Spherical SERS substrate and preparation method and application thereof

Abstract

The invention relates to the field of surface-enhanced Raman detection, and discloses a spherical SERS (Surface Enhanced Raman Scattering) substrate as well as a preparation method and application thereof. The spherical SERS substrate is of a spherical structure formed by silver nanowires. The spherical SERS substrate is of a spherical structure formed by the silver nanowires, molecules to be detected can be introduced into an electromagnetic field enhancement area between the silver nanowires without introducing modification groups, and therefore high-sensitivity detection of multiple molecules to be detected such as polycyclic aromatic hydrocarbon is achieved. The preparation method of the spherical SERS substrate has the characteristics that the steps are simple, the size is controllable, and large expensive instruments do not need to be used, a freeze drying technology is combined, so that the silver nanowires are self-assembled into a net-shaped structure, a loose and porous spherical structure is further formed, and to-be-detected molecules in a solution are conveniently adsorbed.

Description

Technical Field

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

[0002] Polycyclic aromatic hydrocarbons (PAHs) are products of incomplete combustion of fossil fuels or carbon-containing materials such as wood and tobacco. They belong to a class of persistent organic pollutants (POPs). They have the characteristics of a wide variety, wide distribution range, long degradation cycle, strong mutagenicity and carcinogenicity, etc., which pose a great threat to the ecological environment and human health. In order to effectively control and control the pollution of PAHs, it is necessary to achieve qualitative and quantitative detection of related trace substances in the environment. At present, the detection of PAHs mainly includes gas chromatography-mass spectrometry, fluorescence spectroscopy, electrochemical methods, etc. Although these methods are highly sensitive, they have the characteristics of complex sample pretreatment steps, cumbersome operations, and can only be carried out under laboratory conditions. Therefore, establishing a set of rapid, real-time and convenient PAH detection and analysis technologies is of great significance to meet the severe safety and environmental protection situation in the chemical industry.

[0003] Surface Enhanced Raman Spectroscopy (SERS) technology has the advantages of strong signal amplification, high sensitivity, rich chemical fingerprint information, simple operation, and in-situ detection. It is widely used in material, chemical, biological, and medical detection and identification. To detect PAHs through SERS technology, on the one hand, it is necessary to construct metal nanostructures to form nanogaps and electromagnetic field enhancement areas; on the other hand, it is necessary to enrich PAHs in the gaps of metal nanostructures. However, there are few substituents on PAHs that can undergo chemical reactions, and it is difficult to directly adsorb them to the substrate through covalent bonds. Raman detection is mostly achieved by connecting them to the substrate through non-covalent bonding forces (physical adsorption, hydrophobic interaction, π-π stacking, etc.).

[0004] The detection of polycyclic aromatic hydrocarbons by SERS technology has attracted more and more attention. Patent application CN 102706853A provides a Raman enhanced substrate material and its preparation and application method. First, prepare TiO 2Nanotube array, then graphene is deposited on it, and finally nanosilver sol is added to the substrate surface and dried to form a composite material. The Raman enhanced substrate realizes the adsorption of benzo(a)pyrene through the π-π stacking effect of graphene, thereby realizing the simple and rapid detection of various harmful substances in environmental samples, especially benzo(a)pyrene. Patent application CN 103364392 A provides a surface enhanced Raman analysis and detection method for benzo(a)pyrene. First, gold nanoparticles are synthesized in a solution phase, and the gold nanoparticles are modified by thiol. The nanoparticles will self-assemble into a large area of ​​gold nanoparticle film at the gas-liquid interface, and then transferred to a silicon wafer for use as a SERS substrate. The hydrophobic carbon chain end of the thiol can capture benzo(a)pyrene molecules, making them within the effective range of the magnetic field of the plasma resonance of the gold nanoparticles, thereby realizing the surface enhanced Raman analysis and detection of benzo(a)pyrene. Patent application CN 107478635 A provides a MOF-noble metal composite SERS substrate and a preparation method thereof. The method includes: in an alcohol solution, through electrostatic interaction, CTAB-modified positively charged noble metal nanoparticles are loaded on the surface of MOF materials to form a MOF-noble metal nanocomposite SERS substrate. This scheme loads noble metal nanoparticles onto the MOF surface through electrostatic interaction, while maintaining the high porosity, specific surface area and excellent adsorption capacity of the MOF material, it can achieve precise control of the morphology, size and density of metal nanoparticles on the MOF surface, prepare a large number of Raman active sites, and realize direct and highly sensitive detection of molecules such as fluoranthene.

