Synthesis method of gold and silver nanoparticles with chiral optical properties regulated and controlled by acid and alkali under multi-head-based surfactant system

Abstract

The invention discloses a method for synthesizing gold and silver nanoparticles with chiral optical properties regulated and controlled by acid and alkali under a multi-head-based surfactant system. The synthesis adjusting method comprises the following steps: adding gold nanoparticle cores into a solution of a multi-head-based surfactant, then adding a chiral inducer, and reducing silver ions by adjusting the pH value of a system to obtain the gold and silver nanoparticles with different circular dichroism properties including circular dichroism signal inversion. The multi-head cationic surface active agent is introduced, the ionization condition of the head group of the cationic surface active agent is changed by adjusting the pH value, and regulation and control of weak interaction such as Van der Waals force among molecules of the multi-head cationic surface active agent with different ionic states and electrostatic interaction with metal nanoparticles are achieved; therefore, chiral optical signals including positive and negative circular dichroism signals are simply regulated and controlled in the synthesis process of the gold and silver nanoparticles, and synthesis of the gold and silver nanoparticles with different chiral optical properties is achieved.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing gold and silver nanoparticles with acid-base regulated chiral optical properties under a multi-head group surfactant system, and belongs to the field of preparation of inorganic nanomaterials. Background Art

[0002] Chirality widely exists in nature, referring to the phenomenon that the mirror image of a substance cannot coincide with itself. If this object is a molecule and cannot coincide with its mirror image, then this molecule is a chiral molecule. According to the different roots of destroying molecular symmetry, chiral molecules can be classified into categories such as central chirality, axial chirality, planar chirality, and helical chirality. The research on chirality has also extended to materials science.

[0003] In recent years, the research on chiral gold nanoparticles has received extensive attention. This is mainly because nanoparticles of noble metals such as gold exhibit surface plasmon resonance different from general absorption at a nanoscale much smaller than the macroscopic scale on the basis of excellent electromagnetic and thermal properties such as high electrical conductivity and high thermal conductivity of noble metals, thus showing unique spectroscopic characteristics. This unique spectroscopic property can form a strong chiral optical signal through chiral coupling with ligands, nanoparticle morphology, and self- and co-assemblies. For example, some work synthesized nearly ellipsoidal gold and silver nanoparticles with circular dichroism signals through cysteine induction, and some work introduced aromatic small molecules with mercapto groups into the surfactant system to obtain a double square pyramid structure. There are also reports of synthesizing helical gold and silver alloy double arrow particles by simultaneously introducing cysteine and organic small molecules with mercapto groups. In addition, some work introduced cubic seeds and induced various morphologies with mercapto-modified peptides, and at the same time obtained chiral optical signals. However, these methods rely on the regulation of mercapto-containing molecules, and there are few methods to regulate the chiral optical properties of gold and silver nanoparticles by simply regulating ordinary physical and chemical properties. Therefore, the present invention is proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for regulating the circular dichroism properties of synthesized gold and silver nanoparticles. By introducing a multi-head group cationic surfactant and adjusting the acidity and alkalinity to change the ionization of the surfactant head groups, the regulation of weak interactions such as van der Waals forces between different ionic state multi-head group cationic surfactant molecules and electrostatic interactions with metal nanoparticles is realized. Simply during the synthesis process of gold and silver nanoparticles, the chiral optical signals including the positive and negative of the circular dichroism signal are regulated, and the synthesis of gold and silver nanoparticles with different chiral optical properties is achieved.

[0005] The method for synthesizing and regulating the circular dichroism properties of gold and silver nanoparticles provided by the present invention includes the following steps: Add the gold nanoparticle core into the solution of the multi-headed surfactant, then add the chiral inducer, and reduce silver ions by adjusting the pH of the system (preferably 2 - 8, more preferably 5.0 - 7.5) to obtain gold-silver nanoparticles with different circular dichroism properties including circular dichroism signal inversion.

[0006] The present invention focuses on the simple property of acidity and alkalinity in the synthesis process. By adjusting the acidity and alkalinity of the reaction system, it realizes the simple regulation of the chiral optical properties of gold-silver nanoparticles during the synthesis process, provides methods and inspirations for the mechanism and methods of regulating chiral optical properties such as chiral plasmonic materials by simple physical and chemical properties during the synthesis process, is conducive to further improving the understanding of chiral plasmonic materials, and provides the necessary theoretical and practical basis for the wider application of chiral materials.

