Preparation of composite silver film coupled with surface plasmon and its application in SERS detection of tobramycin

Abstract

The application relates to the field of analysis and detection, and relates to preparation of a composite silver film coupled with surface plasmons and application of the composite silver film in SERS detection of tobramycin. The preparation of the composite silver film comprises preparation of two layers of silver films, one layer being a self-assembled silver nanoparticle film loaded on the front surface of PDMS, and the other layer being a silver cube film loaded on the back surface of the PDMS. The surface plasmons of the two layers of silver films are coupled with each other by controlling the thickness of the PDMS, and the two layers of silver films are used as a SERS substrate for analysis and detection, so that the sensitivity of detection can be greatly improved. The detection limit of tobramycin can be as low as 2.36*10 ‑12 M, and the linear detection range is 10 ‑5 ~10 ‑11 M, and the relative standard deviation of SERS intensity is less than 10%. The composite silver film prepared by the application has high sensitivity, good universality and practical prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of analytical detection, in particular to the preparation of surface plasmon coupled composite silver film and its application in SERS detection of tobramycin. BACKGROUND

[0002] Tobramycin is a glycoside antibiotic connected by oxygen bridge between amino sugar and aminocycloalcohol. It is mainly used for inhibiting and killing sensitive aerobic gram-negative bacteria because it can inhibit protein synthesis. However, tobramycin left in animal food and environment will pose a potential threat to human health due to its obvious ototoxicity, nephrotoxicity and neuromuscular blocking effect. Therefore, in order to protect food safety, the maximum residue limit of aminoglycoside antibiotics in milk is 10 μg / kg in GB T22969-2008 "Determination of streptomycin, dihydrostreptomycin and kanamycin residues in milk powder and milk by liquid chromatography-tandem mass spectrometry". It is of great significance to establish rapid screening and detection of tobramycin residues in dairy products for maintaining human dietary health.

[0003] The currently reported detection methods for tobramycin and similar antibiotics mainly include liquid chromatography-tandem mass spectrometry, fluorescence immunoassay and enzyme-linked adsorption immunoassay. Among them, the operation process of liquid chromatography-tandem mass spectrometry is complex and the detection time is long. The cost of fluorescence immunoassay is high, and it is often affected by light bleaching and interference, which is not suitable for rapid screening of large quantities of samples. The false positive probability of enzyme-linked adsorption immunoassay is high and the sensitivity is low. SUMMARY

[0004] The present application aims to solve the above problems in the prior art, and provides the preparation of surface plasmon coupled composite silver film and its application in SERS detection of tobramycin.

[0005] The present application prepares surface plasmon coupled composite silver film, regulates the distance between silver nanoparticle film and silver cubic film, improves the degree of surface plasmon coupling, and enhances the Raman spectrum of tobramycin adsorbed on the composite silver film. The thickness of the polydimethylsiloxane (PDMS) film of the composite silver film and the pH value of the tobramycin detection conditions are optimized. Under the optimal PDMS film thickness and pH value, the standard curve of the intensity of the SERS characteristic peak and the concentration is established to realize the quantitative analysis of tobramycin. The linear detection range of tobramycin is 10 -5 ~10 -11 M, and the detection limit is 2.36 x 10 -12M, the relative standard deviation of SERS intensity is less than 10%. The surface plasmon coupled composite silver film prepared by the method has high sensitivity, good universality and practical prospect.

[0006] To achieve the above object, the application adopts the following technical scheme:

[0007] The preparation method of the surface plasmon coupled composite silver film comprises the following steps:

[0008] 1) forming a silver nanoparticle interfacial film by liquid-liquid self-assembly of a silver nanoparticle solution, and then transferring to a PDMS film to complete the preparation of the silver nanoparticle film;

[0009] 2) forming a silver cube interfacial film by liquid-liquid self-assembly of a silver cube solution, and then transferring to the hydrophobic back of the silver nanoparticle film to complete the preparation of the composite silver film.

[0010] The application of the surface plasmon coupled composite silver film is used for detecting tobramycin.

[0011] The composite silver film is soaked in a sample solution containing tobramycin, and the sample solution is detected by surface enhanced Raman scattering at the optimal excitation wavelength, and the analysis and detection of tobramycin are realized by measuring the Raman peak intensity of tobramycin at a specific wavelength.

