A method for preparing surface-enhanced Raman labels

Abstract

The present invention relates to a method for broadening the surface enhanced Raman molecule library based on the use of gold@silver@silicon oxide and gold@silicon oxide core-shell structures. The present invention belongs to the field of inorganic nanocomposite materials. Raman tags can be prepared using the following methods: (1) inducing aggregation of gold particles incubated with Raman active molecules; (2) coating an Ag layer on the product of (1) to further enhance the stability of the Raman tag; (3) coating a silicon oxide layer on the product of (2). A three-step enhancement strategy is used to expand the library to 6 types of molecules (nitrogen heterocycles, dyes, thiophenes, sulfides, alkynyls, and thiol molecules), totaling 26 Raman active molecules.

Description

Technical Field

[0001] The present invention relates to the field of preparation of inorganic nanocomposite materials, in particular to a technology for preparing Raman labels by combining metal nanoparticles with silicon oxide. Background Art

[0002] Surface-enhanced Raman scattering (SERS) is widely used in many applications for detection, sensing, and imaging. Although most Raman-active molecules have inherently small Raman cross-sections, their weak signals can be greatly enhanced by attaching them to metal nanoparticles (NPs). Compared to the widely used fluorescence technique, SERS can be excited by lasers of non-specific wavelengths, and different laser wavelengths can provide molecule-specific fingerprint spectra. In addition, the Raman-active molecules in close proximity to metals have excellent photostability. These advantages make SERS a perfect alternative to fluorescence in multiplex detection.

[0003] Using SERS multiplexing requires the use of multiple types of signal molecules. However, the number and variety of signal molecules currently available for use as SERS labels are relatively limited, which is the biggest bottleneck in the field of SERS multiplexing.

[0004] To maximize the SERS signal intensity of molecules, various strategies have been developed. These include: 1. Inducing chain aggregation of nanoparticles to create "hot spots" and increase the number of nanoparticle tips, thereby enhancing the molecular SERS signal through the generated high electromagnetic field (EM); 2. Encapsulating signal molecules between the core and shell of metal nanoparticles to enhance the molecular SERS signal through the strong coupling between adjacent cores and shells; and 3. Coating the outermost layer of the nanoparticles with silicon oxide or polymer compounds to maintain the long-term SERS intensity of the signal molecules and the stability of the nanoparticles.

[0005] Currently, there are few universal methods developed to expand the SERS molecular library, and they are generally only applicable to thiolated molecules with aromatic rings or dye molecules with large conjugated structures and strong adsorption. Commonly used ones include: benzenethiol (BT), 4-mercaptobenzoic acid (4-MBA), 2-naphthalenethiol (2-NaT), rhodamine 6G (R6G), etc. Using the same type of signal molecule, even if the substituent groups are different, is prone to spectral overlap, which greatly reduces the number of signal molecules available for encoding. Therefore, it is urgent to find a method that can simultaneously enhance the Raman signals of multiple types of molecules. Summary of the Invention

[0006] The technical problem solved by the present invention is: to propose a preparation method of surface-enhanced Raman labels, a three-step enhancement strategy using gold nanoparticles to enhance the Raman signals of Raman-active molecules, which has now been expanded to 6 categories and 26 molecules.

[0007] In order to solve the above technical problems, the technical solution proposed in the present invention is: a method for preparing a surface-enhanced Raman label, a universal method using a Raman label encapsulated with silica, using salt to induce aggregation of gold particles, the aggregates are chain-shaped, and according to the degree of Raman signal enhancement of the ligand Raman signal molecules after the gold aggregates are coated with a silver layer, the ligand Raman signal molecules are divided into two categories: the first category is that the Raman signal is enhanced after the aggregates are coated with a silver layer, and the aggregates are then coated with silica after the silver layer; the second category is that the Raman signal is reduced after the aggregates are coated with a silver layer, and the aggregates are directly coated with silica.

