Method for improving SERS (Surface Enhanced Raman Scattering) detection sensitivity

Abstract

The invention discloses a method for improving SERS (Surface Enhanced Raman Scattering) detection sensitivity. The method comprises the following steps: preparing a solution of an object to be detected by using a mixed solvent, and carrying out SERS detection, wherein the mixed solvent is composed of a first solvent and a second solvent, the surface tension and wettability are controlled by adjusting the proportion of the mixed solvent, molecules of an object to be detected are promoted to enter the SERS substrate, and hot spots are activated. According to the method, two or more solvents are mixed, the surface tension of the mixed solvent and the wettability of the mixed solvent to the SERS substrate are adjusted, so that the substrate wettability and the molecular diffusion characteristic are balanced, conveying of the solvents in a nanostructure is accurately controlled, and effective molecular mass transfer is achieved; the method disclosed by the invention has the advantages of universality, high reproducibility, high sensitivity and simplicity and rapidness in operation, provides a new solution for an SERS detection method, and has a wide application prospect; the detection limit of the SERS substrate can be generally improved by 2-3 orders of magnitude.

Description

Technical Field

[0001] The invention relates to the technical field of SERS detection, and in particular to a method for improving the sensitivity of SERS detection. Background Art

[0002] Surface enhanced Raman spectroscopy (SERS) is a highly sensitive and selective analytical technique that can significantly enhance the Raman scattering signal of molecules and shows great potential in the fields of chemical analysis, biomedical diagnosis and environmental monitoring. For the practical application of SERS, two key requirements must be met: first, to construct highly ordered plasmonic nanostructures and precisely design and fabricate highly active SERS hotspots, and second, molecules must enter the hotspots at the gaps between the nanostructures. However, only a few molecules can enter with an enhancement factor (EF) greater than 10 7 The hotspots contribute nearly 70% of the overall SERS signal intensity. Therefore, whether molecules can enter the hotspots is crucial to achieve high SERS sensitivity.

[0003] However, delivering the analyte to such a tiny hotspot remains a major challenge, especially for molecules with small Raman scattering cross sections and no metal affinity. Currently, the simplest and most direct way to introduce the analyte into the nanoscale gap is by droplet deposition, immersion or spin coating. In these cases, the analyte molecules are more widely distributed throughout the sensor surface, and only a small portion of the molecules are delivered to the hotspot that produces the enhanced molecular vibration absorption signal. Most of the analyte molecules are located outside the hotspot and do not contribute significantly to the overall sensing signal. The detection sensitivity of SERS needs to be improved. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a method for improving the sensitivity of SERS detection, which has universality, high reproducibility and high sensitivity, and the present invention is simple and fast to operate without complex manufacturing processes or specific conditions. The present invention not only challenges the existing understanding of molecular transport capabilities, but also provides new insights into the SERS detection method, and the present invention has broad application prospects.

[0005] The present invention proposes a method for improving the sensitivity of SERS detection, comprising the following steps: preparing a test object solution with a mixed solvent for SERS detection;

[0006] The mixed solvent is composed of a first solvent and a second solvent, which can adjust the surface tension and wettability of the mixed solvent, promote the molecules of the analyte to enter the hot spots of the SERS substrate and activate the hot spots.

[0007] Preferably, the contact angle of the second solvent on the surface of the SERS substrate is less than the contact angle of the mixed solvent on the surface of the SERS substrate and less than the contact angle of the first solvent on the surface of the SERS substrate.

[0008] Preferably, the contact angle of the mixed solvent on the surface of the SERS substrate is greater than 0° and less than 140°.

[0009] Preferably, the contact angle of the mixed solvent on the surface of the SERS substrate is 30-120°.

[0010] Preferably, the contact angle of the mixed solvent on the surface of the SERS substrate is 80-120°.

[0011] Preferably, the contact angle of the first solvent on the surface of the SERS substrate is ≥130°.

[0012] Preferably, the contact angle of the second solvent on the surface of the SERS substrate is ≤5°.

[0013] Preferably, the surface tension of the second solvent is less than the surface tension of the mixed solvent and less than the surface tension of the first solvent.

