Flexible SERS (Surface Enhanced Raman Scattering) substrate based on flexoelectric effect and preparation method thereof

Abstract

The invention belongs to the field of Raman detection, and relates to a flexible SERS (Surface Enhanced Raman Scattering) substrate based on a flexoelectric effect and a preparation method thereof. The flexible SERS substrate based on the flexoelectric effect comprises a polydimethylsiloxane substrate, and a barium titanate film, a barium ferrite film and a silver film which are sequentially arranged on the polydimethylsiloxane substrate from bottom to top. Barium titanate is sputtered onto a polydimethylsiloxane substrate through a magnetron sputtering film deposition system, barium ferrite and a silver film are sequentially sputtered after annealing, and the flexible SERS substrate based on the flexoelectric effect can be obtained through polarization. The flexible SERS substrate has the advantages of high SERS sensitivity, low cost, simple operation steps, long service life, good uniformity and repeatability and the like, and the structure can further promote application and popularization of SERS in practice. The preparation method of the flexible SERS substrate is simple, low in cost and easy for batch production.

Description

Technical Field

[0001] The present invention belongs to the field of Raman detection, relates to a Raman enhanced signal spectroscopy (SERS) substrate, and particularly relates to a flexible SERS substrate based on the flexoelectric effect and a preparation method thereof. Background Art

[0002] Surface-enhanced Raman spectroscopy (SERS) is a non-invasive fingerprint spectral information detection technology that can achieve specific identification of unique molecular structures and chemical groups within a substance. In the long-term SERS research, precious metal substrates (Au, Ag, Cu, etc.) have become a hotspot in the SERS field due to their excellent SERS enhancement effect. However, achieving ultra-sensitive SERS signal output depends on the stimulation of high-intensity hotspots, which requires an expensive and cumbersome manufacturing process. At the same time, the irreversible binding and denaturation of molecules at the hotspots are difficult to fundamentally solve, which greatly affects the accuracy of detection.

[0003] The flexoelectric effect is widely present in dielectric materials. When subjected to stress, these materials bend and deform unevenly, inducing electric polarization through changes in the material's strain gradient. This requires the material to be stretchable and stable, which is a good match for flexible SERS technology.

[0004] Barium ferrite (BaFe 12 O 19 ), a ferromagnetic dielectric material with extremely high flexoelectric coefficient and chemical stability, and existing technology has made it possible to prepare barium ferrite materials into functional films. Researchers have used the changes in its ferromagnetic state to enhance thermoelectric transmission performance, further effectively preventing the performance degradation of thermoelectric materials in the excitation region. Although barium ferrite (BaFe 12 O 19 ) films have been proven to have excellent electrical transmission properties, but no researchers have yet applied this type of flexoelectric effect material to the field of flexible SERS detection. Summary of the Invention

[0005] Based on the above, the present invention provides a novel, ultrasensitive, flexible SERS substrate based on the flexoelectric effect and its preparation method. The substrate is constructed from a composite silver film / barium ferrite / barium titanate / polydimethylsiloxane (Ag / BFO / BTO / PDMS) film layer. PDMS serves as a flexible underlying skeleton, effectively supporting the functional layer materials on the surface while also providing the substrate with ductility and elasticity. BTO, as a supporting membrane material, provides a surface and a stable structure for the functional layer BFO, which facilitates the generation of the flexoelectric polarization field within the BFO functional layer. During the preparation process, BTO, BFO, and Ag are sequentially sputtered onto the PDMS substrate using a magnetron sputtering thin film deposition system. After polarization, a high-quality Ag / BFO / BTO / PDMS flexible SERS substrate with co-directional polarization characteristics is obtained. This eliminates the tedious process of hotspot construction, as all materials are film-based. This strategy effectively reduces reliance on electromagnetic enhancement, relying on the interlayer flexoelectric polarization field to guide SERS enhancement while effectively ensuring uniform SERS signal output.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is a flexible SERS substrate based on the flexoelectric effect, which includes a polydimethylsiloxane-based sheet, and a barium titanate film, a barium ferrite film and a silver film arranged on the polydimethylsiloxane-based sheet from bottom to top.

