Preparation method of SERS (Surface Enhanced Raman Scattering) substrate of ultrahigh-sensitivity aventurine nanoparticle / MOF-808

Abstract

The invention discloses a preparation method of an ultra-high-sensitivity gold star nanoparticle / MOF-808 SERS (Surface Enhanced Raman Scattering) substrate, which comprises the following steps: firstly, synthesizing sea urchin-shaped gold star nanoparticles (GNS) with a multi-tip structure in the presence of an amphiphilic block copolymer by a seed mediated growth method; then, by taking zirconium oxychloride octahydrate and 1, 3, 5-benzene tricarboxylic acid as precursors, performing hydrothermal reaction to synthesize an MOF-808 metal organic framework carrier; finally, GNS and MOF-808 are combined in a self-assembly mode, and the solid SERS substrate is obtained through ultrasonic loading, centrifugation, freeze drying and grinding. The method is simple and convenient in preparation process and low in cost, and the prepared substrate is high in uniformity, good in signal reproducibility and high in sensitivity and shows excellent structural stability. Wherein the multi-tip structure of the sea urchin-shaped aventuris effectively enhances a local electromagnetic field, and the SERS detection sensitivity is remarkably improved.

Description

Technical Field

[0001] This invention relates to a method for preparing a SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808, belonging to the field of surface-enhanced Raman spectroscopy technology. Background Technology

[0002] Surface-enhanced Raman spectroscopy (SERS) is a unique molecular fingerprinting technique that significantly enhances the Raman scattering signal of molecules adsorbed on specific metal surfaces (such as gold, silver, and copper with rough or nanostructured surfaces). Since its discovery in 1974, SERS has been widely used in hazardous substance detection, environmental analysis, art authentication, drug analysis, and biomolecular recognition due to its high sensitivity, accuracy, and speed. However, traditional noble metal substrates have revealed bottlenecks such as poor stability, low sensitivity, high cost, matrix interference, and poor affinity between noble metal surfaces and analytes.

[0003] Metal-organic frameworks (MOFs), as porous coordination polymers, have the characteristics of large specific surface area, high adsorption capacity, and stable framework structure, making them one of the research hotspots in the field of SERS.

[0004] In recent years, MOF materials have been increasingly widely used in SERS detection, and many researchers have actively devoted themselves to the research and development of MOF-based SERS substrates. For example, Liang Pei et al. invented a patent with patent number 202111280642.8, entitled "A Method for Preparing an Au / Fe3O4 / MIL-101(Cr) Composite Material SERS Substrate." This mainly involves loading single-metal nanoparticles onto MOFs and simultaneously using Fe3O4 for sample enrichment. However, the hotspot region of metal nanoparticles in SERS detection is limited, resulting in low detection sensitivity. Summary of the Invention

[0005] In view of the shortcomings and needs of the existing technology, the purpose of this invention is to provide a method for preparing a sea urchin-shaped metal SERS substrate based on MOF, which aims to solve the problems of complex preparation, poor stability, low sensitivity and selective adsorption of SERS substrate.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a SERS substrate with ultra-high sensitivity Venus nanoparticles / MOF-808 includes the following steps:

[0008] 1) Preparation of gold nanoparticle solution: Mix 0.2-0.3 mM chloroauric acid aqueous solution and 2.2-2.5 μM citrate-terminated gold seed solution, then add 1 M hydrochloric acid, 2.5-3.5 mM silver nitrate aqueous solution and 95-105 mM ascorbic acid aqueous solution in sequence, stir evenly, then add 1 M hexadecyltrimethylammonium chloride aqueous solution, stir for 1 h, centrifuge, filter, and redisperse in deionized water to obtain a gold nanoparticle solution with a volume concentration of 5-8%;

[0009] 2) Loading gold nanoparticles onto the surface of MOF-808:

[0010] 21) MOF-808 powder was dispersed in ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL;

[0011] 22) Mix the MOF-808 dispersion with the Venus nanoparticle liquid, then mix at high speed in a vortex mixer for 1.5-2 hours and incubate at room temperature for 25-30 minutes. Wash the product repeatedly with deionized water, dry and grind to obtain GNS / MOF-808.

