A SERS substrate based on the light-concentrating properties of microspheres and its preparation method

Abstract

This invention discloses a SERS substrate based on the light-concentrating properties of microspheres. The SERS substrate includes a glass substrate, an array of microstructures, a noble metal thin film layer, and light-concentrating microspheres. The array of microstructures consists of polystyrene microspheres arranged in a single layer and tightly packed on the surface of the glass substrate. The noble metal thin film layer covers the surface of the array of microstructures, and the light-concentrating microspheres are arranged in a single layer and tightly packed array on the surface of the noble metal thin film layer. This invention also provides a method for preparing the above-mentioned SERS substrate based on the light-concentrating properties of microspheres, resulting in a self-assembled SERS substrate. The self-assembled SERS substrate provided by this invention has the characteristics of good uniformity and high sensitivity. The SERS substrate based on the light-concentrating properties of microspheres prepared by this invention exhibits excellent Raman enhancement effect.

Description

Technical Field

[0001] This invention relates to the field of nanotechnology, specifically to a SERS substrate based on the light-gathering properties of microspheres and its preparation method. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) is a highly sensitive chemical analysis technique with excellent molecular specificity. It mainly utilizes the localized surface plasmon resonance of microstructured noble metal thin films or noble metal nanoparticles to greatly enhance the Raman scattering signal intensity of analyte molecules. It is now widely used in food safety, environmental monitoring, real-time monitoring, and biomedicine. In terms of detection technology, SERS is considered a fast, sensitive, and universal technique, with a detection limit that can reach the single-molecule level.

[0003] Self-assembly processes have the advantages of low cost and convenient operation, but traditional self-assembly SERS substrate preparation methods often fail to achieve high Raman enhancement effects. Generally, self-assembly is combined with ion beam lithography to significantly improve the SERS enhancement effect of the substrate, but this requires high process requirements and is expensive to prepare, which deviates from the original intention of reducing substrate preparation costs through self-assembly.

[0004] Patent CN113702354A discloses a flexible SERS substrate based on an array of microstructures and its preparation method. The main Raman enhancement structure of this method is gold nanoparticles in an array of porous structures, which undoubtedly greatly increases the preparation cost of the substrate. Patent CN103938158A discloses a SERS substrate with a self-assembled spherical array and its preparation method. This is an array of noble metal thin film structures based on a self-assembled array of nanospheres. Its structure is relatively simple, and its Raman enhancement effect is limited. It is also difficult to overcome the structural limitations to improve the detection accuracy of Raman spectroscopy, making it difficult to play a role in detection environments that require higher precision.

[0005] This invention addresses the shortcomings of traditional self-assembled SERS substrates in terms of poor detection accuracy by designing a self-assembled SERS substrate based on the light-concentrating properties of microspheres. Summary of the Invention

[0006] In view of the above-mentioned shortcomings, the present invention provides a SERS substrate based on the light-gathering properties of microspheres and its preparation method. The self-assembled SERS substrate provided by the present invention has the characteristics of good uniformity and high sensitivity.

[0007] To achieve the above objectives, the present invention provides a SERS substrate based on the light-concentrating properties of microspheres. The SERS substrate includes a glass substrate, an array of microstructures, a noble metal thin film layer, and light-concentrating microspheres. The array of microstructures is composed of polystyrene microspheres distributed on the surface of the glass substrate and arranged in a single layer in a close-packed manner. The noble metal thin film layer covers the surface of the array of microstructures, and the light-concentrating microspheres are distributed in a single layer in a close-packed array on the surface of the noble metal thin film layer.

[0008] According to one aspect of the present invention, the glass substrate is a glass slide, and the polystyrene microspheres have a particle size of 0.3 to 0.8 μm.

[0009] According to one aspect of the present invention, the noble metal thin film layer is divided into two layers, including an upper layer and a lower layer; the upper layer is gold with a thickness of 50-60 nm; and the lower layer is silver with a thickness of 50-60 nm.

[0010] According to one aspect of the present invention, the material of the light-concentrating microspheres is silicon dioxide, and the diameter of the microspheres is 800-1000 nm.