[0012] According to the different positions of the SERS characteristic peaks of tobramycin and other aminoglycoside antibiotics, specific detection of tobramycin is realized.

[0013] The other aminoglycoside antibiotics include kanamycin, neomycin and streptomycin, and the SERS characteristic peaks with different positions are 606 cm -1 and 1020 cm -1 .

[0014] The composite silver film is soaked in a sample solution containing tobramycin, taken out, dried, and detected by SERS at the optimal excitation wavelength, and the intensity value of the SERS characteristic peak in the spectrum is recorded and a standard curve is established with the corresponding concentration of tobramycin for quantitative analysis and detection.

[0015] The SERS characteristic peak in the spectrum refers to the SERS characteristic peak of tobramycin at 1020 cm -1 ; the linear detection range of tobramycin is 10 -5 ~10 -11 M, the detection limit is 2.36*10 -12 M, and the relative standard deviation of SERS intensity is less than 10%.

[0016] The optimal excitation wavelength refers to the excitation wavelength of 785 nm.

[0017] The PDMS film thickness is 100-500 μm; the pH of the detection condition is 2-10.

[0018] Compared with the prior art, the technical scheme of the present application has the beneficial effects that:

[0019] The present application is based on the surface plasmon coupling phenomenon between the silver nanoparticle film and the silver cubic film, greatly improving the SERS intensity of the tobramycin adsorbed on the composite silver film. The surface plasmon coupled composite silver film prepared by the present application has the advantages of simple operation, convenience, low cost and good reproducibility in detection. The experimental results show that the linear detection range of tobramycin is 10 -5 ~10 -11 M, the detection limit is 2.36×10 -12 M, and the relative standard deviation of the SERS intensity is less than 10%. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is an optical photo of the PDMS film with different thicknesses;

[0021] Figure 2 In the middle A, it is an SEM photo of the silver nanoparticle film; Figure 2 In the middle B, it is an SEM photo of the silver cubic film;

[0022] Figure 3 It is a SERS spectrum of the composite silver film detecting tobramycin under the condition of the PDMS film with different thicknesses;

[0023] Figure 4 It is a SERS spectrum of the composite silver film detecting tobramycin under the condition of different pH;

[0024] Figure 5 In the middle A, it is a SERS spectrum of the composite silver film detecting tobramycin, and the SERS spectrum is parallel for ten times, Figure 5 In the middle B, it is a SERS spectrum of the composite silver film detecting tobramycin, and the relative standard deviation of the SERS peak intensity at 1020 cm -1 is shown;

[0025] Figure 6 In the middle A, it is a SERS spectrum of the composite silver film detecting tobramycin with different concentrations, Figure 6 In the middle B, it is a linear relationship diagram of the SERS intensity of tobramycin at 1020 cm -1 and the negative logarithm of the concentration;

[0026] Figure 7 It is a SERS spectrum of the composite silver film detecting tobramycin and other aminoglycoside antibiotic solutions. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, specific and understandable, the present application will be further described in detail below in combination with the drawings and examples.

[0028] The present application comprises the following steps

[0029] 1) Preparation of PDMS film.

[0030] Sylgard 184 prepolymer and catalyst are mixed in a suitable mass ratio, cured in an oven, and cut to the desired thickness.

[0031] 2) Synthesis of silver nanoparticle solution.

[0032] Uniform silver nanoparticles are prepared by controlling reaction parameters using the trisodium citrate and ascorbic acid method.

[0033] 3) Self-assembly, transfer and preparation of silver nanoparticle film.

[0034] The silver nanoparticle solution and dichloromethane are mixed, and tetrabutylammonium nitrate solution is added to form a silver nanoparticle interfacial film by liquid-liquid self-assembly. The film is transferred to the front side of the PDMS film using a silicon wafer, and the preparation of the silver nanoparticle film is completed.

[0035] 4) Synthesis of silver cubes. First, gold seed solution and growth solution are prepared, and the two solutions are mixed and left to stand to obtain a gold core solution; then the gold core solution is reacted with CTAC, and silver nitrate solution and CTAC-ascorbic acid solution are sequentially injected, and uniform silver cubes are prepared by controlling reaction parameters.

