A water-soluble red light carbon dot and its preparation method and application

Abstract

A water-soluble red-light carbon dot and its preparation method and application, the method comprising the following steps: adding dicyandiamide and o-phenylenediamine to deionized water containing sulfuric acid and stirring for 20-30 minutes to form a suspension; placing the suspension in an autoclave and heating the reaction at 100-200°C for 6-12 hours to form a dark blue carbon dot solution; after cooling the dark blue carbon dot solution to room temperature, filtering it with a water-based microporous membrane and dialysis bag, respectively, to remove impurities and obtain pure water-soluble red-light carbon dots. This method has the advantages of simple process, easy operation, low cost, and no pollution, and can be used for industrial production; the prepared water-soluble red-light carbon dots are small in size, have good monodispersity, a graphene-like structure, and water solubility, and can significantly improve the absorption and transport of potassium and sodium ions by the roots of field crops under drought stress and salt stress, thereby increasing the photosynthetic rate and stomatal conductance of the crops and alleviating drought and salt stress in field crops.

Description

Technical Field

[0001] The present invention relates to carbon nanomaterials and their application fields, and in particular to water-soluble red-light carbon dots and a preparation method and application thereof. Background Art

[0002] Light not only provides the radiant energy that drives photosynthesis but also serves as a signal to optimize plant growth, development, and environmental adaptability. With the rapid development of the basic theory of plant light signaling, plant factories worldwide can improve food yield and quality by modifying the LED spectrum, but this is limited to leafy vegetables and herbs. For field crops such as sweet potatoes, corn, and rice, the application of light signaling theory and light regulation technology is still lacking. Therefore, it is crucial to develop new production technologies that target and regulate light signals to achieve stress and disease resistance and improve yield and quality in field crops.

[0003] As a new type of carbon nanomaterial, carbon quantum dots are widely used due to their small particle size (1-10nm), photoluminescence, rich surface functional groups, high biocompatibility, and low toxicity. For example, red-light carbon dots are prepared to feed silkworms to obtain bright fluorescent silk, and solid-state fluorescent carbon dots are prepared to replace LED lighting or LED light sources in plant growth greenhouses. However, carbon dots with different biological properties prepared by different preparation methods have different effects on plants. Currently, drought and salinization pose a major threat to global food security and cause serious losses to agricultural production. Therefore, the preparation of a water-soluble carbon dot with a red or far-red emission spectrum that improves the drought and salt tolerance of field crops has important research significance and practical application value for crop production. Summary of the Invention

[0004] The present invention aims to provide a water-soluble red light-emitting carbon dot and a preparation method and application thereof. The method has the advantages of simple process, easy operation, low cost and no pollution, and can be used for industrial production. The prepared water-soluble red light-emitting carbon dots are small in size, have good monodispersity, a graphene-like structure and water solubility, and can significantly improve the absorption and transport of potassium and sodium ions by the roots of field crops under drought stress and salt stress, increase the photosynthetic rate and stomatal conductance of crops, and alleviate drought and salt stress of field crops.

[0005] To achieve the above object, the present invention provides a method for preparing water-soluble red-light-emitting carbon dots, comprising the following steps:

[0006] S1, dicyandiamide and o-phenylenediamine are added to deionized water containing a certain amount of sulfuric acid, and stirred for 20-30 minutes to form a suspension; in the suspension, the concentration of dicyandiamide is 2.0mM-3.5mM, and the concentration of o-phenylenediamine is 5.0mM-6.5mM;

[0007] S2. placing the suspension obtained in step S1 in a high-pressure reactor and heating the reaction at 100-200° C. for 6-12 h to form a dark blue carbon dot solution;

[0008] S3. After cooling the dark blue carbon dot solution obtained in step S2 to room temperature, the solution is filtered through a water-based microporous membrane and dialyzed through a dialysis bag to remove impurities and obtain pure water-soluble red carbon dots.

[0009] Preferably, in step S1, in the suspension, the concentration of dicyandiamide is 2.97 mM, and the concentration of o-phenylenediamine is 5.94 mM.

[0010] Preferably, in step S1, the concentration of sulfuric acid in the deionized water containing sulfuric acid is 1%.

[0011] Preferably, in step S2, the suspension is reacted at 200° C. for 10 h to form a dark blue carbon dot solution.

[0012] Preferably, in step S3, the pore size of the water-based microporous filter membrane is 0.22 μm, and the molecular weight of the dialysis bag is 1000 Da.