[0008] The second technical solution of the present invention is a method for preparing the above-mentioned flexible SERS substrate based on the flexoelectric effect, comprising the following steps:

[0009] Depositing a layer of barium titanate film on the surface of the polydimethylsiloxane-based sheet, and then annealing to obtain an annealed BTO / PDMS substrate;

[0010] A barium ferrite film and a silver film are sequentially deposited on the barium titanate film surface of the annealed BTO / PDMS substrate, followed by polarization treatment to obtain the flexible SERS substrate based on the flexoelectric effect (i.e., Ag / BFO / BTO / PDMS flexible SERS substrate).

[0011] The third technical solution of the present invention is the application of the above-mentioned flexible SERS substrate based on the flexoelectric effect in the preparation of biosensors or chemical analysis detection instruments.

[0012] A fourth technical solution of the present invention is a SERS sensor comprising the above-mentioned flexible SERS substrate based on the flexoelectric effect.

[0013] A fifth technical solution of the present invention is a SERS sensing system, the above-mentioned SERS sensor.

[0014] The present invention discloses the following technical effects:

[0015] The Ag / BFO / BTO / PDMS flexible SERS substrate provided by the present invention has the advantages of high SERS sensitivity, low cost, simple operation steps, long substrate life, good uniformity and repeatability, etc. This structure can further promote the application and promotion of SERS in practice.

[0016] The preparation method of the flexible SERS substrate of the present invention is simple, low-cost and easy to mass-produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 Scanning electron microscope images of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1; wherein, (a) the cross-sectional morphology of the BFO / BTO / PDMS substrate, and (b) the surface morphology of the Ag / BFO / BTO / PDMS substrate.

[0019] Figure 2 This is the electrical signal spectrum of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1; among them, (a) the current-time curve under positive bending and (b) the current-time curve under negative bending.

[0020] Figure 3 Comparison of the Raman enhancement effects of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 on Rhodamine 6G molecules under different bending states.

[0021] Figure 4 Detection results of Pityrosporum using the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1.

[0022] Figure 5 Comparison of the Raman enhancement effects of the Ag / BFO / PDMS flexible SERS substrate prepared in comparative example 1 on Rhodamine 6G molecules under different bending states.

[0023] Figure 6 Comparison of the Raman enhancement effects of the Ag / BTO / PDMS flexible SERS substrate prepared in comparative example 2 on Rhodamine 6G molecules under different bending states.

[0024] Figure 7Comparison of the Raman enhancement effects of the Ag / PDMS flexible SERS substrate prepared in comparative example 3 on Rhodamine 6G molecules under different bending states.

[0025] Figure 8 Comparison of the Raman enhancement effects of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 on crystal violet molecules under different bending states.

[0026] Figure 9 Comparison of the Raman enhancement effects of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 on methylene blue molecules under different bending states.

[0027] Figure 10 The rhodamine 6G molecule on the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 is at 613 cm -1 Peak plane diagram at the characteristic peak. DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0031] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0032] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0033] A first aspect of the present invention provides a flexible SERS substrate based on the flexoelectric effect, comprising a polydimethylsiloxane-based sheet, and a barium titanate film, a barium ferrite film and a silver film sequentially arranged on the polydimethylsiloxane-based sheet from bottom to top.

[0034] In the present invention, polydimethylsiloxane (PDMS) is used as the bottom flexible skeleton, barium titanate (BTO) film is used as the supporting membrane base material, barium ferrite (BFO) film is used as the functional layer material, and silver film (Ag) is used as the surface layer material.

[0035] The flexible SERS substrate based on the flexoelectric effect of the present invention possesses flexoelectric polarization properties and is a composite film layer with flexoelectric effect. This flexible SERS substrate offers superior Raman enhancement while saving costs, significantly promoting the application of SERS substrates in various fields. The proposed strategy for developing a surface layer material (Ag / BFO / BTO) that combines the flexoelectric effect with the SERS field is groundbreaking.