[0012] 23) GNS / MOF-808 was dispersed in deionized water to obtain a GNS / MOF-808 dispersion with a concentration of 1 mg / mL. The dispersion was then drop-coated onto a silicon wafer and dried to obtain a SERS substrate of ultra-sensitive Venus nanoparticles / MOF-808.

[0013] This application generates a very significant positive synergistic promoting effect by loading the above-mentioned Venus nanoparticles onto MOF-808 powder, which significantly improves the sensitivity of SERS detection and achieves ultra-high sensitivity SERS detection of trace substances.

[0014] The inventors unexpectedly discovered in the experiment that in step 1) above, the amount of gold seed used is not necessarily better the more it is used. When the volume of the gold seed gradually increases, the SERS function of the substrate will first increase and then decrease. Preferably, the volume ratio of chloroauric acid aqueous solution to citrate-terminated gold seed solution is 50:(0.4~0.7), more preferably 50:0.5.

[0015] To further improve the sensitivity of SERS detection, the volume ratio of chloroauric acid aqueous solution, hydrochloric acid, silver nitrate aqueous solution, ascorbic acid aqueous solution, and hexadecyltrimethylammonium chloride aqueous solution is 50: (0.4~0.6): (0.2~0.3): (0.2~0.3): (8~12).

[0016] Experiments have shown that the amount of Venus nanoparticle liquid in step 22) is not necessarily better the more it is used. In order to avoid problems such as agglomeration and damage to the framework, the volume ratio of MOF-808 dispersion to Venus nanoparticle liquid is preferably 1:(1~4), and more preferably, the volume ratio of MOF-808 dispersion to Venus nanoparticle liquid is 1:2.

[0017] In step 22) above, the stirring speed of the vortex mixer is 1500~2500 rpm.

[0018] In step 21) above, the preparation of MOF-808 powder is as follows: zirconium tetrachloride and benzene-1,3,5-tricarboxylic acid in a mass ratio of (3~3.5):1 are added to a mixed solvent of N,N-dimethylformamide / formic acid, stirred continuously at room temperature for 0.5~1 h, then ultrasonically treated for 20~30 min, then transferred to a Teflon-lined stainless steel reactor, heated to 110~130 ℃ and reacted for 12~24 h, naturally cooled, centrifuged and washed until a pure white powder is obtained, and dried under vacuum at 80~100 ℃ for 8~12 h.

[0019] In the above-mentioned N,N-dimethylformamide / formic acid mixed solvent, the volume ratio of N,N-dimethylformamide to formic acid is 1:1; the washing is performed by washing with N,N-dimethylformamide and acetone 2 to 3 times respectively.

[0020] In step 1) above, the preparation method of citrate-terminated gold seed solution is as follows: heat a 0.01% chloroauric acid aqueous solution to 95~100℃, then add a 1% sodium citrate aqueous solution, and react at 95~100℃ for 15 minutes. During this process, the solution color changes from the initial light yellow to the final wine red, and then remains stable without color change. After natural cooling, the citrate-terminated gold seed solution is obtained.

[0021] The volume ratio of the above-mentioned chloroauric acid aqueous solution to sodium citrate aqueous solution is 50:(1.3~1.5).

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The gold nanoparticle / MOF-808 composite material prepared in this invention innovatively combines gold nanoparticles with multiple sharp tips with highly porosity MOF-808. Gold nanoparticles can generate extremely strong local electromagnetic field enhancement under illumination, while the huge specific surface area and adsorption properties of MOF-808 can efficiently enrich target analytes into these "hot spot" regions (hot spots refer to special tiny regions on the surface or in the interstices of metal nanostructures that can generate strong local electromagnetic fields, thereby enhancing Raman signals by millions or even billions of times). The synergistic effect of these two components enables ultra-high sensitivity SERS detection of trace substances.

