The concentration of FJAT-49333 bacterial solution was 2.56×10 7 CFU / mL, add 200 μL of liquid, spread evenly, and observe the growth of FJAT-49333 after incubation at 30℃ for 48 h.

[0041] 2 Results and Analysis

[0042] 2.1 Morphology and structure of PC-CQDs

[0043] The TEM results of PC-CQDs are as follows Figure 1 As shown in a, carbon quantum dots are evenly dispersed in aqueous solution, and their diameter distribution range is 2.508±0.940nm ( Figure 1 b). PC-CQDs have a clear lattice structure ( Figure 1 c), the lattice interlayer spacing is about 0.21nm, which is attributed to the graphite (100) crystal plane in the carbon core. The 2θ diffraction angle calculated according to the Bragg equation nλ=2dsinθ should be 21.5°, which is close to the diffraction peak 2θ=21.23° appearing in the XRD pattern of PC-CQDs ( Figure 1 d), the crystallinity was calculated to be 17.13% by Jade-6 software analysis.

[0044] 2.2 Analysis of surface functional groups of PC-CQDs

[0045] The FT-IR analysis results of PC-CQDs are shown in Figure 2. Figure 2 As shown in a. At 3371cm -1 、1297cm -1 and 2938cm -1 The peak at 1600 cm comes from the vibration absorption of OH / NH, C-OH and CH, indicating the presence of hydroxyl and amino groups on the surface of PC-CQDs; -1 The absorption peak at 1084 cm is caused by C=O in the fatty acid structure, indicating the presence of carboxyl groups in PC-CQDs; -1 The absorption peak at 677 cm is caused by COC, indicating the presence of ether structure in the surface groups of PC-CQDs; -1 CS at 1415cm -1 S=O at 1084cm -1 SO at 1415 cm indicates the presence of sulfonic acid groups on the surface of PC-CQDs; -1 CN at 3371cm -1 NH at 1600 cm -1 The C=O at the position indicates the presence of amide groups. In summary, there are hydroxyl, amino, carboxyl, ether, sulfonic acid and amide groups on the surface of PC-CQDs.

[0046] XPS was used to further analyze the surface elemental composition and chemical state of PC-CQDs. Figure 2b) shows the four main binding energies of PC-CQDs at 285.20eV, 399.87eV, 531.86eV and 163.17eV, which are assigned to the 1s orbital of C, N, O and the 2p orbital of S, indicating that PC-CQDs are mainly composed of these four elements, accounting for 55.63%, 4.49%, 33.79% and 0.85% respectively; the content of elements such as Mg, K, Ca, Cl and P accounts for 5.24%. C1s spectrum ( Figure 2 c) The three peaks at 284.8eV, 286.2eV and 288.2eV belong to CC / CH, CO and C=O respectively); N1 spectrum ( Figure 2 d) consists of three characteristic peaks at 398.72eV, 399.85eV and 401.75eV, corresponding to -N=, CN and NR4 (RC / RH), respectively; O1s spectrum ( Figure 2 e) The two peaks at 531.3eV and 532.64eV are C=O and CO respectively; S2p spectrum ( Figure 2 f) corresponds to CS, R-SO, and -SO3, respectively. XPS results show that there are hydroxyl, amino, carboxyl, ether, sulfonic acid, and amide groups on the surface of PC-CQDs, which is consistent with the results of Fourier transform infrared spectroscopy.

[0047] The polar groups such as hydroxyl, amino, carboxyl, sulfonic acid and amide groups on the surface of PC-CQDs easily adsorb water molecules, making it easy to form a thick hydration layer in water. The hydrated particle size range eventually reaches 476.2±53.7nm ( Figure 2 g); In general, carboxyl and sulfonic acid groups carry negative charges, while hydroxyl, amide, and ether groups are neutral, and amino groups carry positive charges only under acidic conditions. Therefore, the overall potential of PC-CQDs is ultimately negatively charged, and its Zeta potential distribution is -12.09±5.07mV ( Figure 2 h).