[0036] In a preferred embodiment of the present invention, the thickness of the polydimethylsiloxane-based sheet is 1-3 mm; the thickness of the barium titanate film is 200-300 nm; the thickness of the barium ferrite film is 200-400 nm; and the thickness of the silver film is 20-50 nm.

[0037] The BFO film of the present invention exhibits the strongest flexoelectric effect at the optimal thickness described above. Excessive thickness can affect its conformability to the bending of the flexible PDMS matrix, while excessively low thickness can hinder its continuity, thus affecting Raman signal measurement. Only when the parameters fall within the ranges described in the present invention does the prepared substrate exhibit the most superior SERS effect.

[0038] A second aspect of the present invention provides a method for preparing the above-mentioned flexible SERS substrate based on the flexoelectric effect. First, BTO is sputtered onto a PDMS substrate using a magnetron sputtering thin film deposition system. After annealing, BFO and Ag are sputtered in sequence. After polarization, a high-quality Ag / BFO / BTO / PDMS flexible substrate with co-directional polarization characteristics can be obtained. The method specifically comprises the following steps:

[0039] Depositing a layer of barium titanate film on the surface of the polydimethylsiloxane-based sheet, and then annealing to obtain an annealed BTO / PDMS substrate;

[0040] A barium ferrite film and a silver film are sequentially deposited on the barium titanate film surface of the annealed BTO / PDMS substrate, followed by polarization treatment to obtain the flexible SERS substrate based on the flexoelectric effect (i.e., Ag / BFO / BTO / PDMS flexible SERS substrate).

[0041] In a preferred embodiment of the present invention, the deposition is specifically carried out by vacuum evaporation coating method, magnetron sputtering coating method or ion plating method.

[0042] In a preferred embodiment of the present invention, the annealing temperature is 70-100°C and the time is 60-120 minutes. Considering the Curie temperature of BTO material, the annealing temperature used in the present invention is relatively low, 70-100°C.

[0043] In a preferred embodiment of the present invention, the polarization treatment conditions are set as follows: voltage is 10 to 15 kV, and time is 60 to 120 minutes.

[0044] A third aspect of the present invention provides the use of the above-mentioned flexible SERS substrate based on the flexoelectric effect in the preparation of biosensors or chemical analysis detection instruments.

[0045] A fourth aspect of the present invention provides a SERS sensor comprising the above-mentioned flexible SERS substrate based on the flexoelectric effect.

[0046] A fifth aspect of the present invention provides a SERS sensing system, the above-mentioned SERS sensor.

[0047] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or are publicly available.

[0048] The polydimethylsiloxane (PDMS) used in the embodiments of the present invention is Dow Corning DC184, with a density of 0.965 g / mL and a curing temperature of 25-150°C. It is made of a colloid and a curing agent. The curing agent plays a cross-linking role in the PDMS colloid, causing the colloid to cure into an elastomer after heating.

[0049] The polarized power supply device used in the embodiment of the present invention is a high-voltage DC power supply purchased from Dongwen High Voltage Power Supply Co., Ltd.

[0050] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] 1. Preparation of PDMS substrate:

[0053] PDMS is made by mixing a colloid and a curing agent in a ratio of 1:9. The mixture is stirred thoroughly in a magnetic stirrer for 15 minutes and then refrigerated for 1 hour to eliminate bubbles. One milliliter of the mixture is dropped onto a 2 cm x 3 cm quartz template and homogenized at 1000 rpm three times. Then, another 1 ml of the mixture is added. The template is dried in a 60°C oven for 2 hours and then peeled off, resulting in a 2 cm x 3 cm PDMS substrate with a thickness of 2 mm.

