Preparation method of gold nanorod assembly

Abstract

The invention belongs to the field of material chemistry and molecular electronics, and discloses a preparation method of a gold nanorod assembly. Comprising the following steps: providing a dispersion system containing a plurality of gold nanorods in a liquid-phase medium; introducing a heterocyclic ring assembly molecule anchored on the surface of the gold nanorod into the dispersion system, wherein the heterocyclic ring assembly molecule comprises an aromatic heterocyclic ring providing structural rigidity, a sulfur-containing anchoring group forming a coordinate bond with the gold surface, and a group or atom capable of forming a hydrogen bond; the gold nanorod assembly comprises at least two gold nanorods and heterocyclic ring assembly molecules located on the gold nanorods respectively, and the two gold nanorods are connected with each other through hydrogen bond supramolecular interaction formed between complementary functional groups of the heterocyclic ring assembly molecules. The preparation of the gold nanorod assembly with high yield and linear orientation is realized by utilizing the heterocyclic ring assembly molecules.

Description

Technical Field

[0001] This invention belongs to the fields of materials chemistry and molecular electronics, and specifically relates to a method for preparing gold nanorod assemblies. Background Technology

[0002] Currently, bottom-up self-assembly technology has evolved into a multi-scale technology system encompassing atomic, molecular, and biological systems, and its applications are expanding from basic assembly to the fabrication of functional devices. However, in fields such as molecular electronics that require the construction of precise electrode-molecule interfaces, electrode materials must simultaneously meet the stringent requirements of nanoscale feature sizes (to achieve atomic-level molecular contact) and surface chemical modifiability (to support precise control of self-assembly). Gold nanorods, with their unique geometric anisotropy and excellent surface chemical activity, have become ideal candidate electrode materials. Nevertheless, constructing stable gold nanorod assemblies suitable for high-yield molecular structure construction still faces significant challenges such as low yield and orientation bends. Low yield affects the success rate of subsequent molecular device fabrication, while orientation bends limit the overlay connection between the assembly and external circuitry, thus restricting its practical application in molecular electronic devices. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention provides a method for preparing gold nanorod assemblies, which achieves high yield and linear orientation of gold nanorod assemblies by utilizing heterocyclic assembly molecules.

[0004] The objective of this invention is achieved through the following technical solution: This invention provides a method for preparing a gold nanorod assembly, comprising the following steps: A dispersion system containing multiple gold nanorods in a liquid medium is provided; Introduce heterocyclic assembly molecules anchored to the surface of the gold nanorods into the dispersion system. The heterocyclic assembly molecules include aromatic heterocycles that provide structural rigidity, sulfur-containing anchoring groups that form coordination bonds with the gold surface, and groups or atoms that can form hydrogen bonds. The gold nanorod assembly comprises at least two gold nanorods and heterocyclic assembly molecules located on each gold nanorod, wherein the two gold nanorods are interconnected by at least two hydrogen bonds formed between complementary functional groups of the heterocyclic assembly molecules.

[0005] In some embodiments, the aromatic heterocycle is a pyridine ring.

[0006] In some embodiments, the sulfur-containing anchoring group that forms a coordination bond with the gold surface is at least one of mercapto or thiomethyl.

[0007] In some embodiments, the sulfur-containing anchoring group that forms a coordination bond with the gold surface is a thiomethyl group.

[0008] In some embodiments, the group or atom capable of forming hydrogen bonds is at least one of pyridine nitrogen and amino groups.

[0009] In some embodiments, the groups or atoms capable of forming hydrogen bonds are pyridine nitrogen and amino groups.

[0010] In some embodiments, the heterocyclic assembly molecule is 2-amino-4-methylthio-pyridine.

[0011] In some embodiments, the gold nanorods have a length of 75.0 ± 0.5 nm and a width of 18.5 ± 0.3 nm.

[0012] In some embodiments, the molar ratio of gold nanorods to heterocyclic assembled molecules in the dispersion system is 1:2250000 to 1:3500000.

