Spherical composite SERS substrate and preparation method and application thereof

Abstract

The invention relates to the technical field of surface-enhanced Raman detection, and discloses a spherical composite SERS (Surface Enhanced Raman Scattering) substrate as well as a preparation method and application thereof. The spherical composite SERS substrate is of a spherical structure formed by silver nanowires and metal nanoparticles, and the metal nanoparticles are attached to the silver nanowires. The spherical composite SERS substrate is of a spherical structure formed by silver nanowires and metal nanoparticles, and polycyclic aromatic hydrocarbon can be detected without introducing modification molecules. The silver nanowires and the metal nanoparticles are in a loose and porous state, and can rapidly absorb a target solution and then collapse, target molecules are fixed in nano gaps formed by the silver nanowires and the metal nanoparticles, Raman signals of the target molecules are amplified, and then qualitative and quantitative detection of trace substances in various water environments is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of surface enhanced Raman detection, and in particular to a spherical composite SERS substrate and a preparation method and application thereof. Background Art

[0002] In 1974, Fleischmann et al. accidentally discovered the phenomenon of signal enhancement when measuring the Raman spectrum of pyridine molecules on the surface of a rough silver electrode. Since its discovery, surface enhanced Raman spectroscopy (SERS) has become one of the most sensitive and emerging trace analysis techniques. SERS technology retains the advantages of conventional Raman spectroscopy, while having higher sensitivity and specificity. It can detect analytes at ultra-low concentrations and has a wide range of applications in detection and identification of materials, chemistry, biology, and medicine.

[0003] There are two key factors in SERS detection: one is to construct a suitable metal nanostructure substrate to produce enough nanogaps to induce the electromagnetic field enhancement region; the other is to fix the target molecule in the electromagnetic field enhancement region to achieve the amplification of the Raman signal. At present, the SERS substrate is mainly composed of metal particles such as gold, silver, and copper, which can produce a strong coupling effect with the incident light to obtain the electromagnetic field enhancement region. For the target molecule, it can be fixed in the electromagnetic field enhancement region by covalent bonds or non-covalent bonds. Especially for polycyclic aromatic hydrocarbon molecules such as pyrene and phenanthrene, there are fewer substituents that can undergo chemical reactions, and it is difficult to directly adsorb to the vicinity of the substrate through covalent bonds. More adsorption is carried out through non-covalent bond forces (physical adsorption, hydrophobic effect, π-π stacking effect, etc.), such as the introduction of molecules such as thiol and graphene, but the introduction of these molecules may cover the Raman characteristic peaks of the target molecule. Therefore, how to construct a new SERS substrate and fix the target molecule in the nanogaps conveniently and efficiently is an important research content in SERS detection.

[0004] Patent application CN 106525813 A discloses a porous graphene-silver nanocube composite material and its preparation method and use. The method comprises the following steps: firstly mixing graphene oxide, sodium bisulfite and deionized water and then subjecting the mixture to ultrasonic vibration, then placing the obtained mixture at 90-100°C and cooling it, then rinsing the obtained black graphene gel suspended in water with deionized water and freeze-drying it, then immersing the obtained sponge-like porous graphene in an ethanol dispersion of silver nanocubes and taking it out to obtain an intermediate product, and then compressing the dried intermediate product to obtain the target product. Patent application CN 102706853 A provides a Raman enhanced substrate material and its preparation and application method. First, prepare TiO 2Nanotube array, then graphene is deposited thereon, and finally nanosilver sol is added to the substrate surface and dried to form a composite material. This material can be used in the detection of benzo(a)pyrene. Compared with the traditional method, the surface enhanced Raman detection method using this material has the advantages of short time and simple sample processing. Patent application CN 104089942 A discloses a surface enhanced Raman substrate with super hydrophobic properties and its application in the detection of polycyclic aromatic hydrocarbons. A substrate with super hydrophobic properties is obtained by modification with long alkyl chain thiol. This method prepares a SERS substrate through simple steps, and the super hydrophobic substrate obtained after modification can adsorb organic pollutants such as polycyclic aromatic hydrocarbons and detect them. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems existing in the prior art that the existing SERS substrate has to introduce modified molecules in order to adsorb the target molecules into the nanogaps, which leads to the problem that it is easy to interfere with the detection of the target molecules and the preparation process is complicated, and to provide a spherical composite SERS substrate and its preparation method and application.

[0006] In order to achieve the above object, the first aspect of the present invention provides a spherical composite SERS substrate, wherein the spherical composite SERS substrate is a spherical structure formed by silver nanowires and metal nanoparticles, and the metal nanoparticles are attached to the silver nanowires.