[0005] The above-mentioned existing technologies all obtain SERS substrates through gold and silver nanoparticles, and then achieve adsorption of target molecules by adding modified molecules (graphene, thiol, MOF materials), thereby achieving trace detection of polycyclic aromatic hydrocarbons. The addition of modified molecules will not only introduce additional Raman characteristic peaks, interfering with the detection of target molecules; it will also make the preparation steps of SERS substrates more complicated, which is not conducive to the further promotion and application of technology. Therefore, how to simply and conveniently prepare SERS substrates, adsorb target molecules in the gaps between metal particles without introducing modified molecules, and improve detection sensitivity, is a topic worthy of study. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems that the existing SERS substrate has to introduce modified molecules in order to adsorb the target molecules into the nanogaps, which leads to interference with the detection of the target molecules and complex preparation process, and to provide a spherical SERS substrate and its preparation method and application.

[0007] In order to achieve the above object, the present invention provides a spherical SERS substrate in a first aspect. The spherical SERS substrate is a spherical structure formed by silver nanowires.

[0008] Preferably, the diameter of the spherical structure is 1-5 mm.

[0009] Preferably, the diameter of the silver nanowire is 10-50 nm;

[0010] Preferably, the length of the silver nanowire is 10-30 μm.

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

[0012] Wherein, in the solution containing silver nanowires, the concentration of silver nanowires is 20-50 mg / mL.

[0013] Preferably, the diameter of the silver nanowire is 10-50 nm;

[0014] Preferably, the length of the silver nanowire is 10-30 μm.

[0015] Preferably, the volume of the droplets dropped into the liquid nitrogen is 5-15 μL / drop.

[0016] Preferably, the freeze-drying conditions include: pressure of 1-50 Pa, and time of 8-30 h.

[0017] The third aspect of the present invention provides a spherical SERS substrate prepared according to the method described above.

[0018] A fourth aspect of the present invention provides application of the spherical SERS substrate described above in the detection of polycyclic aromatic hydrocarbons.

[0019] Preferably, the polycyclic aromatic hydrocarbons are selected from at least one of naphthalene, anthracene, phenanthrene, pyrene and benzopyrene.

[0020] Preferably, the spherical SERS substrate has a detection concentration of ≥10 -9 mol / L.

[0021] 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 SERS substrate described above, and performing SERS detection using a Raman spectrometer.

[0022] Preferably, the volume of the solution to be tested is 3-10 μL.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The spherical SERS substrate of the present invention is a spherical structure formed by silver nanowires, and the detection of polycyclic aromatic hydrocarbons can be achieved without introducing modified molecules. Specifically, the spherical SERS substrate (i.e., silver nanowire ball) is a spherical structure formed by silver nanowires interweaving into a network, which has the characteristics of looseness and porosity, can quickly absorb the target solution, and then collapse, fixing the target molecule in the nano-gap of the silver nanowire ball.

[0025] 2. The preparation method of the spherical 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 self-assemble into a network structure, and then form a loose and porous spherical structure, which is convenient for adsorbing the molecules to be tested in the solution.

[0026] 3. The detection method of polycyclic aromatic hydrocarbons of the present invention has the advantages of being convenient, rapid and highly sensitive, and is suitable for the detection of trace amounts of polycyclic aromatic hydrocarbons in various water quality detection fields such as factory sewage, river water and groundwater. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a process of using the spherical SERS substrate of the present invention to process a solution to be tested;

[0028] Figure 2 This is a characterization result diagram of the product prepared in Example 1 taken using a microscope;

[0029] Figure 3 This is a result diagram of characterizing the product prepared in Example 1 using SEM;

[0030] Figure 4 is the Raman signal diagram of different concentrations of pyrene on the spherical SERS substrate;

[0031] Figure 5 This is a graph showing the relationship between the concentration of pyrene and the Raman signal intensity. DETAILED DESCRIPTION

[0032] 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.