[0007] In the synthesis regulation method of the present invention, the seed growth method is used to prepare the gold nanoparticle core from the gold seeds; The preparation method of the gold seeds is as follows: Add the gold source into the cetyltrimethylammonium bromide solution, stir constantly at a constant temperature in a water bath, and then add the reducing agent A, and obtain it through reaction; The concentration of the cetyltrimethylammonium bromide solution is 0.05 - 0.25 M, and the addition amount can be 5 - 25 mL; The gold source is chloroauric acid, which is added in the form of a solution with a mass-volume fraction of 0.1 - 2% (g / 100 mL), and the addition amount can be 20 - 100 μL; The reducing agent A is sodium borohydride, which is added in the form of a solution with a concentration of 5 - 20 mM, and the addition amount can be 0.2 - 1 mL; The temperature of the water bath is 20 - 50 °C; The stirring time is longer than 5 min, such as 15 min.

[0008] In the synthesis regulation method of the present invention, the seed growth method includes the following steps: Add the silver source and the gold source into the composite surfactant solution, then add hydrochloric acid, the reducing agent B and the gold seeds, and obtain it through growth.

[0009] In the synthesis regulation method of the present invention, the composite surfactant includes cetyltrimethylammonium bromide and sodium oleate. The concentration of the cetyltrimethylammonium bromide is 10 - 200 mM, and the concentration of the sodium oleate is 1 - 50 mM; The silver source is silver nitrate, which is added in the form of a solution with a concentration of 0.05 - 0.5 M; The gold source is chloroauric acid, which is added in the form of a solution with a mass-volume fraction of 0.1 - 2%; The reducing agent B is ascorbic acid, which is added in the form of a solution with a concentration of 10-100 mM; The amount of the seed solution added can be 10-50 μL; The gold-silver nanoparticles are obtained by centrifugal separation and purification; the centripetal acceleration during the centrifugal separation and purification process can be 1000-7500 g , preferably 2500 g ; the centrifugation time can be 3-10 min, preferably 5 min; then the supernatant is removed, water is added, and centrifugation is performed again to remove the supernatant.

[0010] In the synthesis regulation method of the present invention, the multi-headed surfactant is N , N -bis(aminoethylacylmethylethyl)octadecylamine, which is added in the form of a solution with a concentration of 1-10 mM; The chiral inducer is cysteine, which is added in the form of a solution with a concentration of 0.5–100 mM.

[0011] In the synthesis regulation method of the present invention, ascorbic acid is used to reduce silver nitrate to realize the reduction of silver ions; The ascorbic acid is added in the form of a solution with a concentration of 10-100 mM; The silver nitrate is added in the form of a solution with a concentration of 0.05-0.5 M.

[0012] In the synthesis regulation method of the present invention, when the amount of the gold nanoparticle core is 1 mL, the amount of hydrochloric acid, nitric acid or sulfuric acid added is 0-200 μL (but not zero) to change the pH of the system to 2-8, preferably 50-100 μL of hydrochloric acid is added to change the pH of the system to 5.0-7.5.

[0013] In the synthesis regulation method of the present invention, after adding various solutions, stirring should not exceed 5 min and then standing for at least 15 min; the stirring speed can be 50-250 rpm.

[0014] In the present invention, a multi-headed cationic surfactant is introduced. By adjusting the pH to change the ionization of the surfactant head group, the regulation of weak interactions such as van der Waals forces between different ionic multi-headed cationic surfactant molecules and electrostatic interactions with metal nanoparticles is realized, so as to simply regulate chiral optical signals including the positive and negative of circular dichroism signals during the synthesis of gold-silver nanoparticles, and realize the synthesis of gold-silver nanoparticles with different chiral optical properties. Description of the Drawings

[0015] Figure 1 is the ultraviolet-visible spectrum of the gold nanoparticle core in step (1) prepared in Example 1 of the present invention.

[0016] Figure 2 Scanning electron microscope photograph of the gold nanoparticle core prepared in Example 1 of the present invention.

