Method for efficient in-situ synthesis of gold nanorods

Abstract

The invention provides a method for efficient in-situ synthesis of gold nanorods, and belongs to the technical field of medical materials. Compared with a traditional gold seed synthesis method, the synthesis method has the advantages that the step of preparing a seed solution in advance is omitted, the chloroauric acid solution is directly added into the CTAB solution, then the silver nitrate solution and the ascorbic acid solution are sequentially added, finally, the sodium borohydride solution is dropwise added, the reaction solution becomes purple red from colorless, and therefore the stable gold nanorod is generated. According to the method, synthesis of the gold nanorod can be completed within one hour, meanwhile, the dosage of silver nitrate, sodium borohydride and ascorbic acid is greatly reduced, and the rapid, energy-saving, efficient and environment-friendly preparation process is achieved; and the prepared gold nanorod is uniform in size, is in a regular rod shape, is good in reproducibility, is convenient for high-yield output, and can promote wide application of GNRs.

Description

Technical Field

[0001] The invention relates to the technical field of medical materials, and in particular to a method for efficiently synthesizing gold nanorods in situ. Background Art

[0002] Gold nanorods (GNRs) are rod-shaped nanomaterials, generally referring to a class of nanoparticles with an aspect ratio between 2 and 25. Due to their unique optical properties, GNRs have been widely used in the biomedical field, especially in optical biomedical imaging and tumor photothermal therapy, playing an important role as contrast agents and therapeutic media. GNRs are one of the few metal materials whose surface plasmon resonance (SPR) is in the visible light wavelength range.

[0003] GNRs have independent electronic vibration modes in the long axis and diameter directions, where the vibration along the radius direction can resonate with light of a specific wavelength, while the resonance wavelength along the long axis direction varies with the aspect ratio, covering a wide range from visible light to near-infrared light. In biomedical imaging, the SPR peak of GNRs can be adjusted to the near-infrared region, which helps to reduce the autofluorescence and light absorption interference of biological samples (such as proteins, cells, and DNA molecules) because these samples have relatively low absorption in the near-infrared region. In addition, compared with organic dyes, GNRs have higher chemical stability and photostability and are not prone to photobleaching. Using near-infrared lasers, high-resolution imaging of deep biological tissues can be achieved. The imaging technology of GNRs achieves excellent imaging contrast by utilizing its longitudinal SPR resonance peak (LSPR) in the near-infrared region, significantly improving the ability to distinguish different biological samples. The technology also demonstrates efficient bio-labeling capabilities, which can accurately identify and track biological molecules. In addition, its stability and good penetration into deep tissues provide strong technical support for surgical navigation and real-time imaging. Therefore, GNRs show broad application potential in biomedical imaging, sensing technology, photothermal therapy and other fields due to their unique optical properties and biocompatibility.

[0004] At present, the method for synthesizing gold nanorods is mainly the traditional gold seed synthesis method: 1. First, gold seeds are synthesized using chloroauric acid (HAuCl4) and sodium borohydride (NaBH4); chloroauric acid is quickly reduced to gold under the action of the reducing agent sodium borohydride to form 3-4nm gold nanoseed particles, which are stabilized by the CTAB surfactant to prevent aggregation. 2. Preparation of growth solution: Add silver nitrate, ascorbic acid and seed solution to the chloroauric acid solution. The role of AgNO3 is to regulate the growth rate of gold nanorods and control their aspect ratio. Ascorbic acid, as a weak reducing agent, slowly reduces chloroauric acid, allowing gold ions to gradually deposit on the seed particles, thereby promoting the growth of gold nanorods. 3. Growth process: In the growth solution, the gold seeds begin to grow isotropically. During this process, some seeds will twin and change their growth habits to form nanorod cores. The nanorod core grows along one dimension to form nanorods. This process involves the preferential deposition of gold ions on specific crystal planes, which is usually affected by surfactants and silver ions. 4. Regulation of aspect ratio: Gold nanorods with different aspect ratios can be prepared by adjusting the amount of seed solution added and the silver content in the growth solution. The synergistic effect of silver ions and surfactants (such as CTAB) has an important influence on the symmetry breaking efficiency and effective particle number of gold nanorods, thereby affecting the size and shape of the final gold nanorods. 5. Purification process: Impurities such as CTAB are removed by centrifugation and washing to obtain pure gold nanorods. However, the traditional seed-mediated synthesis method has some limitations, mainly including a long synthesis cycle (18 to 24 hours) and a large demand for chemical reagents. These factors not only lead to an increase in production costs, but may also produce harmful byproducts due to the use and treatment of chemical reagents, which imposes a burden on the environment. Summary of the invention