[0011] Based on the same inventive concept, the present invention also provides a method for preparing any of the above-mentioned SERS substrates based on the light-gathering properties of microspheres, comprising the following steps:

[0012] Step 1: After ultrasonic cleaning and drying, a clean glass substrate is obtained;

[0013] Step 2: Spin-coat the dispersion containing polystyrene microspheres onto a clean glass substrate to obtain an array-like microstructure formed by a single layer of polystyrene microspheres;

[0014] Step 3: Sputter a noble metal thin film layer onto the array-type microstructure using magnetron sputtering;

[0015] Step 4: Spin-coat a dispersion containing silica microspheres onto a noble metal thin film layer to obtain light-concentrating microspheres composed of a closely packed monolayer array of silica microspheres.

[0016] According to one aspect of the present invention, in step 1, the ultrasonic cleaning specifically involves using an ultrasonic cleaner to sequentially perform ultrasonic cleaning of the glass substrate using an acetone bath, an ethanol bath, and a deionized water bath.

[0017] According to one aspect of the present invention, in step 2, the preparation process of the dispersion containing polystyrene microspheres specifically involves: centrifuging the polystyrene microsphere solution to remove the supernatant, then adding sodium dodecyl sulfate solution and deionized water into a centrifuge tube and mixing them evenly to form a dispersion.

[0018] According to one aspect of the present invention, in step 2, the spin coating speed is 2000-4000 r / min and the time is 10-40 s.

[0019] According to one aspect of the present invention, in step 3, the noble metal thin film layer comprises a lower silver film of 50-60 nm and an upper gold film of 50-60 nm; the magnetron sputtering current is 38-40 mA, and the magnetron sputtering time is 60-180 s.

[0020] According to one aspect of the present invention, in step 4, the preparation process of the dispersion containing silica microspheres specifically includes: centrifuging a silica microsphere solution with a microsphere particle size of 800-1000 nm, removing the supernatant, and then adding sodium dodecyl sulfate solution into a centrifuge tube and mixing evenly to form a dispersion; the spin coating speed is 2000-4000 r / min and the time is 10-40 s.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention provides a self-assembled SERS substrate based on the light-concentrating properties of microspheres, wherein the array-type microstructure based on monolayer close-packed PS microspheres has a large number of nanoscale structures. After sputtering a noble metal thin film layer, its size resonates with the incident laser, generating a large electromagnetic field enhancement "hot spot" that enhances the Raman signal of the analyte molecules; at the same time, the light-concentrating microspheres focus the incident laser on a local area, greatly enhancing the "hot spot" within that area.

[0023] The intensity further enhances the Raman signal; thus, it can be seen that, based on the array-type microstructure and the light-gathering properties of the microspheres, the Raman signal of the analyte molecules is enhanced together, and the present invention has the advantages of good uniformity and high sensitivity.

[0024] (2) The silica-focusing microspheres of this invention are located above a double-layer noble metal film. This array-type focusing microsphere structure can achieve secondary enhancement of the lower SERS substrate through light focusing characteristics. The silica microspheres act as micro-nano convex lenses in the structure, which can focus the incident laser on a local area of ​​the surface of the lower SERS substrate, thereby greatly improving the intensity of the "hot spot" of local surface plasmon resonance, and thus further improving the Raman enhancement effect.

[0025] (3) The SERS substrate preparation process based on the light-concentrating properties of microspheres provided by the present invention is simple and has low preparation cost, which is conducive to industrial production.

[0026] (4) The light-concentrating microsphere structure provided by the present invention can further enhance Raman scattering through low-cost materials and convenient self-assembly methods, thereby achieving higher detection accuracy. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the SERS substrate based on the light-concentrating properties of microspheres as described in an embodiment of the present invention;

[0028] Figure 2 This is a process flow diagram of spin coating a dispersion containing polystyrene microspheres onto a glass substrate according to an embodiment of the present invention.

[0029] Figure 3 This is a SEM image of the array-type microstructure obtained by spin-coating a dispersion containing polystyrene microspheres onto a glass substrate according to an embodiment of the present invention.