[0013] To achieve the above object, the present invention further provides a water-soluble red-light-emitting carbon dot, which is prepared by the above preparation method.

[0014] Furthermore, the water-soluble red-light carbon dots are spherical and form a graphene-like structure; the water-soluble red-light carbon dots emit red light, and the photoluminescence properties are independent of excitation.

[0015] To achieve the above objectives, the present invention also provides the use of the above water-soluble red light-emitting carbon dots in improving the drought resistance of sweet potato seedlings and wheat seedlings.

[0016] To achieve the above objectives, the present invention also provides the use of the above water-soluble red light carbon dots in improving the salt tolerance of sweet potato seedlings, corn seedlings, rice seedlings, and soybean seedlings.

[0017] Preferably, the water-soluble red-light carbon dots are prepared into a carbon dot nutrient solution with a carbon dot concentration of 0.6 mg / mL.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The present invention uses distilled water as a solvent to prepare carbon dots through a one-step hydrothermal method. The process is simple, easy to operate, low in cost, the reaction is completed within 12 hours, is pollution-free, and can be used for industrial production. The water-soluble red-light carbon dots prepared by the present invention are spherical, small in size, have good monodispersity, a graphene-like structure, and water solubility. They can significantly improve the absorption and transport of potassium and sodium ions by the roots of field crops under drought stress and salt stress, increase the photosynthetic rate and stomatal conductance of the crops, alleviate drought and salt stress of field crops, can be used in agricultural production to improve the yield and quality of crops under drought and salt stress, and are suitable for wide promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 (a) Photograph of water-soluble red carbon dots prepared in an embodiment of the present invention under ultraviolet light irradiation and (b) photoluminescence spectrum under 360-640 nm excitation;

[0021] Figure 2 Transmission electron microscopy (a) and particle size distribution (b) of water-soluble red-emitting carbon dots prepared in an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on the growth of sweet potato seedlings under PEG-simulated drought stress (a) and the effect on chlorophyll content (b);

[0023] Figure 4 Schematic diagram of the effect of red-light-emitting carbon dots prepared in an embodiment of the present invention on photosynthetic parameters of sweet potato leaves under PEG-simulated drought stress; (a) net photosynthetic rate, (b) stomatal conductance, and (c) intrinsic water use efficiency;

[0024] Figure 5 Schematic diagram of the effects of different treatments on the expression levels of IbAKT1, IbSKOR in sweet potato roots and IbAKT2 in sweet potato leaves; (a) IbAKT1 in sweet potato roots, (b) IbSKOR in sweet potato roots, (c) IbAKT2 in sweet potato leaves;

[0025] Figure 6 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on potassium content in sweet potato roots, stems and leaves under PEG-simulated drought stress;

[0026] Figure 7 Schematic diagram of the effects of red-light-emitting carbon dots prepared in an embodiment of the present invention on wheat seedling growth and leaf photosynthetic parameters under soil drought stress; (a) wheat seedling growth, (b) net photosynthetic rate, and (c) intrinsic water use efficiency;

[0027] Figure 8 Schematic diagram showing the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on the growth (a) and survival rate (b) of sweet potato seedlings under salt stress;

[0028] Figure 9 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on sodium ion efflux from sweet potato roots (a) and sodium ion content in leaves (b) under salt stress;

[0029] Figure 10 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on the expression levels of IbSOS1, IbSOS2, and IbSOS3 genes in sweet potato roots under salt stress; (a) IbSOS1, (b) IbSOS2, (c) IbSOS3;

[0030] Figure 11 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on the sodium ion efflux (a) and average sodium ion flow rate (b) of rice roots under salt stress;

[0031] Figure 12 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on sodium ion efflux (a) and average sodium ion flow rate (b) from corn roots under salt stress;

[0032] Figure 13 Schematic diagram of the effect of red light-emitting carbon dots prepared in an embodiment of the present invention on sodium ion efflux (a) and average sodium ion flow rate (b) from soybean roots under salt stress. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Example

[0035] A method for preparing water-soluble red-light-emitting carbon dots comprises the following steps:

[0036] S1. Add dicyandiamide and o-phenylenediamine to 50 mL of deionized water containing 1% sulfuric acid and stir for 20-30 min to form a suspension; in the suspension, the concentration of dicyandiamide is 2.97 mM, and the concentration of o-phenylenediamine is 5.94 mM;

[0037] S2, placing the suspension obtained in step S1 in a high-pressure reactor, and heating the reaction at 200° C. for 10 h to form a dark blue carbon dot solution;

[0038] S3. After cooling the dark blue carbon dot solution obtained in step S2 to room temperature, the solution was filtered through a water-based microporous filter membrane with a pore size of 0.22 μM and dialyzed through a dialysis bag with a molecular weight of 1000 Da. After removing impurities, pure water-soluble red carbon dots were obtained.