[0008] The first type of ligand Raman signal molecule is any one of the following: phenylacetylene, 4-ethynylbiphenyl, 4-ethynylanisole, 1-ethynyl-4-(phenylethynyl)benzene, basic blue 3, dibenzyl sulfide, bis(2-thienyl)disulfide, bis(4-methoxyphenyl)disulfide, 4,4'-diaminodiphenyl disulfide, 2-thionaphthol, 3-methylbenzo[B]thiophene, 5-methylbenzo[B]thiophene, 3-bromobenzo[B]thiophene;

[0009] The second type of ligand Raman signal molecule is any one of the following: 4-ethylbiphenylacetylene, 2,2'-bipyridine, 5,5`-dimethyl-2,2`-bipyridine, 4,4'-dimethoxy-2,2'-bipyridine, rhodamine 6G, methylene blue, crystal violet, p-toluene disulfide, 4-ethylthiophenol, 2-mercaptopyridine, 4-methoxythiophenol, 6-methoxybenzothiophene or 5-chlorobenzothiophene.

[0010] Preferably, the gold particles used are 40 nm gold particles stabilized by sodium citrate.

[0011] Preferably, the first type of Raman signal molecules are suitable, and the Raman signal molecules are encapsulated between the gold and silver core-shell, mainly including aromatic ring compounds containing thiol groups, aromatic compounds containing alkynyl groups, heterocyclic compounds containing sulfur, and dye molecules.

[0012] Preferably, the second type of Raman signal molecules are suitable, and the Raman signal molecules are encapsulated between the gold and silica core-shell, and their molecular characteristics are mainly aromatic ring compounds containing thiol groups, aromatic compounds containing alkynyl groups, heterocyclic compounds containing sulfur, bipyridine molecules containing nitrogen, and dye molecules.

[0013] Preferably, ethanol solution and sodium hydroxide reagent are used for coating silicon oxide. Conventional isopropyl alcohol solution and ammonia solution will aggravate the aggregation of aggregates, causing the aggregates to be too large and precipitate, thereby causing the Raman signal molecular signal to disappear.

[0014] Preferably, some Raman signal molecules coated with silica on the aggregate need to be induced by mercaptoundecanoic acid molecules, and the signal molecules include 22: phenylacetylene, 4-ethynylbiphenyl, basic blue 3, dibenzyl sulfide, bis(2-thienyl)disulfide, bis(4-methoxyphenyl)disulfide, 4,4'-diaminodiphenyl disulfide, 2-naphthol, 3-methylbenzo[B]thiophene, 5-methylbenzo[B]thiophene, 3-bromobenzo[B]thiophene, 4-ethylbiphenylacetylene, 5,5'-dimethyl-2,2' -bipyridine, 4,4'-dimethoxy-2,2'-bipyridine, methylene blue, crystal violet, p-toluene disulfide, 4-ethylthiophenol, 2-mercaptopyridine, 4-methoxythiophenol, 6-methoxybenzothiophene, 5-chlorobenzothiophene. Some molecules can also be coated with silica without the use of mercaptoundecanoic acid, including: 4-ethynylanisole, 1-ethynyl-4-(phenylethynyl)benzene, 2,2'-bipyridine, and rhodamine 6G. The Raman signals of these four molecules are greatly weakened after using mercaptoundecanoic acid.

[0015] Preferably, the first type of Raman signal molecules used have a relatively strong interaction with gold particles, do not coordinate with silver ions, and exist stably in weakly alkaline aqueous alcohol solutions.

[0016] Preferably, the Raman signal molecules used have a relatively strong interaction with the gold particles and are stably present in a weakly alkaline aqueous alcohol solution.

[0017] Preferably, the gold aggregate preparation step is: taking 1 ml of 40 nm gold particles, adding sodium hydroxide solution and 1.5-8 μL of Raman signal molecule solution, incubating, then adding 7-115 mL of sodium chloride solution, and incubating again.

[0018] Preferably, the steps for preparing the gold-silver core-shell structure are: adding a hydroquinone aqueous solution and a silver nitrate aqueous solution to a gold aggregate solution and allowing the solution to stand;

[0019] The preparation steps of the coating silicon oxide are as follows: adding ethanol, tetraethyl orthosilicate and sodium hydroxide solution into the aggregate or the aggregate-coated silver solution and letting it stand.

