Preparation method and application of nano-silver and composite bacteriostatic agent thereof

Abstract

The invention discloses nano-silver and a preparation method and application of a composite bacteriostatic agent of the nano-silver, and the preparation method of the nano-silver comprises the following steps: adding a reducing agent into a silver nitrate solution, mixing and stirring, adding an alkali reagent, mixing and stirring until the color of the solution is changed from colorless to yellowish brown to generate nano-silver particles, and then modifying the surface of the nano-silver to obtain the nano-silver. And then adding an auxiliary bacteriostatic agent to prepare the compound bacteriostatic agent. The nano-silver particles prepared through the method are narrow in particle size distribution and are in a regular spherical shape, the average particle size is 58.04 + / -1.28 nm, and compared with single nano-silver and commercial products, the nano-silver particles have the better antibacterial effect and have significant difference. In the long-term storage process, no precipitate is generated, the color is stable, and the stability is high. The prepared nano-silver / cysteine / chitosan bacteriostatic agent adopts safe and non-toxic raw materials, is biodegradable, low in production cost, simple in preparation method, excellent in performance and suitable for commercial large-scale production.

Description

Technical Field

[0001] The invention belongs to the field of biotechnology, and specifically relates to a preparation method and application of nano silver and a composite antibacterial agent thereof. Background Art

[0002] As people pay more and more attention to health and hygiene, the demand for efficient and safe antibacterial agents is increasing, and the research and application of antibacterial materials has become an important field. As an antibacterial material with broad application prospects, the background technology of composite antibacterial agents has a deep scientific foundation and practical needs.

[0003] Traditional antibacterial methods mainly include the use of antibiotics, disinfectants, etc., but these methods often have some limitations, such as the development of drug resistance, environmental impact, etc. With the development of nanotechnology, nanomaterials have brought new breakthroughs in the antibacterial field due to their unique physical and chemical properties.

[0004] As a classic nanomaterial, nanosilver has excellent antibacterial properties. Its antibacterial mechanism mainly includes binding to the surface of bacterial cells, destroying the integrity of cell membranes, and interfering with metabolic processes within cells. The small size of nanosilver enables it to contact and kill bacteria more effectively, showing high antibacterial activity.

[0005] Cysteine ​​is an amino acid with physiological functions. It is the only amino acid with a reducing group thiol (-SH) among the more than 20 amino acids that make up proteins. It has good biocompatibility and antibacterial activity. In the prior art, D-cysteine ​​and L-cysteine ​​have broad-spectrum antibacterial activity against Escherichia coli and other bacteria. It has been widely used in medicine, food additives and cosmetics.

[0006] Chitosan is a product of the natural polysaccharide chitin with some acetyl groups removed. It has good biocompatibility, biodegradability and antibacterial properties. It can play an antibacterial role in many ways, such as binding to bacterial cell walls, inhibiting bacterial growth and reproduction, etc. Chitosan also has biomedical functions such as promoting wound healing and reducing inflammatory responses, making it an ideal choice for combining with nanosilver.

[0007] In the medical field, the demand for antibacterial materials is particularly urgent. Hospital infection is a global problem. The surface of medical devices and medical dressings is prone to breeding bacteria, leading to the occurrence and spread of infection. Composite antibacterial agents can be used in the surface treatment of medical devices, the preparation of medical dressings, etc., effectively reducing the risk of infection, improving medical quality and patient safety. In daily life, antibacterial products are also increasingly favored by consumers. From personal care products to household cleaning products, people have a wide range of needs for products with antibacterial functions. Composite antibacterial agents can provide these products with more efficient and safe antibacterial solutions to ensure people's healthy lives. In addition, antibacterial materials also have important application value in the food industry, agriculture and other fields. Food preservation and antiseptic, crop disease prevention and control, and water environment sterilization and disinfection all require effective antibacterial means to ensure product quality and safety.