[0030] Figure 4 This is a SEM image of the SERS substrate based on the light-gathering properties of microspheres obtained by the preparation method described in the embodiments of the present invention;

[0031] Figure 5 The image shows the Raman spectrum of a 100 mM 4-ATP solution obtained from the SERS substrate prepared by the method described in this embodiment of the invention.

[0032] Figure 6 The images show a comparison of the Raman spectra of a 100 mM 4-ATP solution obtained from the noble metal thin film described in the embodiments of the present invention, the noble metal thin film with an array microstructure, and the SERS substrate based on the light-gathering properties of microspheres. Detailed Implementation

[0033] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0034] It should be noted that the polystyrene microsphere solution and silica microsphere solution described in Example 1 of this application are both commercially available products, purchased from Tianjin Bestlé Chromatography Technology Development Center.

[0035] Traditional self-assembled SERS substrate fabrication methods often fail to achieve high Raman enhancement effects. Generally, self-assembly is combined with ion beam lithography to significantly improve the SERS enhancement effect of the substrate, but this requires high process requirements and is expensive to prepare, which deviates from the original intention of reducing substrate preparation costs through self-assembly.

[0036] This invention addresses the drawback of poor detection accuracy in traditional self-assembled SERS substrates by designing a self-assembled SERS substrate based on the light-concentrating properties of microspheres, such as... Figure 1 As shown, the SERS substrate includes a glass substrate, an array of microstructures, a noble metal thin film layer, and light-concentrating microspheres. The array of microstructures consists of polystyrene (PS) microspheres distributed on the surface of the glass substrate in a single layer of close arrangement. The noble metal thin film layer covers the surface of the array of microstructures, and the light-concentrating microspheres are distributed in a single layer of close arrangement on the surface of the noble metal thin film layer.

[0037] In some embodiments of this application, the glass substrate is a glass slide cut to a size of 5mm × 5mm.

[0038] In some embodiments of this application, the polystyrene microspheres have a particle size of 0.3–0.8 μm.

[0039] In some embodiments of this application, the noble metal thin film layer is divided into two layers, such as... Figure 1 As shown, it includes an upper layer and a lower layer; the upper layer is gold with a thickness of 50-60 nm; the lower layer is silver with a thickness of 50-60 nm.

[0040] In some embodiments of this application, the material of the light-concentrating microspheres is silicon dioxide, and the diameter of the spheres is 800-1000 nm.

[0041] This invention also provides a method for preparing the above-mentioned self-assembled SERS substrate based on the light-concentrating properties of microspheres, comprising the following steps:

[0042] Step 1: After ultrasonic cleaning and drying, a clean glass substrate is obtained;

[0043] Step 2: As Figure 2 As shown, a dispersion containing polystyrene microspheres was spin-coated onto a clean glass substrate to obtain an array-like microstructure formed by a single layer of polystyrene microspheres.

[0044] Step 3: Sputter a noble metal thin film layer onto the array-type microstructure using magnetron sputtering;

[0045] Step 4: Spin-coat a dispersion containing silica microspheres onto a noble metal thin film layer to obtain light-concentrating microspheres composed of a closely packed monolayer array of silica microspheres.

[0046] In some embodiments of this application, in step 1, the ultrasonic cleaning specifically involves using an ultrasonic cleaner to sequentially perform ultrasonic cleaning of the glass substrate using an acetone bath, an ethanol bath, and a deionized water bath.

[0047] In some embodiments of this application, in step 2, such as Figure 2 As shown, the preparation process of the dispersion containing polystyrene microspheres is as follows: after centrifuging the polystyrene microsphere solution, the supernatant is removed, and then sodium dodecyl sulfate (SDS) solution and deionized water (DI) are added to the centrifuge tube and mixed evenly to form a dispersion.

[0048] In some embodiments of this application, in step 2, the spin coating speed is 2000-4000 r / min and the time is 10-40 s.

[0049] In some embodiments of this application, in step 3, the noble metal thin film layer includes a lower 50-60 nm silver film and an upper 50-60 nm gold film; the magnetron sputtering current is 38-40 mA, and the magnetron sputtering time is 60-180 s.