[0005] The purpose of the present invention is to provide a method for efficiently synthesizing gold nanorods in situ, which is efficient, environmentally friendly, can reduce the use of chemical reagents and shorten the synthesis time.

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

[0007] The present invention provides a method for efficiently synthesizing gold nanorods in situ, comprising the following steps:

[0008] The aqueous solution of hexadecyltrimethylammonium bromide and the aqueous solution of chloroauric acid are first mixed to obtain a first mixture;

[0009] performing a second mixing of the first mixture and an aqueous solution of silver nitrate to obtain a second mixture;

[0010] After adding an ascorbic acid aqueous solution dropwise to the second mixture, an aqueous sodium borohydride solution is added dropwise to obtain a third mixture;

[0011] The third mixture is allowed to stand to obtain gold nanorods;

[0012] The molar ratio of sodium borohydride in the sodium borohydride aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 0.002-0.003:1;

[0013] The standing temperature is 20-30° C., and the standing time is 0.5-1 h.

[0014] Preferably, the molar ratio of cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 223:1.

[0015] Preferably, the stirring speed of the first mixing is 300-500 rpm, and the stirring time is 5 min.

[0016] Preferably, the molar ratio of silver nitrate in the silver nitrate aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 0.24:1.

[0017] Preferably, the stirring speed of the second mixing is 150-250 rpm, and the time is 2 min.

[0018] Preferably, the molar ratio of ascorbic acid in the ascorbic acid aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 2.4:1.

[0019] Preferably, the dripping speed of the ascorbic acid aqueous solution is 8 to 12 drops / min.

[0020] Preferably, the dropping speed of the sodium borohydride aqueous solution is 4 to 6 drops / min.

[0021] Preferably, the preparation method of the sodium borohydride aqueous solution is: cooling distilled water to freezing point to obtain ice water, dissolving sodium borohydride solid in the ice water to obtain the sodium borohydride aqueous solution.

[0022] The invention provides a method for efficiently synthesizing gold nanorods in situ. Compared with a traditional gold seed synthesis method, the synthesis method of the invention omits the step of preparing a seed solution in advance, and directly adds a chloroauric acid solution to a CTAB solution, then adds a silver nitrate solution, and then adds an ascorbic acid solution to change the reaction solution from yellow to colorless and transparent, and finally drops a sodium borohydride solution to change the color from colorless to purple-red, thereby generating stable gold nanorods.

[0023] In the present invention, the role of CTAB: CTAB (hexadecyltrimethylammonium bromide) surfactant can form a stable protective layer on the surface of gold nanoparticles to prevent particle aggregation. The addition of CTAB helps to form CTA + -AuCl4 - -Ag +The complexes act as templates in the subsequent reduction process, promoting the formation of gold nanorods. The role of silver nitrate: The silver ions (Ag + ) plays a key role in the synthesis process; an appropriate amount of silver ions can promote the orderly arrangement of CTAB in the lateral part of the gold nanorods, slowing down the growth rate, thereby promoting the longitudinal growth and affecting the aspect ratio of the gold nanorods. The role of ascorbic acid: Ascorbic acid (AA) as a reducing agent can convert the gold ions (Au 3+ ) is reduced to low-valent gold ions (Au + ), producing gold nanoparticles. The phenomenon is that the solution changes from yellow to colorless and transparent. The role of sodium borohydride: Sodium borohydride (NaBH4) is a strong reducing agent that can further accelerate the reduction to produce gold particles. It only takes 0.5 hours for gold nanorods to grow on the already formed gold nanoparticles. This shows that the crystallization speed of the regular growth of gold nanorods is still higher than the aggregation speed, which is the key to the final formation of gold nanorods with a fixed aspect ratio; the addition of sodium borohydride causes the solution to change from colorless to purple-red (a sign of the formation of gold nanorods, the purple-red color is due to the surface plasmon resonance absorption of gold nanorods).