[0008] Composite antibacterial agents are natural and environmentally friendly, and they meet the requirements of modern society for sustainable development. In general, the background technology of composite antibacterial agents reflects the continuous exploration and innovation of human antibacterial needs. The emergence of such composite antibacterial agents has brought new hope and possibilities to the antibacterial field, and will play an important role in protecting human health and promoting social development. However, how to make the raw materials of composite antibacterial agents safer to use, the preparation method simple and easy to operate, and the price of raw materials and the convenience of obtaining them are issues that need to be solved urgently. Summary of the invention

[0009] Purpose of the invention: In view of a series of problems existing in the prior art, the present invention provides a nano-silver composite antibacterial agent and its preparation method and application, wherein the prepared nano-silver particles have a narrow particle size distribution, present a regular spherical shape, and an average particle size of 58.04±1.28nm, thereby effectively solving the problems of the complexity of the existing nano-silver preparation method and the aggregation of nano-silver during storage. Compared with single nano-silver, the composite antibacterial agent has better antibacterial effect, with significant differences.

[0010] Technical solution: In order to achieve the above-mentioned purpose, the present invention proposes a method for preparing nano silver, comprising the following steps: adding a reducing agent to a silver nitrate solution, mixing and stirring, adding an alkaline reagent, mixing and stirring until the color of the solution changes from colorless to yellow-brown, thereby generating nano silver particles.

[0011] Wherein, the reducing agent is any one or more of glucose, sodium borohydride, hydrazine, sodium dithionite, maltose, trisodium citrate and hydrogen peroxide.

[0012] Further, a reducing agent is added to the stirred AgNO3 solution at room temperature, mixed and stirred, and an alkali reagent is continuously added, and mixed and stirred until the color of the solution changes from colorless to yellow-brown to generate nanosilver particles, and the stirring speed is 300-600 rpm.

[0013] Preferably, the stirring speed is 450-550 rpm.

[0014] The volume ratio of the AgNO3 solution to the reducing agent is 1:200-1:500, the silver nitrate solution is 150-200 mmol / L, and the reducing agent concentration is 87.5-1400 mM.

[0015] Wherein, the alkaline reagent is sodium hydroxide solution with a concentration of 0.6-0.8 mol / L, Ag + and OH - The molar ratio is 1:1-1:2,

[0016] Preferably, the preferred molar ratio is 1:1.8.

[0017] The nano silver prepared by the preparation method of the present invention has a narrow particle size distribution, presents a regular spherical shape, and has an average particle size of 58.04±1.28nm.

[0018] The nano-silver composite antibacterial agent of the present invention comprises the nano-silver prepared according to claim 1 which is modified and has an auxiliary antibacterial agent added thereto.

[0019] The modified nanosilver has thiol groups connected to its surface, namely, Ag-S-CH2-CH(NH2)-COOH.

[0020] Among them, the nanosilver solution and the cysteine ​​solution are mixed evenly at room temperature to connect the thiol groups on the surface of the nanosilver particles, and the concentration of cysteine ​​is controlled to be 17.5-35mM; the auxiliary antibacterial agent solution is continued to be added and mixed evenly at room temperature to make the nanosilver particles evenly dispersed, and the final concentration of the auxiliary antibacterial agent is controlled to be 0.1%-0.5% g / mL.

[0021] Wherein, the auxiliary antibacterial agent includes chitosan, gelatin, sodium alginate, polyethylene glycol, polyvinyl alcohol, sodium carboxymethyl cellulose and the like.

[0022] Wherein, the auxiliary antibacterial agent is chitosan, which not only plays an auxiliary antibacterial effect but also has a stabilizing or dispersing effect.

[0023] The nano silver or the nano silver composite antibacterial agent of the present invention is used in the preparation of antibacterial dressings, antibacterial hand sanitizers, antibacterial toothpastes and food packaging materials.