[0039] The water-soluble red carbon dots prepared in the embodiment are irradiated under ultraviolet light to obtain a red emission spectrum. Under the light, the water-soluble red carbon dots solution has a unique red emission characteristic ( Figure 1 a), luminescence spectrum of red light carbon dots under 360-640nm excitation ( Figure 1 b) It can be seen that the photoluminescence properties of red carbon dots are independent of excitation; transmission electron microscopy images show that the red carbon dots obtained by the present invention are spherical and have good monodispersity. The synthesized CDs have obvious lattice fringes with a lattice spacing of 0.21 nm ( Figure 2 a), with an average particle size of 3.84 nm and a graphene-like structure ( Figure 2 b).

[0040] Application Example 1

[0041] The water-soluble red-light carbon dots prepared in the example were applied to the field crop, sweet potato, and their effect on the growth of sweet potato seedlings was explored using drought stress as an example. The specific application process is as follows:

[0042] The dicotyledonous sweet potato plant was used as a model. 20 cm thick, robust sweet potato vine cuttings were cut and cultured in 1 / 4 Hoagland nutrient solution under natural light conditions, with the solution refreshed every two days. Two weeks later, uniformly sized and growing sweet potato seedlings were transplanted into four different nutrient solutions: Group A received 1 / 4 Hoagland nutrient solution (control); Group B received foliar spraying of 0.6 mg / mL Red Light Carbon Dots plus 1 / 4 Hoagland nutrient solution (control + Red Light Carbon Dots); Group C received 1 / 4 Hoagland nutrient solution containing 10% polyethylene glycol 6000 (PEG) (drought stress); and Group D received foliar spraying of 0.6 mg / mL Red Light Carbon Dots plus 10% PEG (drought stress + Red Light Carbon Dots). Treatment solutions were refreshed every two days, with 24 replicates per treatment.

[0043] The Hoagland nutrient solution consists of 945 mg / L calcium nitrate tetrahydrate, 506 mg / L potassium nitrate, 80 mg / L ammonium nitrate, 136 mg / L potassium dihydrogen phosphate, 493 mg / L magnesium sulfate heptahydrate, 0.31 mL / L iron salt solution, and 0.63 mL / L trace element solution. The iron salt solution consists of 1.39 g / L ferrous sulfate heptahydrate and 1.87 g / L disodium ethylenediaminetetraacetic acid. The trace element solution consists of 0.83 mg / L potassium iodide, 6.2 mg / L boric acid, 22.3 mg / L manganese sulfate, 8.6 mg / L zinc sulfate, 0.25 mg / L sodium molybdate, 0.025 mg / L copper sulfate, and 0.025 mg / L cobalt chloride.

[0044] The results of the effects of drought treatment on the growth and chlorophyll content of sweet potato seedlings are as follows: compared with group C, group D significantly alleviated the wilting degree of sweet potato seedlings ( Figure 3a), compared with group C, the chlorophyll content in group D increased significantly ( Figure 3 b) It can be seen that the red light carbon dots prepared by the present invention effectively improve the drought tolerance of sweet potato plants. Figure 4 It can also be seen that compared with group C, the net photosynthetic rate, stomatal conductance and intrinsic water use efficiency of sweet potato leaves in group D were higher.

[0045] Potassium is the most important osmotic regulator in plants. Under PEG-simulated drought treatment, red light carbon dots showed dynamic changes in the regulation of potassium channel genes. At 10:00 am, the expression of the sweet potato root potassium ion absorption gene IbAKT1, the stem transport gene IbSKOR, and the leaf phloem potassium ion transport gene IbAKT2 was significantly upregulated ( Figure 5 ), resulting in a significant upregulation of potassium ions in the stem ( Figure 6 ). It can be seen from this that the red light carbon dots prepared by the present invention can enhance the drought resistance of plants by improving the absorption and transport of potassium ions.