[0036] 5) Self-assembly and transfer of silver cube film, and preparation of composite silver film. First, silver cubes and PVP ethanol solution are mixed. Then the silver cube PVP ethanol solution is added to a mixed solution of n-hexane, chloroform and ultrapure water, and a silver cube interfacial film is formed by liquid-liquid self-assembly. The film is transferred to the back side of the PDMS film using a silicon wafer, and the preparation of the composite silver film is completed.

[0037] 6) SERS quantitative analysis and detection of tobramycin on the composite silver film.

[0038] The composite silver film is immersed in different concentrations of tobramycin solution, and SERS detection is carried out under the optimal excitation wavelength, the optimal PDMS film thickness and the optimal pH conditions. The intensity values of the SERS characteristic peaks in the spectrum are recorded, and a standard curve is established with the corresponding tobramycin concentration for quantitative analysis. Since the positions of the SERS characteristic peaks of tobramycin and other aminoglycoside antibiotics are different, specific detection of tobramycin is carried out.

[0039] Different concentrations of tobramycin are prepared using ultrapure water as the solvent -5~10 -11 M tobramycin solution; at the optimal excitation wavelength of 785 nm, the concentration of the tobramycin solution was controlled at 10. -5 Under M conditions, PDMS membrane thicknesses of 100–500 μm and pH values ​​of 2–10 were used for detection, and the optimal PDMS membrane thickness and pH conditions were optimized. Composite silver membranes were immersed in tobramycin solutions of different concentrations for SERS detection. The characteristic SERS peak at 1020 cm⁻¹ was recorded. -1 The intensity values ​​were compared with the corresponding tobramycin concentrations to establish a standard curve for quantitative analysis; based on the SERS characteristic peaks (606 cm⁻¹) of tobramycin with those of kanamycin, neomycin, and streptomycin, the results were analyzed. -1 1020 cm -1 The differences between ) and tobramycin 1020 cm -1 Its intensity is much higher than that of gentamicin, amikacin, sisomicin and netilmicin, enabling the specific detection of tobramycin.

[0040] Example 1

[0041] 1. Preparation of PDMS membrane.

[0042] The Sylgard 184 prepolymer and catalyst were thoroughly mixed at a suitable mass ratio of 10:1, cured in an oven for 0.5–3 hours, and then cut into pieces with the required thickness of 100–500 μm. Specifically, in this embodiment, the curing time was 1 hour.

[0043] Figure 1 Optical photographs of PDMS films of different thicknesses, from left to right: 100, 300, and 500 μm.

[0044] 2. Synthesis of silver nanoparticle solution.

[0045] Dissolve 50–100 mg of trisodium citrate and 100–500 mg of ascorbic acid simultaneously in 300–500 mL of ultrapure water. Heat in a water bath at 60–80 °C for 40–60 min. Then add 1–5 mL of 0.01–0.05 mM silver nitrate solution and heat in a water bath at 60–80 °C for 20–30 min. Stop heating and allow to cool naturally to room temperature to obtain a solution of silver nanoparticles with uniform particle size. Store at 4 °C protected from light.

[0046] Specifically, in this embodiment, 50 mg of trisodium citrate, 100 mg of ascorbic acid, 300 mL of ultrapure water, and silver nitrate solution with a concentration of 0.01 mM and a volume of 1 mL are used.

[0047] 3. Self-assembly, transfer and preparation of silver nanoparticle films.

[0048] Take 1 ~ 5 mL of silver nanoparticles solution and 1 ~ 5 mL of dichloromethane, add 10 -3 ~10 -5 M, volume of 100 ~ 500 μL of tetrabutylammonium nitrate solution, shake vigorously. Silver nanoparticles solution will be liquid-liquid self-assembly in water and organic phase, forming silver nanoparticles interface film. The hydrophilic side of the silver nanoparticles interface film in the water phase is adsorbed by the hydrophilic silicon wafer, and is transferred to the water-air interface. The hydrophobic side of the PDMS film is exposed to the air, and the hydrophobic side of the PDMS film is exposed to the air. The horizontal stripping is washed with ultrapure water and dried with nitrogen.

[0049] Specifically, in this embodiment, the silver nanoparticles solution is 1 mL, dichloromethane is 1 mL, the concentration of tetrabutylammonium nitrate solution is 10 -3 M, volume of 100 μL.