[0024] Preferably, the present invention first adds the prepared silver nitrate solution into a round-bottom flask, drops a reducing agent according to a volume ratio, and mixes and stirs at 450rpm. Sodium hydroxide (0.7mol / L) is slowly dropped into the round-bottom flask, and mixed and stirred at 450rpm until the color of the solution changes (colorless→light yellow→golden yellow→yellow brown) to generate nano silver particles. Then, a cysteine ​​solution (17.5mM) is added, mixed and stirred, and then an auxiliary antibacterial agent or a dispersant is added. The preparation method is simple and easy, has high repeatability, and can be mass-produced. The nano silver particles prepared by the present invention have a narrow particle size distribution, present a regular spherical shape, and the average particle size is 58.04±1.28nm. During long-term storage, no precipitation is generated, the color is stable, and it has high stability. The nano silver / cysteine / chitosan antibacterial agent prepared by the present invention uses safe and non-toxic raw materials and is biodegradable, has low production cost, a simple preparation method, excellent performance, and is suitable for commercial large-scale production

[0025] Preferably, the nano-silver composite antibacterial agent mainly comprises nano-silver particles, cysteine ​​and auxiliary antibacterial agent chitosan according to the ingredients. Among them, the particle size of the nano-silver particles is 58.04±1.28nm, which ensures good antibacterial effect and stability. The nano-silver composite antibacterial agent of the present invention has excellent antibacterial effect on Vibrio parahaemolyticus and the like. Under experimental conditions, it shows good antibacterial activity with significant differences. The nano-silver antibacterial agent of the present invention can be widely used in the fields of medical treatment, hygiene, daily chemicals, food, etc. For example, it can be used to prepare products such as antibacterial dressings, antibacterial hand sanitizers, antibacterial toothpastes, food packaging materials, etc., and has broad market prospects and application value.

[0026] The preparation of nano silver in the present invention only requires three raw materials: silver nitrate, reducing agent, and alkaline reagent, and the reaction can be stirred at room temperature. Compared with the existing reduction method for preparing nano silver, the preparation of the present invention does not require the addition of raw materials such as colloids, nor does it require heating reaction, which is more simple and efficient. The present invention mainly utilizes the chemical reduction method, a relatively simple method for preparing nano silver, and selects other substances to act as stabilizers and auxiliary antibacterial agents, thereby forming an antibacterial agent in combination, thereby enhancing the antibacterial effect.

[0027] In addition, the synthetic composite antibacterial agent of the present invention only requires nanosilver, cysteine ​​and chitosan to be evenly mixed at room temperature, and only a trace amount of cysteine ​​and chitosan needs to be added to obtain a composite antibacterial agent with high antibacterial activity, and is significantly superior to single nanosilver, and the combination of nanosilver and cysteine ​​or nanosilver and chitosan.