[0020] The preparation method of Raman tags using functionalized gold nanoaggregates is as follows:

[0021] 1. Synthesis method of 40nm gold particles:

[0022] 1. Add 99 mL of pure water to a 250 mL two-necked flask, then add 1 mL of chloroauric acid trihydrate solution (10 mg / mL in aqueous solution) and reflux at 130°C until the solution boils. Then add 3 mL of sodium citrate solution (1%, mass fraction, in aqueous solution). The solution color turns purple in about 1 minute, then immediately turns red. Condensate and reflux for another half an hour, and cool naturally. 15 nm gold particles are obtained.

[0023] 2. Take the synthesized 15 nm gold particles and add them to a two-necked flask, then add 45 mL of pure water, condense and reflux at 130 ° C until the solution boils, then add 250 μL of sodium citrate solution (1%, mass fraction, configured in aqueous solution) and then add 300 μL of trihydrate chloroauric acid solution (10 mg / mL configured in aqueous solution) and react for half an hour, then add 250 μL of sodium citrate solution (1%, mass fraction, configured in aqueous solution) and then add 300 μL of trihydrate chloroauric acid solution (10 mg / mL configured in aqueous solution) and react for half an hour, then add 250 μL of sodium citrate solution (1%, mass fraction, configured in aqueous solution) and then add 300 μL of trihydrate chloroauric acid solution (10 mg / mL configured in aqueous solution) and react for half an hour, then add 1 mL of sodium citrate solution (1%, mass fraction, configured in aqueous solution) and react for ten minutes, and the reaction is complete.

[0024] 2. Raman Tag Preparation Process

[0025] First-class Raman label production

[0026] Step (1): The gold nanoparticles are purified by centrifugation and then redispersed in pure water, with the volume of the solution being the same as before centrifugation.

[0027] Step (2): using the gold nanoparticle solution in step (1) to incubate with the Raman active molecule solution and the sodium hydroxide aqueous solution in an oven;

[0028] Step (3): adding a sodium chloride aqueous solution to the solution after incubation in step (2) under shaking, and then placing the solution in an oven for static incubation;

[0029] Step (4): While standing, add the hydroquinone aqueous solution and then the silver nitrate aqueous solution to the gold nanoparticle aggregate solution in step (3), mix well, and stand for half an hour; then add the mercaptonoundecanoic acid solution.

[0030] Step (5): Add the mixed solution from step (4) to anhydrous ethanol, sodium hydroxide aqueous solution, and tetraethyl silicate, mix well, and let stand at room temperature for 6 hours. After the reaction is complete, centrifuge and wash the solution twice with water before use.

[0031] Preferably, the gold nanoparticles in step (1) have a diameter of 40±2 nm and are centrifuged at a speed of 5000 rpm for 15 min. After the supernatant is removed by centrifugation, an equal amount of pure water is used for dispersion.

[0032] Preferably, in step (2), 1 mL of gold nanoparticles is redispersed in pure water; 1.5-8 μL of Raman active molecules are added to the above 1 mL solution; the color of the solution remains the original red after incubation; 2 μL of sodium hydroxide aqueous solution has a concentration of 250 mM; the incubation temperature is 60° C.; and the incubation time is 2 h.

[0033] Preferably, in step (3), the concentration of the sodium chloride aqueous solution is 250 mM, and an appropriate amount of solution is taken; the incubation temperature is 60° C.; the incubation time is 2 h; and 7-115 μL of sodium chloride solution is added so that the solution turns purple after incubation.

[0034] Preferably, in step (4), 10 mM hydroquinone, 25 μL; 10 mM silver nitrate, 25 μL; and 0-10 μL mercaptoundecanoic acid, 3 mg / mL, are added during the static state.

[0035] Preferably, the solution in step (4) is used in step (5) without centrifugation; 5 mL of ethanol solution, 0.6 μL of pure tetraethyl silicate solution, 10 μL of 250 mM sodium hydroxide aqueous solution, and the reaction is carried out at room temperature for 6 hours. The centrifugal washing speed is 8000 rpm for 6 minutes.

[0036] The second type of Raman label production

[0037] Step (1): The gold nanoparticles are purified by centrifugation and then redispersed in pure water, with the volume of the solution being the same as before centrifugation.

[0038] Step (2): using the gold nanoparticle solution in step (1) to incubate with the Raman active molecule solution and the sodium hydroxide aqueous solution in an oven;

[0039] Step (3): adding a sodium chloride aqueous solution to the solution after incubation in step (2) under shaking, and then placing the solution in an oven for static incubation; and then adding the mercaptonoundecanoic acid solution.