[0050] The liquid-liquid self-assembly of silver nanoparticles interface film is to use the tetrabutylammonium ion generated by the hydrolysis of tetrabutylammonium nitrate to form a positive charge arrangement at the water-oil interface. The negative charged silver nanoparticles are attracted by electrostatic attraction, and the liquid-liquid self-assembly occurs in water and organic phase.

[0051] 4. Synthesis of silver cube.

[0052] First, mix 0.05 ~ 0.5 mM of chloroauric acid with a volume of 5 ~ 10 mL and 150 ~ 200 mM of cetyltrimethylammonium bromide solution with a volume of 5 ~ 10 mL, and react at room temperature for 30 min. Then add 10 ~ 20 mM of sodium borohydride solution with a volume of 0.5 ~ 1 mL to complete the preparation of gold seed solution; take 150 ~ 200 mM of CTAC with a volume of 15 ~ 20 mL, 60 ~ 100 mM of ascorbic acid with a volume of 10 ~ 15 mL and 0.05 ~ 0.5 mM of chloroauric acid with a volume of 2 ~ 20 mL as growth solution; add 0.5 ~ 2 mL of gold seed solution to 27 ~ 55 mL of growth solution, mix and stand for 2 h to obtain gold core solution.

[0053] Specifically, in this embodiment, the concentration of chloroauric acid is 0.1 mM, and the volume is 5 mL; the concentration of cetyltrimethylammonium bromide solution is 50 mM, and the volume is 5 mL; the concentration of sodium borohydride solution is 10 mM, and the volume is 0.5 mL; the concentration of CTAC is 150 mM, and the volume is 15 mL; the concentration of ascorbic acid is 60 mM, and the volume is 10 mL; the concentration of chloroauric acid is 0.1 mM, and the volume is 2 mL; the gold seed solution is 0.5 mL, and the growth solution is 27 mL.

[0054] In the second step, 0.1–1.5 mL of the gold core solution was reacted with 1.9–4.5 mL of CTAC (200–400 mM). Then, 1.5–5 mL of silver nitrate solution (0.5–2 mM) and a CTAC-ascorbic acid solution (40–80 mM CTAC and 60–100 mM ascorbic acid in a 1:1 volume ratio) were sequentially injected. The mixture was incubated in a water bath at 60–80 °C for 4–6 h. Heating was then stopped, and the mixture was allowed to cool naturally to room temperature to obtain uniformly sized silver cubes, which were stored at 4 °C in the dark.

[0055] Specifically, in this embodiment, the gold core solution is 1.5 mL; the CTAC concentration is 200 mM and the volume is 1.9 mL; the silver nitrate solution concentration is 0.5 mM and the volume is 1.5 mL; the CTAC concentration is 40 mM; and the ascorbic acid concentration is 60 mM.

[0056] 5. Self-assembly and transfer of silver cubic films to prepare composite silver films.

[0057] The first step is to mix 10-20 mL of silver cubes with a PVP ethanol solution containing 0.9%-1.2% by mass. Specifically, in this example, the silver cubes are 10 mL and the PVP ethanol solution has a mass fraction of 1%.

[0058] In the second step, the obtained silver cube PVP ethanol solution was added to a 1:1:1 mixture of n-hexane, chloroform, and ultrapure water. After gentle shaking, the silver cubes underwent liquid-liquid self-assembly in the aqueous and organic phases to form a silver cube interface film. The hydrophilic ends of the silver cube interface film in the aqueous phase were adsorbed onto a hydrophilic silicon wafer and transferred to the water-air interface. Then, the back side of the PDMS membrane was placed in contact with the hydrophobic ends of the silver cube interface film exposed to air, horizontally peeled off, rinsed with ultrapure water, and dried under nitrogen for later use.

[0059] The liquid-liquid self-assembly forming of the silver cube interface film utilizes PVP to partially replace the CTA on the surface of the silver cube. + The groups provide hydrophobicity while reducing surface potential. Driven by Brownian motion, the silver cubes move toward the interface and self-assemble in the aqueous and organic phases to form a silver cube interface film.

[0060] Figure 2 Image A is a SEM image of the silver nanoparticle film. The inset is a histogram of the particle size of the silver nanoparticles on the film. It can be seen that the silver nanoparticles are spherical with a particle size of approximately 51.08 ± 4.17 nm. Figure 2 Image B in the figure is an SEM image of the silver cube film. The inset is a histogram of the particle size of the silver cubes on the film. It can be seen that the silver cubes have good uniformity and the particle size is about 69.96±6.56 nm.