[0017] Figure 3 Transmission electron microscope photograph of the gold nanoparticle core prepared in Example 1 of the present invention.

[0018] Figure 4 UV-Vis spectrum of the gold-silver nanoparticles with different circular dichroism properties under pH regulation prepared in Example 2 of the present invention.

[0019] Figure 5 Circular dichroism spectrum of the gold-silver nanoparticles with different circular dichroism properties under pH regulation prepared in Example 2 of the present invention.

[0020] Figure 6 Scanning electron microscope photograph (scale bar is 500 nm) of the gold-silver nanoparticles with different circular dichroism properties under pH regulation prepared in Example 2 of the present invention.

[0021] Figure 7 Transmission electron microscope photograph (scale bar is 100 nm) of the gold-silver nanoparticles with different circular dichroism properties under pH regulation prepared in Example 2 of the present invention. Detailed implementation manners

[0022] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0023] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial channels.

[0024] The multi-headed surfactants involved in the present invention refer to surfactants that contain multiple hydrophilic head groups or multiple hydrophobic chains in one molecular structure.

[0025] The circular dichroism signal involved in the present invention is the spectral characteristic exhibited by the absorption difference of chiral substances for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP).

[0026] The circular dichroism signal inversion involved in the present invention refers to the change in the sign of the ellipticity (θ) at a specific wavelength in the circular dichroism spectrum (CD spectrum) (for example, from a positive peak to a negative peak, or vice versa).

[0027] The present invention realizes the change of chiral optical signals including the positive and negative of circular dichroism signals and intensity by introducing multi-headed cationic surfactants during the synthesis process and regulating the pH. The present invention utilizes the simple property of acidity and alkalinity during the synthesis process, and realizes the simple regulation of the chiral optical properties of gold and silver nanoparticles during the synthesis process by adjusting the acidity and alkalinity of the reaction system.

[0028] The multi-headed surfactants used in the following examples N , N -Bis(aminoethylacylmethylethyl)octadecylamine was prepared according to the method provided in the following literature: Wang W, Lu W, Jiang L. Influence of pHon the aggregation morphology of a novel surfactant with single hydrocarbonchain and multi-amine headgroups. J Phys Chem B . 2008, 112, 1409-1413.

[0029] Example 1. Preparation of gold nanoparticle cores by the seed growth method 1) Preparation of gold seeds Add 50 μL of chloroauric acid (2 w / v%) to 10 mL of cetyltrimethylammonium bromide solution (0.1 M). After stirring with a magnetic stirrer in a 30 °C water bath for 15 minutes, add 0.6 mL of sodium borohydride (10 mM) for reaction to obtain gold seeds.

[0030] 2) Take 12.5 mmol of cetyltrimethylammonium bromide and 2.5 mmol of sodium oleate, add 125 mL of water, stir with a magnetic stirrer in a 30 °C water bath for 2 hours and then let stand for 2 hours to obtain a composite surfactant solution of cetyltrimethylammonium bromide and sodium oleate. Subsequently, add 500 μL of silver nitrate (0.1 M), stir for 1 min and then let stand for 15 minutes. After adding 2.5 mL of chloroauric acid (2 w / v, g / 100 mL) and 125 mL of water and stirring, add 10 mL of hydrochloric acid (1 M), continue to stir for 15 minutes, add 750 μL of ascorbic acid (50 mM) and 20 μL of the gold seeds prepared above, let stand in a 30 °C water bath for 4 hours, take out the reaction solution, and centrifuge at 7000 g Centrifuge for 10 minutes, aspirate the supernatant to remove the surfactant, then add water and centrifuge in the same way, aspirate the supernatant again and add water to make up the volume to 25 mL.

[0031] The ultraviolet-visible spectrum of the gold nanoparticle cores obtained in this example is as Figure 1 shown, and the scanning electron microscope photograph is asFigure 2 As shown, the transmission electron microscope photograph is as Figure 3 shown.

[0032] From Figure 1 it can be seen that a strong absorption peak of the gold nanoparticle core is located at 830 nm, and another weaker absorption peak is located at 510 nm, which is consistent with the surface plasmon extinction property of noble metal nanorods.