[0007] Preferably, the diameter of the spherical structure is 1.5-6 mm.

[0008] Preferably, the silver nanowires have a diameter of 20-60 nm and a length of 15-40 μm.

[0009] Preferably, the metal nanoparticles are gold nanoparticles or silver nanoparticles;

[0010] Preferably, the size of the metal nanoparticles is 10-70 nm.

[0011] The second aspect of the present invention provides a method for preparing a spherical composite SERS substrate, the method comprising: dropping a mixed solution containing silver nanowires and metal nanoparticles into liquid nitrogen, and then freeze-drying;

[0012] Wherein, in the mixed solution containing silver nanowires and metal nanoparticles, the concentration of silver nanowires is 12-45 mg / mL.

[0013] Preferably, in the solution containing silver nanowires and metal nanoparticles, the weight ratio of silver nanowires to metal nanoparticles is 3-10:1.

[0014] Preferably, the silver nanowires have a diameter of 20-60 nm and a length of 15-40 μm.

[0015] Preferably, the metal nanoparticles are gold nanoparticles or silver nanoparticles;

[0016] Preferably, the size of the metal nanoparticles is 10-70 nm.

[0017] Preferably, the volume of the droplets dropped into the liquid nitrogen is 3-15 μL / drop.

[0018] Preferably, the freeze-drying conditions include: a pressure of 1-100 Pa and a time of 10-30 h.

[0019] The third aspect of the present invention provides a spherical composite SERS substrate prepared according to the method described above.

[0020] A fourth aspect of the present invention provides application of the spherical composite SERS substrate described above in the detection of polycyclic aromatic hydrocarbons.

[0021] Preferably, the polycyclic aromatic hydrocarbon is selected from at least one of naphthalene, anthracene, phenanthrene, pyrene and benzopyrene;

[0022] Preferably, the spherical composite SERS substrate has a detection concentration of ≥10 -9 mol / L.

[0023] A fifth aspect of the present invention provides a method for detecting the concentration of polycyclic aromatic hydrocarbons in a solution, the method comprising: dropping the solution to be tested onto the spherical composite SERS substrate described above, and performing SERS detection using a Raman spectrometer.

[0024] Preferably, the volume of the solution to be tested is 2-12 μL.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The spherical composite SERS substrate of the present invention is a spherical structure formed by silver nanowires and metal nanoparticles, and the detection of polycyclic aromatic hydrocarbons can be achieved without introducing modified molecules. Specifically, the spherical composite material is a spherical structural skeleton formed by interweaving silver nanowires into a network, and the metal nanoparticles are loaded on the silver nanowires, thereby obtaining the spherical composite SERS substrate. The spherical composite SERS substrate is in a loose and porous state, has the advantage of a large specific surface area, can quickly absorb the target solution, and then collapse, and fix the target molecule in the nano gap formed by the silver nanowires and the metal nanoparticles.

[0027] 2. The preparation method of the spherical composite SERS substrate described in the present invention has the characteristics of simple steps, controllable size and no need to use large and expensive instruments. Combined with freeze-drying technology, the silver nanowires can self-assemble into a network structure, thereby forming a loose and porous spherical structure. At the same time, metal nanoparticles are attached to the silver nanowires to facilitate the adsorption of the molecules to be tested in the solution.

[0028] 3. The detection method of polycyclic aromatic hydrocarbons of the present invention has the advantages of being simple, convenient, efficient and sensitive. It is suitable for detecting trace amounts of polycyclic aromatic hydrocarbons and petroleum substances in various water quality detection fields such as industrial wastewater and domestic sewage of petrochemical enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of a process of using the spherical composite SERS substrate of the present invention to process a solution to be tested;

[0030] Figure 2 The following is the characterization result of photographing the product prepared in Example 1 using a microscope:

[0031] Figure 3 This is a result diagram of characterizing the product prepared in Example 1 using SEM;

[0032] Figure 4 It is the Raman signal diagram of different concentrations of phenanthrene on the spherical composite SERS substrate;

[0033] Figure 5 It is a graph showing the relationship between the concentration of phenanthrene and the intensity of the Raman signal. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0035] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0036] A first aspect of the present invention provides a spherical composite SERS substrate, wherein the spherical composite SERS substrate is a spherical structure formed by silver nanowires and metal nanoparticles, and the metal nanoparticles are attached to the silver nanowires.