[0013] In some embodiments, the molar ratio of gold nanorods to heterocyclic assembled molecules in the dispersion system is 1:2500000.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The method for preparing gold nanorod assemblies provided by this invention uses assemblies that enhance the efficiency of gold anchoring by replacing traditional thiol groups with more stable thiomethyl groups. At the same time, due to the rigid molecular structure and the directional hydrogen bonding of aromatic heterocycles that can form hydrogen bonds, as well as the π-π stacking of aromatic heterocycles, efficient assembly under multi-mode synergistic effect is achieved. This solves the technical bottlenecks of low assembly yield and orientation bending caused by the conformational distribution of traditional flexible alkyl chain hydrogen bond molecules, and achieves the acquisition of gold nanorod assemblies with high yield and linear orientation. Attached Figure Description

[0015] Figure 1 It is 2-amino-4-methylthio-pyridine 1 1H NMR (CDCl3, 298 K) spectrum; Figure 2 Scanning electron microscopy (SEM) images of gold nanorods in Example 1 (a, b); UV absorption spectrum of gold nanorods (c); size measurement of gold nanorods (de). Figure 3 This is a scanning electron microscope image of the gold nanorod assembly from Example 1; Figure 4 The diagram shows the assembly mechanism of gold nanorods in Example 1 (a); the UV-Vis absorption spectrum is shown in (b). Figure 5Transmission electron microscopy characterization of the gold nanorod assembly obtained in Example 1 (a); statistical distribution of nano-intervals (sample size: 120) (b); schematic diagram of theoretically calculated length (c). Figure 6 Transmission electron microscopy (TEM) images of the gold nanorod assemblies obtained in Examples 2-4 (a, b, c); statistical distribution of nano-gap (sample size: 120) (d, e, f); schematic diagram of theoretically calculated length (g, h, i). Figure 7 Electron microscopy distribution of gold nanorods obtained in Example 1 under various assembly conditions (a); Comparison of assembly yield between Example 1 and Examples 2-4 (b). Figure 8 A schematic diagram of the orientation angle of gold nanorod dimers (a); a comparison diagram of the orientation angles of gold nanorod dimers obtained in Examples 1-4 (sample size: 100) (b). Figure 9 The images show scanning electron microscope (SEM) images and solution color photographs of the gold nanorod assemblies obtained in Examples 1 and 7-9. Detailed Implementation

[0016] This invention provides a method for preparing a gold nanorod assembly, comprising the following steps: (1) Preparation of gold nanorods: First, a mixture of chloroauric acid and hexadecyltrimethylammonium bromide (CTAB) was reduced with sodium borohydride to obtain gold seeds. Then, alkali, silver nitrate morphology directing agent, hydroquinone weak reducing agent and gold seeds were added sequentially to the mixed solution of chloroauric acid and CTAB. Gold nanorods were grown using these as seed crystals. The length of the obtained gold nanorods was 75.0±0.5 nm, the width was 18.5±0.3 nm, and the aspect ratio was 3.9. (2) Assembly of gold nanorods: The gold nanorod solution is mixed with the assembly molecule solution dissolved in a specific solvent. The assembly molecule is a heterocyclic assembly molecule, which includes an aromatic heterocycle that provides structural rigidity, a sulfur-containing anchoring group that forms a coordination bond with the gold surface, and a group or atom that can form hydrogen bonds. Specifically, the aromatic heterocycle is a pyridine ring, and the sulfur-containing anchoring group that forms a coordination bond with the gold surface is at least one of mercapto or thiomethyl. Thiomethyl perfectly solves the problem that traditional mercapto is easily oxidized and causes molecular failure. The group or atom that can form hydrogen bonds is at least one of pyridine nitrogen or amino, preferably pyridine nitrogen and amino. The heterocyclic assembly molecule is 2-amino-4-methylthio-pyridine. The molar ratio of gold nanorods to assembly molecules is 1:2250000~1:3500000, and is not limited to this. The solvent used is 1:2250000, 1:2300000, 1:2400000, 1:2500000, 1:2600000, 1:2700000, 1:2800000, 1:2900000, 1:3000000, 1:3100000, 1:3125000, 1:3150000, 1:3200000, 1:3300000, 1:3400000, 1:3500000, with 1:2500000 being the preferred ratio. The solvent used is related to the heterocyclic molecule used. For example, when the assembled molecule is 2-amino-4-methylthio-pyridine, ethanol is required as a solvent, but it is not limited to ethanol. Any solvent that can achieve uniform mixing of the gold nanorod solution and the assembled molecule is acceptable.