[0014] Preferably, at 20° C., the surface tension of the mixed solvent is 32-57 mN / m.

[0015] Preferably, at 20° C., the surface tension of the first solvent is 60-80 mN / m.

[0016] Preferably, at 20° C., the surface tension of the second solvent is 15-30 mN / m.

[0017] Preferably, the first solvent is miscible with the second solvent.

[0018] Preferably, the first solvent is water.

[0019] Preferably, the second solvent includes one or more of methanol, ethanol, propanol, butanol, pentanol, acetone, acetonitrile, tetrahydrofuran, and formamide.

[0020] Preferably, the volume fraction of the second solvent in the mixed solvent is greater than 0% and less than 100%.

[0021] Preferably, the volume fraction of the second solvent in the mixed solvent is 10-50%.

[0022] Preferably, the volume fraction of the second solvent in the mixed solvent is 10-25%.

[0023] The present invention achieves a balance between substrate wetting and molecular diffusion characteristics by mixing two or more solvents and adjusting the surface tension of the mixed solvent to the wettability of the SERS substrate, accurately controlling the transport of the solvent in the nanostructure, and realizing effective molecular mass transfer, thereby greatly improving the sensitivity of SERS detection and having high reproducibility. The present invention can be widely applied to various nanostructures and various molecules to be detected (covering more than 20 molecules to be detected), making maximum use of the native hot spots, thereby realizing broad-spectrum SERS detection.

[0024] The present invention is simple and fast to operate without complicated manufacturing processes or specific conditions. This innovative method provides new impetus for the advancement of SERS technology and lays a solid foundation for its wide adoption in various analytical applications. The method described in the present invention not only challenges the existing understanding of the molecular transport mechanism, but also provides new insights into the SERS detection method. The present invention has broad application prospects. The present invention significantly improves the practicality and detection sensitivity of SERS technology, laying a solid foundation for its promotion in the fields of rapid detection, chemical analysis, biomedical diagnosis, environmental monitoring, etc. of charged or neutral molecules such as drugs, pesticide residues, explosives, stimulants, environmental pollutants, illegal additives, and biological molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the process of different solvents entering the hot spots in the SERS substrate.

[0026] Figure 2 Are the detection limits and probability results of CV for different solvents, where a is the detection limit and probability of CV, 0%, 10%, 25%, 50%, and 100% are ethanol aqueous solutions with ethanol volume fractions of 0%, 10%, 25%, 50%, and 100%, respectively; b is the SERS spectrum of ethanol aqueous solution with a volume fraction of 25%.

[0027] Figure 3 The contact angle, diffusion area, reflection spectrum and diffusion area of ​​different solvents on the surface of gold nano-SERS substrate, where a is the contact angle, b is the diffusion area, c is the reflection spectrum, d is the diffusion area, and 0%, 10%, 25%, 50% and 100% are ethanol aqueous solutions with ethanol volume fractions of 0%, 10%, 25%, 50% and 100% respectively.

[0028] Figure 4 The SERS detection limit results of crystal violet in different mixed solvents.

[0029] Figure 5 The crystal violet detection limit results for different SERS substrates, where the black line is the crystal violet detection limit for pure water.

[0030] Figure 6 The detection limits of five thiol-containing molecules are shown in Figure 2.

[0031] Figure 7 The detection limits of five dye molecules are shown in Figure 2.

[0032] Figure 8 The detection limits of five pigment molecules are shown in Figure 2.

[0033] Fig. 9 The detection limits of five PAH molecules are shown in Figure 2.

[0034] Fig.10 The repeatability and stability results of the method of the present invention are shown in Figure 1, where a is the result of 25% ethanol aqueous solution, b is the result of water, 1 is the SERS spectrum of 20 tests, and 2 is 1617 cm -1 The RSD result of the peak intensity histogram at 3 is 1172 cm -1 The RSD result of the peak intensity histogram at 4 is 1617 cm -1 and 1172cm -1 Concentration dependence curve of the peak intensity at . DETAILED DESCRIPTION

[0035] The present invention provides a method for improving the sensitivity of SERS detection, comprising the following steps: preparing a test object solution with a mixed solvent for SERS detection;

[0036] The mixed solvent is composed of a first solvent and a second solvent, which can adjust the surface tension and wettability of the mixed solvent, promote the molecules of the analyte to enter the hot spots of the SERS substrate and activate the hot spots.