[0037] In the present invention, silver nanowires are interwoven into a network by themselves, thereby forming a spherical structure with loose and porous characteristics, and metal nanoparticles are attached to the silver nanowires. Among them, the silver nanowires, on the one hand, serve as the skeleton of the spherical structure to ensure the stability of the structure, and on the other hand, can serve as a carrier of the metal nanoparticles. Through the coordination of silver nanowires and metal nanoparticles, more nanogaps can be formed, providing a stronger and denser electromagnetic field enhancement area, thereby improving the sensitivity of detection.

[0038] In order to further improve the detection sensitivity of the spherical composite SERS substrate, in a preferred embodiment, the diameter of the spherical structure is 1.5-6 mm. If the size of the spherical structure is too small, it is difficult to drip the test substance into the spherical substrate, and if the size is too large, it will increase the cost.

[0039] In a preferred embodiment, the silver nanowires have a diameter of 20-60 nm and a length of 15-40 μm.

[0040] In a preferred embodiment, the metal nanoparticles are gold nanoparticles or silver nanoparticles, for example, gold nanospheres, silver nanospheres, gold nanorods, silver nanocubes, gold nanotriangles, and the like.

[0041] In a preferred embodiment, the metal nanoparticles have a geometric size of 10-70 nm.

[0042] Further preferably, the metal nanoparticles are gold nanorods with a diameter of 10-70 nm.

[0043] A second aspect of the present invention provides a method for preparing a spherical composite SERS substrate, the method comprising: dropping a mixed solution containing silver nanowires and metal nanoparticles into liquid nitrogen, and then freeze-drying;

[0044] Wherein, in the solution containing silver nanowires and metal nanoparticles, the concentration of silver nanowires is 12-45 mg / mL.

[0045] In the method of the present invention, a solution containing silver nanowires and metal nanoparticles is dripped into liquid nitrogen, and the ultra-low temperature of liquid nitrogen can quickly transform the droplets into solid spheres, and then the solvent can be sublimated by freeze-drying technology without destroying the structure formed by the silver nanowires and metal nanoparticles. The present invention obtains a spherical composite SERS substrate by combining freeze-drying technology, and does not involve large and expensive instruments such as vacuum coating machines and electron beam etcher. The spherical structural skeleton of the substrate is formed by silver nanowires interwoven into a network, and metal nanoparticles are attached to the silver nanowires.

[0046] In the method described in the present invention, the concentration of silver nanowires in the solution is reasonably controlled. If the concentration is too low, the supporting force of the mesh structure is insufficient to form a spherical structure during freeze drying. If the concentration is too high, the cost will increase. Therefore, limiting the concentration of silver nanowires in the solution to a range of 12-45 mg / mL can not only ensure the formation of a spherical structure, but also help control the density of the formed spherical structure, ensure that the target molecules can be distributed in the nanogaps of the entire silver nanowire, and ensure the economic practicability of the method, effectively improving the sensitivity of detection.

[0047] In a preferred embodiment, in the solution containing silver nanowires and metal nanoparticles, the weight ratio of silver nanowires to metal nanoparticles can be 3-10:1; specifically, it can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1.

[0048] In a preferred embodiment, the silver nanowires have a diameter of 20-60 nm and a length of 15-40 μm.

[0049] In the method described in the present invention, the silver nanowires and metal nanoparticles can be commercially available products or homemade in the laboratory.

[0050] According to some specific embodiments of the present invention, the silver nanowires can be prepared according to the following steps:

[0051] A1: Mix polyvinyl pyrrolidone with water and then add AgNO 3 mixing to obtain a mixed material;

[0052] A2: The mixture is subjected to a hydrothermal reaction and then solid-liquid separation is performed.

[0053] Preferably, the conditions of the hydrothermal reaction include: temperature of 110-190° C. and time of 4-10 h.

[0054] Preferably, the weight ratio of polyvinyl pyrrolidone to silver nitrate is 12-40:1.

[0055] Preferably, the solid-liquid separation can be performed by centrifugation to separate unreacted substances, which can be repeated 2-5 times.

[0056] In a preferred embodiment, the metal nanoparticles are gold nanoparticles or silver nanoparticles, for example, gold nanospheres, silver nanospheres, gold nanorods, silver nanocubes, gold nanotriangles, and the like.

[0057] In a preferred embodiment, the metal nanoparticles have a geometric size of 10-70 nm.

[0058] Further preferably, the metal nanoparticles are gold nanorods with a diameter of 10-70 nm.