[0017] The gold nanorod assembly comprises at least two gold nanorods and a heterocyclic assembly molecule located on each gold nanorod, wherein the two gold nanorods are interconnected by at least two hydrogen bonds formed between complementary functional groups of the heterocyclic assembly molecule.

[0018] The synthetic method for the heterocyclic assembly molecule 2-amino-4-methylthio-pyridine is as follows: 4-Chloroprene-2-amine (500 mg, 3.89 mmol), sodium methanethiol (1.36 g, 19.4 mmol), and 50 mL of acetonitrile were added to a 100 mL sealed tube. The mixture was heated to 110 °C under an argon atmosphere and stirred overnight. After the reaction was complete, the reaction mixture was concentrated under reduced pressure. Ethyl acetate and water were added, and the mixture was extracted twice with ethyl acetate (2 × 100 mL). The organic phases were combined, washed with saturated brine, and dried over anhydrous sodium sulfate to obtain the crude product. The crude product was purified by column chromatography to obtain a white product. The white product was analyzed by nuclear magnetic resonance (400 MHz, deuterated chloroform), and its 1H NMR spectrum is shown below. Figure 1As shown, a singlet appears at δ 2.44, corresponding to the three hydrogen atoms of the methylthio group (-SCH3); a singlet appears at δ 4.37, corresponding to the two hydrogen atoms of the amino group (-NH2); the aromatic region shows three hydrogen signals, including a singlet at δ 6.29, attributed to a hydrogen atom (ArH) on the pyridine ring, a doublet at δ 6.51 (J = 5.0 Hz), attributed to another hydrogen atom on the pyridine ring, and a doublet at δ 7.88 (J = 5.6 Hz), attributed to the hydrogen atom adjacent to nitrogen on the pyridine ring. These data are consistent with the structural characteristics of the target compound 2-amino-4-methylthiopyridine, confirming that the white product is 2-amino-4-methylthiopyridine (Py).

[0019] The present invention will be further described in detail with reference to specific embodiments. The following embodiments can enable those skilled in the art to have a more comprehensive understanding of the present invention, but do not limit the present invention in any way.

[0020] Example 1: This embodiment provides a method for preparing a gold nanorod assembly, including the following steps: Preparation of the gold seed: First, 12 μL of chloroauric acid aqueous solution (0.2 mol / L) was added to 5 mL of CTAB solution (0.1 mol / L) and mixed. Then, under vigorous stirring, 600 μL of ice-cold sodium borohydride solution (0.01 mol / L) was rapidly added to this mixture. The solution immediately changed from yellow to dark brown, indicating the formation of the gold seed.

[0021] Growth of gold nanorods: 50 μL of a 0.1 mol / L gold seed solution was added to 500 mL of a 0.1 mol / L CTAB aqueous solution. Subsequently, under stirring, 7.5 mL of a 1 mol / L NaOH solution was added sequentially to provide an alkaline environment, 150 μL of a 0.01 mol / L silver nitrate solution was added as a morphology directing agent, and 200 μL of a 0.1 mol / L hydroquinone as a mild reducing agent. After the addition of the reducing agent, the system color gradually changed from deep yellow to colorless, indicating that the gold precursor had undergone a pre-reduction reaction. The CTAB-coated gold seed will undergo anisotropic growth in the solution to form gold nanorods. The solution was allowed to stand overnight to obtain the gold nanorod stock solution.

[0022] Assembly of gold nanorods: First, take 40 μL of gold nanorod stock solution diluted to 1 nM and transfer it to a centrifuge tube. Then, add 10 μL of 10 mM 2-amino-4-methylthio-pyridine (Py) / ethanol molecular solution and mix with a mixer for 10 seconds. Repeat twice to obtain the gold nanorod assembly. The molar ratio of gold nanorods to assembled molecules is 1:2500000.

[0023] The absorbance of the diluted gold rod was measured by ultraviolet spectroscopy, and the concentration c was calculated according to the absorption formula A=lg(1 / T)=Kbc, where A is the absorbance, T is the transmittance, K is the molar absorptivity, and b is the thickness of the absorption layer.

[0024] Example 2: This embodiment provides a method for preparing gold nanorod assemblies. Compared with Example 1, the assembly molecular solution and its amount are 3 μL of 2mM HS-(CH2)2-NH2(C2) water molecule solution, and other conditions are the same.