[0040] Step (4): Add the mixed solution from step (3) to anhydrous ethanol, sodium hydroxide aqueous solution, and tetraethyl silicate, mix well, and let stand at room temperature for 6 hours. After the reaction is complete, centrifuge and wash the solution twice with water before use.

[0041] Preferably, the gold nanoparticles in step (1) have a diameter of 40±2 nm and are centrifuged at a speed of 5000 rpm for 15 min. After the supernatant is removed by centrifugation, an equal amount of pure water is used for dispersion.

[0042] Preferably, in step (2), 1 mL of gold nanoparticles is redispersed in pure water; 1.5-8 μL of Raman active molecules are added to the above 1 mL solution; the color of the solution remains the original red after incubation; 2 μL of sodium hydroxide aqueous solution has a concentration of 250 mM; the incubation temperature is 60° C.; and the incubation time is 2 h.

[0043] Preferably, in step (3), a sodium chloride aqueous solution with a concentration of 250 mM is prepared, and an appropriate amount of the solution is incubated at 60°C for 2 hours. 7-115 μL of the sodium chloride solution is added until the solution turns purple after incubation. 0-10 μL of 3 mg / mL mercaptoundecanoic acid is prepared in an ethanol solution.

[0044] Preferably, the solution in step (3) is used in step (4) without centrifugation; 5 mL of ethanol solution, 0.6 μL of pure tetraethyl silicate solution, 10 μL of 250 mM sodium hydroxide aqueous solution, and the reaction is carried out at room temperature for 6 hours. The centrifugal washing speed is 8000 rpm for 6 minutes.

[0045] In order to solve the above technical problems, the present invention proposes another technical solution: a functionalized nano-tag prepared by any of the above methods.

[0046] Beneficial effects of the present invention:

[0047] (1) This method is simple and universal. Our method can expand the number of Raman reporter molecules to 6 types of molecules, a total of 26. The methods currently reported in the literature are generally only applicable to one or two molecules, which greatly limits the use of Raman spectroscopy for anti-counterfeiting applications.

[0048] (2) We distinguished and classified Raman signal molecules that are suitable for coating silver layers. (3) Our method has the potential to further expand the range of Raman active molecules.

[0049] (4) Our previous method is only suitable for thiol molecules. When other molecules are used, the Raman signal disappears after coating the polystyrene-polyacrylic acid block copolymer.

[0050] (5) Now, we have divided the Raman signal molecules into two methods to make Raman tags according to the enhancement and weakening of the Raman signal after coating with a silver layer. Since the Raman signal disappears after these molecules are coated with polystyrene-polyacrylic acid block copolymer, we have improved the reaction route and changed the coating of polystyrene-polyacrylic acid block copolymer to coating with silicon oxide. After coating with silicon oxide, the Raman signal can be retained to a large extent.

[0051] (6) We encapsulated each Raman signal molecule into silica and adjusted the optimal amount of mercaptoundecanoic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention will be further described below with reference to the accompanying drawings.

[0053] Figure 1 is the classification of Raman signal molecules and the molecular formula of each molecule.

[0054] Figure 2 The color changes of gold nanoparticles at each step. (a is a 40nm gold nanoparticle solution; b is the solution color after aggregation with sodium chloride, which turns purple; c is the solution color after silver coating, which turns brown; d is the sample after silica coating)

[0055] Figure 3 The Raman signal of phenylacetylene (a) and the TEM image after coating with silicon oxide (b)

[0056] Figure 4 The Raman signal of 4-ethynylbiphenyl (a) and the TEM image after coating with silicon oxide (b)

[0057] Figure 5 The Raman signal of 4-ethynylanisole (a) and the TEM image after coating with silicon oxide (b)

[0058] Figure 6 The Raman signal of 1-ethynyl-4-(phenylethynyl)benzene (a) and the TEM image after coating with silicon oxide (b)

[0059] Figure 7 The Raman signal of Basic Blue 3 (a) and the TEM image after coating with silicon oxide (b)

[0060] Figure 8 The Raman signal of dibenzyl sulfide (a) and the TEM image after coating with silicon oxide (b)