[0059] According to some specific embodiments of the present invention, gold nanorods can be prepared according to the following steps:

[0060] B1: Hexadecyltrimethylammonium bromide (CTAB), HAuCl 4 Mix with water and then add NaBH 4 Mixing to obtain a first mixed solution;

[0061] B2; CTAB, HAuCl 4 and water, and then adding ascorbic acid and mixing to obtain a second mixed solution;

[0062] B3: The first mixed solution and the second mixed solution are mixed to react, and then NaCl is added to continue the reaction, solid-liquid separation, and washing.

[0063] In a preferred embodiment, in step B1, CTAB, HAuCl 4 and NaBH 4 The molar ratio of the dosage is 1:2-3:0.03-0.1.

[0064] In a preferred embodiment, in step B2, CTAB, HAuCl 4 The molar ratio of the amount of ascorbic acid can be 1:0.01-0.02:0.01-0.07.

[0065] In a preferred embodiment, in step B3, when the first mixed solution and the second mixed solution are mixed, the dosage ratio of the first mixed solution to the second mixed solution is 3.5×10 -3 ~7.5×10 -3 : 1, wherein the amount of the first mixed solution is based on the molar amount of CTAB added when preparing the first mixed solution, and the amount of the second mixed solution is based on the molar amount of CTAB added when preparing the second mixed solution.

[0066] In the method of the present invention, the size of the spherical structure obtained can be controlled by controlling the volume of each drop of solution dripped into the liquid nitrogen. In a preferred embodiment, the volume of the droplet dripped into the liquid nitrogen is 3-15 μL / drop. By controlling the volume of each droplet within the above range, it is beneficial to obtain a spherical structure with a diameter of 1.5-6 mm.

[0067] In a preferred embodiment, the freeze-drying conditions include: a pressure of 1-100 Pa and a time of 10-30 h. In the present invention, the pressure refers to absolute pressure.

[0068] The third aspect of the present invention provides a spherical composite SERS substrate prepared according to the method described above.

[0069] A fourth aspect of the present invention provides application of the spherical composite SERS substrate described above in the detection of polycyclic aromatic hydrocarbons.

[0070] Combined with reference Figure 1 It can be seen that the process of treating the test solution during Raman detection using the spherical SERS composite substrate described in the present invention includes: after the test solution is added dropwise, the test solution quickly fills the entire substrate, and as the solvent evaporates, the substrate collapses, and the target molecules are wrapped in the nanogaps between the silver nanowires and the metal nanoparticles.

[0071] Preferably, the polycyclic aromatic hydrocarbons are selected from at least one of naphthalene, anthracene, phenanthrene, pyrene and benzopyrene;

[0072] Preferably, the spherical composite SERS substrate has a detection concentration of ≥10 -9 mol / L.

[0073] A fifth aspect of the present invention provides a method for detecting the concentration of polycyclic aromatic hydrocarbons in a solution, the method comprising: dropping the solution to be tested onto the spherical composite SERS substrate described above, and performing SERS detection using a Raman spectrometer.

[0074] Preferably, the volume of the solution to be tested is 2-12 μL.

[0075] In a specific embodiment, polycyclic aromatic hydrocarbons can be quantitatively detected. The testing process includes the following steps:

[0076] S1: Add the PAH standard solution onto the spherical SERS substrate and dry it. After the solvent evaporates, use Raman spectrometer to perform SERS detection and record the peak intensity.

[0077] S2: With the negative number of the logarithm of the concentration as the abscissa and the peak intensity as the ordinate, fitting is performed to obtain the relationship between concentration and peak intensity;

[0078] S3: Add the solution to be tested dropwise onto the spherical SERS substrate and dry it. After the solvent evaporates, use a Raman spectrometer to perform SERS detection, record the peak intensity, and then substitute the peak intensity into the relationship for calculation to obtain the concentration of polycyclic aromatic hydrocarbons in the solution to be tested.

[0079] The spherical composite SERS substrate and its preparation method of the present invention are further described by examples. The examples are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0080] Example 1

[0081] Preparation of silver nanowires:

[0082] A1: 0.4 g polyvinyl pyrrolidone (PVP, M W =55 000) was added to 50 mL of deionized water and stirred for 30 minutes to form a clear solution, and then 0.02 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0083] A2: The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150°C for 7 hours. After the reaction, the suspension was taken out and centrifuged at 4500 rpm for 10 minutes. This was repeated 2-5 times to remove unreacted substances to obtain silver nanowires with a diameter of 35 nm and a length of 25 μm.