[0028] The composite antibacterial agent prepared by combining nanosilver, cysteine ​​and chitosan in the present invention has the following advantages in application: 1. Enhanced antibacterial effect: Nanosilver and chitosan can more comprehensively and effectively inhibit the growth and reproduction of various pathogens through synergistic action. They can play a role from different targets and mechanisms, thereby improving the overall antibacterial efficacy, and have more significant antibacterial advantages compared to single nanosilver or chitosan. 2. Improved stability: The strong covalent bond between the thiol (-SH) and the silver atoms on the surface of the nanosilver, that is, the Ag-S bond, prevents the nanosilver particles from directly contacting the external environment like a "protective shell", reducing the occurrence of reactions such as oxidation; the modified nanosilver is wrapped by chitosan, which improves its dispersion effect under different environmental conditions (such as temperature, humidity, etc.), prevents the aggregation and sedimentation of nanosilver particles, and enables it to maintain good antibacterial performance for a longer time. This helps to extend the shelf life and service life of the composite antibacterial agent. 3. Broaden the scope of application: Due to its excellent antibacterial properties and stability, this composite antibacterial agent can be widely used in multiple fields such as medical fields (such as wound dressings, medical device disinfection, etc.), food industry (such as food packaging, preservation, etc.), daily chemical products (such as antibacterial lotions, skin care products, etc.) to meet the needs of different scenarios. 4. High safety: Cysteine ​​and chitosan are natural substances with good biocompatibility and biodegradability. When used in combination with nanosilver, it can reduce potential safety risks and reduce adverse effects on the human body and the environment. 5. Versatility: In addition to the antibacterial function, this composite antibacterial agent may also have other beneficial properties such as promoting wound healing and anti-oxidation, providing more possibilities for its effects in different applications.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0030] The nano silver prepared by the present invention has a broad-spectrum antibacterial property, can inhibit a variety of pathogens, including Gram-positive bacteria, Gram-negative bacteria, fungi, viruses, etc., and has a significant inhibitory effect on a variety of microorganisms; has a strong antibacterial ability, can quickly combine with bacteria and other microorganisms, and efficiently kill bacteria by destroying their cell membranes, interfering with their metabolism, etc., showing a strong antibacterial effect; is not easy to produce drug resistance, and bacteria are difficult to produce adaptive mutations to nano silver, thereby reducing the probability of drug resistance, and compared with traditional antibiotics, has more advantages in long-term use; has good stability: nano silver can maintain the stability of its structure and performance under certain conditions, is not easily affected by external environmental factors, thereby ensuring the durability of its antibacterial effect; has a rapid effect: compared with other antibacterial agents, nano silver can take effect in a short time and quickly inhibit the growth and reproduction of microorganisms.

[0031] The nano silver / cysteine / chitosan composite antibacterial agent prepared by the present invention has a synergistic effect, which further enhances the antibacterial effect. They can act together on different targets of bacteria, improve the efficiency and broad spectrum of antibacterial activity, and achieve the effect of "1+1+1>3". This combination can not only improve the antibacterial ability, but also reduce the side effects that may be caused by a single component, providing a more reliable solution for the application of antibacterial agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The effect of adding different volumes of NaOH on the absorbance of nanosilver in Example 1;

[0033] Figure 2 The effect of different Glu flow rates on the absorbance of nanosilver in Example 2;

[0034] Figure 3 Effect of adding different concentrations of Glu on the absorbance of nanosilver (Ag + :OH - =1:1; Glu concentration: A: 87.5mM, B: 175mM, C: 350mM, D: 700mM, E: 1400mM);

[0035] Figure 4 Effect of adding different concentrations of Glu on the absorbance of nanosilver (1:1 <Ag + :OH - <1:2; Glu concentration: a: 87.5 mM, b: 175 mM, c: 350 mM, d: 700 mM, e: 1400 mM);

[0036] Figure 5 Example 3: Preparation of storage diagrams corresponding to nanosilver by adding different concentrations of Glu (Ag + :OH - =1:1; Glu concentration: A 87.5 mM, B: 175 mM, C: 350 mM, D: 700 mM, E: 1400 mM);

[0037] Figure 6 The storage diagram (1:1) of nanosilver was prepared by adding different concentrations of Glu to Example 4. <Ag + :OH - <1:2; Glu concentration: a: 87.5 mM, b: 175 mM, c: 350 mM, d: 700 mM, e: 1400 mM);

[0038] Figure 7 Electron micrographs of the silver nanoparticles prepared by adding different concentrations of Glu in Example 4 (1:1 <Ag + :OH -<1:2; Glu concentration: c: 350 mM, d: 700 mM, e: 1400 mM);

[0039] Figure 8 Storage electron microscopy images of nano-silver antibacterial agents prepared by adding CS at different concentrations in Example 5;

[0040] Fig. 9 The antibacterial circle diagrams corresponding to the antibacterial agents with different components in Experimental Example 1 (A: single AgNPs, B: AgNPs+Cys, C: AgNPs+CS, D: AgNPs+Cys+CS;);

[0041] Fig.10 This is the quantitative analysis chart of the diameter of the antibacterial zone corresponding to the antibacterial agents containing different ingredients in Experimental Example 1. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0043] The raw and auxiliary materials, reagents, instruments, etc. used in the present invention are all well known in the art, and other experimental equipment well known in the art can be applied to the implementation of the present invention in the following manners.