[0061] Example 2

[0062] SERS detection of tobramycin by composite silver film under different thickness of PDMS film.

[0063] The concentration of tobramycin solution was fixed at 10 -5 M, the thickness of PDMS film was 100, 300 and 500 μm respectively, and the composite silver film was immersed in tobramycin solution, taken out, dried at room temperature, and SERS spectrum was collected. Figure 3 It can be seen that when the thickness of PDMS film is 500 μm, the SERS intensity of tobramycin reaches the strongest, so the composite silver film with a thickness of 500 μm is used to detect tobramycin in the subsequent experiment.

[0064] Example 3

[0065] SERS spectrum of tobramycin detected by composite silver film under different pH conditions.

[0066] The concentration of tobramycin solution was fixed at 10 -5 M, the thickness of PDMS film was fixed at 500 μm, the pH of tobramycin solution for immersing the composite silver film was adjusted to 2, 4, 6, 8 and 10, the composite silver film was taken out, dried at room temperature, and SERS spectrum was collected. Figure 4 It can be seen that when the pH is 6, the SERS intensity of tobramycin reaches the strongest, so the optimal pH of the detection system of tobramycin is 6 in the subsequent experiment.

[0067] Example 4

[0068] Uniformity of tobramycin detected by composite silver film.

[0069] The concentration of tobramycin solution was fixed at 10 -5 M, the optimal thickness of PDMS film was 500 μm, the optimal pH was 6, the composite silver film coupled with surface plasmon was immersed in tobramycin solution, taken out, dried at room temperature, and SERS spectrum was collected randomly ten times on the substrate with an excitation wavelength of 785 nm, the SERS peak intensity of tobramycin collected ten times in parallel was compared to determine the uniformity of the SERS substrate.

[0070] Figure 5 A is the experimental result of Example 4, that is, the SERS spectrum of tobramycin measured ten times in parallel by the composite silver film; Figure 5 B is the column chart of SERS peak intensity of tobramycin measured ten times in parallel at 1020 cm -1 It can be seen that the relative standard deviation (RSD) calculated from the SERS peak intensity of 10 parallel samples is 4.35%, which is less than 10%, indicating that the uniformity of the SERS substrate is good and can be applied to the SERS quantitative analysis of tobramycin.

[0071] Example 5

[0072] SERS detection of tobramycin on composite silver film.

[0073] SERS quantitative analysis of tobramycin on composite silver film: The different concentrations of tobramycin solution were prepared with ultrapure water as solvent; under the conditions of optimal excitation wavelength 785 nm, optimal excitation wavelength 785 nm, optimal PDMS film thickness 500 μm, and optimal pH = 6, the composite silver film was immersed in different concentrations of tobramycin solution, taken out, dried at room temperature, and subjected to SERS detection. The intensity value of the SERS characteristic peak 1020 cm -5 ~10 -11 M of tobramycin solution; under the conditions of optimal excitation wavelength 785 nm, optimal excitation wavelength 785 nm, optimal PDMS film thickness 500 μm, and optimal pH = 6, the composite silver film was immersed in different concentrations of tobramycin solution, taken out, dried at room temperature, and subjected to SERS detection. The intensity value of the SERS characteristic peak 1020 cm -1 was recorded and a standard curve was established with the corresponding concentration of tobramycin for quantitative analysis.

[0074] Figure 6 Figure 5A is the experimental results of Example 5, i.e. the SERS spectra of different concentrations of 10 -5 M, 10 -6 M, 10 -7 M, 10 -8 M, 10 -9 M, 10 -10 M, 10 -11 M of tobramycin, it can be seen that the SERS intensity of tobramycin decreases with the decrease of concentration.

[0075] Figure 6 Figure 5B is the standard curve established after detecting different concentrations of tobramycin standard solution in Example 5, within the range of 10 -5 ~10 -11 M / L, the intensity of the 1020 cm -1 characteristic peak of tobramycin is negatively correlated with the concentration of tobramycin (y = 3053.88x + 35314.57), R 2 = 0.974. In addition, the detection limit is 2.36 x 10 -12 M.

[0076] Example 6

[0077] Detection of tobramycin and other aminoglycoside antibiotic solutions on composite silver film.