[0024] 2. The gold nanoparticle / MOF-808 substrate prepared by this invention utilizes the regular pore structure of MOF-808 as a carrier to achieve uniform and high-density loading of gold nanoparticles on its surface, effectively avoiding the aggregation of noble metal nanoparticles, thereby forming a large number of uniformly distributed and stable SERS active sites.

[0025] 3. The MOF-808 material used in this invention has high pore volume, large specific surface area and adjustable pore environment. It exhibits excellent adsorption and enrichment capabilities for a variety of small organic molecules, especially hydrophobic molecules or molecules containing specific functional groups. Attached Figure Description

[0026] Figure 1 This is a SEM image of the SERS substrate in Embodiment 2 of the present invention;

[0027] Figure 2 This is the XRD pattern of the SERS substrate in Embodiment 2 of the present invention;

[0028] Figure 3 The image shows the effect of enhancing the Raman spectrum of Rhodamine 6G (R6G) on the SERS substrates of GNS / MOF-808 prepared under the conditions of gold seed volumes of 400 μL, 500 μL, 600 μL and 700 μL in Examples 1-4 of this invention.

[0029] Figure 4 The image shows the effect of enhancing the Raman spectrum of Rhodamine 6G (R6G) using GNS / MOF-808 composite materials prepared by MOF-808 solution and GNS solution with different volume ratios in Examples 2 and 5-7 of this invention as SERS substrates.

[0030] Figure 5 The image shows the Raman spectral enhancement effect of the Venus nanoparticles / MOF-808 composite material prepared in Example 2 of this invention as a SERS substrate on different concentrations of Rhodamine 6G (R6G) molecules.

[0031] Figure 6 The effect of storage time on the Venus nanoparticle / MOF-808 composite material prepared in Example 2 of this invention as a SERS substrate;

[0032] Figure 7 The image shows the Raman spectral enhancement effect of the Venus nanoparticle / MOF-808 composite material prepared in Example 2 of this invention as a SERS substrate on different concentrations of the antibiotic sulfathiazole (STZ) molecules. Detailed Implementation

[0033] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0034] In all cases, unless otherwise specified, the process was carried out at room temperature (15~25℃); unless otherwise specified, the stirring speed was 200r / min; the ultrasonic power was 200W; unless otherwise specified, the vacuum degree of vacuum drying was 0.07MPa.

[0035] A method for preparing a SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 includes the following steps:

[0036] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were successively placed in a 250 mL Erlenmeyer flask. The mixture was heated to 100 °C in an oil bath with vigorous stirring. After the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red color, after which it remained stable and unchanged in color. After the reaction was completed, the solution was allowed to cool naturally to room temperature and stored in a refrigerator (4 °C) for later use.

[0037] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 400 μL, 500 μL, 600 μL, and 700 μL of citrate-terminated gold seed solutions. Then, 250 μL of 3 mM silver nitrate aqueous solution and 250 μL of 100 mM ascorbic acid aqueous solution were added to the solution at 5 s intervals. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min and then dispersed in 500 µL of deionized water to obtain the GNS solution.

[0038] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by sonication for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally, and the product was centrifuged for 15 min to remove unreacted substances. The separated microcrystalline powder was vigorously washed three times with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried overnight in a vacuum oven at 100 °C.

[0039] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at ratios of 1:1, 1:2, 1:3, and 1:4. Then, the mixture was vigorously mixed at high speed for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried, and then GNS / MOF-808 with SERS activity was obtained. The powder was ground into powder (approximately 600 nm) and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0040] Example:

[0041] The present invention will be described in detail below with reference to specific embodiments:

[0042] Example 1:

[0043] An implementation scheme with a gold seed solution volume of 400 μL and a MOF-808 solution to GNS solution volume ratio of 1:2:

[0044] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0045] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 400 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0046] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0047] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a ratio of 1:2. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried to obtain SERS-active GNS / MOF-808, ground into powder (approximately 600 nm), and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0048] Example 2:

[0049] An implementation scheme with a gold seed solution volume of 500 μL and a MOF-808 solution to GNS solution volume ratio of 1:2:

[0050] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0051] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 500 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0052] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0053] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a ratio of 1:2. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried to obtain SERS-active GNS / MOF-808, ground into powder (approximately 600 nm), and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0054] Example 3:

[0055] An implementation scheme with a gold seed solution volume of 600 μL and a MOF-808 solution to GNS solution volume ratio of 1:2:

[0056] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0057] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 600 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0058] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0059] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a ratio of 1:2. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried to obtain SERS-active GNS / MOF-808, ground into powder (approximately 600 nm), and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0060] Example 4:

[0061] An implementation scheme with a gold seed solution volume of 700 μL and a MOF-808 solution to GNS solution volume ratio of 1:2:

[0062] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0063] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 700 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0064] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0065] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a ratio of 1:2. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried to obtain SERS-active GNS / MOF-808, ground into powder (approximately 600 nm), and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0066] Example 5:

[0067] An implementation scheme with a gold seed solution volume of 500 μL and a MOF-808 solution to GNS solution volume ratio of 1:1:

[0068] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0069] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 500 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0070] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0071] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a 1:1 ratio. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried, and then GNS / MOF-808 with SERS activity was obtained. The powder was ground into powder (approximately 600 nm) and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0072] Example 6:

[0073] An implementation scheme with a gold seed solution volume of 500 μL and a MOF-808 solution to GNS solution volume ratio of 1:3:

[0074] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0075] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 500 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0076] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0077] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a ratio of 1:3. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried, and then GNS / MOF-808 with SERS activity was obtained. The powder was ground into powder (approximately 600 nm) and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0078] Example 7:

[0079] An implementation scheme with a gold seed solution volume of 500 μL and a MOF-808 solution to GNS solution volume ratio of 1:4:

[0080] Step 1: Preparation of gold nanoparticle solution (AuNPs): 50 mL of deionized water and 0.5 mL of 1% chloroauric acid aqueous solution were placed sequentially into a 250 mL Erlenmeyer flask. The flask was heated to 100 °C in an oil bath at 800 rpm. Once the solution reached boiling point, 1.4 mL of 1% sodium citrate aqueous solution was quickly added. Heating and stirring continued for 15 min. During this process, the solution color changed from an initial light yellow to a wine red, after which it remained stable and unchanged in color. After the reaction was complete, the solution was allowed to cool naturally to room temperature to obtain a citrate-terminated gold seed solution, which was stored in a refrigerator (4 °C) for later use.

[0081] Step 2: Preparation of Gold Star Nanoparticles (GNS): 50 μL of 1 M hydrochloric acid solution was added to a solution containing 50 mL of 0.25 mM chloroauric acid aqueous solution and 500 μL of citrate-terminated gold seed solution. Then, 250 μL of 3 mM silver nitrate aqueous solution was added to the solution, and after 5 s, 250 μL of 100 mM ascorbic acid aqueous solution was added. After stirring the solution for 2 min, 10 mL of 0.1 M hexadecyltrimethylammonium chloride solution was added to the gold star nanoparticle solution and stirred for 1 h. The solution was centrifuged at 4000 rpm for 12 min, and then the solid was filtered out and dispersed in 500 µL of deionized water to obtain the GNS solution.

[0082] Step 3: Preparation of MOF-808 powder: 0.325 g of zirconium tetrachloride and 0.105 g of benzene-1,3,5-tricarboxylic acid were added to a solvent mixture of N,N-dimethylformamide / formic acid (15 mL / 15 mL) and stirred continuously at room temperature for 1 h, followed by ultrasonic treatment for 30 min to ensure complete dissolution. The homogeneous mixture was then transferred to a 100 mL Teflon-lined stainless steel reactor and heated to 130 °C for 1 day. The reactor was allowed to cool naturally and centrifuged at 4000 rpm for 15 min. The separated microcrystalline powder was then vigorously washed three times (6000 rpm, 10 min) with 15 mL of N,N-dimethylformamide and 15 mL of acetone, respectively, to obtain a pure white powder. The obtained product was dried in a vacuum oven at 100 °C for 12 h to obtain MOF-808 powder.