[0033] 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.

[0034] A first aspect of the present invention provides a spherical SERS substrate, wherein the spherical SERS substrate is a spherical structure formed by silver nanowires.

[0035] In the present invention, the silver nanowires are self-assembled and interwoven into a network to form a spherical structure with loose and porous characteristics. This unique spherical structure can adsorb the target molecule into the nanogap without introducing a modifying molecule, thereby achieving high-sensitivity detection of the target molecule.

[0036] In the present invention, if the size of the spherical structure is too small, the solution to be tested is not easy to be dripped into the spherical base, and if the size of the spherical structure is too large, it will increase the manufacturing cost. In a preferred embodiment, the diameter of the spherical structure is 1-5 mm, more preferably 2-4 mm.

[0037] In a preferred embodiment, the diameter of the silver nanowires is 10-50 nm, more preferably 20-40 nm.

[0038] In a preferred embodiment, the length of the silver nanowires is 10-30 μm.

[0039] A second aspect of the present invention provides a method for preparing a spherical SERS substrate, the method comprising: dropping a solution containing silver nanowires into liquid nitrogen, and then freeze-drying;

[0040] Wherein, in the solution containing silver nanowires, the concentration of silver nanowires is 20-50 mg / mL.

[0041] In the method of the present invention, a solution containing silver nanowires is dripped into liquid nitrogen, and the ultra-low temperature of the 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. The present invention can obtain a spherical structure with a loose porous structure assembled by silver nanowires by combining freeze-drying technology, and does not involve large and expensive instruments such as vacuum coating machines and electron beam etcher, which is convenient for further promotion and application.

[0042] 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 during freeze drying and the spherical structure cannot be formed. If the concentration is too high, the cost will increase. Therefore, limiting the concentration of silver nanowires in the solution to a range of 20-50 mg / mL can ensure the formation of the spherical structure, 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.

[0043] In a preferred embodiment, the diameter of the silver nanowires is 10-50 nm, more preferably 20-40 nm.

[0044] In a preferred embodiment, the length of the silver nanowires is 10-30 μm.

[0045] In the method of the present invention, the silver nanowires can be commercially available products or can be obtained in the laboratory. The solvent used in the solution containing the silver nanowires can be water.

[0046] According to some specific embodiments of the present invention, the silver nanowires can be prepared according to the following steps:

[0047] (1) mixing polyvinyl pyrrolidone with water, and then adding silver nitrate to mix, to obtain a mixture;

[0048] (2) subjecting the mixture to a hydrothermal reaction, and then performing solid-liquid separation;

[0049] Preferably, the conditions of the hydrothermal reaction include: temperature of 120-180° C. and time of 3-9 h.

[0050] Preferably, the weight ratio of polyvinyl pyrrolidone to silver nitrate is 10-30:1.

[0051] Preferably, the solid-liquid separation can be performed by centrifugation to separate unreacted substances, which can be repeated 2-5 times.

[0052] 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 5-15 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 mm.

[0053] In a preferred embodiment, the solution containing silver nanowires can be dropped into liquid nitrogen using a pipette, and the pipette can use a tip with a caliber of 3-7 mm.

[0054] In a preferred embodiment, the freeze-drying conditions include: a pressure of 1-50 Pa and a time of 8-30 h. In the present invention, the pressure refers to absolute pressure.

[0055] The third aspect of the present invention provides a spherical SERS substrate prepared according to the method described above.

[0056] A fourth aspect of the present invention provides application of the spherical SERS substrate described above in the detection of polycyclic aromatic hydrocarbons.

[0057] Combined with reference Figure 1It can be seen that the process of using the spherical SES substrate described in the present invention to treat the test solution during Raman detection 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 of the silver nanowires.

[0058] Preferably, the polycyclic aromatic hydrocarbon is selected from at least one of naphthalene, anthracene, phenanthrene, pyrene and benzopyrene;

[0059] Preferably, the spherical SERS substrate has a detection concentration of ≥10 -9 mol / L.

[0060] 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 SERS substrate described above, and performing SERS detection using a Raman spectrometer.