[0061] Figure 9 The Raman signal of bis(2-thienyl) disulfide (a) and the TEM image after coating with silicon oxide (b)

[0062] Figure 10 The Raman signal of bis(4-methoxyphenyl) disulfide (a) and the TEM image after coating with silicon oxide (b)

[0063] Figure 11 The Raman signal of 4,4'-diaminodiphenyl disulfide (a) and the TEM image after coating with silicon oxide (b)

[0064] Figure 12 The Raman signal of 2-naphthol (a) and the TEM image after coating with silicon oxide (b)

[0065] Figure 13 The Raman signal of 3-methylbenzo[B]thiophene (a) and the TEM image after coating with silicon oxide (b)

[0066] Figure 14 The Raman signal of 5-methylbenzo[B]thiophene (a) and the TEM image after coating with silicon oxide (b)

[0067] Figure 15 The Raman signal of 3-bromobenzo[B]thiophene (a) and the TEM image after coating with silicon oxide (b)

[0068] Figure 16 The Raman signal of 4-ethylbiphenylacetylene (a) and the TEM image after coating with silicon oxide (b)

[0069] Figure 17 The Raman signal of 2,2'-bipyridine (a) and the TEM image after coating with silicon oxide (b)

[0070] Figure 18 The Raman signal of 5,5'-dimethyl-2,2'-bipyridine (a) and the TEM image after coating with silicon oxide (b)

[0071] Figure 19 The Raman signal of 4,4'-dimethoxy-2,2'-bipyridine (a) and the TEM image after coating with silicon oxide (b)

[0072] Figure 20 The Raman signal of Rhodamine 6G (a) and the TEM image after coating with silicon oxide (b)

[0073] Figure 21 The Raman signal of methylene blue (a) and the TEM image after coating with silicon oxide (b)

[0074] Figure 22 The Raman signal of crystal violet (a) and the TEM image after coating with silicon oxide (b)

[0075] Figure 23 The Raman signal of p-toluene disulfide (a) and the TEM image after coating with silicon oxide (b)

[0076] Figure 24 The Raman signal of 4-ethylthiophenol (a) and the TEM image after coating with silicon oxide (b)

[0077] Figure 25 The Raman signal of 2-mercaptopyridine (a) and the TEM image after coating with silicon oxide (b)

[0078] Figure 26 The Raman signal of 4-methoxythiophenol (a) and the TEM image after coating with silicon oxide (b)

[0079] Figure 27 The Raman signal of 6-methoxybenzothiophene (a) and the TEM image after coating with silicon oxide (b)

[0080] Figure 28 The Raman signal of 5-chlorobenzothiophene (a) and the TEM image after coating with silicon oxide (b) DETAILED DESCRIPTION

[0081] Example 1

[0082] Signal molecules must possess the following characteristics: 1. They must have a strong interaction with metal nanoparticles and be able to adsorb to the nanoparticle surface. 2. They must have a large Raman scattering cross section, stimulating a strong SERS signal. 3. For further application, the nanoparticles encoded with the signal molecule must be stable in solution.

[0083] According to the Raman signal enhancement (first category) or weakening (second category) of the Raman signal molecules after using the silver coating strategy, the Raman signal molecules are divided into two categories:

[0084] The first type of ligand Raman signal molecule is any one of the following: phenylacetylene, 4-ethynylbiphenyl, 4-ethynylanisole, 1-ethynyl-4-(phenylethynyl)benzene, basic blue 3, dibenzyl sulfide, bis(2-thienyl)disulfide, bis(4-methoxyphenyl)disulfide, 4,4'-diaminodiphenyl disulfide, 2-thionaphthol, 3-methylbenzo[B]thiophene, 5-methylbenzo[B]thiophene, 3-bromobenzo[B]thiophene;

[0085] The second type of ligand Raman signal molecule is any one of the following: 4-ethylbiphenylacetylene, 2,2'-bipyridine, 5,5`-dimethyl-2,2`-bipyridine, 4,4'-dimethoxy-2,2'-bipyridine, rhodamine 6G, methylene blue, crystal violet, p-toluene disulfide, 4-ethylthiophenol, 2-mercaptopyridine, 4-methoxythiophenol, 6-methoxybenzothiophene or 5-chlorobenzothiophene.