[0048] Thermal stability of PC-CQDs

[0049] Thermogravimetric curves of PC-CQDs are shown in Figure 2. Figure 3As shown, it can be seen that the decomposition of PC-CQDs can be divided into five stages. When t < 120 °C, the weight loss of PC-CQDs is about 3.88%, and the loss at this stage is caused by the evaporation of water molecules adsorbed by PC-CQDs due to heat. When 120 < t < 340 °C, the weight loss is about 28.59%, which is due to the decomposition of surface groups such as hydroxyl, carboxyl, and amino groups. Decarboxylation reaction occurs for carboxyl groups at this stage and CO2 is generated. In the stage of 340 < t < 500 °C, the weight loss is about 20.9%, because groups such as amide groups and ether bonds on the surface of PC-CQDs are decomposed at this stage. The last stage is 500 < t < 700 °C, and the weight loss at this stage is 6.28%, because the polycyclic structure that may be generated by the condensation of sulfonic acid groups and carbon skeletons is decomposed at this stage. When t > 700 °C, the amorphous carbon in the carbon core begins to decompose and rearrange, transforming into graphite microcrystals, and the sp 2 carbon ratio increases, and the degree of graphitization improves. It shows that PC-CQDs have stronger thermal stability.

[0050] 2.4 Optical properties of PC-CQDs

[0051] The ultraviolet-visible spectrum of PC-CQDs is as Figure 4 shown in a, and there are two absorption peaks. There is an obvious absorption peak at 275 nm, attributed to the π-π 2 transition of C=C and C=N in the carbon core; there is a weak absorption peak at 325 nm, attributed to the n-π * transition of C=O that is prone to generating lone pair electrons in the surface groups. The optical properties of carbon quantum dots are determined by the π electron states of sp * carbon clusters. When the π electrons transition to the excited state π 2 , the radiative transition of electron-hole pairs in the sp * carbon clusters can generate fluorescence. Therefore, under ultraviolet irradiation with a short excitation wavelength (365 nm), PC-CQDs emit blue fluorescence ( 2 b), and its maximum excitation wavelength / emission wavelength are 380 nm / 460 nm ( Figure 4 c), and its emission has an obvious wavelength dependence ( Figure 4 d). As the excitation wavelength increases from 330 nm to 430 nm, its maximum emission wavelength also redshifts from 425 nm to 505 nm, and the intensity of the emission peak first increases and then decreases. Figure 4 d), with the excitation wavelength increasing from 330 nm to 430 nm, its maximum emission wavelength also redshifts from 425 nm to 505 nm, and the intensity of the emission peak first increases and then decreases.

[0052] 2.5 Antibacterial performance of PC-CQDs against FJAT-49333

[0053] The inhibitory effect of the antibacterial zone of PC-CQDs against FJAT-49333 is as Figure 5As shown in Figure a, PC-CQDs exhibited a significant inhibitory effect against FJAT-49333, positively correlated with concentration. When PC-CQD concentrations were 100, 150, 200, 250, and 300 mg / mL, the corresponding inhibition zone diameters were 10.283±0.965 mm, 12.781±1.045 mm, 14.955±1.070 mm, 16.701±0.998 mm, and 18.085±1.409 mm. The antibacterial effect of PC-CQDs was more pronounced than the inhibition zone diameters of essential oils extracted from thyme, rosemary, eucalyptus, fennel, and coriander against P. carrotus (8.1 mm, 16.5 mm, 11 mm, 7.6 mm, and 7.5 mm, respectively).

[0054] MIC test results (see Table 1, Figure 5 b, c) show that the MIC of PC-CQDs was 18.8 mg / mL at 6, 12, and 24 h of incubation. A PC-CQD concentration of 1 / 2 the MIC (9.4 mg / mL) significantly inhibited the growth and reproduction of FJAT-49333. The MIC concentration of PC-CQDs was lower than the MIC of N-CDs prepared with citric acid and histidine (25 mg / mL) against bacteria and the MIC of potassium tetraborate tetrahydrate against Pectobacter carotovora (30.552 mg / mL).

[0055] The MIC of PC-CQDs to FJAT-49333 was further verified by the poison plate method. Figure 5 As shown in Figure d, the inhibitory effect of PC-CQDs on FJAT-49333 gradually increased as the concentration in the plate increased from 0 mg / mL to 30 mg / mL. At a PC-CQD concentration of 10 mg / mL, the growth of the pathogen was significantly inhibited. At concentrations ≥ 20 mg / mL, FJAT-49333 was unable to grow and reproduce on the plate, a result consistent with the MIC test results. PC, however, had no significant inhibitory effect on FJAT-49333, further demonstrating the advantages of preparing carbon quantum dots from the stems and leaves of Polygonatum multiflorum.

[0056] Table 1 Inhibition zone diameters of FJAT-49333 with different concentrations of PC-CQDs

[0057]

[0058]

[0059] Note: Different letters in the table indicate significant differences at the 0.05 level detected by Duncan method.