[0024] The method of the invention can complete the synthesis of gold nanorods within 1 hour, and at the same time greatly reduces the dosage of silver nitrate, sodium borohydride and ascorbic acid (the molar ratio of hexadecyltrimethylammonium bromide, silver nitrate, ascorbic acid, sodium borohydride and chloroauric acid is 223:0.24:2.4:0.002-0.003:1), thereby realizing a rapid, energy-saving, efficient and environmentally friendly preparation process; and the gold nanorods are uniform in size, present a regular rod shape, have good reproducibility, are convenient for high-yield output, and can promote the widespread application of GNRs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a transmission electron microscope image of the gold nanorods prepared by the traditional synthesis method in Comparative Example 1;

[0026] Figure 2 This is the particle size distribution diagram of the gold nanorods prepared in Comparative Example 1;

[0027] Figure 3 is a transmission electron microscopy image of the gold nanorods prepared in Example 1;

[0028] Figure 4 This is a particle size distribution diagram of the gold nanorods prepared in Example 1;

[0029] Figure 5 This is a TEM image of the product obtained by adding excess sodium borohydride in Comparative Example 2;

[0030] Figure 6 This is a TEM image of the product before sodium borohydride is added in Example 1;

[0031] Figure 7 This is a TEM image of the product after sodium borohydride was added for 2 minutes in Example 1;

[0032] Figure 8 This is a physical picture of the color of the solution after adding chloroauric acid to the CTAB solution in Example 1, wherein a is a side view of the beaker solution, and b is a top view of the beaker solution;

[0033] Fig. 9 The color of the solution after adding ascorbic acid in Example 1 is a physical picture, wherein a is a side view of the solution in the beaker, and b is a top view of the solution in the beaker;

[0034] Fig.10 This is a physical picture of the color of the solution after sodium borohydride is added in Example 1, wherein a is a side view of the solution in the beaker, and b is a top view of the solution in the beaker. DETAILED DESCRIPTION

[0035] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0036] The present invention provides a method for efficiently synthesizing gold nanorods in situ, comprising the following steps:

[0037] The aqueous solution of hexadecyltrimethylammonium bromide and the aqueous solution of chloroauric acid are first mixed to obtain a first mixture;

[0038] performing a second mixing of the first mixture and an aqueous solution of silver nitrate to obtain a second mixture;

[0039] After adding an ascorbic acid aqueous solution dropwise to the second mixture, an aqueous sodium borohydride solution is added dropwise to obtain a third mixture;

[0040] The third mixture is allowed to stand to obtain gold nanorods;

[0041] The molar ratio of sodium borohydride in the sodium borohydride aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 0.002-0.003:1;

[0042] The standing temperature is 20-30° C., and the standing time is 0.5-1 h.

[0043] In the present invention, the molar ratio of cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is preferably 223:1.

[0044] The present invention preferably adds an aqueous solution of chloroauric acid to an aqueous solution of hexadecyltrimethylammonium bromide, and performs a first mixing under stirring. The present invention has no particular limitation on the concentrations of the aqueous solution of hexadecyltrimethylammonium bromide and the aqueous solution of chloroauric acid, and the molar ratio can be adjusted to meet the required requirements according to actual needs.