[0037] Existing studies generally attribute the difficulty of analyte molecules entering hotspots to steric hindrance and chemical environment (surface ligand steric hindrance) effects. For a long time, people have believed that surface ligands in nanogaps can prevent analyte molecules from entering hotspots. However, the inventors found in their research that even if clean SERS substrates are made using methods such as laser ablation or physical vapor deposition, steric hindrance at the nanogaps still exists.

[0038] To address this issue, the inventors conducted a number of experiments and found that the existing view that the reason why it is difficult for the analyte molecules to enter the SERS substrate hotspots is a major misunderstanding, which greatly hinders the promotion and improvement of the SERS detection method.

[0039] The inventors have found that the impact of hydrocarbon pollutants in the air is often ignored, although their concentrations usually range from one trillionth to one millionth, and the adsorption layer is usually as thin as an atom, which is difficult to detect directly, and it is also difficult to avoid or remove during use. However, the surface of nanomaterials easily adsorbs hydrocarbon pollutants in the air, making the SERS substrate change from hydrophilic to hydrophobic, making it highly hydrophobic (for example, after research, the water contact angle of three layers of nanofilms self-assembled from gold nanoparticles as SERS substrates placed in the air for different times is 5min (91.0°), 8min (100.0°), 10min (130.0°), 13min (135.0°), 15min (135.0°), 18min (135.0°) and 20min (135.0°)); the hot spots in the SERS substrate are located at the tiny gaps between the nanoparticles, and the existing test objects generally use water as a solvent, and as a surface property, the wettability of water is very sensitive to surface contamination.

[0040] Take water as an example. Figure 1 As shown in a, the process of filling tiny empty nanostructure gaps with water is usually difficult, and the metal surface is not well wetted. The adsorption of pollutants in the air reduces the wettability of water in the nanogap, seriously hindering the molecules of the analyte from entering the hotspot, and the hotspot in the nanogap is not effectively utilized. For example, when gold nanoparticles self-assemble into three layers of nanofilm as the SERS substrate and water is used as the solvent for CV detection, the detection limit is only 10 -9 M.

[0041] In order to promote the molecules of the test object to enter the hot spot, the inventors replaced water with a solvent with better wettability. For example, gold nanoparticles were self-assembled into three layers of nanofilm as the SERS substrate, and ethanol was used as the solvent to detect CV. The detection limit was only 10 -9 M; water was replaced with a solvent with good wettability (such as ethanol), but the detection limit was still not improved. When the inventors mixed water and ethanol as solvents, they unexpectedly found that the detection limit of CV was 10 -12 M, its detection limit is improved by 2-3 orders of magnitude compared with single water or ethanol.

[0042] The inventors have found through multiple experimental analyses that when using a solvent with good wettability (such as ethanol), although it has strong wettability, it also has strong diffusivity on the SERS substrate, which will significantly reduce the concentration of the analyte molecules in the detection area, resulting in only a small number of analyte molecules entering the hotspot, and the number density of the analyte molecules in the hotspot area is significantly reduced. Figure 1 As shown in c;

[0043] By mixing two or more solvents, adjusting the surface tension of the mixed solvent and the wettability to the SERS substrate, a balance is achieved between the surface tension and the molecular diffusion characteristics, and the transport of the solvent in the nanostructure is precisely controlled to achieve effective molecular mass transfer. On the one hand, the aggregation and shrinkage caused by solvents with too high surface tension and poor wettability can be overcome, and the molecules of the analyte can be promoted to enter the hotspot and be activated. On the other hand, the chaotic diffusion caused by solvents with too low surface tension and good wettability can be suppressed, so that more molecules of the analyte can enter the hotspot and activate the hotspot, thereby improving the efficiency and effective concentration of the molecules of the analyte entering the hotspot, and realizing the effective utilization of large-area hotspot nanostructures, thereby significantly enhancing the SERS signal intensity. Figure 1 As shown in b.