[0044] Chitosan was purchased from Sangon Biotechnology (Shanghai) Co., Ltd., with a grade of Reagent Grade and an EINECS number of 222-311-2.

[0045] Cysteine ​​was purchased from Shanghai Huixing Biochemical Reagent Co., Ltd. with a purity of 98.5%.

[0046] Example 1

[0047] 100 μL of silver nitrate solution (175 mmol / L) was added to a round-bottom flask, and 30 mL of glucose solution (87.5 mM) was added dropwise at a stirring speed of 450 rpm, with a flow rate of 6 mL / min. After the addition of the glucose solution, 15, 30, 45, 60, 75, 90, and 100 μL of sodium hydroxide (0.7 mol / L) solution were added dropwise at a stirring speed of 450 rpm at a flow rate of 5 μL / min to the round-bottom flask, and the mixture was mixed and stirred at 450 rpm until the color of the solution changed to yellow-brown (colorless → light yellow → golden yellow → yellow-brown). Appropriate nanosilver solution was diluted 10 times, and a full wavelength scan of 200 to 800 nm was performed using an ultraviolet spectrophotometer. Nanosilver had a specific absorption peak between 350 and 450 nm.

[0048] The size of the nanosilver was measured using a nanoparticle size potential analyzer (Malvern, UK). 15 μL of the nanosilver sample was diluted 1000 times (the diluent was ultrapure water), and the sample was placed in a cuvette and analyzed at a constant temperature of 25°C with an equilibrium time of 120 seconds.

[0049] like Figure 1 As shown in the figure, when the volume of NaOH added is 45 μL, the absorption peak of the nanosilver particles reaches the highest. Except for the added volume of 15 μL, the prepared nanosilver particle size is about 100 nm. The particle size values ​​of nanosilver prepared by adding different volumes of NaOH are shown in Table 1.

[0050] Table 1 Particle size values ​​corresponding to the preparation of nanosilver by adding different volumes of NaOH

[0051]

[0052]

[0053] Example 2

[0054] The preparation method of Example 2 is the same as that of Example 1, except that when glucose is added dropwise, the flow rate is 1.5 mL / min, 3 mL / min and 6 mL / min; and 45 μL of sodium hydroxide solution is added dropwise.

[0055] like Figure 2 The results showed that the glucose droplet velocity had no effect on the absorbance and particle size of nanosilver (Table 2).

[0056] Table 2 Particle size values ​​of nanosilver prepared at different Glu flow rates

[0057]

[0058] Example 3

[0059] Example 3 is prepared in the same manner as Example 1, except that when glucose is added dropwise, the glucose concentration is 87.5 mM, 175 mM, 350 mM, 700 mM, 1400 mM, and the flow rate is 6 mL / min; 25 μL of sodium hydroxide solution (Ag + :OH - =1:1).

[0060] like Figure 3 The results showed that when the glucose concentration was 700 mM, the OD value of nanosilver was 0.7449, the particle size was 38.67 ± 1.11 (Table 3), and the absorption peak did not shift; Figure 5As shown, after 10 days of storage, the color changes from light to dark. This may be due to insufficient amount of sodium hydroxide added, which may cause some silver ions to not be fully reduced. These incompletely reduced silver ions may further react during storage, leading to aggregation or oxidation of nanosilver.

[0061] Table 3 Adding different concentrations of Glu to prepare the corresponding particle size values ​​of nanosilver (Ag + :OH - =1:1)

[0062]

[0063] Example 4

[0064] Example 4 is prepared in the same manner as Example 1, except that when glucose is added dropwise, the glucose concentration is 87.5 mM, 175 mM, 350 mM, 700 mM, and 1400 mM, the flow rate is 6 mL / min, and 45 μL of sodium hydroxide solution (1:1 <Ag + :OH - <1:2).