[0025] Example 3: This embodiment provides a method for preparing gold nanorod assemblies. Compared with Example 1, the assembly molecular solution and its amount are 3 μL of 5mM HS-(CH2)3-NH2(C3) water molecule solution, and other conditions are the same.

[0026] Example 4: This embodiment provides a method for preparing gold nanorod assemblies. Compared with Example 1, the assembly molecular solution and its amount are 4 μL 4mM HS-(CH2)4-NH2(C4) water molecule solution, and other conditions are the same.

[0027] Example 5: This embodiment provides a method for preparing a gold nanorod assembly. Compared with Example 1, the amount of the assembly molecular solution used is 7 μL, and other conditions are the same.

[0028] Example 6: This embodiment provides a method for preparing a gold nanorod assembly. Compared with Example 1, the amount of the assembly molecular solution used is 8 μL, and other conditions are the same.

[0029] Example 7: This embodiment provides a method for preparing a gold nanorod assembly. Compared with Example 1, the amount of the assembly molecule solution used is 9 μL, the molar ratio of gold nanorods to assembly molecules is 1:2250000, and other conditions are the same.

[0030] Example 8: This embodiment provides a method for preparing a gold nanorod assembly. Compared with Example 1, the amount of the assembly molecule solution is 12.5 μL, the molar ratio of gold nanorods to assembly molecules is 1:3125000, and other conditions are the same.

[0031] Example 9: This embodiment provides a method for preparing a gold nanorod assembly. Compared with Example 1, the amount of the assembly molecule solution is 14 μL, the molar ratio of gold nanorods to assembly molecules is 1:3500000, and other conditions are the same.

[0032] The materials obtained in the examples were subjected to a series of tests and characterizations: The gold nanorod stock solution from Example 1 was subjected to ultraviolet absorption spectroscopy (LAMBDA 1050+) and microstructure characterization (JEOL JEM-2100plus) using a UV-Vis spectrophotometer and transmission electron microscope to verify the growth quality and structural consistency of the gold nanorods. The results are as follows: Figure 2 As shown, the obtained gold nanorods have a uniform structure with a length of 75.0±0.5 nm, a width of 18.5±0.3 nm, and an aspect ratio of 3.9.

[0033] 10 μL of the gold nanorod assembly obtained in Example 1 was dropped onto a clean silicon wafer surface and allowed to stand for 5-10 minutes until the assembly was fully deposited. Afterward, a gentle nitrogen stream was used to purge any residual solvent. The assembly was then characterized using UV-Vis absorption spectroscopy (LAMBDA 1050+) and scanning electron microscopy (Gemini SEM 360) to confirm the assembly status of the gold nanorods in Example 1. The results are as follows: Figure 3 and Figure 4 As shown, SEM results demonstrate the successful assembly of gold nanorods into dimer and polymeric structures. UV-Vis absorption spectroscopy revealed a gradual decrease in solution absorbance during the assembly process; furthermore, the solution color gradually lightened. These changes in optical properties are consistent with the assembly behavior of the gold nanorods observed in the SEM characterization, confirming the successful self-assembly of the gold nanorods.

[0034] Furthermore, the lengths of the supramolecular junctions (i.e., the nano-gap sizes between gold nanorod dimers) obtained in 120 Examples 1-4 were measured using a transmission electron microscope (JEOL JEM-2100plus), and the data distribution was statistically analyzed. The results are as follows: Figure 5 and Figure 6 As shown, for the Py molecule, the average nano-gap size is 1.43 nm, which is consistent with the theoretically calculated length of 1.46 nm. For the C2, C3, and C4 molecules, the average nano-gap sizes are 0.85, 0.99, and 1.02 nm, respectively, which are highly consistent with the theoretically calculated lengths (0.89, 1.04, and 1.05 nm), thus indicating that the nano-gap is generated by the connection of the hydrogen bond molecular system.