[0044] Preferably, the contact angle of the second solvent on the surface of the SERS substrate is less than the contact angle of the mixed solvent on the surface of the SERS substrate and less than the contact angle of the first solvent on the surface of the SERS substrate.

[0045] Since the surface properties of different SERS substrates are different, the contact angles of the mixed solvent on the surfaces of different SERS substrates will also be different.

[0046] By adjusting the mixed solvent so that the contact angle of the second solvent on the SERS substrate surface is less than the contact angle of the mixed solvent on the SERS substrate surface and less than the contact angle of the first solvent on the SERS substrate surface, a balance between the substrate wetting and molecular diffusion characteristics of the mixed solvent on the SERS substrate can be achieved, effective molecular mass transfer can be achieved, and the sensitivity of SERS detection can be improved.

[0047] Preferably, the contact angle of the mixed solvent on the surface of the SERS substrate is greater than 0° and less than 140°.

[0048] Preferably, the contact angle of the mixed solvent on the surface of the SERS substrate is 30-120°.

[0049] Preferably, the contact angle of the mixed solvent on the surface of the SERS substrate is 80-120°.

[0050] Preferably, the contact angle of the first solvent on the surface of the SERS substrate is ≥130°.

[0051] Preferably, the contact angle of the second solvent on the surface of the SERS substrate is ≤5°.

[0052] Preferably, the surface tension of the second solvent is less than the surface tension of the mixed solvent and less than the surface tension of the first solvent.

[0053] Preferably, at 20° C., the surface tension of the mixed solvent is 32-57 mN / m; more preferably 47.2-56.8 mN / m.

[0054] Preferably, at 20° C., the surface tension of the first solvent is 60-80 mN / m; more preferably 70-75 mN / m, and most preferably 72.8 mN / m.

[0055] Preferably, at 20° C., the surface tension of the second solvent is 15-30 mN / m; more preferably 19-26 mN / m.

[0056] The inventors found through multiple experiments that when the mixed solvent is adjusted so that the contact angle of the second solvent on the SERS substrate surface is less than the contact angle of the mixed solvent on the SERS substrate surface < the contact angle of the first solvent on the SERS substrate surface, and the surface tension of the second solvent is less than the surface tension of the mixed solvent < the surface tension of the first solvent, it can balance the wettability of the molecules of the analyte on the SERS substrate and the molecular diffusion characteristics, thereby improving the detection sensitivity.

[0057] Preferably, the first solvent is miscible with the second solvent.

[0058] Preferably, the first solvent is water.

[0059] Preferably, the second solvent includes one or more of methanol, ethanol, propanol, butanol, pentanol, acetone, acetonitrile, tetrahydrofuran, and formamide.

[0060] Preferably, the volume fraction of the second solvent in the mixed solvent is greater than 0% and less than 100%.

[0061] The ratio of the first solvent to the second solvent is not limited, as long as the surface tension and contact angle of the mixed solvent meet the requirements. For example, the volume ratio of the first solvent to the second solvent can be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, etc.

[0062] Preferably, the volume fraction of the second solvent in the mixed solvent is 10-50%.

[0063] Preferably, the volume fraction of the second solvent in the mixed solvent is 10-25%.

[0064] The above water is all deionized water or purified water.

[0065] The size of the nanomaterials used to prepare the SERS substrate is 1-100nm, and the materials of the nanomaterials include but are not limited to precious metals such as gold, silver, copper, etc. that have the effect of enhancing Raman signals, and materials containing non-precious metals such as carbon, titanium, zinc, copper, molybdenum, tungsten, etc. that have the effect of enhancing Raman signals; the structures of the nanomaterials include but are not limited to zero-dimensional (such as nanoparticles, atomic clusters, etc.), one-dimensional (such as nanowires, nanotubes, nanorods, etc.), two-dimensional (superlattices, ultrathin films, multilayer films), three-dimensional (such as nano-mesoporous materials, etc.), etc.