[0061] Preferably, the volume of the solution to be tested is 3-10 μL.

[0062] In a specific embodiment, polycyclic aromatic hydrocarbons can be quantitatively detected. The testing process includes the following steps:

[0063] 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.

[0064] S2: The negative number of the concentration logarithm is the horizontal axis, and the peak intensity is the vertical axis. Fitting is performed to obtain the relationship between concentration and peak intensity;

[0065] 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.

[0066] The spherical 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.

[0067] Example 1

[0068] Preparation of silver nanowire suspension:

[0069] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution; then 0.015 g of AgNO3 , stirring vigorously for 10 minutes to obtain a mixture;

[0070] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours; after the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes, repeated 3 times to remove unreacted substances, and diluted to obtain a silver nanowire (diameter 30 nm, length 20 μm) suspension with a concentration of 40 mg / mL.

[0071] Preparation of spherical SERS substrate:

[0072] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 5 Pa for 20 hours to obtain a spherical SERS substrate with a diameter of 3 mm.

[0073] Example 2

[0074] Preparation of silver nanowire suspension:

[0075] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution. Then 0.012 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0076] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours. After the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes, repeated 3 times to remove the unreacted substances, and diluted to obtain a silver nanowire (diameter 20 nm, length 18 μm) suspension with a concentration of 40 mg / mL.

[0077] Preparation of spherical SERS substrate:

[0078] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 5 Pa for 20 hours to obtain a spherical SERS substrate with a diameter of 3 mm.

[0079] Example 3

[0080] Preparation of silver nanowire suspension:

[0081] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution, and then 0.017 g of AgNO was added.3 , stirring vigorously for 10 minutes to obtain a mixture;

[0082] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours; after the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes, repeated 3 times to remove unreacted substances, and diluted to obtain a silver nanowire (diameter 40 nm, length 29 μm) suspension with a concentration of 40 mg / mL.

[0083] Preparation of spherical SERS substrate:

[0084] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 5 Pa for 20 hours to obtain a spherical SERS substrate with a diameter of 3 mm.

[0085] Example 4

[0086] Preparation of silver nanowire suspension:

[0087] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution, and then 0.015 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0088] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours. After the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes. This was repeated 3 times to remove unreacted substances and dilute to obtain a silver nanowire (diameter 30 nm, length 20 μm) suspension with a concentration of 40 mg / mL.

[0089] Preparation of spherical SERS substrate:

[0090] Use a pipette (with a tip diameter of 5 mm) to take 12 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then put it into a freeze dryer and place it at a vacuum pressure of 5 Pa for 20 hours to obtain a spherical SERS substrate with a diameter of 4 mm.

[0091] Example 5

[0092] Preparation of silver nanowire suspension:

[0093] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution. Then 0.015 g of AgNO3 , stirring vigorously for 10 minutes to obtain a mixture;

[0094] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours. After the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes. This was repeated 3 times to remove unreacted substances and dilute to obtain a silver nanowire (diameter 30 nm, length 20 μm) suspension with a concentration of 40 mg / mL.

[0095] Preparation of spherical SERS substrate:

[0096] Use a pipette (with a tip diameter of 5 mm) to take 5 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then put it into a freeze dryer and place it under a vacuum pressure of 5 Pa for 20 hours to obtain a spherical SERS substrate with a diameter of 2.5 mm.

[0097] Example 6

[0098] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution; then 0.015 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0099] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours; after the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes, repeated 3 times to remove unreacted substances, and diluted to obtain a silver nanowire (diameter 30 nm, length 20 μm) suspension with a concentration of 30 mg / mL.

[0100] Preparation of spherical SERS substrate:

[0101] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then put it into a freeze dryer at a pressure of 5 Pa for 20 hours to obtain a spherical SERS substrate with a diameter of 3 mm.

[0102] Example 7

[0103] (1) 0.3 g polyvinyl pyrrolidone (PVP, M W =55000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution; then 0.015 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0104] (2) Transfer the mixture to a hydrothermal reactor (with a volume of 50 mL), and seal it at 150 °C for 6 hours; after the reaction, take out the suspension, centrifuge it at 4000 rpm for 6 minutes, repeat 3 times, remove the unreacted substances, and dilute it to obtain a suspension of silver nanowires (with a diameter of 30 nm and a length of 20 μm) with a concentration of 48 mg / mL.