[0065] like Figure 4 The results show that when the glucose concentration is 700mM or 1400mM, the absorption peak of nanosilver reaches the maximum value, and the particle size is less than 80nm (Table 4), and it is not easy to produce precipitation and color change during storage ( Figure 6 ).

[0066] Table 4 Adding different concentrations of Glu to prepare the corresponding particle size values ​​of nanosilver (1:1 <Ag + :OH - <1:2)

[0067]

[0068] Example 5

[0069] The prepared nanosilver with glucose concentrations of 350 mM, 700 mM and 1400 mM in Example 4 were selected and characterized using a transmission electron microscope after storage for 0 and 5 days.

[0070] like Figure 7 The results shown show that the prepared silver nanoparticles present a regular spherical morphology, and their size is consistent with the results of particle size measurement.

[0071] In summary, the optimal method for preparing nanosilver is to absorb 100 μL of silver nitrate solution (175 mmol / L) into a round-bottom flask, add 30 mL of glucose solution (700 mM) at a stirring speed of 450 rpm, and the flow rate is 6 mL / min. After the addition of the glucose solution, continue to add 45 μL of sodium hydroxide (0.7 mol / L) solution to the round-bottom flask at 5 μL / min under the stirring condition of 450 rpm, and mix and stir at 450 rpm until the color of the solution changes to yellow-brown (colorless→light yellow→golden yellow→yellow-brown).

[0072] Example 6

[0073] Preparation of chitosan solution: Weigh 2.2 g chitosan (CS) and dissolve it in 40 mL ultrapure water, add 3% (v / v) acetic acid to the total volume, and heat at 56° C. to completely dissolve the chitosan.

[0074] Chitosan with a final concentration of 0%, 0.1%, 0.3%, and 0.5% g / mL was added to the nanosilver solution prepared by the best method in Example 5, mixed at room temperature, and stored for 10 days without precipitation or color change. Figure 8 After 10 days of storage, the nanosilver began to aggregate. Based on this, the addition of chitosan played a role in dispersion and stabilization, greatly improving the stability of the nanosilver ( Figure 8 ), and according to the method of Experimental Example 1, adding 0.3% chitosan has the best antibacterial effect.

[0075] Example 7

[0076] Preparation of cysteine ​​solution: Weigh 0.0022 g of cysteine ​​(Cys) and dissolve it in 1 mL, which is 17.5 mM Cys.

[0077] Preparation of chitosan solution: Weigh 2.2 g chitosan (CS) and dissolve it in 40 mL ultrapure water, add 3% (v / v) acetic acid to the total volume, and heat at 56° C. to completely dissolve the chitosan.

[0078] 100 μL of 17.5 mM Cys was added to the nanosilver solution prepared by the optimal method of Example 5, and the mixture was evenly mixed. Then, chitosan (final concentration was 0.1% g / mL) was added and mixed at room temperature. The addition of chitosan played a role in dispersion and stabilization, which greatly improved the antibacterial effect of nanosilver.

[0079] Test Example 1

[0080] AgNPs+Cys+CS, AgNPs, AgNPs+Cys, and AgNPs+CS prepared in Example 7 were used for quantitative bactericidal tests to test the bactericidal effects on Vibrio parahaemolyticus. 200 μL of the bacterial solution cultured to the logarithmic phase was plated (OD600 =0.69±0.0047), take 20 μL of sample stock solution to wet the filter paper, stick it to the plate, and incubate at 37°C for 3-5h, then use a vernier caliper to measure the diameter of the inhibition zone.

[0081] Among them, AgNPs is the best method in Example 5.

[0082] The AgNPs+Cys method was as in Example 7, wherein 200 μL of 17.5 mM Cys was added and mixed evenly, and chitosan was not added.