[0066] The above-mentioned SERS substrate is a solid SERS substrate.

[0067] The above method can be applied to the detection of neutral or charged molecules such as drugs, pesticide residues, explosives, stimulants, environmental pollutants, illegal additives, proteins, biological molecules, etc.

[0068] In addition, for solid-state SERS substrates, the spatial variability of the nanostructures on the substrates leads to random arrangement of hot spots and wide distribution of electric field intensity. Therefore, the SERS signal intensity obtained from the substrate is spatially non-uniform, which is the main reason for the poor stability of SERS. In addition, the hot spots are located in the narrow gaps between the metal nanoparticles, resulting in significant spatial variations in the Raman signal intensity, especially under low adsorption conditions, because the hot spots are confined to the narrow gaps between the metal nanoparticles and the analytes attached to different positions on the gold nanoparticles. This spatial variability limits the ability to obtain repeatable SERS signals by simply enhancing the uniformity of the nanostructures, resulting in poor repeatability of SERS detection.

[0069] The present invention achieves a balance between substrate wettability and molecular diffusion characteristics by mixing two or more solvents and adjusting the surface tension of the mixed solvent and the wettability to the SERS substrate, thereby improving the uniform utilization of hot spots and effectively improving the stability and sensitivity of the SERS signal on the substrate. The high uniformity and repeatability of the SERS signal can be attributed to the uniform adsorption of the molecules of the analyte, which is very beneficial for practical sensing applications. The present invention provides new insights into the development of SERS methods that achieve high sensitivity and spatial uniformity for low-concentration analytes, which is crucial for biological and chemical sensing.

[0070] The technical solution of the present invention is described in detail below through specific embodiments.

[0071] Example 1

[0072] Preparation of gold nanoparticles: Small-sized gold nanoparticles 1 were prepared according to the classic sodium citrate reduction method, which specifically includes the following steps: 99 mL ultrapure water and 1 wt% HAuCl 4 1 mL of the solution was added to a 250 mL three-necked flask and heated with a heating mantle. When it began to boil, 10 mL of a 1 wt % sodium citrate solution was quickly added while stirring and kept boiling for 20 min to obtain a gold nanoparticle solution.

[0073] Gold nanoparticles are self-assembled at a liquid / liquid interface to obtain a gold nano SERS substrate, which specifically includes the following steps: adding an appropriate amount of water to a container so that the bottom of the container is filled and covered, and then dropping cyclohexane on the water layer to form an incompatible cyclohexane-water liquid interface; then centrifuging the above gold nanoparticle solution (12 mL) at 6000 rpm for 10 minutes to collect the precipitate, and then diluting it with ethanol (4 mL), and slowly adding it to the liquid / liquid interface. As the cyclohexane evaporates, the gold nanoparticles spontaneously self-assemble into a highly densely stacked film over a large area at the cyclohexane / water liquid phase interface; then transferring the self-assembled single-layer film to a silicon wafer or a glass slide, and after drying, repeating the above operation to continuously stack the single-layer films, and finally obtaining a self-assembled 3-layer gold nano film as a gold nano SERS substrate.

[0074] Crystal violet CV was used as the test substance, and the test substance solution was prepared with water, ethanol, and a mixture of water and ethanol, respectively, and then dropped onto the gold nano-SERS substrate. After drying, the excitation wavelength was adjusted to 633 nm for detection, and the detection limit of each group was investigated. The results are as follows: Figure 2 shown.

[0075] Figure 2 Are the detection limits and probability results of CV for different solvents, where a is the detection limit and probability of CV, 0%, 10%, 25%, 50%, and 100% are ethanol aqueous solutions with ethanol volume fractions of 0%, 10%, 25%, 50%, and 100%, respectively; b is the SERS spectrum of ethanol aqueous solution with a volume fraction of 25%.

