CN107243645B

CN107243645B - Method for synthesizing precious metal nanoparticles by using lactobacillus plantarum exopolysaccharides

Info

Publication number: CN107243645B
Application number: CN201710417943.8A
Authority: CN
Inventors: 林凤鸣; 李程程; 周乐
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2017-06-06
Filing date: 2017-06-06
Publication date: 2019-12-10
Anticipated expiration: 2037-06-06
Also published as: CN107243645A

Abstract

The invention discloses a method for synthesizing noble metal nanoparticles by utilizing extracellular polysaccharide obtained by fermenting lactobacillus plantarum. The lactobacillus plantarum exopolysaccharide and the noble metal solution are used as raw materials to react to obtain the noble metal nano-particles. The synthesized noble metal nano particles have uniform particle size and good dispersibility. In addition, the method has short reaction time and low energy consumption, does not need to add any chemical reagent, and realizes the green synthesis of the noble metal nano particles.

Description

method for synthesizing precious metal nanoparticles by using lactobacillus plantarum exopolysaccharides

Technical Field

The invention belongs to the field of biotechnology and nano materials, and particularly relates to application of lactobacillus plantarum exopolysaccharide in synthesis of precious metal nano particles.

Background

The traditional noble metal nanoparticle synthesis method mostly adopts a chemical reagent reduction method, wherein chemical reducing agents such as ethylenediamine, sodium borohydride and the like are involved, and the use of the chemical reducing agents brings potential problems of environmental pollution, biological toxicity and the like. Therefore, alternative methods for synthesizing noble metal nanoparticles are being sought to achieve green, sustainable development. Polysaccharides have proven to be useful in the synthesis of noble metal nanoparticles as their derivatives, including lentinan, carboxymethyl chitosan, pullulan, dextran, carboxymethyl cellulose, guar gum, and the like. However, there are certain drawbacks in the synthesis of noble metal nanoparticles using these polysaccharides and their derivatives. For example, cellulose and chitin are chemically modified to carboxymethyl compounds prior to synthesis of precious metal nanoparticles; lentinan is firstly heated to 140 ℃ to reach the optimal state, and the shape of the synthesized metal nano-particles is related to the structure of the lentinan; dextran as a reducing agent requires a pH of 11 and a synthesis time of 12-16h while pullulan and guar gum require high temperatures and long reaction times. In order to overcome the above drawbacks of the synthesis of noble metal nanoparticles using polysaccharides as reducing agents to achieve a truly green synthesis, it is very interesting to find and develop new polysaccharides capable of synthesizing nanoparticles.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for synthesizing noble metal nanoparticles by using exopolysaccharides as a reducing agent, so as to solve the problems of energy consumption, time consumption, environmental pollution and the like in the existing noble metal nanoparticle synthesis.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

A method for synthesizing noble metal nano particles comprises the following steps: and adding an extracellular polysaccharide solution into the noble metal solution to react to obtain noble metal nano-particles, wherein the extracellular polysaccharide is a reducing agent.

preferably, the exopolysaccharide is obtained by fermenting Lactobacillus plantarum, wherein the Lactobacillus plantarum is separated from Yunnan pickle, is classified and named as Lactobacillus plantarum (Lactobacillus plantarum), has a strain number of LCC-605, is preserved in China center for type culture Collection, and has a preservation address of 430072, Wuhan university, China. The preservation number is CCTCC NO: M2016491, and the accession number on NCBI is: KX443590 with the preservation date of 2016, 9, 18 and applies for Chinese patent 201710025113.0.

The method for obtaining exopolysaccharide by fermenting Lactobacillus plantarum (Lactobacillus plantarum) CCTCC NO: M2016491 is described in Chinese patent 201710025113.0, and the specific preparation method is as follows:

(1) Inoculating lactobacillus plantarum LCC-605 in an MRS culture medium according to the volume ratio of 3%, and fermenting at 31 ℃ for 24h to obtain fermentation liquor;

(2) Centrifuging the fermentation liquid at 14000rpm at 4 ℃ for 30min, removing thalli, adding 80% trichloroacetic acid into the supernatant until the final concentration of the trichloroacetic acid is 4%, placing in a refrigerator at 4 ℃ overnight, and precipitating protein;

(3) And (3) centrifuging the system obtained in the step (2) at 14000rpm and 4 ℃ for 30min every other day, removing precipitated protein, adding 3 times of volume of absolute ethyl alcohol into the supernatant, and placing the supernatant in a refrigerator at 4 ℃ overnight to precipitate the exopolysaccharide. Centrifuging at 14000rpm for 30min at 4 ℃ every other day, and collecting precipitate to obtain extracellular polysaccharide.