[0046] Application Example 2

[0047] The water-soluble red-light-emitting carbon dots prepared in the example were applied to field crops, namely wheat. Taking drought stress as an example, the effect of the carbon dots on the growth of wheat seedlings was investigated. The specific application process is as follows:

[0048] Wheat seedlings (three leaves and one heart) with consistent growth and planted in sandy soil were divided into three groups: Group A, which received normal irrigation (control; soil relative volumetric water content approximately 28%); Group B, which received a 33-day drought (drought); and Group C, which received a 33-day drought combined with foliar spraying of 0.6 mg / mL red carbon dots (drought + red carbon dots). Group C was sprayed with red carbon dots every three days, while Groups A and B received distilled water. Each treatment consisted of 24 seedlings. After 11 treatments, samples were collected to observe plant growth.

[0049] Depend on Figure 7 Compared to Group B, wheat seedlings treated with red light carbon dots showed a lower overall wilting rate after 33 days, with brighter green leaves and better growth. This was reflected in the wheat's phenotype, net photosynthetic rate, and intrinsic water use efficiency. The net photosynthetic rate of wheat leaves increased significantly by 94.3%, and the intrinsic water use efficiency increased by 2.3 times. This suggests that the red light carbon dots can alleviate drought conditions in wheat cultivation and can be used as a biofertilizer.

[0050] Application Example 3

[0051] The water-soluble red-light carbon dots prepared in the example were applied to the field crop, sweet potato, and their effect on the growth of sweet potato seedlings was explored using salt stress as an example. The specific application process is as follows:

[0052] Using the dicotyledonous sweet potato plant as a model, 20 cm thick, robust sweet potato vine cuttings were cut and cultured in 1 / 4 Hoagland nutrient solution under natural light, with the solution refreshed every two days. Two weeks later, uniformly sized and growing sweet potato seedlings were transplanted into four different nutrient solutions: Group A (control), Group B (1 / 4 Hoagland nutrient solution plus foliar spray of 0.6 mg / mL Red Light Carbon Dots), Group C (1 / 4 Hoagland nutrient solution containing 150 mM NaCl) (salt stress), and Group D (1 / 4 Hoagland nutrient solution containing 150 mM NaCl plus foliar spray of 0.6 mg / mL Red Light Carbon Dots). The treatment solution was refreshed every two days, with 24 replicates per treatment.

[0053] The above-mentioned Hoagland nutrient solution is the same as the nutrient solution used for drought stress.

[0054] The results of the effects of salt stress on the growth and survival rate of sweet potato seedlings are as follows: compared with group C, the degree of chlorosis and wilting of sweet potato leaves in group D was significantly reduced ( Figure 8 a). Compared with group C, group D significantly improved the survival rate of sweet potato seedlings under salt stress ( Figure 8 b). Sodium homeostasis and efflux in plant roots are crucial for salt tolerance in sweet potatoes. Compared with group C, group D showed a significant increase in sodium ion efflux from the meristem and elongation zones of the sweet potato roots, resulting in a significant decrease in sodium ion accumulation in the cells of the roots and leaves ( Figure 9 ), which is mainly attributed to the significant increase in the expression of SOS signaling pathway-related genes (IbSOS1, IbSOS2, and IbSOS3) at night ( Figure 10 ). It can be seen that the red light carbon dots prepared by the present invention can effectively improve the salt tolerance of sweet potato plants by targeting the efflux of sodium ions from the root system.

[0055] Application Example 4

[0056] The water-soluble red-light carbon dots prepared in the example were applied to field crops, namely rice, corn, and soybean. Taking salt stress as an example, the effects of the red-light carbon dots on the growth of rice seedlings, corn seedlings, and soybean seedlings were investigated. The specific application process is as follows:

[0057] After sterilizing, rice, corn, and soybean seeds were planted in 1 / 4 Hoagland nutrient solution for germination. Culture conditions: 16 hours of light, 8 hours of darkness, and a light temperature of 26°C. After germination, healthy seedlings with consistent growth were divided into two groups. Group A was treated with distilled water (control), and Group B was treated with 0.6 mg / mL red light carbon dots (red light carbon dots) sprayed on the leaves. Spraying was done once every three days, and after four treatments, 100 mM NaCl salt stress treatment was started. After 48 hours of salt stress treatment, the root tips of each treatment were taken to measure the sodium ion flux.

[0058] The above-mentioned Hoagland nutrient solution is the same as the nutrient solution used for drought stress.

[0059] Depend on Figure 11-13 It can be seen that spraying red light carbon dots on leaves under salt stress can also enhance the sodium ion efflux from the roots of other field crops such as soybeans, corn and rice. This shows that this nanotechnology can improve the salt tolerance of field crops by targeting sodium ion efflux and has broad application prospects.