[0086] (1) Use 40 nm gold particles to centrifuge at 5000 rpm for 15 min, redisperse in pure water, take 1 mL of gold particle solution and add it to a 4 mL reaction bottle. Add 2 μL of sodium hydroxide solution (250 mM, dissolved in pure water) and 8 μL of phenylacetylene solution (0.57 mM, dissolved in DMF solution) under vortexing, and place in a 60 ° C oven for reaction for 2 h.

[0087] (2) After the reaction solution was cooled, 20 μL of sodium chloride solution (250

[0088] mM, dissolved in pure water), and placed in a 60°C oven for reaction for 2 h.

[0089] (3) After the reaction solution has cooled, add 25 μL of hydroquinone solution (10 mM, dissolved in pure water) and then add 25 μL of silver nitrate solution (10 mM, dissolved in pure water) to the reaction flask. React for 30 minutes.

[0090] (4) Add the reaction solution from step 5 to a mixture (5 mL of anhydrous ethanol, 0.6 μL of tetraethyl silicate as a pure solution, and 10 μL of a 250 mM sodium hydroxide aqueous solution) and allow to react at room temperature for 6 h. Centrifuge and wash at 8000 rpm for 6 min.

[0091] The Raman signal diagram of the enhancement effect of Example 1 and the TEM diagram after coating with silicon oxide are shown in FIG. Figure 2

[0092] Example 2-13

[0093] The ligands in Example 1 can be replaced by other types of ligands, which can be obtained by this method.

[0094] The Raman signal of the ligand is effectively enhanced by the method. Except that the concentration, volume, amount of sodium chloride and concentration of mercaptoundecanoic acid of the ligand solution need to be adjusted, the other steps are basically the same as those in Example 1. The specific experimental amounts are shown in Table 1 below

[0095] Table 1

[0096]

[0097] The Raman signal diagram of the enhancement effect of the ligand of Example 2-13 and the TEM diagram after coating with silicon oxide are shown in Figure 3-15

[0098] Example 14

[0099] (1) Synthesis of 40 nm gold nanoparticles: The 40 nm gold particles were centrifuged at 5000 rpm for 15 min and redispersed in pure water. 1 mL of the gold particle solution was added to a 4 mL reaction flask. 2 μL of sodium hydroxide solution (250 mM, dissolved in pure water) and 5 μL of 4-ethylbiphenylacetylene solution (5.7 μL, dissolved in DMF solution) were added under shaking, and the mixture was placed in a 60°C oven for reaction for 2 h.

[0100] (2) After the reaction solution has cooled, add 15 μL of sodium chloride solution (250 mM, dissolved in pure water) to the reaction flask and place it in a 60°C oven for 2 h.

[0101] (3) After the reaction solution has cooled, add 5 μL of mercaptonoundecanoic acid solution (3 mg / mL, dissolved in anhydrous ethanol) to the reaction flask and let it stand at room temperature for 10 min.

[0102] (4) Add the reaction solution from step 3 to a mixture (5 mL of anhydrous ethanol, 0.6 μL of tetraethyl silicate as a pure solution, and 10 μL of a 250 mM sodium hydroxide aqueous solution) and allow to react at room temperature for 6 h. Centrifuge and wash at 8000 rpm for 6 min.

[0103] The Raman signal diagram of the enhancement effect of Example 14 and the TEM diagram after coating with silicon oxide are shown in FIG. Figure 15 .

[0104] Examples 15-26

[0105] The ligand in Example 14 can be replaced with other ligands, and the Raman signal of the ligand can still be effectively enhanced using this method. The steps are essentially the same as in Example 14, except that the concentration and volume of the ligand solution, the amount of sodium chloride used, and the concentration of mercaptoundecanoic acid need to be adjusted, and silver nitrate and hydroquinone are omitted. The specific experimental amounts are shown in Table 2 below:

[0106]

[0107] The Raman signal diagram of the enhancement effect of the ligand of Example 14-26 and the TEM diagram after coating with silicon oxide are shown in FIG. Figure 16-28

[0108] To demonstrate the enhancement effect of our enhancement strategy, we calculated the enhancement factors of 23 Raman signal molecules, as shown in Table 3.