[0054] 2. Preparation of BTO film:

[0055] The prepared PDMS substrate was placed in a magnetron sputtering thin film deposition system. The evaporation source used a barium titanate target with a purity of 99.9% and the vacuum was pumped to 3×10 -4 After adjusting the deposition pressure to 2.5 Pa, the pre-sputtering was performed at a power of 100 W for 30 s, and then a BTO film with a thickness of 220 nm was deposited on the clean and flat substrate to obtain a BTO / PDMS substrate.

[0056] 3. Annealing treatment:

[0057] The BTO / PDMS substrate was placed in an oven and heated at 80° C. for 60 minutes to obtain an annealed BTO / PDMS substrate.

[0058] 4. Preparation of Ag film and BFO functional layer:

[0059] The annealed BTO / PDMS substrate was placed in a magnetron sputtering thin film deposition system. The evaporation source used a 99.9% pure barium ferrite target and the vacuum was pumped to 3×10 -4 After adjusting the deposition pressure to 2.5 Pa, a pre-sputtering process was performed at 100 W for 30 seconds, followed by the deposition of a 300 nm thick BFO film on a clean, flat substrate. The evaporation source was then switched to 99.9% Ag, and the deposition pressure was adjusted to 1 Pa, resulting in a 40 nm thick Ag film on the substrate. This resulted in an Ag / BFO / BTO / PDMS composite.

[0060] 5. Polarization treatment to obtain Ag / BFO / BTO / PDMS flexible SERS substrate:

[0061] The Ag / BFO / BTO / PDMS obtained in step 4 was connected to a copper sheet and placed in the positive electrode of a polarized power supply device; the voltage was adjusted to 10 kV and continued for 60 minutes to obtain an Ag / BFO / BTO / PDMS flexible SERS substrate, that is, a flexible SERS substrate based on the flexoelectric effect.

[0062] Detection:

[0063] Figure 1This is a scanning electron microscope image of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 of the present invention. Figure 1 It can be seen that: (1) the film layers are clearly spaced, the BFO functional layers are evenly arranged without any breaks; (2) the surface Ag film has good connectivity.

[0064] Figure 2 This is the electrical signal diagram of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 of the present invention. Figure 2 It can be seen that the positive and negative bending states will cause current signals in different directions, that is, generate electric polarization fields in different directions.

[0065] Figure 3 Comparison of the Raman enhancement effect of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 of the present invention on the Rhodamine 6G molecule in different bending states (test method: using 1uM Rhodamine 6G as the probe molecule, comparing the Raman spectra of the normal state (i.e., unbent state), positive bending state, and negative bending state; the excitation laser is 532nm, and the integration time is 4s). Figure 3 It can be seen that the best SERS enhancement effect is achieved in the positive bending state.

[0066] The Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 was applied to the detection of Pityrosporum. The specific test method was as follows: first, 2 μL of PBS buffer containing Pityrosporum was added to the substrate. Then, the flexible substrate was fixed in a positive or negative bending state under a Raman microscope. The test was performed using a 532 nm laser with a power of 10%, an integration time of 4 s, and an integration number of 2. The results are shown in FIG. Figure 4 As shown by Figure 4 It can be seen that Pityrosporum is at 396cm -1 、1330cm -1 and 1592cm -1 It has obvious Raman characteristic peaks and obvious SERS enhancement effect in the positive bending state.

[0067] The Ag / BFO / BTO / PDMS flexible SERS substrates prepared in Examples 2-5 have similar performance to that of Example 1.

[0068] Comparative Example 1

[0069] The only difference from Example 1 is that step 2 is omitted, and the remaining steps and parameters are the same as those in Example 1; an Ag / BFO / PDMS flexible SERS substrate is prepared.

[0070] The flexible SERS substrate prepared in Comparative Example 1 was tested in the same manner as in Example 1. The results are as follows: Figure 5 As shown by Figure 5 It can be seen that the Ag / BFO / PDMS substrate still has the flexoelectric effect, but its effect is lower than that of the Ag / BFO / BTO / PDMS substrate.