[0083] Wherein, AgNPs+CS is prepared by adding 0.3% g / mL chitosan to the nanosilver solution prepared by the optimal method of Example 5 and mixing at room temperature.

[0084] The results are as follows Fig. 9 , Fig.10 As shown in Table 5: The diameter of the inhibition zone produced by AgNPs+Cys+CS is 29.05±0.27 and the diameter of the inhibition zone produced by single AgNPs is 15.36±1.31, and there is a significant difference between the two (P<0.0001); the diameter of the inhibition zone produced by the composite antibacterial agent containing Cys or CS is 23.09±0.82 and 19.76±0.67, respectively, and there is also a significant difference between the two and AgNPs+Cys+CS (P<0.0001). In addition, compared with AgNPs+Cys and AgNPs+CS, even if the concentration of Cys and CS is reduced by half, the antibacterial effect of AgNPs+Cys+CS is significantly higher than that of AgNPs+Cys and AgNPs+CS, which further illustrates that the nanosilver / cysteine / chitosan composite antibacterial agent prepared by the present invention has a significant synergistic antibacterial effect.

[0085] Table 5 Antibacterial zone diameters corresponding to antibacterial agents with different ingredients.

[0086]

[0087]

Claims

1. A method for preparing nano silver, characterized in that: The method comprises the following steps: adding a reducing agent to a silver nitrate solution, mixing and stirring, adding an alkali reagent, mixing and stirring until the color of the solution changes from colorless to yellow-brown, and generating nano silver particles.

2. The preparation method according to claim 1, characterized in that: The reducing agent is any one or more of glucose, sodium borohydride, hydrazine, sodium dithionite, maltose, trisodium citrate and hydrogen peroxide.

3. The preparation method according to claim 1, characterized in that: Add a reducing agent to the stirred AgNO3 solution at room temperature, mix and stir, continue to add an alkali reagent, continue to mix and stir until the color of the solution changes from colorless to yellow-brown, and nanosilver particles are generated. The stirring speed is 300-600rpm.

4. The preparation method according to claim 1, characterized in that: The volume ratio of the AgNO3 solution to the reducing agent is 1:200-1:500, the silver nitrate solution is 150-200 mmol / L, and the reducing agent concentration is 87.5-1400 mM.

5. The preparation method according to claim 1, characterized in that: The alkaline reagent is a sodium hydroxide solution with a concentration of 0.6-0.8 mol / L. + and OH - The molar ratio is preferably 1:1-1:

2.

6. Nanosilver prepared by the preparation method according to claim 1, characterized in that: The nano silver particles have a narrow particle size distribution, present a regular spherical shape, and have an average particle size of 58.04±1.28 nm.

7. A nano-silver composite antibacterial agent, characterized in that: The nano-silver composite antibacterial agent comprises the modified nano-silver prepared according to claim 1 and an auxiliary antibacterial agent.

8. The nano-silver composite antibacterial agent according to claim 7, characterized in that: The modified nanosilver has a thiol group connected to its surface, namely Ag-S-CH2-CH(NH2)-COOH; the auxiliary antibacterial agent includes any one or more of chitosan, gelatin, sodium alginate, polyethylene glycol, polyvinyl alcohol or sodium carboxymethyl cellulose.

9. A method for preparing the nano-silver composite antibacterial agent according to claim 7, characterized in that: The method comprises the following steps: mixing a nano silver solution and a cysteine ​​solution at room temperature to make the surface of the nano silver particles connected with thiol groups, and controlling the concentration of cysteine ​​to be 17.5-35 mM; continuing to add an auxiliary antibacterial agent solution and mixing them at room temperature to make the nano silver particles evenly dispersed, and controlling the final concentration of the auxiliary antibacterial agent to be 0.1%-0.5% g / mL.

10. Use of the nanosilver according to claim 1 or the nanosilver composite antibacterial agent according to claim 7 in the preparation of antibacterial dressings, antibacterial hand soap, antibacterial toothpaste, and food packaging materials.

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