[0109]

[0110] Ligand concentration 1 : Indicates the concentration of free ligand in dichloromethane solution. Ligand concentration 2 : Assumed to be the concentration of ligands incorporated into silica.

Claims

1. A method for preparing a surface-enhanced Raman label, characterized in that: A universal method for using silica-encapsulated Raman tags uses salt to induce gold particle aggregation, resulting in chain-like aggregates. Based on the degree of Raman signal enhancement after the gold aggregates are coated with a silver layer, the ligand Raman signal molecules are divided into two categories: the first category is where the Raman signal is enhanced after the aggregates are coated with silver and then coated with silica; the second category is where the Raman signal is reduced after the aggregates are coated with silver and then coated with silica. The first type of ligand Raman signal molecule is any one of the following: phenylacetylene, 4-ethynylbiphenyl, 4-ethynylanisole, 1-ethynyl-4-(phenylethynyl)benzene, basic blue 3, dibenzyl sulfide, bis(2-thienyl)disulfide, bis(4-methoxyphenyl)disulfide, 4,4'-diaminodiphenyl disulfide, 2-thionaphthol, 3-methylbenzo[B]thiophene, 5-methylbenzo[B]thiophene, 3-bromobenzo[B]thiophene; The second type of ligand Raman signal molecule is any one of the following: 4-ethylbiphenylacetylene, 2,2'-bipyridine, 5,5'-dimethyl-2,2'-bipyridine, 4,4'-dimethoxy-2,2'-bipyridine, rhodamine 6G, methylene blue, crystal violet, p-toluene disulfide, 4-ethylthiophenol, 2-mercaptopyridine, 4-methoxythiophenol, 6-methoxybenzothiophene or 5-chlorobenzothiophene; The gold aggregate preparation steps are as follows: taking 1 mL of 40 nm gold particles, adding sodium hydroxide solution and 1.5-8 μL of Raman signal molecule solution, incubating, then adding 7-115 mL of sodium chloride solution, and incubating again; The steps for preparing the gold-silver core-shell structure are as follows: adding a hydroquinone aqueous solution and a silver nitrate aqueous solution to a gold aggregate solution and allowing the solution to stand; The preparation steps of the coated silicon oxide are as follows: adding ethanol, tetraethyl orthosilicate and sodium hydroxide solution into the aggregate or the aggregate-coated silver solution and letting the solution stand.

2. The method for preparing a surface-enhanced Raman label according to claim 1, wherein: The gold particles used were 40 nm gold particles stabilized with sodium citrate.

3. The method for preparing a surface-enhanced Raman label according to claim 1, wherein: Some Raman signal molecules coated with silica on the aggregate need to be induced by mercaptoundecanoic acid molecules. The signal molecules include 22: phenylacetylene, 4-ethynylbiphenyl, basic blue 3, dibenzyl sulfide, bis(2-thienyl) disulfide, bis(4-methoxyphenyl) disulfide, 4,4'-diaminodiphenyl disulfide, 2-naphthol, 3-methylbenzo[B]thiophene, 5-methylbenzo[B]thiophene, 3-bromobenzo[B]thiophene, 4-ethylbiphenylacetylene, 5,5'-dimethyl-2,2'-bipyridine, 4,4'-dimethoxy-2,2'-bipyridine, methylene blue, crystal violet, p-toluene disulfide, 4-ethylthiophenol, 2-Mercaptopyridine, 4-methoxythiophenol, 6-methoxybenzothiophene, 5-chlorobenzothiophene, and some molecules can also be coated with silica without the use of mercaptoundecanoic acid, including: 4-ethynylanisole, 1-ethynyl-4-(phenylethynyl)benzene, 2,2'-bipyridine, and rhodamine 6G. The Raman signals of these four molecules are greatly weakened after using mercaptoundecanoic acid.

4. The method for preparing a surface-enhanced Raman label according to claim 1, wherein: The first type of Raman signal molecules used have a relatively strong interaction with gold particles, do not coordinate with silver ions, and exist stably in weakly alkaline aqueous alcohol solutions.

5. The method for preparing a surface-enhanced Raman label according to claim 1, wherein: The Raman signal molecules used have a relatively strong interaction with the gold particles and exist stably in the weakly alkaline aqueous alcohol solution.

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