Preparation method of high-performance SERS (Surface Enhanced Raman Scattering) substrate based on PDMS (Polydimethylsiloxane) microwrinkles and application of high-performance SERS

Abstract

The invention discloses a preparation method of a high-performance SERS (Surface Enhanced Raman Scattering) substrate based on PDMS (Polydimethylsiloxane) micro-wrinkles and application of the high-performance SERS substrate in penicillin potassium detection, which is characterized by comprising the following steps: firstly, preparing and manufacturing a PDMS sheet with specific hardness and shape, then fixing a bent and stretched PDMS substrate in a special mold, and spraying 60nm gold nanoparticles on the bent surface of the PDMS substrate in a vacuum sputtering manner. After the bent PDMS substrate is unfolded, tiny wrinkles capable of being coupled with hot spots and retaining to-be-detected substances are naturally formed on the surface of the PDMS substrate, the Raman signal intensity can be greatly improved in cooperation with detection of a drip evaporation method, and the method has the advantages of being simple and efficient.

Description

Technical Field

[0001] The present invention relates to a preparation method of a SERS substrate, in particular to a high-performance flexible SERS substrate constructed based on PDMS surface micro-wrinkles and an application method thereof in detecting penicillin potassium in a solution. Background Art

[0002] In 1928, Indian physicist C.V. Raman, while conducting a scattering spectrum experiment on liquid benzene, discovered that after scattering, the incident light spectrum showed two symmetrically distributed spectral lines with shifted frequencies. He called this phenomenon of different frequencies between the incident and scattered light Raman scattering. The Raman spectrum obtained by detecting Raman scattered light can reflect information about the rotational and vibrational levels of molecules. Different functional groups correspond to different Raman shifts, and the Raman peak width is narrow and the spectral band resolution is high, which contains a wealth of molecular structural information about the substance being tested. Furthermore, Raman spectroscopy requires simple preprocessing and can achieve non-destructive analysis, making it a common method for studying the molecular structure of substances. However, Raman scattering signals are often very weak, making them difficult to detect and analyze. This led to the development of surface-enhanced Raman spectroscopy (SERS).

[0003] Surface-enhanced Raman scattering (SERS), one of the most widely known and commonly used Raman enhancement techniques, was independently discovered by two scientists, Spraman and Livingston, in the 1970s. They discovered that when molecules are adsorbed on a metal surface, the intensity of the Raman scattering signal is greatly enhanced. This phenomenon sparked the interest of researchers, who began to explore the mechanism and potential applications of this Raman signal enhancement phenomenon. It uses the local electric field effect generated on the surface of metal nanoparticles (usually silver or gold) to enhance the Raman signal. The electric field generated by these nanoparticles can significantly increase the intensity of the scattered light, making the Raman signal easier to detect. Surface-enhanced Raman scattering is a Raman enhancement technique that significantly enhances the intensity of the Raman scattering signal through the local electric field effect and surface plasmon resonance effect generated on the surface of metal nanostructures, making weak Raman signals easier to detect and analyze.

[0004] Currently, the most widely used SERS substrates are often rigid substrates, such as silicon wafers, quartz wafers, etc. However, traditional rigid substrates have certain limitations. They are usually expensive and non-portable, and require complex pretreatment when detecting solid samples with non-planar surfaces. They are not suitable for truly complex surface analysis and cannot perform non-invasive detection. Stretchability, adhesion, biocompatibility, elastic stretchability support, transparency, and good physical and chemical stability have led to the widespread development and application of flexible SERS substrates. The combination of flexible substrates and plasma units gives the nanoparticles between adjacent substrates an adjustable distance. Flexible substrates can be well attached to curved surfaces, facilitating the detection of complex and irregular surfaces. They can be cut into any desired shape and size for on-demand use, thus enabling non-destructive or even in-situ detection, providing portability. Some flexible materials have good biocompatibility and wearability, playing a huge role in human biological detection. Summary of the Invention

[0005] This invention addresses the complex and expensive preparation issues of existing rigid SERS substrates. By utilizing the stretching and deformation of the flexible PDMS material, it creates micro-wrinkles on its surface that can three-dimensionally couple hotspots and retain analytes. This increases the number of hotspots per unit area, shortens the spacing between hotspots, and enhances the detection performance of the SERS substrate. This invention provides a method for preparing a flexible SERS substrate with simple process steps, strong operability, and the ability to effectively enhance Raman signals, as well as its application in detection.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a high-performance SERS substrate based on PDMS micro-folds and its application in the detection of penicillin potassium in medical wastewater, comprising the following steps:

[0007] Preparation of PDMS sheets: PDMS and curing agent were mixed in a 15:1 ratio, stirred thoroughly on a magnetic stirrer for 30 minutes, and then placed in a vacuum chamber for 30 minutes to remove air bubbles. The liquid PDMS was then poured onto a clean, dry glass slide and placed on a hot plate at 120°C for 5 minutes to complete crosslinking and curing, forming a PDMS sheet approximately 3 mm thick. After curing, the PDMS was sectioned into 45 mm × 25 mm × 3 mm sheets and repeatedly ultrasonically cleaned in anhydrous ethanol.

[0008] Vacuum sputtering deposition of gold nanoparticles: The PDMS sheet obtained in the previous step is bent along its longer edge and fixed in a 35mm × 12mm × 5mm slot-shaped stainless steel mold. A vacuum sputtering coater is then used to deposit a 60nm thick layer of gold at the center of the curved PDMS surface, maintaining an operating pressure of 8Pa and a current of 10mA. Upon completion, the PDMS substrate is removed and allowed to cool and unfold naturally. Upon completion, the surface of the PDMS substrate will naturally form tiny wrinkles that can couple to SERS detection "hot spots," increase the number of "hot spots" per unit area, and retain the analytes.

[0009] Use the "drip evaporation method" for detection: Place the flexible SERS substrate obtained in the above steps on a 110°C heating table, use a pipette to take 500μL of 0.01mol / L penicillin potassium solution, and add it drop by drop on the center area of ​​PDMS. After one drop evaporates, add the next drop. Using the "drip evaporation method" for detection can increase the concentration of the analyte in the tiny wrinkles on the PDMS surface, which not only enables quantitative analysis of the solution to be tested, but also greatly improves the detection capability of the SERS substrate. After completion, place it under a micro-Raman spectrometer for Raman spectroscopy testing. The excitation wavelength of the Raman spectrometer is 635nm, the laser power is 40mW, the integration time is 10s, and the number of integrations is 2 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Fixing method of PDMS substrate in steel tank.

[0011] Figure 2 The formation process of micro-wrinkles on the PDMS surface.

[0012] Figure 3 Tiny wrinkles on the PDMS surface under an optical microscope.

[0013] Figure 4 PDMS flexible Raman substrate, the measured Raman spectrum of 0.1 mol / L penicillin potassium solution, and the Raman spectrum of 99% solid penicillin potassium.

[0014] Figure 5 Raman spectra of 0.1 mol / L penicillin potassium solution measured by the "drip evaporation method" and direct detection respectively. DETAILED DESCRIPTION

[0015] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0016] First, prepare a PDMS sheet: PDMS and curing agent are mixed in a ratio of 15:1, stirred thoroughly on a magnetic stirrer for 30 minutes, and then placed in a vacuum chamber for 30 minutes to remove air bubbles. The liquid PDMS is then poured onto a clean, dry glass slide and placed on a hot plate at 120°C for 5 minutes to complete cross-linking and curing, forming a PDMS sheet approximately 3 mm thick. After curing, the PDMS is sectioned into 45 mm × 25 mm × 3 mm sheets and repeatedly ultrasonically cleaned in anhydrous ethanol.

[0017] Then, a vacuum sputtering coater was used to deposit gold nanoparticles on the PDMS substrate: the PDMS sheet obtained in the above steps was bent from the longer side, and the PDMS sheet was bent from the longer side. Figure 1 It is fixed in a 35mm×12mm×5mm slot-shaped stainless steel mold. Then a vacuum sputtering coater is used to deposit 60nm thick gold in the center of the PDMS curved surface, and the working pressure and current are controlled at 8Pa and 10mA, respectively. After completion, the PDMS substrate is removed and allowed to cool and unfold naturally. After completion, tiny wrinkles will naturally form on the surface of the PDMS substrate that can couple to the SERS detection "hotspot" and retain the detected object, as shown in the sample effect and wrinkle formation mechanism diagram respectively. Figure 2 、 3 shown.