(4) Dissolving the exopolysaccharide with small amount of water, dialyzing with 7000Da dialysis bag for three days, changing water every 4h to remove monosaccharide, and lyophilizing to obtain exopolysaccharide of Lactobacillus plantarum LCC-605.

Preferably, the noble metal solution is 10-100 mg/L AgNO ₃ solution or 10-100 mg/L HAuCl ₄ solution.

more preferably, the noble metal solution is 100 mg/mL.

Preferably, the concentration of the exopolysaccharide solution is 0.2-5 mg/mL.

more preferably, the concentration of the exopolysaccharide is 2 mg/mL.

Preferably, the volume ratio of the extracellular polysaccharide solution to the noble metal solution is 1: 5-1: 15.

More preferably, the volume ratio of the exopolysaccharide solution to the noble metal solution is 1: 10.

Preferably, the reaction temperature is 25-100 ℃.

More preferably, the reaction temperature is 100 ℃.

Preferably, the reaction time is 1-40 min.

More preferably, the reaction time is 15 min.

Has the advantages that: compared with the prior art, the invention has the following advantages:

1. The method for synthesizing the noble metal nano-particles does not need to adjust the pH, only needs to heat to 100 ℃ for reaction for 15min, has short reaction time and greatly reduces the energy consumption.

2. The method does not need to add any chemical reducing agent when synthesizing the noble metal nano particles, eliminates the pollution of chemical reagents and realizes green synthesis.

3. According to the invention, lactobacillus plantarum exopolysaccharide is used as a reducing agent, chloroauric acid or silver nitrate solution is used as a raw material, and the raw material is heated and boiled in a short time to prepare the noble metal nano particles which are uniformly distributed, wherein the prepared gold nano particles are stable for a long time. The transmission electron microscope shows that the synthesized noble metal nanoparticles are uniform in size distribution, the average size of the gold nanoparticles is about 12.2nm, the average size of the silver nanoparticles is about 25.0nm, and the silver nanoparticles have good dispersibility. The method has the advantages of safe and harmless raw material sources, short reaction time and only 100 ℃ of reaction temperature, so the method is expected to be widely applied to the green synthesis of the noble metal nano particles.

Drawings

FIG. 1 is a schematic diagram showing the color change of the gold nanoparticles synthesized from the extracellular polysaccharide of Lactobacillus plantarum in example 2 at different reaction times (0, 3, 10, 15, and 30min from left to right).

fig. 2 is a schematic ultraviolet spectrum diagram of gold (a) and silver (B) nanoparticles in example 5.

FIG. 3 is a diagram showing the X-ray photoelectron spectroscopy detection result of the gold nanoparticles in example 6.

FIG. 4 is a schematic scanning electron microscope of gold (A) and silver (B) nanoparticles in example 7.

FIG. 5 is a schematic transmission electron microscope of gold (A) and silver (B) nanoparticles in example 8.

Fig. 6 is a schematic diagram of the gold (a) and silver (B) nanoparticles in example 8 with ultrahigh resolution, showing that the synthesized gold and silver nanoparticles have a face-centered cubic structure.

FIG. 7 is a graph showing the distribution of the particle sizes of gold (A) and silver (B) nanoparticles in example 8, wherein the synthesized gold nanoparticles have a particle size of about 12.2nm (A) and the synthesized silver nanoparticles have a particle size of about 25 nm.

Detailed Description

The invention will be better understood from the following examples. However, those skilled in the art will readily appreciate that the description of the embodiments is only for illustrating the present invention and should not be taken as limiting the invention as detailed in the claims.

example 1 preparation of exopolysaccharides

A thallus sample of lactobacillus plantarum LCC-605 is taken and activated three times by using an MRS culture medium. The cells were removed by centrifugation at 14000g for 30min at 4 ℃. And after centrifugation, pouring the supernatant into a beaker, centrifuging the remaining thalli once again, pouring the supernatant into the beaker again, pouring 80% trichloroacetic acid into the beaker until the final concentration of the trichloroacetic acid is 4%, putting the beaker into a refrigerator at 4 ℃ for overnight, and precipitating the protein. Every other day, the solution in the beaker was centrifuged again to separate the precipitated protein. Removing precipitate, pouring out supernatant, adding three times of anhydrous ethanol, and placing in refrigerator at 4 deg.C overnight to precipitate extracellular polysaccharide. And centrifuging the solution in the beaker every other day, and precipitating to obtain the polysaccharide. Dissolving polysaccharide in a small amount of ultrapure water, placing into a dialysis bag, placing into a large beaker, dialyzing for three days, and changing water every 4h to remove monosaccharide. And after three days, putting the lactobacillus plantarum LCC-605 into a vacuum freeze dryer for freeze drying to obtain the extracellular polysaccharide of the lactobacillus plantarum LCC-605.