[0078] SERS specific detection of tobramycin and its homologues on composite silver film: The different concentrations of tobramycin and its homologues were prepared with ultrapure water as solvent; under the conditions of optimal excitation wavelength 785 nm, optimal excitation wavelength 785 nm, optimal PDMS film thickness 500 μm, and optimal pH = 6, the composite silver film was immersed in different concentrations of tobramycin and its homologues, taken out, dried at room temperature, and subjected to SERS detection. The intensity value of the SERS characteristic peak 1020 cm -5M is tobramycin (TOB), kanamycin (KANA), neomycin (NEO), streptomycin (STR), gentamycin (GEN), amikacin (AMK), sisomicin (SISO) and netilmicin (MET), under the conditions of the best excitation wavelength 785 nm, the best PDMS film thickness 500 μm, and the best pH = 6, the composite silver film is respectively immersed in the above solution, taken out, dried at room temperature, and SERS detection is carried out.

[0079] Figure 7 is the experimental result of Example 6, kanamycin, neomycin and streptomycin have their own unique peaks at 606 cm -1 , and the SERS intensity of other aminoglycoside antibiotics at 1020 cm -1 is far lower than that of tobramycin. Therefore, the composite silver film can specifically detect tobramycin in the tobramycin and other aminoglycoside antibiotic solution.

Claims

1. A method for preparing a composite silver film coupled with surface plasmons, characterized in that, The method comprises the following steps: 1) Preparation of silver nanoparticle film: mixing silver nanoparticle solution and dichloromethane, adding tetrabutylammonium nitrate solution, liquid-liquid self-assembly to form silver nanoparticle interface film, then transferring to the front side of the PDMS film with a silicon wafer, and completing the preparation of the silver nanoparticle film; 2) Synthesis of silver cube: first, preparing gold seed solution and growth solution, mixing the two solutions to obtain gold core solution; then, reacting the gold core solution with CTAC, and sequentially injecting silver nitrate solution and CTAC-ascorbic acid solution, to prepare silver cubes with uniform particle size by controlling reaction parameters; 3) Self-assembly and transfer of silver cube film, and preparation of composite silver film: first, mixing silver cubes and PVP ethanol solution, then adding the silver cube PVP ethanol solution into a mixed solution of n-hexane, chloroform and ultrapure water, liquid-liquid self-assembly to form silver cube interface film, and finally transferring to the back side of the PDMS film with a silicon wafer, to complete the preparation of the composite silver film.

2. A composite silver film coupled to surface plasmons, characterized in that: The composite silver film is prepared by the method of claim 1.

3. Application of the surface plasmon-coupled composite silver film of claim 2 in SERS detection of tobramycin.

4. Use according to claim 3, wherein: The composite silver film is immersed in a sample solution containing tobramycin, taken out, dried, and subjected to surface-enhanced Raman scattering detection at the optimal excitation wavelength, so as to realize analysis and detection of tobramycin by measuring the Raman peak intensity of tobramycin at a specific wavelength.

5. Use according to claim 4, wherein: According to the different positions of SERS characteristic peaks of tobramycin and other aminoglycoside antibiotics, specific detection of tobramycin is realized.

6. Use according to claim 5, characterized in that: The other aminoglycoside antibiotics include kanamycin, neomycin and streptomycin, and the SERS characteristic peaks at different positions are 606 cm -1 and 1020 cm -1 .

7. The use according to claim 4, wherein: The composite silver film is immersed in tobramycin solutions with different concentrations, respectively, and subjected to SERS detection at the optimal excitation wavelength, so as to record the intensity values of SERS characteristic peaks in the spectrum and establish a standard curve of the intensity values and the corresponding concentrations of tobramycin, for quantitative analysis and detection.

8. Use according to claim 7, characterized in that: The SERS characteristic peak in the recorded spectrum refers to the SERS characteristic peak of tobramycin at 1020 cm -1 The linear detection range of tobramycin is 10 -5 ~10 -11 The detection limit is 2.36 x 10 -12 M, and the relative standard deviation of SERS intensity is less than 10%.

9. Use according to claim 4, characterized in that: The optimal excitation wavelength is 785 nm.

10. Use according to claim 4, characterized in that: The thickness of the PDMS film is 100-500 μm; and the pH of the detection condition is 2-10.

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