[0083] Step 4: Finally, the GNS particles were loaded onto the MOF-808 surface using a self-assembly method. First, 30 mg of MOF-808 powder was dispersed in 30 mL of ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL. Next, the MOF-808 dispersion was mixed with the prepared GNS solution at a ratio of 1:4. Then, the mixture was vigorously mixed at high speed (2000 rpm) for 2 h in a vortex mixer and incubated at room temperature for 30 min. Finally, to remove residual solvent from the product, it was washed three times with deionized water (10 mL each time), vacuum dried, and then GNS / MOF-808 with SERS activity was obtained. The powder was ground into powder (approximately 600 nm) and stored in a refrigerator (4 °C) for later use. Subsequently, GNS / MOF-808 was dispersed in deionized water to obtain a dispersion with a concentration of 1 mg / mL, and then dropped onto silicon wafers with a size of 5 mm * 5 mm (20 μL per wafer). The wafers were then placed in a vacuum drying oven and dried at a temperature of 70 °C for 1 h to obtain a SERS substrate of GNS / MOF-808 for Raman testing.

[0084] Figure 1 The image shows a SEM image of GNS loaded on MOF-808 in Example 2 of this invention. It can be seen that the MOF-808 is approximately 500 nm in size, exhibiting a typical octahedral structure. The upper left corner clearly shows that the GNS has extremely high crystallinity, with a urchin-like crystal morphology and a branched arrangement, with a size of approximately 40 nm. The surface morphology of GNS attached to MOF-808 shows that the surface of MOF-808 becomes rough, and although GNS is distributed on the surface, the octahedral structure of MOF-808 still maintains its highly ordered morphology.

[0085] Figure 2 The XRD patterns of GNS / MOF-808 show diffraction peaks at 38.1°, 44.4°, 64.6°, and 77.5°, corresponding to the (111), (200), (220), and (311) crystal layers of GNS, indicating that GNS exhibits distinct crystalline characteristics within MOF-808. Comparing the diffraction peaks of MOF-808 before and after GNS integration, no significant changes were observed, suggesting that the crystal structure of MOF-808 remains intact in the GNS / MOF-808 nanocomposite material.

[0086] Figure 3 The images show the Raman spectra of SERS-enhanced Rhodamine 6G (R6G) prepared using GNS / MOF-808 with different gold seed volumes, as presented in this invention. A concentration of 10... -6The SERS performance of the substrate was evaluated using a mol / L R6G solution. The figure shows that as the gold seed volume gradually increased, the SERS function of the substrate initially increased and then decreased. This is because the number of complete, sharp gold nanostars formed increases linearly with the increase in gold seed volume. However, when the number of gold seeds is too large, the densely packed gold nanostars are prone to contact and entanglement during growth, forming large, amorphous gold aggregates, leading to a decrease in SERS performance. Therefore, the substrate exhibited the best Raman enhancement performance when the citrate-capped gold seed solution was 500 μL.

[0087] Figure 4 For R6G in 10 -6 The labeled Raman spectroscopy results of SERS substrates prepared with zirconium-based MOF-808 solutions and GNS solutions at different volume ratios were compared at a concentration of mol / L. This shows that by changing the proportion of GNS incorporated, the Raman intensity of the SERS substrate can be further optimized and improved. The fundamental reason for this phenomenon is that as the volume ratio of GNS increases, the amount of GNS increases, thereby enhancing the SERS performance. However, when the volume ratio of GNS expands to a certain threshold, it will form agglomerates. Furthermore, the basic structure of MOF-808 may also be damaged, thus reducing its SERS properties. Therefore, when the volume ratio of zirconium-based MOF-808 solution to GNS solution is 1:2, the SERS performance of this SERS substrate reaches its optimal level.