[0084] Preparation of gold nanorods:

[0085] B1: Take 5 mL of 0.2 mol / L CTAB solution and 5 mL of 0.5 mol / L HAuCl 4 The solution was mixed, and then 0.6 mL of freshly prepared 0.1 mol / L NaBH 4 The solution changed from light yellow to bright brown-yellow, and stirring was continued for 2 min to obtain the first mixed solution;

[0086] B2: Take a clean 50mL round-bottom flask, add 5mL of 0.2mol / L CTAB solution, and then drop 2mL of 8mmol / L HAuCl 4 After the solution is stable, 0.5 mL of 0.08 mol / L ascorbic acid solution is quickly added, and when the solution changes from yellow to colorless, pure water is added to make the total volume 25 mL to obtain a second mixed solution;

[0087] B3: Add 50 μL of the first mixed solution (i.e., the amount of CTAB required to prepare the solution is about 4.7×10 -3 mmol), that is, the dosage ratio of the first mixed solution to the second mixed solution is 4.7×10 -3 : 1, after reacting at room temperature for 2 hours, 0.65 mL of 4 mol / L NaCl solution was added, and the reaction was continued for 12 hours. Then, after centrifugation and washing at a speed of 7000 r / min, gold nanorods with a diameter of 20 nm and a length of 50 nm were obtained.

[0088] Preparation of spherical composite SERS substrate:

[0089] Ultrasonic mixing of the silver nanowires, the gold nanorods and water to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 35 mg / mL and the concentration of the gold nanorods is controlled to be 7 mg / mL;

[0090] 8 μL of the mixed solution was taken with a pipette (with a tip diameter of 5 mm), dropped into liquid nitrogen, and then placed in a freeze dryer at a pressure of 2 Pa for 16 h to obtain a spherical composite SERS substrate with a diameter of 3 mm.

[0091] Example 2

[0092] Preparation of silver nanowires:

[0093] A1: 0.4 g polyvinyl pyrrolidone (PVP, M W =55 000) was added to 50 mL of deionized water and stirred for 30 minutes to form a clear solution, and then 0.028 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0094] A2: The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150°C for 7 hours. After the reaction, the suspension was taken out and centrifuged at 4500 rpm for 10 minutes. This was repeated 2-5 times to remove unreacted substances to obtain silver nanowires with a diameter of 45 nm and a length of 30 μm.

[0095] Preparation of spherical composite SERS substrate:

[0096] The silver nanowires, gold nanorods (same as in Example 1) and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 40 mg / mL and the concentration of the gold nanorods is controlled to be 7 mg / mL;

[0097] 8 μL of the mixed solution was taken with a pipette (with a tip diameter of 5 mm), dropped into liquid nitrogen, and then placed in a freeze dryer at a pressure of 2 Pa for 16 h to obtain a spherical composite SERS substrate with a diameter of 3 mm.

[0098] Example 3

[0099] Preparation of gold nanorods:

[0100] B1: Take 5 mL of 0.2 mol / L CTAB solution and 5 mL of 0.5 mol / L HAuCl 4 The solution was mixed, and then 0.6 mL of freshly prepared 0.1 mol / L NaBH 4 The solution changed from light yellow to bright brown-yellow, and stirring was continued for 2 min to obtain the first mixed solution;

[0101] B2: Take a clean 50mL round-bottom flask, add 5mL of 0.2mol / L CTAB solution, and then drop 2mL of 8mmol / L HAuCl 4 After the solution is stable, 0.5 mL of 0.08 mol / L ascorbic acid solution is quickly added, and when the solution changes from yellow to colorless, pure water is added to make the total volume 25 mL to obtain a second mixed solution;

[0102] B3: Add 75 μL of the first mixed solution (i.e., the amount of CTAB required to prepare the solution is about 7.05×10 -3 mmol), that is, the dosage ratio of the first mixed solution to the second mixed solution is 7.05×10 -3 : 1, after reacting at room temperature for 2 hours, 0.65 mL of 4 mol / L NaCl solution was added, and the reaction was continued for 12 hours. Then, after centrifugation and washing at a speed of 7000 r / min, gold nanorods with a diameter of 25 nm and a length of 55 nm were obtained.

[0103] Preparation of spherical composite SERS substrate:

[0104] The silver nanowires (same as in Example 1), the gold nanorods and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 35 mg / mL and the concentration of the gold nanorods is controlled to be 10 mg / mL;

[0105] 8 μL of the mixed solution was taken with a pipette (with a tip diameter of 5 mm), dropped into liquid nitrogen, and then placed in a freeze dryer at a pressure of 2 Pa for 16 h to obtain a spherical composite SERS substrate with a diameter of 3 mm.