[0033] From Figure 2 it can be seen that the synthesized gold nanoparticle core has a cylindrical rod-like structure, and there is a widespread side-by-side self-assembly phenomenon in the sample prepared by sampling and drying on a silicon wafer.

[0034] From Figure 3 it can be seen that the synthesized gold nanoparticle core has a cylindrical rod-like structure, and the major axis and minor axis dimensions are (93±6) nm and (24±2) nm respectively obtained by measurement and statistics.

[0035] Example 2: Synthesis of gold-silver nanoparticles with reversed circular dichroism signal Take 0.025 mmol N , N -bis(aminoethylacylmethylethyl)octadecylamine, add 5 mL of water and 0 / 10 / 50 / 100 / 150 / 200 μL of hydrochloric acid (1 M), stir for 15 minutes in a 30 °C water bath, and add 1 mL of the gold nanoparticle core colloid prepared in the example. After stirring for 15 minutes, add 60 μL of L-cysteine (10 mM), stir for 1 hour, add 60 μL of silver nitrate (0.1 M) and 300 μL of ascorbic acid (0.1 M), and let it stand in a 30 °C water bath for 4 hours after stirring for 1 hour. Take out the reaction solution, centrifuge at 2500 g for 10 minutes, then suck out the supernatant to remove the surfactant, add water and centrifuge in the same way, and after sucking out the supernatant again, add water to make up the volume to 1 mL.

[0036] Among them, when the addition amounts of hydrochloric acid (1 M) are 1, 10, 50, 100, 150, and 200 μL, the corresponding pH values of the systems are 8.5, 8.0, 7.5, 5.0, 3.5, and 2.5 in sequence.

[0037] The ultraviolet-visible spectrum of the gold-silver nanoparticles prepared in this example is as Figure 4 shown, the circular dichroism spectrum is as Figure 5 shown, the scanning electron microscope photograph is as Figure 6 shown, and the transmission electron microscope photograph is as Figure 7 shown. Figure 6 and Figure 7Figures a)-f) therein are the scanning electron microscope photos and transmission electron microscope photos when the hydrochloric acid concentration is 0, 10 μL, 50 μL, 100 μL, 150 μL, and 200 μL respectively.

[0038] It can be seen from Figure 4 that the absorption peak at 600 - 800 nm shows a trend of first blue shift and then red shift with the increase of the amount of added hydrochloric acid. According to the law of surface plasmon extinction of noble metal nanorods, it can be seen that with the increase of the amount of hydrochloric acid, it is initially beneficial to the growth of silver on the gold nanoparticle core, but it becomes unfavorable after the pH decreases to a certain extent.

[0039] It can be seen from Figure 5 that by changing the pH with the amount of added hydrochloric acid, the enhancement of the circular dichroism signal of the synthesized gold-silver nanoparticles is achieved. Especially when the amount of added hydrochloric acid (1 M) increases from 50 μL to 100 μL, the circular dichroism signal is reversed.

[0040] It can be seen from Figure 6 and Figure 7 that when the amount of added hydrochloric acid is too low, no obvious circular dichroism signal can be detected. Comparing the numerous small particles photographed in Figures a) and b) in Figure 6 and Figures a) and b) in Figure 7 , it is speculated that the reason is that the too low amount of hydrochloric acid leads to a relatively high pH of the reaction solution, thus causing the multi-headed surfactant N , N -bis(aminoethylacylmethylethyl)octadecylamine not to be fully dissolved to form micelles, which hinders the growth of the reduced silver atoms on the gold nanorod core and causes the silver atoms to crystallize to form particles. While in Figure c) in Figure 6 and Figure c) in Figure 7 , an arrow shape with a concave middle can be observed. This asymmetry may be the reason for the more obvious circular dichroism signal of the silver-shell gold-silver nanoparticles synthesized with 50 μL of hydrochloric acid (1M).

[0041] In contrast, Figure 6 in Figures e) and f) in Figure 7 and Figures e) and f) in Figure 5 , it can be observed that the shape of the synthesized silver-shell gold-silver nanoparticles is close to a symmetric cylinder, indicating that too much hydrochloric acid is also unfavorable for the generation of the asymmetry of the silver-shell gold-silver nanoparticles. This can be confirmed by the circular dichroism spectra of the silver-shell gold-silver nanoparticles synthesized with 100 μL and 200 μL of hydrochloric acid (1 M) in

[0042] In summary, it can be seen that by introducing a multi-headed surfactant during the synthesis process and changing the pH with the amount of added hydrochloric acid, the morphology and circular dichroism signal of the synthesized gold-silver nanoparticles are regulated, including the regulation of the positive and negative and intensity of the circular dichroism signal.