[0060] The potential antibacterial mechanism of PC-CQDs against Pectobacterium carrotus is as follows: Figure 6As shown in the figure: On the one hand, as for PC-CQDs as a whole, (1) the negative charge they carry makes PC-CQDs easier to recognize and interact with cations. When they interact with divalent cations such as Ca on the bacterial cell wall that maintain membrane integrity, 2+ Mg 2+ When chelated in the same phase, it will affect the function of cations in maintaining the integrity of the cell wall, causing damage to the cell wall and achieving the purpose of inhibiting the growth of microorganisms. (2) The nanometer diameter of PC-CQDs is only 2.5nm, which can enhance its ability to enter bacterial cells through its own small size effect, promote interaction with bacterial intracellular proteins, nucleic acids, etc., and affect their normal function. This is consistent with the results that carbon quantum dots (diameter 2.0±0.3nm) prepared with chlorhexidine gluconate can easily enter bacterial cells and interact with their proteins and nucleic acids. (3) PC-CQDs have a clear lattice structure, and the sp 2 The hybridized carbon atoms form conjugated π bonds, which can efficiently transfer electrons. Under light excitation, electrons jump to form electron-holes, reducing oxygen, hydrogen peroxide, etc. to superoxide free radicals, assisting in the production of reactive oxygen species, which can damage structures such as cell membranes, proteins and naked DNA.

[0061] In summary, the present invention uses a byproduct of Polygonatum multiflorum as a carbon source and adopts a hydrothermal method with simple preparation process, low cost, and environmentally friendly technology to synthesize carbon quantum dots PC-CQDs. PC-CQDs have good fluorescence properties and emit blue fluorescence under short-wavelength ultraviolet light. PC-CQDs have a spherical structure and are rich in functional groups such as hydroxyl, amino, carboxyl, ether, sulfonic acid, and amide groups on their surface. The minimum inhibitory concentration (MIC) of PC-CQDs against carrot soft rot pectinobacterium FJAT-49333 is 18.8 mg / mL; when the concentration is 1 / 2 of the MIC, it can significantly inhibit the growth of FJAT-49333.

[0062] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of the present invention. Therefore, based on the innovative concept of the present invention, changes and modifications to the embodiments described herein, or equivalent structural or equivalent process transformations made using the contents of the present invention's specification and drawings, and direct or indirect application of the above technical solutions to other related technical fields, are all included in the scope of patent protection of the present invention.

Claims

1. A method for preparing carbon quantum dots from Polygonatum sibiricum, characterized in that: The preparation method uses the stem and leaf parts of the by-product of Polygonatum cyrtonema as a carbon source and adopts a hydrothermal method to prepare carbon quantum dots.

2. The method for preparing carbon quantum dots from Polygonatum odoratum according to claim 1, wherein The following steps are involved: Weigh the powder of Polygonatum sibiricum stems and leaves, disperse it evenly with ultrapure water, put the sample into a polyfluoroethylene reactor, and carry out hydrothermal reaction at 170-190°C for 6-10 hours; after natural cooling, filter it 2-3 times with filter paper, filter it with a 0.22μm nylon filter head, and dialyze it with a 100-500Da dialysis bag for 18-24 hours, changing the water every 6-8 hours; and freeze-dry the solution in the dialysis bag.

3. The method for preparing carbon quantum dots from Polygonatum odoratum according to claim 1 or 2, wherein: Hydroxyl, amino, carboxyl, ether, sulfonic acid and amide groups exist on the surface of the polygonatum sibiricum carbon quantum dots.

4. The method for preparing carbon quantum dots from Polygonatum odoratum according to claim 1 or 2, wherein: The polygonatum sibiricum carbon quantum dots are nearly spherical nanoparticles with a diameter of 2.508±0.940 nm, have a distinct graphene lattice structure, and a crystallinity of 17-18%.

5. The method for preparing carbon quantum dots from Polygonatum cyrtonema according to claim 1 or 2, wherein: The maximum excitation wavelength / emission wavelength of the fluorescence of the polygonatum sibiricum carbon quantum dots are 380nm / 460nm respectively.

6. Use of the carbon quantum dots of Polygonatum cyrtonema as claimed in any one of claims 1 to 5 in preventing and treating soft rot of Parsley cyrtonema.

7. The use of the polygonatum sibiricum carbon quantum dots in preventing and treating soft rot of Parsley sibiricum according to claim 6, characterized in that: The polygonatum sibiricum carbon quantum dots are prepared into a 9.4-18.8 mg / mL solution, and sprayed on the roots or stems and leaves of the seven-leaf gentian.

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