[0106] Example 4

[0107] Preparation of silver nanowires:

[0108] A1: 0.4 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 50 mL of deionized water and stirred for 30 minutes to form a clear solution, and then 0.015 g of AgNO was added 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0109] A2: The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150°C for 7 hours. After the reaction, the suspension was taken out and centrifuged at 4500 rpm for 10 minutes. This was repeated 2-5 times to remove unreacted substances to obtain silver nanowires with a diameter of 30 nm and a length of 20 μm.

[0110] Preparation of gold nanorods:

[0111] B1: Take 5 mL of 0.2 mol / L CTAB solution and 5 mL of 0.5 mol / L HAuCl 4 The solution was mixed, and then 0.6 mL of freshly prepared 0.1 mol / L NaBH 4 The solution changed from light yellow to bright brown-yellow, and stirring was continued for 2 min to obtain the first mixed solution;

[0112] B2: Take a clean 50mL round-bottom flask, add 5mL of 0.2mol / L CTAB solution, and then drop 2mL of 8mmol / L HAuCl 4 After the solution is stable, 0.5 mL of 0.08 mol / L ascorbic acid solution is quickly added, and when the solution changes from yellow to colorless, pure water is added to make the total volume 25 mL to obtain a second mixed solution;

[0113] B3: Add 40 μL of the first mixed solution (i.e., the amount of CTAB required to prepare the solution is about 3.76×10 -3 mmol), that is, the dosage ratio of the first mixed solution to the second mixed solution is 3.76×10 -3 : 1, after reacting at room temperature for 2 hours, 0.65 mL of 4 mol / L NaCl solution was added, and the reaction was continued for 12 hours. Then, after centrifugation and washing at a speed of 7000 r / min, gold nanorods with a diameter of 15 nm and a length of 40 nm were obtained.

[0114] Preparation of spherical composite SERS substrate:

[0115] Ultrasonic mixing of the silver nanowires, the gold nanorods and water to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 30 mg / mL and the concentration of the gold nanorods is controlled to be 9 mg / mL;

[0116] 8 μL of the mixed solution was taken with a pipette (with a tip diameter of 5 mm), dropped into liquid nitrogen, and then placed in a freeze dryer at a pressure of 2 Pa for 16 h to obtain a spherical composite SERS substrate with a diameter of 3 mm.

[0117] Example 5

[0118] Preparation of spherical composite SERS substrate:

[0119] The silver nanowires (same as in Example 1), the gold nanorods (same as in Example 1) and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 35 mg / mL and the concentration of the gold nanorods is controlled to be 5 mg / mL;

[0120] 8 μL of the mixed solution was taken with a pipette (with a tip diameter of 5 mm), dropped into liquid nitrogen, and then placed in a freeze dryer at a pressure of 2 Pa for 16 h to obtain a spherical composite SERS substrate with a diameter of 3 mm.

[0121] Example 6

[0122] Preparation of spherical composite SERS substrate:

[0123] The silver nanowires (same as in Example 1), the gold nanorods (same as in Example 1) and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 30 mg / mL and the concentration of the gold nanorods is controlled to be 7 mg / mL;

[0124] Take 8 μL of the mixed solution with a pipette (the tip diameter is 5 mm), drop it into liquid nitrogen, and then put it into a freeze dryer under a pressure of 2 Pa for 16 hours to obtain a spherical composite SERS substrate with a diameter of 3 mm.

[0125] Example 7

[0126] Preparation of spherical composite SERS substrate:

[0127] The silver nanowires (same as in Example 1), the gold nanorods (same as in Example 1) and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 35 mg / mL and the concentration of the gold nanorods is controlled to be 7 mg / mL;

[0128] Use a pipette (the tip diameter is 5 mm) to take 4.6 μL of the mixed solution, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 2 Pa for 16 hours to obtain a spherical composite SERS substrate with a diameter of 2.5 mm.

[0129] Example 8

[0130] Preparation of spherical composite SERS substrate:

[0131] The silver nanowires (same as in Example 1), the gold nanorods (same as in Example 1) and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 35 mg / mL and the concentration of the gold nanorods is controlled to be 7 mg / mL;

[0132] Use a pipette (the tip diameter is 5 mm) to take 12.8 μL of the mixed solution, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 2 Pa for 16 hours to obtain a spherical composite SERS substrate with a diameter of 3.5 mm.