[0071] Comparative Example 2

[0072] The only difference from Example 1 is that the preparation of the BFO film in step 4 is omitted, and the remaining steps and parameters are the same as those in Example 1; an Ag / BTO / PDMS flexible SERS substrate is prepared.

[0073] The flexible SERS substrate prepared in Comparative Example 2 was tested in the same manner as in Example 1. The results are shown in Figure 2. Figure 6 As shown by Figure 6 It can be seen that the enhancement effect of Ag / BTO / PDMS is much lower than that of Ag / BFO / PDMS and Ag / BFO / BTO / PDMS substrates.

[0074] Comparative Example 3

[0075] The only difference from Example 1 is that the preparation of the BFO film in step 2 and step 4 is omitted, and the remaining steps and parameters are the same as those in Example 1; an Ag / PDMS flexible SERS substrate is prepared.

[0076] The flexible SERS substrate prepared in Comparative Example 2 was tested in the same manner as in Example 1. The results are shown in Figure 2. Figure 7 As shown by Figure 7 It can be seen that the enhancement effect of the Ag / PDMS substrate is very weak and does not have good flexoelectric properties.

[0077] Figure 8 Comparison of the Raman enhancement effect of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 on crystal violet molecules under different bending states; Figure 8 It can be seen that for the crystal violet molecule, an enhancing effect is still exhibited in the positive bending state, and a weakening effect is exhibited in the negative bending state.

[0078] Figure 9 Comparison of the Raman enhancement effect of the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 on methylene blue molecules under different bending states; Figure 9 It can be seen that for methylene blue molecules, an enhancement effect is still shown in the positive bending state, and a weakening effect is shown in the negative bending state, which indicates the good universality of the Ag / BFO / BTO / PDMS flexible SERS substrate.

[0079] Figure 10The rhodamine 6G molecule on the Ag / BFO / BTO / PDMS flexible SERS substrate prepared in Example 1 is at 613 cm -1 Peak plane diagram at characteristic peak; Figure 10 It can be seen that the collected Raman signal is smooth, that is, the substrate has good uniformity.

[0080] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A flexible SERS substrate based on flexoelectric effect, characterized in that: The invention comprises a polydimethylsiloxane-based sheet, and a barium titanate film, a barium ferrite film and a silver film which are sequentially arranged on the polydimethylsiloxane-based sheet from bottom to top.

2. The flexible SERS substrate based on flexoelectric effect according to claim 1, characterized in that: The thickness of the barium titanate film is 200-300 nm; the thickness of the barium ferrite film is 200-400 nm; and the thickness of the silver film is 20-50 nm.

3. A method for preparing a flexible SERS substrate based on flexoelectric effect according to claim 1 or 2, characterized in that: The following steps are involved: Depositing a layer of barium titanate film on the surface of the polydimethylsiloxane-based sheet, and then annealing to obtain an annealed BTO / PDMS substrate; A barium ferrite film and a silver film are sequentially deposited on the surface of the barium titanate film of the annealed BTO / PDMS substrate, followed by polarization treatment to obtain the flexible SERS substrate based on the flexoelectric effect.

4. The method for preparing a flexible SERS substrate based on the flexoelectric effect according to claim 3, wherein: The deposition is specifically performed by vacuum evaporation coating method, magnetron sputtering coating method or ion plating method.

5. The method for preparing a flexible SERS substrate based on flexoelectric effect according to claim 3, wherein: The annealing temperature is 70-100° C., and the annealing time is 60-120 minutes.

6. The method for preparing a flexible SERS substrate based on flexoelectric effect according to claim 3, wherein: The polarization treatment conditions are set as follows: voltage is 10-15 kV, and time is 60-120 minutes.

7. Use of the flexible SERS substrate based on flexoelectric effect as claimed in claim 1 or 2 in the preparation of biosensors or chemical analysis detection instruments.

8. A SERS sensor, characterized in that: It comprises the flexible SERS substrate based on the flexoelectric effect as described in claim 1 or 2.

9. A SERS sensing system, characterized in that: The SERS sensor according to claim 8 is included.

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