[0105] Preparation of spherical SERS substrate:

[0106] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then place it in a freeze dryer. Under the condition of a pressure of 5 Pa, place it for 20 h to obtain a spherical SERS substrate with a diameter of 3 mm.

[0107] Example 8

[0108] (1) Add 0.3 g of polyvinylpyrrolidone (PVP, M W = 55000) to 45 mL of deionized water, stir for 30 minutes to form a clear solution; then add 0.015 g of AgNO 3 , stir vigorously for 10 minutes to obtain a mixture;

[0109] (2) Transfer the mixture to a hydrothermal reactor (with a volume of 50 mL), and seal it at 150 °C for 6 hours; after the reaction, take out the suspension, centrifuge it at 4000 rpm for 6 minutes, repeat 3 times, remove the unreacted substances, and dilute it to obtain a suspension of silver nanowires (with a diameter of 30 nm and a length of 20 μm) with a concentration of 40 mg / mL.

[0110] Preparation of spherical SERS substrate:

[0111] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension, drop it into liquid nitrogen, and then place it in a freeze dryer. Under the condition of a pressure of 5 Pa, place it for 10 h to obtain a spherical SERS substrate with a diameter of 3 mm.

[0112] Comparative Example 1

[0113] Preparation of SERS substrate:

[0114] Use a pipette (with a tip diameter of 5 mm) to take 8 μL of the silver nanowire suspension (the same as in Example 1), and directly drop it onto a glass slide. After the solvent has evaporated completely, obtain a SERS substrate based on silver nanowires.

[0115] Comparative Example 2

[0116] Preparation of silver nanowire suspension:

[0117] (1) 0.3 g of polyvinyl pyrrolidone (PVP, MW = 55 000) was added to 45 mL of deionized water and stirred for 30 minutes to form a clear solution. Then 0.015 g of AgNO 3 , stirring vigorously for 10 minutes to obtain a mixture;

[0118] (2) The mixture was transferred to a hydrothermal reactor (volume 50 mL) and sealed at 150° C. for 6 hours. After the reaction, the suspension was taken out and centrifuged at 4000 rpm for 6 minutes. This was repeated 3 times to remove unreacted substances and dilute to obtain a silver nanowire (diameter 30 nm, length 20 μm) suspension with a concentration of 10 mg / mL.

[0119] Preparation of SERS substrate:

[0120] Take 8 μL of silver nanowire suspension with a pipette (with a tip diameter of 5 mm), drop it into liquid nitrogen, and then put it into a freeze dryer and place it for 20 hours under a vacuum pressure of 5 Pa. During the placement process, it was found that the silver nanowire network structure collapsed and could not form a spherical structure. This may be because the concentration of the silver nanowire suspension is too low, the support force of the formed network structure is insufficient, and ultimately the spherical structure cannot be formed.

[0121] Test Example 1

[0122] 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.

[0123] Depend on Figure 2-Figure 3 It can be seen that through Figure 2 It can be seen that the product prepared in Example 1 is a small ball with a diameter of about 3 mm, and Figure 3 It can be observed that the interior of the sphere is a porous network structure formed by interweaving silver nanowires.

[0124] Test Example 2

[0125] The performance of the products prepared in Examples 1-8 and Comparative Example 1 was tested. The test process was as follows: 6 uL of a 10 -6 The ethanol solution of pyrene was added dropwise onto the substrate to be tested. After the solvent evaporated, the substrate was tested using a Horiba Xplus confocal Raman spectrometer with a wavelength of 633 nm, a power of 0.5 mW, an integration time of 40 s, and two integration times. -1 Taking the strength at as an example, the results are shown in Table 1.

[0126] Table 1

[0127] serial number strength serial number strength Example 1 11584 Example 6 10279 Example 2 10128 Example 7 11603 Example 3 11237 Example 8 11427 Example 4 11754 Example 5 10856 Comparative Example 1 7869

[0128] 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, which may be due to the fact that the silver nanowires in the substrate are tightly packed. After the test solution is added, the target molecules can only be adsorbed on the surface of the silver nanowires, and the number of molecules entering the nanogap is reduced, and the Raman signal is reduced.