[0045] In the present invention, the stirring speed of the first mixing is preferably 300-500 rpm, and the stirring time is preferably 5 min.

[0046] In the present invention, the molar ratio of silver nitrate in the silver nitrate aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is preferably 0.24:1.

[0047] In the present invention, preferably, silver nitrate aqueous solution is added to the first mixture, and the second mixing is performed under stirring conditions. The present invention has no particular limitation on the concentration of the silver nitrate aqueous solution, and the concentration can be adjusted to meet the required molar ratio according to actual needs.

[0048] In the present invention, the stirring speed of the second mixing is preferably 150-250 rpm, and the time is preferably 2 min.

[0049] In the present invention, the molar ratio of ascorbic acid in the ascorbic acid aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is preferably 2.4:1.

[0050] In the present invention, the dripping speed of the ascorbic acid aqueous solution is preferably 8 to 12 drops / min, more preferably 8 drops / min. If the volume of the ascorbic acid aqueous solution is large, a multi-dropper can be used to drip multiple drops separately and simultaneously, and the dripping is controlled to be completed within 1 to 2 minutes. The present invention has no special limitation on the concentration of the ascorbic acid aqueous solution, and the required molar ratio can be adjusted according to actual needs.

[0051] After the ascorbic acid aqueous solution is added dropwise, in order to ensure the reducing activity of sodium borohydride, the present invention preferably immediately adds dropwise a freshly prepared sodium borohydride aqueous solution with ice water. The immediately and freshly described in the present invention have no special meanings, and the sodium borohydride aqueous solution can be used immediately after being prepared according to the preparation process of the sodium borohydride aqueous solution well known in the art.

[0052] In the present invention, the preparation method of the sodium borohydride aqueous solution is preferably: cooling distilled water to freezing point to obtain ice water, dissolving sodium borohydride solid in the ice water, and obtaining a freshly prepared sodium borohydride aqueous solution. The present invention has no particular limitation on the concentration of the sodium borohydride aqueous solution, and the concentration can be adjusted to meet the required molar ratio according to actual needs.

[0053] In the present invention, the molar ratio of sodium borohydride in the sodium borohydride aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 0.002-0.003:1, preferably 0.0024-0.0029:1.

[0054] In the present invention, the dripping speed of the sodium borohydride aqueous solution is preferably 4 to 6 drops / min, more preferably 6 drops / min. If the volume of the newly prepared sodium borohydride aqueous solution is large, a multi-dropper can be used to drip multiple drops separately and simultaneously, and the dripping is controlled to be completed within 1 minute.

[0055] After the addition of the sodium borohydride aqueous solution is completed, the present invention allows the obtained third mixture to stand at a temperature of 20 to 30° C., more preferably 25° C., for 0.5 to 1 h, more preferably 0.5 h.

[0056] After the standing, the gold nanorod product is centrifuged at 8000 rpm for 10 min, washed with water for 3 times, and redispersed in a 0.05% mass concentration of hexadecyltrimethylammonium bromide aqueous solution for standby use.

[0057] The gold nanorods of the present invention exist in the form of a dispersion.

[0058] The order of adding sodium borohydride (NaBH4) will affect its role in the synthesis of gold nanorods. The specific influence and mechanism of the order of adding sodium borohydride in the synthesis method of the present invention and the traditional gold seed synthesis method are as follows:

[0059] In the traditional gold seed synthesis method, sodium borohydride is usually added before synthesizing the gold seed, that is, sodium borohydride is added first to synthesize the gold seed, and then the remaining ingredients are added.

[0060] Mechanism of action: Formation of gold seeds: Sodium borohydride, as a strong reducing agent, can quickly reduce the gold ions in chloroauric acid to the zero-valent state of gold (Au 0 ), forming small gold nanoseeds. These gold seeds are the basis for the subsequent growth of gold nanorods.

[0061] Selective deposition: After the seeds are formed, the gold and silver ions in the subsequent reactions will selectively deposit on the surface of the gold seeds, causing the gold nanorods to grow in a certain direction. At this time, the role of sodium borohydride is mainly to ensure the formation of gold seeds rather than directly interfering with subsequent growth.