[0043] The present invention has been described in detail above. For those skilled in the art, without departing from the spirit and scope of the present invention and without unnecessary experiments, the present invention can be implemented within a relatively wide range under equivalent parameters, concentrations, and conditions. Although specific embodiments of the present invention are given, it should be understood that the present invention can be further improved. In short, according to the principle of the present invention, this application intends to cover any modifications, uses, or improvements to the present invention, including changes made using conventional techniques known in the art that depart from the scope disclosed in this application.

Claims

1. A method for synthesizing and adjusting the circular dichroism properties of gold and silver nanoparticles, comprising the following steps: The gold nanoparticle core is added to a solution of a multi-head surfactant, and then a chiral inducer is added. By adjusting the pH of the system, silver ions are reduced to obtain gold and silver nanoparticles with different circular dichroism properties including circular dichroism signal inversion.

2. The synthesis adjustment method according to claim 1, characterized in that: The gold nanoparticle core is prepared from gold seeds by using a seed growth method; The preparation method of the gold seed is as follows: The gold source is added to the hexadecyltrimethylammonium bromide solution, and the reducing agent A is added after constant temperature stirring in a water bath to obtain; The concentration of the hexadecyltrimethylammonium bromide solution is 0.05-0.25 M; The gold source is chloroauric acid, which is added in the form of a solution with a mass volume fraction of 0.1-2%; The reducing agent A is sodium borohydride, which is added in the form of a solution with a concentration of 5-20 mM; The temperature of the water bath is 20-50°C; The stirring time is longer than 5 min.

3. The synthesis adjustment method according to claim 2, characterized in that: The seed growth method comprises the following steps: A silver source and a gold source are added to a composite surfactant solution, and then hydrochloric acid, a reducing agent B and the gold seed are added to obtain the composite surfactant solution through growth.

4. The synthesis adjustment method according to claim 3, characterized in that: The composite surfactant comprises hexadecyltrimethylammonium bromide and sodium oleate, wherein the concentration of the hexadecyltrimethylammonium bromide is 10-200 mM, and the concentration of the sodium oleate is 1-50 mM; The silver source is silver nitrate, which is added in the form of a solution with a concentration of 0.05-0.5 M; The gold source is chloroauric acid, which is added in the form of a solution with a mass volume fraction of 0.1-2%; The reducing agent B is ascorbic acid, which is added in the form of a solution with a concentration of 10-100 mM; The amount of gold seed solution added was 10-50 μL; The gold and silver nanoparticles are obtained by centrifugal separation and purification.

5. The synthetic regulation method according to any one of claims 1 to 4, characterized in that: The multi-head surfactant is N , N - di(aminoethylacylmethylethyl)octadecylamine, added in the form of a solution at a concentration of 1-10 mM; The chiral inducing agent is cysteine, which is added in the form of a solution with a concentration of 0.5-100 mM.

6. The synthetic regulation method according to any one of claims 1 to 5, characterized in that: Reduction of silver ions is achieved by reducing silver nitrate with ascorbic acid; The ascorbic acid is added in the form of a solution having a concentration of 10-100 mM; The silver nitrate is added in the form of a solution with a concentration of 0.05-0.5 M.

7. The synthetic regulation method according to any one of claims 1 to 6, characterized in that: When the amount of the nano-gold particle core is 1 mL, the amount of hydrochloric acid, nitric acid or sulfuric acid added is 0-200 μL to change the pH of the system.

8. Gold and silver nanoparticles with circular dichroism properties synthesized by the method of any one of claims 1 to 7.

9. Application of multi-head cationic surfactants in regulating changes in chiral optical signals including the positive and negative circular dichroism signals and their intensity; The regulation is achieved under the condition of regulating the pH value of the system; The multi-head surfactant is N , N -Bis(aminoethylacylmethylethyl)octadecylamine.

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