[0133] Comparative Example 1

[0134] Silver nanowires (the same as in Example 1), gold nanorods (the same as in Example 1) and water were ultrasonically mixed to obtain a mixed solution, and the concentration of the silver nanowires in the mixed solution was controlled to be 35 mg / mL and the concentration of the gold nanorods was controlled to be 7 mg / mL.

[0135] Use a pipette (the diameter of the pipette tip is 5 mm) to take 8 μL of the above mixed solution and drop it directly onto the glass slide until the solvent evaporates.

[0136] Comparative Example 2

[0137] Silver nanowires (the same as in Example 1) and water were ultrasonically mixed to obtain a mixed solution, and the concentration of the silver nanowires in the mixed solution was controlled to be 35 mg / mL.

[0138] Use a pipette (the tip diameter is 5 mm) to take 8 μL of the mixed solution, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 2 Pa for 16 hours to obtain a SERS substrate with a diameter of 3 mm.

[0139] Comparative Example 3

[0140] The silver nanowires (same as in Example 1), the gold nanorods (same as in Example 1) and water are ultrasonically mixed to obtain a mixed solution, wherein the concentration of the silver nanowires in the mixed solution is controlled to be 10 mg / mL and the concentration of the gold nanorods is controlled to be 4 mg / mL;

[0141] Take 8 μL of the above mixture with a pipette (the tip diameter is 5 mm), drop it into liquid nitrogen, and then put it into a freeze dryer and place it for 16 hours under a pressure of 2 Pa. During the placement process, it was found that the structure of silver nanowires and gold nanorods collapsed and could not form a spherical structure. This may be because the concentration of silver nanowires is too low, and the support force of the formed network structure is insufficient to form a spherical structure.

[0142] Test Example 1

[0143] The product prepared in Example 1 was photographed using an Olympus CX31 microscope. Figure 2 The product prepared in Example 1 was characterized by SEM, and the results were as shown in Figure 3 shown.

[0144] Depend on Figure 2-Figure 3It can be seen that after freeze-drying, small balls with a diameter of 4 mm can be formed, the interior of which is a mesh porous structure formed by the interweaving of silver nanowires, and gold nanorods are attached to the interwoven silver nanowire mesh structure.

[0145] Test Example 2

[0146] The performance of the products prepared in Examples 1-8 and Comparative Example 1 was tested, and the test process was as follows:

[0147] 6uL of a concentration of 10 -6 mol / L phenanthrene ethanol solution was dripped onto the substrate to be tested. After the solvent evaporated, the substrate was tested using a Horiba Xplus microscope confocal Raman spectrometer, with a laser wavelength of 633nm, a power of 0.5mW, an integration time of 40s, and an integration number of 2 times. -1 Taking the strength at as an example, the strength results are shown in Table 1.

[0148] Table 1

[0149] serial number strength serial number strength Example 1 8951 Example 6 8637 Example 2 8902 Example 7 8869 Example 3 8876 Example 8 8972 Example 4 8824 Comparative Example 1 6543 Example 5 8523 Comparative Example 2 6973

[0150] As shown in Table 1, the spherical SERS substrate prepared in the embodiment has good signal amplification ability when applied to surface enhanced Raman detection. However, the signal intensity of the SERS substrate prepared in Comparative Example 1 is significantly lower than that in the embodiment. The silver nanowires and gold nanorods directly form a compact SERS substrate on the glass sheet. After the test solution is added, the target molecules can only be adsorbed on the surface of the silver nanowires and gold nanorods, and the number of molecules entering the nano gap is reduced, and the Raman signal is reduced.

[0151] Test Example 3

[0152] The concentration of phenanthrene was set to 10 -9 mol / L、10 -8 mol / L、10 -7 mol / L、10 -6 mol / L、10 -5 mol / L、10 - 4 mol / L solution, the corresponding Raman signal is shown in the figure Figure 4 As shown in the figure, it can be seen that the characteristic peaks of phenanthrene molecules are mainly 405cm -1 、546cm -1 、705cm -1 、1035cm -1 、1358cm -1 、1434cm -1 and 1606cm -1It can be seen from the intensity of the characteristic peak that as the concentration gradually decreases, the intensity of the characteristic peak also gradually decreases. It can be seen that the spherical composite SERS substrate of the present invention can achieve the effect of ≥10 -9 Qualitative detection of phenanthrene molecules at mol / L.