[0062] In the synthesis method of the present invention, sodium borohydride is added after ascorbic acid, that is, sodium borohydride is added after gold ions are reduced to gold particles.

[0063] Mechanism of action: Initial reduction: Under the action of ascorbic acid, the gold ions in chloroauric acid are first reduced to tiny gold particles (Au + ), this step does not depend on the seeds but on the reducing ability of ascorbic acid.

[0064] Rapid reduction and particle growth: When sodium borohydride is added, the reaction quickly changes from colorless and transparent to purple-red. Due to the strong reducing ability of sodium borohydride, a small dose of sodium borohydride will enhance the production rate of gold particles, which allows gold nanorods to grow in a shorter time.

[0065] Therefore, the method of the present invention is different from the reducing environment of the traditional gold seed synthesis method: in the gold seed synthesis method, the formation process of the gold seed is relatively mild, mainly relying on controlling the slow deposition of the gold particles; while in the synthesis method of the present invention, the addition of a small dose of sodium borohydride quickly changes the reaction environment, prompting more gold particles to participate in the growth of the gold rods at the same time, rather than quickly producing a large amount of deposition, thereby ensuring the formation of stable gold nanorods.

[0066] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0067] Example 1

[0068] The preparation method of gold nanorods is as follows:

[0069] 1) adding 0.7 mL of 0.01 g / mL chloroauric acid (HAuCl4) aqueous solution to 23 mL of 0.20 mol / L hexadecyltrimethylammonium bromide aqueous solution (CTAB), stirring at 300 rpm for 5 min until the solution becomes clear and transparent, to obtain a first mixture; wherein the molar ratio of hexadecyltrimethylammonium bromide (4.6 mmol) to chloroauric acid (0.0206 mmol) is 223:1;

[0070] 2) adding 0.5 mL of 10 mmol / L silver nitrate (AgNO3) aqueous solution to the first mixture, stirring at 150 rpm for 2 min to obtain a second mixture; wherein the molar ratio of silver nitrate (0.005 mmol) to chloroauric acid (0.0206 mmol) is 0.24:1;

[0071] 3) adding 0.5 mL of 100 mmol / L ascorbic acid aqueous solution to the second mixture at a rate of 8 drops / min; wherein the molar ratio of ascorbic acid (0.05 mmol) to chloroauric acid is 2.4:1;

[0072] 4) adding 50 μL of a 1 mmol / L sodium borohydride (NaBH4) aqueous solution freshly prepared with ice water to the mixture obtained in step 3) at a rate of 6 drops / min, the solution turns purple-red, and the molar ratio of sodium borohydride (0.00005 mmol) to chloroauric acid is 0.0024:1;

[0073] 5) The mixture obtained in step 4) was allowed to stand at room temperature (25° C.) for 30 min, the obtained gold nanorod product was centrifuged at a speed of 8000 rpm for 10 min, washed with water for 3 times, and redispersed in a CTAB aqueous solution with a mass concentration of 0.05% for later use.

[0074] Example 2

[0075] To 46 mL of 0.20 mol / L hexadecyltrimethylammonium bromide aqueous solution (CTAB), 1.42 mL of 0.029 mol / L chloroauric acid (HAuCl4) aqueous solution was added, and the mixture was stirred at 300 rpm for 5 min until the solution became clear and transparent, to obtain a first mixture; wherein the molar ratio of hexadecyltrimethylammonium bromide (9.2 mmol) to chloroauric acid (0.0412 mmol) was 223:1;

[0076] 2) adding 1 mL of 10 mmol / L silver nitrate (AgNO3) aqueous solution to the first mixture, stirring at 150 rpm for 2 min to obtain a second mixture; wherein the molar ratio of silver nitrate (0.01 mmol) to chloroauric acid is 0.24:1;