[0060] In summary, the water-soluble red light carbon dots prepared by the present invention can significantly improve the absorption and transport of potassium and sodium ions by the roots of field crops under drought stress and salt stress, increase the photosynthetic rate and stomatal conductance of crops, alleviate drought and salt stress of field crops, and can be used in agricultural production to improve the yield and quality of crops under drought and salt stress, and are suitable for wide promotion.

Claims

1. An application of water-soluble red-light-emitting carbon dots in improving drought resistance in sweet potato and wheat seedlings, wherein the preparation method of the water-soluble red-light-emitting carbon dots comprises the following steps: S1. Add dicyandiamide and o-phenylenediamine to deionized water containing a certain amount of sulfuric acid and stir for 20-30 minutes to form a suspension; in the suspension, the concentration of dicyandiamide is 2.0-3.5 mM, and the concentration of o-phenylenediamine is 5.0-6.5 mM; S2. Place the suspension obtained in step S1 in a high-pressure reactor and heat the reaction at 100-200°C for 6-12 h to form a dark blue carbon dot solution; S3. After cooling the dark blue carbon dot solution obtained in step S2 to room temperature, the solution is filtered through a water-based microporous membrane and dialyzed through a dialysis bag to remove impurities and obtain pure water-soluble red carbon dots.

2. The use of a water-soluble red light carbon dot in improving drought resistance of sweet potato seedlings and wheat seedlings according to claim 1, characterized in that: In step S1, in the suspension, the concentration of dicyandiamide is 2.97 mM, and the concentration of o-phenylenediamine is 5.94 mM.

3. The use of a water-soluble red light carbon dot in improving drought resistance of sweet potato seedlings and wheat seedlings according to claim 1 or 2, characterized in that: In step S1, the concentration of sulfuric acid in the deionized water containing sulfuric acid is 1%.

4. The use of a water-soluble red light-emitting carbon dot in improving drought resistance of sweet potato seedlings and wheat seedlings according to claim 1 or 2, characterized in that: In step S2, the suspension was reacted at 200°C for 10 h to form a dark blue carbon dot solution.

5. The use of a water-soluble red light-emitting carbon dot in improving drought resistance of sweet potato seedlings and wheat seedlings according to claim 1 or 2, characterized in that: In step S3, the pore size of the water-based microporous filter membrane is 0.22 μm, and the molecular weight of the dialysis bag is 1000 Da.

6. A method for preparing water-soluble red-light-emitting carbon dots, comprising the following steps: S1. Add dicyandiamide and o-phenylenediamine to deionized water containing a certain amount of sulfuric acid and stir for 20-30 minutes to form a suspension; in the suspension, the concentration of dicyandiamide is 2.0-3.5 mM, and the concentration of o-phenylenediamine is 5.0-6.5 mM; S2. Place the suspension obtained in step S1 in a high-pressure reactor and heat the reaction at 100-200°C for 6-12 h to form a dark blue carbon dot solution; S3. After cooling the dark blue carbon dot solution obtained in step S2 to room temperature, the solution is filtered through a water-based microporous membrane and dialyzed through a dialysis bag to remove impurities and obtain pure water-soluble red carbon dots.

7. The use of a water-soluble red light carbon dot according to claim 6 in improving the salt tolerance of sweet potato seedlings, corn seedlings, rice seedlings, and soybean seedlings, characterized in that: In step S1, in the suspension, the concentration of dicyandiamide is 2.97 mM, and the concentration of o-phenylenediamine is 5.94 mM.

8. The use of a water-soluble red light carbon dot according to claim 6 or 7 in improving the salt tolerance of sweet potato seedlings, corn seedlings, rice seedlings, and soybean seedlings, characterized in that: In step S1, the concentration of sulfuric acid in the deionized water containing sulfuric acid is 1%.

9. Use of a water-soluble red light-emitting carbon dot according to claim 6 or 7 in improving salt tolerance of sweet potato seedlings, corn seedlings, rice seedlings, and soybean seedlings, characterized in that: In step S2, the suspension was reacted at 200°C for 10 h to form a dark blue carbon dot solution.

10. Use of a water-soluble red light-emitting carbon dot according to claim 6 or 7 in improving salt tolerance of sweet potato seedlings, corn seedlings, rice seedlings, and soybean seedlings, characterized in that: In step S3, the pore size of the water-based microporous filter membrane is 0.22 μm, and the molecular weight of the dialysis bag is 1000 Da.

11. The use according to claim 1 or 6, characterized in that: The water-soluble red-light carbon dots were prepared into a carbon dot nutrient solution with a carbon dot concentration of 0.6 mg / mL.

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