[0018] Use the "drip evaporation method" to detect: Place the flexible SERS substrate obtained in the above steps on a 110℃ heating platform, use a pipette to take 500μL of 0.01mol / L penicillin potassium solution, and add it drop by drop on the center area of ​​PDMS. After one drop evaporates, add the next drop. Using the "drip evaporation method" to detect can increase the concentration of the analyte in the tiny wrinkles on the PDMS surface, which can not only achieve quantitative analysis of the test solution, but also greatly improve the detection ability of the SERS substrate. The effect is as follows: Figure 4 、 5 After completion, the microscope was placed under a Raman microscope for Raman spectroscopy. The Raman spectrometer had an excitation wavelength of 635 nm, a laser power of 40 mW, an integration time of 10 s, and two integrations.

[0019] It is reiterated that the above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. A method for preparing a high-performance SERS substrate based on PDMS micro-folds and its application in the detection of penicillin potassium. It is characterized by the following steps: (1) Preparation of PDMS sheets: PDMS and curing agent were mixed in a ratio of 15:1, stirred thoroughly on a magnetic stirrer for 30 min, and then placed in a vacuum machine for 30 min to remove bubbles. The liquid PDMS was then poured onto a dry, clean glass sheet and placed on a heating plate at 120°C for 5 min to complete cross-linking and curing, forming a PDMS sheet about 3 mm thick. After curing, the PDMS was divided into 45 mm × 25 mm × 3 mm sheets and repeatedly ultrasonically cleaned in anhydrous ethanol. (2) Vacuum sputtering deposition of gold nanoparticles: The PDMS sheet obtained in step (1) was bent from the longer side and fixed in a 35 mm × 12 mm × 5 mm slot-shaped stainless steel mold. Then, a vacuum sputtering coater was used to deposit 60 nm thick gold on the center of the curved surface of the PDMS. The working pressure was controlled at 8 Pa and the working current was controlled at 10 mA. After completion, the PDMS substrate was removed and allowed to cool naturally and unfold. (3) Use the "drip evaporation method" to detect: Place the flexible SERS substrate obtained in step (2) on a heating platform at 110°C, use a pipette to take 500 μL of 0.01 mol / L penicillin potassium solution, and add it drop by drop on the central area of ​​PDMS. After one drop is evaporated, add the next drop. After completion, place it under a micro Raman spectrometer for Raman spectroscopy testing. The excitation wavelength of the Raman spectrometer is 635 nm, the laser power is 40 mW, the integration time is 10 s, and the number of integrations is 2 times.

2. The method for preparing a high-performance SERS substrate based on PDMS micro-folds according to claim 1, characterized in that In step (1), PDMS and curing agent are mixed in a ratio of 15:

1.

3. The method for preparing a high-performance SERS substrate based on PDMS micro-folds according to claim 1, characterized in that In step (1), PDMS was cross-linked and cured on a heating platform at 120° C. for 5 min, and finally the PDMS was made into a 45 mm×25 mm×3 mm sheet.

4. The method for preparing a high-performance SERS substrate based on PDMS micro-folds according to claim 1, characterized in that In step (2), the PDMS was bent from the longer side and fixed in a 35 mm × 12 mm × 5 mm slot-shaped stainless steel mold.

5. The method for preparing a high-performance SERS substrate based on PDMS micro-folds according to claim 1, characterized in that In step (2), 60 nm thick gold nanoparticles were deposited at the center of the curved surface of PDMS, the working pressure was controlled at 8 Pa, and the working current was controlled at 10 mA.

6. The method for preparing a high-performance SERS substrate based on PDMS micro-folds according to claim 1, characterized in that After completing step (2), micron-scale wrinkles naturally form on the surface of the PDMS sheet.

7. The method for detecting penicillin potassium based on a PDMS flexible SERS substrate according to claim 1, characterized in that Use the SERS substrate prepared in steps (1) and (2), place the substrate on a heating platform, take 500 μL of potassium penicillin solution, and add the next drop after the previous drop of solution evaporates to dryness; preferably, the temperature of the heating platform is controlled at 110°C.

8. The method for detecting penicillin potassium based on a PDMS flexible SERS substrate according to claim 1, characterized in that The Raman spectrometer used in step (3) has an excitation wavelength of 635 nm, a laser power of 40 mW, an integration time of 20 s, and an integration number of 2 times.

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