[0077] 3) adding 1 mL of 100 mmol / L ascorbic acid aqueous solution to the second mixture at a rate of 8 drops / min; wherein the molar ratio of ascorbic acid (0.1 mmol) to chloroauric acid is 2.4:1;

[0078] 4) Add 120 μL of a 1 mmol / L sodium borohydride (NaBH4) aqueous solution prepared with ice water to the mixture obtained in step 3) at a drop rate of 6 drops / min, and the solution turns purple-red. The molar ratio of sodium borohydride (0.00012 mmol) to chloroauric acid is 0.0029:1;

[0079] 5) The mixture obtained in step 4) was allowed to stand at room temperature (25° C.) for 30 min, the obtained gold nanorod product was centrifuged at a speed of 8000 rpm for 10 min, washed with water for 3 times, and redispersed in a CTAB aqueous solution with a mass concentration of 0.05% for later use.

[0080] Comparative Example 1

[0081] Traditional synthesis method: Preparation of gold nanorods using silver ion-assisted seed-mediated synthesis:

[0082] A HAuCl4 aqueous solution (1 mL, 0.0025 mol / L) was added to a CTAB aqueous solution (9 mL, 0.1 mol / L) in a glass tube to prepare a seed solution, and then 0.6 mL of ice-cold 0.01 mol / L NaBH4 was added and magnetically stirred (1200 rpm, 2 min) to obtain a brown-yellow seed solution; the seed solution was stored at room temperature for 2 h before use.

[0083] HAuCl4 (1 mL, 0.0025 mol / L), AgNO3 (240 μL, 0.01 mol / L) and CTAB (20 mL, 0.1 mol / L) were mixed in a glass tube to prepare a growth solution. A freshly prepared L-ascorbic acid solution (160 μL, 0.1 mol / L) was added. After mixing, the growth solution changed from yellow-orange to colorless under mild stirring (indicating that Au 3+ Partially reduced to Au + ), then 400 μL HCl (1.0 mol / L) was added to adjust the pH value to 3.5. After mixing, 24 μL of seed solution was added, and the resulting reaction mixture was stirred for 30 s, allowed to stand at room temperature for 18 h, purified by centrifugation (8500 rpm, 25 min), washed several times with deionized water, the supernatant was discarded, and the precipitate was redispersed in 5 mL of deionized water to obtain a gold nanorod dispersion sample.

[0084] Comparative Example 2

[0085] The only difference from Example 1 is that 100 μL of 1 mmol / L NaBH4 aqueous solution is added dropwise, that is, the molar ratio of sodium borohydride to chloroauric acid is 0.0048:1; and the dripping rate of the sodium borohydride aqueous solution is 6 drops / min.

[0086] Characterization

[0087] Figure 1 This is a transmission electron microscope image of the gold nanorods prepared by the traditional gold seed synthesis method in Comparative Example 1; Figure 2 The particle size distribution diagram of the gold nanorods prepared in Comparative Example 1; Figures 1-2 As shown, the gold nanorods appear to be disordered, uneven, of varying lengths, and cannot present a regular rod shape.

[0088] Figure 3 is a transmission electron microscopy image of the gold nanorods prepared in Example 1; Figure 4 The particle size distribution diagram of the gold nanorods prepared in Example 1; Figures 3-4 As shown, the prepared gold nanorods have uniform size and regular rod-like morphology, and the method has good reproducibility.

[0089] Figure 5 TEM image of the product obtained by adding excess sodium borohydride in Comparative Example 2; Figure 5 As shown, excessive sodium borohydride may trigger a large amount of rapid deposition of gold particles, generating gold nanoparticles of other morphologies (nanospheres, nanoflowers).