[0129] Test Example 3

[0130] The pyrene concentration 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 standard solution, the standard solution was dripped onto 6 spherical SERS substrates prepared according to the method described in Example 1, and after the solvent was evaporated, SERS detection was performed using a Raman spectrometer. The corresponding Raman signal is shown in the figure below. Figure 4 As shown in the figure, the characteristic peaks of pyrene molecules are mainly 408cm -1 、592cm -1 、1062cm -1 、1236cm -1 、1402cm -1 and 1615cm -1 It 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 SERS substrate of the present invention can achieve the effect of ≥10 -9 Qualitative detection of 1 mol / L pyrene molecules.

[0131] Further, in order to achieve quantitative detection of pyrene molecules, according to Figure 4 For the data in, 592cm 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 negative number of the concentration logarithm show a good functional relationship. Characteristic peak intensity y = -3983.14x + 35631.76, R 2 = 0.9951, x is the negative number of the logarithm of the concentration (i.e. -lgC). Based on this mathematical relationship, 592cm -1After measuring the intensity of the characteristic peak, the concentration of the solution can be calculated, thereby achieving quantitative detection of pyrene molecules.

[0132] The concentration of pyrene molecules was 10 -4 mol / L、10 -6 mol / L、10 -8 mol / L solution was used as the test solution, and three spherical SERS substrates prepared according to the method described in Example 1 were prepared. Then the above solution was dripped onto the spherical SERS substrate. After the solvent evaporated, the Raman spectrum was tested and the 592 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.

[0133] Table 2

[0134] Theoretical value Characteristic peak intensity Detection value error <![CDATA[10 -4 ]]> 19540 <![CDATA[10 -4.04 ]]> 8.8％ <![CDATA[10 -6 ]]> 11812 <![CDATA[10 -5.98 ]]> 4.7％ <![CDATA[10 -8 ]]> 3687 <![CDATA[10 -8.02 ]]> 4.5％

[0135] From the results in Table 2, it can be seen that the concentration of pyrene molecules in the solution can be accurately measured using the spherical SERS substrate of the present invention.

[0136] 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 SERS substrate, It is characterized in that The spherical SERS substrate is a spherical structure formed by silver nanowires.

2. The spherical SERS substrate according to claim 1, It is characterized in that The diameter of the spherical structure is 1-5 mm.

3. The spherical SERS substrate according to claim 1 or 2, It is characterized in that The diameter of the silver nanowire is 10-50 nm; Preferably, the length of the silver nanowire is 10-30 μm.

4. A method for preparing a spherical SERS substrate, It is characterized in that The method comprises: dropping a solution containing silver nanowires into liquid nitrogen and then freeze-drying; Wherein, in the solution containing silver nanowires, the concentration of silver nanowires is 20-50 mg / mL.

5. The method according to claim 4, It is characterized in that The diameter of the silver nanowire is 10-50 nm; Preferably, the length of the silver nanowire is 10-30 μm.

6. The method according to claim 4 or 5, It is characterized in that The volume of the droplets dropped into the liquid nitrogen was 5-15 μL / drop.

7. The method according to any one of claims 4 to 6, It is characterized in that The freeze-drying conditions include: pressure of 1-50 Pa and time of 8-30 h.

8. A spherical SERS substrate prepared by the method according to any one of claims 4 to 7.

9. Use of the spherical SERS substrate according to any one of claims 1 to 3 and 8 in the detection of polycyclic aromatic hydrocarbons.

10. The use according to claim 9, It is characterized in that The polycyclic aromatic hydrocarbons are selected from at least one of naphthalene, anthracene, phenanthrene, pyrene and benzopyrene.

11. The use according to claim 9, It is characterized in that The spherical SERS substrate can detect polycyclic aromatic hydrocarbons at a concentration of ≥10 -9 mol / L.

12. 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 SERS substrate described in any one of claims 1 to 3 and 9, and performing SERS detection using a Raman spectrometer.

13. The method according to claim 12, It is characterized in that The volume of the solution to be tested is 3-10 μL.

Images