[0088] Figure 5 Using the GNS / MOF-808 composite material prepared by the method of this invention as a SERS substrate, Raman spectra at different concentrations of R6G were detected. The figures show that as the R6G concentration gradually decreases, the corresponding Raman signal intensity also weakens. However, the Raman signal intensity remains relatively low even at R6G concentrations as low as 2 × 10⁻⁶. ⁻12 Even under conditions of M, the characteristic peak positions can still be clearly identified, indicating that the GNS / MOF-808 composite material has excellent Raman enhancement effect as a SERS substrate, with a detection limit of 2×10⁻⁶ for R6G. ⁻ 12 M.

[0089] Figure 6 The effect of storage time on SERS performance was investigated. The long-term stability of the substrate was evaluated by testing the Raman enhancement effect of the substrate at different storage times (0–28 days). The figures show that the performance remained essentially unchanged in the initial storage period (7 days), indicating good short-term stability. With increasing storage time (7–21 days), the Raman intensities at 612 cm⁻¹ and 1360 cm⁻¹ gradually decreased, indicating a slight reduction in stability while still maintaining certain performance. By 28 days of storage, the rate of intensity decline slowed, demonstrating the substrate's stability during long-term storage.

[0090] Figure 7 To investigate the effects of different concentration ranges of sulfathiazole in aqueous solution using a GNS / MOF-808 substrate (from 10... -3 mol / L to 10 -7 SERS tests were performed at 10 mol / L. The graph clearly shows that the Raman signal intensity of sulfathiazole gradually decreases with decreasing concentration. Even when the concentration drops to 10 mol / L... -7 At concentrations of mol / L, the characteristic peaks of sulfathiazole can still be detected on the substrate, indicating that the SERS detection capability for sulfathiazole on this substrate can reach 5 × 10⁻⁶. -9 mol / L. Among them, 636 cm⁻¹ -1 This is mainly attributed to the coupling between circumferential deformation and the C–N bending mode, 827 cm -1 Breathing from the ring and the N–S stretching and C–H bending patterns, 1078 cm -1 and 1586 cm -1 It is mainly caused by the combination of C–C and S–O stretching patterns.

[0091] Comparative Example 1

[0092] The difference from Example 2 is that step two is omitted, and in step four, the GNS solution is replaced with the gold seed solution obtained in step one. All other steps are the same as in Example 2.

[0093] Comparative Example 2

[0094] Unlike Example 2, steps one and two are performed as follows:

[0095] Step 1: Add 9 mg of AgNO3 solid particles to 50 mL of ultrapure water and heat to boiling with stirring; quickly add 1.8 mL of 1% sodium citrate aqueous solution to the boiling AgNO3 solution and continue boiling for 2 minutes; continue stirring at room temperature for 1 hour until the solution color changes from colorless to yellow-green, cool to room temperature, and make up to 50 mL with ultrapure water to obtain AgNPs solution, which can be stored at 4°C protected from light for later use.

[0096] Step 2: Mix 10.8 mL of ultrapure water and 3.4 mL of 2 mM HAuCl4 aqueous solution thoroughly, then add 2 mL of AgNPs solution and sonicate until homogeneous; quickly add 6.8 mL of 10 mM levodopa solution, and react in an ice-water bath for 30 minutes to obtain GNS solution. The remaining steps are the same as in Example 2.

[0097] Comparative Example 3

[0098] The difference from Example 2 is that the concentration of the chloroauric acid aqueous solution was replaced with 0.8 mM, while all other aspects were the same as in Example 2.

[0099] Comparative Example 4

[0100] The difference from Example 2 is that the concentration of the chloroauric acid aqueous solution was replaced with 0.1 mM, while all other aspects were the same as in Example 2.

[0101] Comparative Example 5

[0102] The difference from Example 2 is that the concentration of the silver nitrate aqueous solution was replaced with 1 mM, while all other aspects were the same as in Example 2.

[0103] Comparative Example 6

[0104] The difference from Example 2 is that the concentration of the silver nitrate aqueous solution was replaced with 5 mM, while the rest were the same as in Example 2.