[0090] Figure 6 This is a TEM image of the product before sodium borohydride is added in Example 1; Figure 7 TEM image of the product after sodium borohydride was added for 2 minutes in Example 1; Figures 6-7By comparison, when sodium borohydride is not present, the rate of gold particle reduction by ascorbic acid is slower and the particle size is smaller ( Figure 6 ); Sodium borohydride is a strong reducing agent, and its addition significantly accelerates the rate at which ascorbic acid is reduced to produce gold particles ( Figure 7 ), we can see that a small amount of gold nanorods have begun to grow. However, the amount of sodium borohydride added needs to be controlled. If excessive sodium borohydride is added, the aggregation rate of gold particles will be higher than the crystal formation rate, resulting in a large amount of deposition, such as Figure 5 .

[0091] Figure 8 : is a physical picture of the color of the solution after adding chloroauric acid to the CTAB solution in Example 1, wherein a is a side view of the beaker solution, and b is a top view of the beaker solution; Figure 8 It can be seen that the solution after mixing CTAB solution and chloroauric acid solution is orange-yellow, which is due to the ion pair complex (CTAB) formed by the electrostatic attraction between CTAB and chloroauric acid. + -AuCl4 - ), which can prevent gold ions from aggregating and make the solution clear and stable.

[0092] Fig. 9 The color of the solution after adding ascorbic acid in Example 1 is a physical picture, wherein a is a side view of the solution in the beaker, and b is a top view of the solution in the beaker; Fig. 9 It can be seen that after adding ascorbic acid, the color of the solution changes from orange to colorless. This change is due to the fact that ascorbic acid destroys AuCl4 - The coordination state makes the solution colorless and acts as a reducing agent to 3+ Reduction to Au + .

[0093] Fig.10 The color of the solution after adding sodium borohydride in Example 1 is a physical picture, wherein a is a side view of the solution in the beaker, and b is a top view of the solution in the beaker; Fig.10 It can be seen that after adding sodium borohydride solution, the solution changes from colorless and transparent to red. Because the reducing property of sodium borohydride is stronger than that of ascorbic acid, it can promote the reduction rate of gold nanoparticles, accelerate the aggregation and growth of particles, and make gold nanoparticles form gold nanorods, causing the position and shape of their surface plasmon resonance (SPR) bands to change, thereby causing color changes.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for efficiently synthesizing gold nanorods in situ, characterized in that: The following steps are involved: The aqueous solution of hexadecyltrimethylammonium bromide and the aqueous solution of chloroauric acid are first mixed to obtain a first mixture; performing a second mixing of the first mixture and an aqueous solution of silver nitrate to obtain a second mixture; After adding an ascorbic acid aqueous solution dropwise to the second mixture, an aqueous sodium borohydride solution is added dropwise to obtain a third mixture; The third mixture is allowed to stand to obtain gold nanorods; The molar ratio of sodium borohydride in the sodium borohydride aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 0.002-0.003:1; The standing temperature is 20-30° C., and the standing time is 0.5-1 h.

2. The method according to claim 1, characterized in that: The molar ratio of cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 223:

1.

3. The method according to claim 1 or 2, characterized in that: The stirring speed of the first mixing is 300-500 rpm, and the stirring time is 5 min.

4. The method according to claim 1, characterized in that: The molar ratio of silver nitrate in the silver nitrate aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 0.24:

1.

5. The method according to claim 1 or 4, characterized in that: The stirring speed of the second mixing is 150-250 rpm, and the time is 2 min.

6. The method according to claim 1, characterized in that The molar ratio of ascorbic acid in the ascorbic acid aqueous solution to chloroauric acid in the chloroauric acid aqueous solution is 2.4:

1.

7. The method according to claim 1 or 6, characterized in that: The dropping speed of the ascorbic acid aqueous solution is 8 to 12 drops / min.

8. The method according to claim 1, characterized in that The dropping speed of the sodium borohydride aqueous solution is 4 to 6 drops / min.

9. The method according to claim 1 or 8, characterized in that: The preparation method of the sodium borohydride aqueous solution comprises: cooling distilled water to freezing point to obtain ice water, and dissolving sodium borohydride solid in the ice water to obtain the sodium borohydride aqueous solution.

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