[0076] Depend on Figure 2 It can be seen that when the volume fraction of ethanol is 25%, when the CV concentration>10 -9 M, the probability of obtaining an observable SERS signal is 100%, and when the CV concentration decreases to 10 -12 M, the probability drops to about 10%; when the volume fraction of ethanol is 10%, the CV concentration is 10 -10 M, the probability is still high, exceeding 30%; while in pure water or pure ethanol, the CV detection limit is only 10 -9 M, the probability is less than 20%; when the volume fraction of ethanol is 50%, the CV detection limit is 10 -9 M, but its probability is higher than 20%; the detection limit using mixed solvents is 3 orders of magnitude higher than that of a single solvent.

[0077] Figure 3The contact angle, diffusion area, reflection spectrum and diffusion area of ​​different solvents on the surface of gold nano-SERS substrate, where a is the contact angle, b is the diffusion area, c is the reflection spectrum, d is the diffusion area, and 0%, 10%, 25%, 50% and 100% are ethanol aqueous solutions with ethanol volume fractions of 0%, 10%, 25%, 50% and 100% respectively.

[0078] Depend on Figure 3 It can be seen from a and b that when the volume fraction of ethanol is 0%, 10%, 25%, 50%, and 100%, the contact angles on the surface of the gold nano-SERS substrate are 133.5°, 120.0°, 91.8°, 35°, and 0°, respectively; with the increase of the volume fraction of ethanol, the diffusion area of ​​the droplet gradually increases;

[0079] Depend on Figure 3 c It can be seen that the pure water droplet exhibits a reflectivity similar to that of the dry nanostructure, because the gas in the nanogap is not wetted by the solvent; compared with pure water, the reflectivity of the 10% ethanol aqueous solution is slightly reduced, indicating that the nanogap is partially wetted and the liquid and gas coexist in the gap; when the 10% ethanol aqueous solution is used, the reflectance spectrum of the nanostructure changes significantly and the reflectivity decreases significantly, indicating that the wettability of the nanostructure surface is significantly improved, the nanogap is completely wetted by the liquid, and the liquid completely replaces the gas originally present in the gap; and as the ethanol volume fraction increases, although a higher ethanol concentration can further enhance the wettability, the too low surface tension will lead to increased diffusion, causing the liquid sample to diffuse on the substrate surface; the diffusion area of ​​100% ethanol is more than 30 times that of pure water (see Figure 3 d), which is unfavorable for trace detection because excessive diffusion can lead to random adsorption of molecules on the nanostructure surface (causing analyte dilution effect); since only a small portion of the analyte is detected, both the analyte and the SERS substrate are not fully utilized depending on the laser spot size.

[0080] The present invention can improve the wettability of the gold nano SERS substrate and adjust the surface tension by adjusting the ratio of ethanol and water, effectively control the wettability and spreading performance of the solvent, inhibit the chaotic diffusion caused by low surface tension, and maintain the effective transportation of molecules into the hot spot; the present invention can significantly improve the molecular transfer efficiency and SERS detection sensitivity by adjusting the surface wettability of the nanostructure through mixed solvents, and provide a new method and approach for high-sensitivity SERS detection.

[0081] It was tested that at 20°C, when the volume fraction of ethanol was 0%, 10%, 25%, 50% and 100%, the surface tension was 72.8, 56.8, 47.2, 33.3 and 22.1 mN / m respectively.

[0082] Example 2

[0083] Using 25% methanol aqueous solution, 25% acetone aqueous solution, 25% isopropanol aqueous solution, and 25% acetonitrile aqueous solution as mixed solvents, the detection limit of crystal violet CV was detected according to the method of Example 1. The results are as follows: Figure 4 shown.

[0084] Figure 4 The SERS detection limit results of crystal violet in different mixed solvents.

[0085] Depend on Figure 4 It can be seen that the detection limit of crystal violet CV for 25% methanol aqueous solution, 25% acetone aqueous solution, 25% isopropanol aqueous solution, and 25% acetonitrile aqueous solution is as high as 10 -12 M, indicating that the method of the present invention has a wide range of organic solvent selection and the method is reproducible.

[0086] Example 3

[0087] Different SERS substrates were prepared respectively, and crystal violet CV solutions were prepared with pure water and 25% ethanol aqueous solution, respectively, to test the detection limit of crystal violet CV. The results are as follows Figure 5 As shown. 1 -d 1 The SERS substrates are:

[0088] a 1 :PDDA-AuNPs is a SERS substrate formed by self-assembly of gold nanoparticles stabilized by polyvinylpyrrolidone (PDDA).