[0035] The assembly of the gold nanorod assemblies obtained from the assembled molecules used in Examples 1-4 was characterized using a scanning electron microscope (Gemini SEM 360). The results are as follows: Figure 7As shown, the yield of gold nanorod assemblies assembled using hydrogen bonds of heterocyclic rigid molecules (Examples 1-4) is higher than that of those assembled using linear hydrogen-bonded molecules. The connection probability of gold rod tips increases from 31.7%, 29.0%, and 27.5% (average about 30%) under linear molecule interaction to 40.7% under heterocyclic molecule interaction. This is because the assembly molecules used in Example 1 have a rigid pyridine ring that can form hydrogen bonds. The directional hydrogen bonding and dense hydrogen bond network structure brought about by its rigid framework enable the acquisition of gold nanorod assemblies with high yield and linear orientation.

[0036] It should be noted that 2-amino-4-methylthio-pyridine molecules coupled with gold nanorods exhibit high yield and maintain linear orientation even during polymer assembly, such as... Figure 8 As shown, the orientation angles of gold nanorod dimers regulated by three linear flexible molecules (C2, C3, and C4) increased from 163.4°, 161.6°, and 156.3° to 168.8° under the influence of rigid heterocyclic molecules (180° represents a completely linear state). This is because the nitrogen atom in the pyridine ring is an excellent hydrogen bond acceptor. When two molecules adsorbed on different gold nanorods approach each other, the amino group (-NH2, hydrogen bond donor) at the end of one molecule forms a strong and highly directional hydrogen bond with the pyridine nitrogen (hydrogen bond acceptor) of the other molecule. Simultaneously, the pyridine ring of this molecule is a rigid aromatic structure. This rigidity effectively transfers the orientation guiding force brought by the hydrogen bond, preventing directional deviation caused by molecular skeleton distortion.

[0037] The molar ratio of gold nanorods to assembled molecules is a key factor affecting the assembly of gold nanorods. If the molar ratio is too high, the gold nanorods will aggregate, while if the molar ratio is too low (as in Examples 5 and 6), the gold nanorods will not assemble. Morphological observations were performed on the gold nanorod assemblies obtained in Examples 1 and 7-9, and the results are as follows: Figure 9 As shown, when the molar ratio was 1:2,250,000 (Example 7), a small number of gold nanorods began to assemble. When the molar ratio was 1:2,500,000 (Example 1), the gold nanorods began to assemble on a large scale. When the molar ratio was 1:3,125,000 (Example 8), the solution turned light purple and the gold nanorods began to aggregate. When the molar ratio was 1:3,500,000 (Example 9), the gold nanorods completely aggregated and the solution turned white.

[0038] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a gold nanorod assembly, characterized in that, Includes the following steps: A dispersion system containing multiple gold nanorods in a liquid medium is provided; Introduce heterocyclic assembly molecules anchored to the surface of the gold nanorods into the dispersion system. The heterocyclic assembly molecules include aromatic heterocycles that provide structural rigidity, sulfur-containing anchoring groups that form coordination bonds with the gold surface, and groups or atoms that can form hydrogen bonds. The gold nanorod assembly comprises at least two gold nanorods and heterocyclic assembly molecules located on each gold nanorod, wherein the two gold nanorods are interconnected by at least two hydrogen bonds formed between complementary functional groups of the heterocyclic assembly molecules.

2. The preparation method according to claim 1, characterized in that, The aromatic heterocycle is a pyridine ring.

3. The preparation method according to claim 1, characterized in that, The sulfur-containing anchoring group that forms a coordination bond with the gold surface is at least one of mercapto or thiomethyl.

4. The preparation method according to claim 1, characterized in that, The sulfur-containing anchoring group that forms a coordinate bond with the gold surface is a thiomethyl group.

5. The preparation method according to claim 1, characterized in that, The group or atom that can form hydrogen bonds is at least one of pyridine nitrogen and amino.

6. The preparation method according to claim 1, characterized in that, The groups or atoms that can form hydrogen bonds are pyridine nitrogen and amino groups.

7. The preparation method according to claim 1, characterized in that, The heterocyclic assembly molecule is 2-amino-4-methylthio-pyridine.

8. The preparation method according to claim 1, characterized in that, The gold nanorods have a length of 75.0 ± 0.5 nm and a width of 18.5 ± 0.3 nm.

9. The preparation method according to claim 1, characterized in that, The molar ratio of gold nanorods to heterocyclic assembled molecules in the dispersion system is 1:2250000 to 1:3500000.

10. The preparation method according to claim 1, characterized in that, The molar ratio of gold nanorods to heterocyclic assembled molecules in the dispersion system is 1:2500000.

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