[0050] In some embodiments of this application, in step 4, the preparation process of the dispersion containing silica microspheres specifically involves: centrifuging a silica microsphere solution with a microsphere size of 800–1000 nm, removing the supernatant, adding SDS solution to a centrifuge tube, and mixing evenly to form a dispersion; the spin coating speed is 2000–4000 r / min, and the time is 10–40 s.

[0051] The following detailed explanation is further illustrated with specific examples.

[0052] Example 1

[0053] This embodiment provides a SERS substrate based on the light-concentrating properties of microspheres, the structure of which is as follows: Figure 1 As shown, the SERS substrate is prepared using the following method, specifically including the following steps:

[0054] A polystyrene microsphere dispersion was spin-coated onto a 5mm × 5mm glass substrate to form a monolayer of tightly packed polystyrene microspheres, such as... Figure 2 Specifically, the process involves cutting a glass slide into several 5mm × 5mm squares. The glass substrate is then ultrasonically cleaned sequentially using an acetone bath, an ethanol bath, and a deionized water bath, with each cleaning session lasting 180 seconds. Simultaneously, 400 μL of a 2.5 wt% polystyrene microsphere solution with a microsphere size of 0.4 μm is centrifuged, and the supernatant is removed. Then, 50 μL of a 5 wt% SDS solution and 100 μL of DI water are added to the centrifuge tube and mixed thoroughly to form a PS microsphere dispersion. Finally, 2 μL of the PS microsphere dispersion is dropped onto a square glass substrate and spin-coated to prepare a single-layer PS microsphere array structure. Figure 3As shown; in the spin coating process, the rotation speed is 4000 r / min and the time is 20 s.

[0055] Two noble metal films were sputtered on the PS microsphere array obtained in step 1 using magnetron sputtering technology. The lower layer was a silver film and the upper layer was a gold film. The sputtering current was controlled at 38mA and the sputtering time was 60s. The thickness of the silver film and the gold film obtained were both about 50nm.

[0056] A silica microsphere dispersion was spin-coated onto a noble metal film to form a tightly packed monolayer silica microsphere array. Specifically, 400 μL of a 2.5 wt% silica microsphere solution with a microsphere size of 800 nm was centrifuged, the supernatant was removed, and then 50 μL of a 5 wt% SDS solution was added to the centrifuge tube and mixed thoroughly to form a silica microsphere dispersion. 3 μL of the silica microsphere dispersion was then dropped onto the noble metal film and spin-coated to prepare a monolayer silica microsphere array. The spin-coating process was performed at a speed of 2000 r / min for 20 s to complete the preparation of the SERS substrate. The final SERS substrate is shown below. Figure 4 As shown.

[0057] The SERS substrate based on the microsphere focusing properties prepared above was used to analyze 4-ATP solution samples: a 100 mM 4-ATP solution was prepared, and 5 μL of the solution was added dropwise to the prepared SERS substrate using a pipette, followed by drying; Raman spectroscopy was used for analysis, with a laser wavelength of 785 nm, a laser intensity of 2 mW, an integration time of 3 s, and 1 integration. Five points were randomly selected from the substrate to collect samples from a distance of 400 cm. -1 -1800cm -1 Raman spectra within the range, then averaged; such as Figure 5 The image shows the Raman spectrum of a 100 μM 4-ATP solution obtained from the prepared SERS substrate. Figure 5 As can be seen, the SERS substrate based on the light-concentrating properties of microspheres prepared in this embodiment has a good Raman signal enhancement effect.

[0058] Meanwhile, the noble metal thin film prepared in this embodiment and the noble metal thin film with an array-like microstructure were used as comparisons for SERS detection of the above-mentioned 4-ATP solution samples; the comparison results are as follows. Figure 6 As shown, by Figure 6 It is evident that the SERS substrate based on the light-concentrating properties of microspheres prepared in this invention exhibits excellent Raman enhancement. This indicates that the noble metal thin film substrate with an array-like microstructure inherently possesses a certain Raman enhancement effect, and the Raman enhancement effect is further improved after adding the light-concentrating microsphere structure.