Example 2 Synthesis of noble Metal nanoparticles with exopolysaccharides

The exopolysaccharide is prepared into a solution of 2mg/mL, 5mL of the exopolysaccharide is added into 50mL of a chloroauric acid solution of 100mg/L or a silver nitrate solution, and the mixture is boiled. Samples were taken at 0, 3, 10, 15 and 30min for analysis. The results are shown in FIG. 1, and the wine red appears in the chloroauric acid polysaccharide solution at 15min, which is the characteristic color of the gold nanoparticles, and shows that the gold nanoparticles are synthesized after 15min of reaction.

Example 3 Synthesis of noble Metal nanoparticles with exopolysaccharides

The exopolysaccharide is prepared into 0.2mg/mL solution, 5mL is added into 25mL 10mg/L chloroauric acid solution or silver nitrate solution, and the reaction is carried out at 25 ℃ for 40min, and then sampling analysis is carried out.

Example 4 Synthesis of noble Metal nanoparticles with exopolysaccharides

The exopolysaccharide is prepared into a solution of 5mg/mL, 5mL of the exopolysaccharide is added into a chloroauric acid solution or a silver nitrate solution of 75mL and 50mg/L, and the mixture is boiled. Samples were taken at 0, 3, 10, 15 and 30min for analysis.

Example 5 ultraviolet absorption of gold and silver nanoparticles

The ultraviolet absorption spectrum detection is carried out on the noble metal nanoparticle sample synthesized in the embodiment 2 in a scanning range of 400-900 nm, the result is shown in fig. 2, and the gold and silver nanoparticles synthesized by the exopolysaccharide have maximum absorption peaks at 550nm (A) and 405nm (B) respectively.

Example 6X-ray photoelectron Spectroscopy (XPS) detection of gold nanoparticles

The gold nanoparticles synthesized in example 2 were lyophilized and then subjected to XPS detection, and the results are shown in fig. 3, where the gold nanoparticles synthesized from the exopolysaccharide have absorption peaks at the binding energies of 83.6 and 87.5eV, and the two peak positions are typical XPS spectrum peaks of gold element.

Example 7 morphology observation of gold and silver nanoparticles by scanning electron microscopy

10uL of the gold and silver nanoparticle solution obtained in the above example 2 was dropped onto a silicon wafer, and the silicon wafer was naturally air-dried and observed by a scanning electron microscope. The results are shown in fig. 4, where the synthesized gold nanoparticles have an approximately spherical structure (a) and the synthesized silver nanoparticles have an irregular structure (B).

Example 8 morphology observation of gold and silver nanoparticles Using Transmission Electron microscopy

10uL of the gold and silver nanoparticle solution obtained in example 2 was dropped onto a 400-mesh copper mesh for transmission electron microscope observation, and the result is shown in FIG. 5, in which the formed gold nanoparticles have a spherical structure and the silver nanoparticles have an ellipsoidal structure. Meanwhile, the lattice structure of the gold nanoparticles and the silver nanoparticles is observed by adopting ultrahigh resolution, and the result is shown in figure 6, which shows that the gold nanoparticles and the silver nanoparticles have the lattice structure. Meanwhile, the particle size distribution statistics is carried out, and the result is shown in figure 7, and the result shows that the particle size of the gold nanoparticles is about 12nm, and the particle size of the silver nanoparticles is about 25 nm.

Claims

1. A synthesis method of precious metal nanoparticles is characterized in that an exopolysaccharide solution is added into a precious metal solution to react to obtain the precious metal nanoparticles, wherein the exopolysaccharide is obtained by fermenting lactobacillus plantarum (Lactobacillus plantarum) CCTCC NO: M2016491, and is a reducing agent;

The reaction temperature is 100 ℃; the reaction time is 15 min;

The noble metal solution is 10-100 mg/L AgNO ₃ solution or 10-100 mg/L HAuCl ₄ solution;

The concentration of the extracellular polysaccharide solution is 2 mg/mL;

The volume ratio of the extracellular polysaccharide solution to the noble metal solution is 1: 5-1: 15.