[0153] Further, in order to achieve quantitative detection of phenanthrene, according to Figure 4 For the data in, 705cm is selected -1 The intensity of the characteristic peak at is the ordinate, and the negative logarithm of the concentration is the abscissa. Figure 5 .from Figure 5 It can be seen that the intensity of the characteristic peak and the logarithm of the concentration show a good functional relationship. Characteristic peak intensity y = -3230.51x + 28654.34, R 2 = 0.9938, x is the negative number of the logarithm of the concentration (i.e. -lgC). Based on this functional relationship, 705cm -1 After measuring the intensity of the characteristic peak, the concentration of the solution can be calculated, thereby achieving quantitative detection of phenanthrene molecules.

[0154] The concentration of phenanthrene was prepared as 10 -5.2 mol / L、10 -6.5 mol / L、10 -8 mol / L solution was used as the test solution, and three spherical composite SERS substrates prepared according to the method described in Example 1 were prepared. Then, the test solution was dripped onto the spherical composite SERS substrate. After the solvent evaporated, the Raman spectrum was tested and the 705 cm -1 The intensity of the characteristic peak at , is substituted into the above relationship to calculate the concentration. The measured results are compared with the theoretical value of the test solution, and the results are shown in Table 2.

[0155] Table 2

[0156] Theoretical value Characteristic peak intensity Detection value error <![CDATA[10 -5.2 ]]> 11726 <![CDATA[10 -5.24 ]]> 8.8％ <![CDATA[10 -6.5 ]]> 7753 <![CDATA[10 -6.47 ]]> 7.2％ <![CDATA[10 -8 ]]> 2713 <![CDATA[10 -8.03 ]]> 6.7％

[0157] It can be seen from the results in Table 2 that the spherical composite SERS substrate of the present invention can accurately measure the concentration of phenanthrene molecules in the solution.

[0158] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A spherical composite SERS substrate, It is characterized in that The spherical composite SERS substrate is a spherical structure formed by silver nanowires and metal nanoparticles, and the metal nanoparticles are attached to the silver nanowires.

2. The spherical composite SERS substrate according to claim 1, It is characterized in that The diameter of the spherical structure is 1.5-6 mm.

3. The spherical composite SERS substrate according to claim 1 or 2, It is characterized in that The diameter of silver nanowires is 20-60nm and the length is 15-40μm.

4. The spherical composite SERS substrate according to any one of claims 1 to 3, It is characterized in that The metal nanoparticles are gold nanoparticles or silver nanoparticles; Preferably, the size of the metal nanoparticles is 10-70 nm.

5. A method for preparing a spherical composite SERS substrate, It is characterized in that The method comprises: dropping a mixed solution containing silver nanowires and metal nanoparticles into liquid nitrogen, and then freeze-drying; Wherein, in the mixed solution containing silver nanowires and metal nanoparticles, the concentration of silver nanowires is 12-45 mg / mL.

6. The method according to claim 5, It is characterized in that In the solution containing silver nanowires and metal nanoparticles, the weight ratio of the silver nanowires to the metal nanoparticles is 3-10:

1.

7. The method according to claim 5 or 6, It is characterized in that The diameter of silver nanowires is 20-60nm and the length is 15-40μm.

8. The method according to any one of claims 5 to 7, It is characterized in that The metal nanoparticles are gold nanoparticles or silver nanoparticles; Preferably, the size of the metal nanoparticles is 10-70 nm.

9. The method according to any one of claims 5 to 8, It is characterized in that The volume of the droplets dropped into the liquid nitrogen was 3-15 μL / drop.

10. The method according to any one of claims 5 to 9, It is characterized in that The freeze-drying conditions include: pressure of 1-100 Pa and time of 10-30 h.

11. A spherical composite SERS substrate prepared by the method according to any one of claims 5 to 10.

12. Use of the spherical composite SERS substrate according to any one of claims 1 to 4 and 11 in the detection of polycyclic aromatic hydrocarbons.

13. The use according to claim 12, wherein the polycyclic aromatic hydrocarbon is at least one selected from naphthalene, anthracene, phenanthrene, pyrene and benzopyrene; Preferably, the spherical composite SERS substrate has a detection concentration of ≥10 -9 mol / L.

14. A method for detecting the concentration of polycyclic aromatic hydrocarbons in a solution, It is characterized in that The method comprises: dropping a solution to be tested onto the spherical composite SERS substrate described in any one of claims 1 to 4 and 11, and performing SERS detection using a Raman spectrometer.

15. The method according to claim 14, It is characterized in that The volume of the solution to be tested is 2-12 μL.

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