[0089] b 1 CTAB-AuNRs are SERS substrates self-assembled from gold nanorods stabilized by cetyltrimethylammonium bromide (CTAB).

[0090] c 1 Gold nanopillar arrays are SERS substrates formed by vapor deposition and etching processes.

[0091] d 1 Klarite chip is a commercial SERS substrate made by depositing gold on a nanostructured silicon wafer.

[0092] Figure 5 The crystal violet detection limit results for different SERS substrates, where the black line is the crystal violet detection limit for pure water.

[0093] Depend on Figure 5It can be seen that under pure water conditions, the crystal violet detection limits of PDDA-Au NPs, CTAB-Au NRs, Gold nanopillararrays, and Klarite chip are 10 -9 M, 10 -10 M, 10 -8 M, 10 -7 M; while for 25% ethanol aqueous solution, the detection limits of crystal violet for each substrate were 10 -11 M, 10 -12 M, 10 -10 M and 10 -9 M, significantly improving the detection limit of crystal violet; indicating that the method of the present invention is widely applicable to nanostructures with different morphologies and surface chemical properties, and has wide applicability in different nanostructures, further verifying the practical application potential of the method of the present invention.

[0094] Example 4

[0095] Crystal violet was replaced with five thiol-containing molecules (4-aminothiophenol (PATP), 4-methylthiophenol, 4-hydroxythiophenol, 4-mercaptobenzonitrile, 4-mercaptobenzoic acid (4-MBA)), and the detection limits of the substances were detected according to the method of Example 1 using pure water, 25% ethanol aqueous solution, and pure ethanol as solvents, respectively. The results are as follows: Figure 6 shown.

[0096] Figure 6 The detection limits of five thiol-containing molecules are shown in Figure 2.

[0097] Depend on Figure 6 It can be seen that the detection sensitivity of using a water-ethanol mixed solvent is increased by 2-4 orders of magnitude compared to using water or ethanol alone.

[0098] Example 5

[0099] The five thiol-containing molecules were replaced with five dye molecules (methylene blue (MB), malachite green (MG), Nile blue (NB), rhodamine 6G (R6G), and rhodamine 800 (RH800)). The detection limits of the substances were determined according to Example 4. The results are as follows: Figure 7 shown.

[0100] Figure 7 The detection limits of five dye molecules are shown in Figure 2.

[0101] Depend on Figure 7 It can be seen that the detection sensitivity of using a water-ethanol mixed solvent is increased by 2-4 orders of magnitude compared to using water or ethanol alone.

[0102] Example 6

[0103] The five thiol-containing molecules were replaced with five pigment molecules (brilliant blue, tartrate yellow, sunset yellow, amaranth, and allura red), and the detection limits of the substances were determined according to Example 4. The results are as follows: Figure 8 shown.

[0104] Figure 8 The detection limits of five pigment molecules are shown in Figure 2.

[0105] Depend on Figure 8 It can be seen that the detection sensitivity of using a water-ethanol mixed solvent is 2-3 orders of magnitude higher than that of using water or ethanol alone.

[0106] Example 7

[0107] The five thiol-containing molecules were replaced with five polycyclic aromatic hydrocarbon molecules (naphthalene, anthracene, phenanthrene, pyrene, and benzopyrene), and the detection limits of the substances were determined according to Example 4. The results are as follows: Fig. 9 shown.

[0108] Fig. 9 The detection limits of five PAH molecules are shown in Figure 2.

[0109] Depend on Fig. 9 It can be seen that the detection sensitivity of using a water-ethanol mixed solvent is increased by 2-4 orders of magnitude compared to using water or ethanol alone.

[0110] Example 8

[0111] Using pure water and 25% ethanol aqueous solution as solvents, the crystal violet was detected 20 times according to the method of Example 1, and the results were compared at 1617 cm -1 and 1172cm -1 The SERS peak intensity at Fig.10 shown.