[0059] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A SERS substrate based on the light-concentrating properties of microspheres, characterized in that, The SERS substrate comprises a glass substrate, an array-type microstructure, a noble metal thin film layer, and light-concentrating microspheres. The array-type microstructure is composed of polystyrene microspheres arranged in a single layer and tightly packed on the surface of the glass substrate. The noble metal thin film layer covers the surface of the array-type microstructure, and the light-concentrating microspheres are arranged in a single layer and tightly packed on the surface of the noble metal thin film layer. The polystyrene microspheres have a particle size of 0.3~0.8μm. The noble metal thin film layer consists of two layers: an upper layer and a lower layer. The upper layer is gold with a thickness of 50~60nm; the lower layer is silver with a thickness of 50~60nm. The light-concentrating microspheres are made of silicon dioxide with a diameter of 800~1000nm. The method for preparing the SERS substrate based on the light-concentrating properties of the microspheres includes the following steps: Step 1: After ultrasonic cleaning and drying, a clean glass substrate is obtained; Step 2: Spin-coat the dispersion containing polystyrene microspheres onto a clean glass substrate to obtain an array-like microstructure formed by a single layer of polystyrene microspheres; Step 3: Sputter a noble metal thin film layer onto the array-type microstructure using magnetron sputtering; Step 4: Spin-coat a dispersion containing silica microspheres onto a noble metal thin film layer to obtain light-concentrating microspheres composed of a closely packed monolayer array of silica microspheres.

2. The SERS substrate based on the light-concentrating properties of microspheres according to claim 1, characterized in that, The glass substrate is a glass slide.

3. A method for preparing a SERS substrate based on the light-concentrating properties of microspheres as described in any one of claims 1-2, characterized in that, Includes the following steps: Step 1: After ultrasonic cleaning and drying, a clean glass substrate is obtained; Step 2: Spin-coat the dispersion containing polystyrene microspheres onto a clean glass substrate to obtain an array-like microstructure formed by a single layer of polystyrene microspheres; Step 3: Sputter a noble metal thin film layer onto the array-type microstructure using magnetron sputtering; Step 4: Spin-coat a dispersion containing silica microspheres onto a noble metal thin film layer to obtain light-concentrating microspheres composed of a closely packed monolayer array of silica microspheres.

4. The method for preparing a SERS substrate based on the light-concentrating properties of microspheres according to claim 3, characterized in that, In step 1, the ultrasonic cleaning specifically involves using an ultrasonic cleaner to sequentially perform ultrasonic cleaning on the glass substrate using an acetone bath, an ethanol bath, and a deionized water bath for a certain period of time.

5. The method for preparing a SERS substrate based on the light-concentrating properties of microspheres according to claim 3, characterized in that, In step 2, the preparation process of the dispersion containing polystyrene microspheres is as follows: after centrifuging the polystyrene microsphere solution, the supernatant is removed, and sodium dodecyl sulfate solution and deionized water are added to the centrifuge tube and mixed evenly to form a dispersion.

6. The method for preparing a SERS substrate based on the light-concentrating properties of microspheres according to claim 3, characterized in that, In step 2, the spin coating speed is 2000~4000 r / min and the time is 10~40 s.

7. The method for preparing a SERS substrate based on the light-concentrating properties of microspheres according to claim 3, characterized in that, In step 3, the noble metal thin film layer includes a lower 50-60 nm silver film and an upper 50-60 nm gold film; the magnetron sputtering current is 38-40 mA and the magnetron sputtering time is 60-180 s.

8. The method for preparing a SERS substrate based on the light-concentrating properties of microspheres according to claim 3, characterized in that, In step 4, the preparation process of the dispersion containing silica microspheres is as follows: after centrifuging the silica microsphere solution with a particle size of 800~1000nm, the supernatant is removed, and sodium dodecyl sulfate solution is added to the centrifuge tube and mixed evenly to form a dispersion; the spin coating speed is 2000~4000r / min and the time is 10~40s.

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