[0105]

Claims

1. A method for preparing a SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808, characterized in that: Includes the following steps: 1) Preparation of gold nanoparticle solution: Mix 0.2-0.3 mM chloroauric acid aqueous solution and 2.2-2.5 μM citrate-terminated gold seed solution, then add 1 M hydrochloric acid, 2.5-3.5 mM silver nitrate aqueous solution and 95-105 mM ascorbic acid aqueous solution in sequence, stir well, then add 1 M hexadecyltrimethylammonium chloride aqueous solution, react at room temperature for 0.5-1 h, centrifuge, filter, and redisperse in deionized water to obtain a gold nanoparticle solution with a volume concentration of 5-8%; 2) Loading gold nanoparticles onto the surface of MOF-808: 21) MOF-808 powder was dispersed in ethanol to obtain a MOF-808 dispersion with a concentration of 1 mg / mL; 22) Mix the MOF-808 dispersion with the Venus nanoparticle liquid, then mix at high speed in a vortex mixer for 1.5-2 hours and incubate at room temperature for 25-30 minutes. Wash the product repeatedly with deionized water, dry and grind to obtain GNS / MOF-808. 23) GNS / MOF-808 was dispersed in deionized water to obtain a GNS / MOF-808 dispersion with a concentration of 1 mg / mL. The dispersion was then drop-coated onto a silicon wafer and dried to obtain a SERS substrate of ultra-sensitive Venus nanoparticles / MOF-808.

2. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to claim 1, characterized in that: In step 1), the volume ratio of chloroauric acid aqueous solution to citrate-terminated gold seed solution is 50:(0.4~0.7); the volume ratio of chloroauric acid aqueous solution, hydrochloric acid, silver nitrate aqueous solution, ascorbic acid aqueous solution, and hexadecyltrimethylammonium chloride aqueous solution is 50:(0.4~0.6):(0.2~0.3):(0.2~0.3):(8~12).

3. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to claim 2, characterized in that: The volume ratio of chloroauric acid aqueous solution to citrate-terminated gold seed solution is 50:0.

5.

4. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to any one of claims 1-3, characterized in that: In step 22), the volume ratio of MOF-808 dispersion to Venus nanoparticle liquid is 1:(1~4).

5. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to claim 4, characterized in that: In step 22), the volume ratio of MOF-808 dispersion to Venus nanoparticle liquid is 1:

2.

6. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to any one of claims 1-3, characterized in that: In step 22), the stirring speed of the vortex mixer is 1500~2500 rpm.

7. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to any one of claims 1-3, characterized in that: In step 21), the preparation of MOF-808 powder is as follows: zirconium tetrachloride and benzene-1,3,5-tricarboxylic acid in a mass ratio of (3~3.5):1 are added to a mixed solvent of N,N-dimethylformamide / formic acid, stirred continuously at room temperature for 0.5~1 h, then ultrasonically treated for 20~30 min, then transferred to a Teflon-lined stainless steel reactor, heated to 110~130 ℃ and reacted for 12~24 h, naturally cooled, centrifuged and washed until a pure white powder is obtained, and dried under vacuum at 80~100 ℃ for 8~12 h.

8. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to claim 7, characterized in that: In the mixed solvent of N,N-dimethylformamide and formic acid, the volume ratio of N,N-dimethylformamide and formic acid is 1:1; the washing is performed by washing with N,N-dimethylformamide and acetone 2 to 3 times respectively.

9. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to any one of claims 1-3, characterized in that: In step 1), the citrate-terminated gold seed solution is prepared by heating a 0.01% chloroauric acid aqueous solution to 95-100°C, then adding a 1% sodium citrate aqueous solution, reacting at 95-100°C for 15 minutes, and then naturally cooling to obtain the citrate-terminated gold seed solution.

10. The method for preparing the SERS substrate of ultra-high sensitivity Venus nanoparticles / MOF-808 according to claim 9, characterized in that: The volume ratio of chloroauric acid aqueous solution to sodium citrate aqueous solution is 50:(1.3~1.5).

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