[0112] Fig.10 The repeatability and stability results of the method of the present invention are shown in Figure 1, where a is the result of 25% ethanol aqueous solution, b is the result of water, 1 is the SERS spectrum of 20 tests, and 2 is 1617 cm -1 The RSD result of the peak intensity histogram at 3 is 1172 cm -1 The RSD result of the peak intensity histogram at 4 is 1617 cm -1 and 1172cm -1 Concentration dependence curve of the peak intensity at .

[0113] Depend on Fig.10 a 1-3 、b 1-3 It can be seen that when using 25% ethanol aqueous solution, 1617cm -1 and 1172cm -1The RSD of the peak intensity at 1617cm -1 and 1172cm -1 The RSDs of the peak intensities at were 26.65% and 37.56%;

[0114] Depend on Fig.10 a 4 、b 4 It can be seen that: 1617cm -1 and 1172cm -1 The concentration-dependent curve of the peak intensity at is fitted and analyzed. The concentration curve R of crystal violet in 25% ethanol aqueous solution is 2 =0.998, concentration curve in water R 2 =0.865. It can be seen from this that the method of the present invention effectively improves the detection stability and repeatability of the object to be tested.

[0115] In addition, for thiol-functionalized aromatic molecules, environmental pollutants, and food colorants, the concentration and SERS intensity fitting curve R 2 It can exceed 0.9. For PAH molecules with weak substrate affinity, R 2 It may also exceed 0.8.

[0116] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for improving the sensitivity of SERS detection, characterized in that: The method comprises the following steps: preparing a test solution with a mixed solvent for SERS detection; The mixed solvent is composed of a first solvent and a second solvent, and the surface tension and wettability of the mixed solvent are adjusted to promote the molecules of the analyte to enter the hot spots of the SERS substrate and activate the hot spots.

2. The method for improving SERS detection sensitivity according to claim 1, characterized in that: The contact angle of the second solvent on the SERS substrate surface is less than the contact angle of the mixed solvent on the SERS substrate surface and less than the contact angle of the first solvent on the SERS substrate surface; preferably, the contact angle of the mixed solvent on the SERS substrate surface is greater than 0° and less than 140°; preferably, the contact angle of the mixed solvent on the SERS substrate surface is 30-120°; preferably, the contact angle of the mixed solvent on the SERS substrate surface is 80-120°.

3. The method for improving SERS detection sensitivity according to claim 1 or 2, characterized in that: The contact angle of the first solvent on the surface of the SERS substrate is ≥130°.

4. The method for improving the SERS detection sensitivity according to any one of claims 1 to 3, characterized in that: The contact angle of the second solvent on the surface of the SERS substrate is ≤5°.

5. The method for improving the SERS detection sensitivity according to any one of claims 1 to 4, characterized in that: The surface tension of the second solvent is less than the surface tension of the mixed solvent and less than the surface tension of the first solvent; preferably, at 20° C., the surface tension of the mixed solvent is 32-57 mN / m.

6. The method for improving the SERS detection sensitivity according to any one of claims 1 to 5, characterized in that: At 20°C, the surface tension of the first solvent is 60-80 mN / m; preferably, at 20°C, the surface tension of the second solvent is 15-30 mN / m.

7. The method for improving the SERS detection sensitivity according to any one of claims 1 to 6, characterized in that: The first solvent is miscible with the second solvent.

8. The method for improving the SERS detection sensitivity according to any one of claims 1 to 7, characterized in that: The first solvent is water.

9. The method for improving the SERS detection sensitivity according to any one of claims 1 to 8, characterized in that: The second solvent includes one or more of methanol, ethanol, propanol, butanol, pentanol, acetone, acetonitrile, tetrahydrofuran, and formamide.

10. The method for improving the SERS detection sensitivity according to any one of claims 1 to 9, characterized in that: The volume fraction of the second solvent in the mixed solvent is greater than 0% and less than 100%; preferably, the volume fraction of the second solvent in the mixed solvent is 10-50%; preferably, the volume fraction of the second solvent in the mixed solvent is 10-25%.

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