Magnetoelectric composite SERS (Surface Enhanced Raman Scattering) substrate based on P (VDF-TrFE) as well as preparation method and application thereof

Abstract

The invention relates to the technical field of Raman detection, in particular to a P (VDF-TrFE)-based magnetoelectric composite SERS (Surface Enhanced Raman Scattering) substrate as well as a preparation method and application thereof. The preparation method comprises the following steps: uniformly mixing CoFe2O4 nanoparticles and graphene oxide powder with N, N-dimethylformamide, then adding P (VDF-TrFE) powder, and uniformly mixing to obtain a mixed solution; pouring the mixed solution onto the surface of a substrate, and then sequentially drying and annealing to obtain a CoFe2O4 / GO / P (VDF-TrFE) film; and depositing a silver nanoparticle array on the surface of the CoFe2O4 / GO / P (VDF-TrFE) thin film to obtain the P (VDF-TrFE)-based magnetoelectric composite SERS substrate. The SERS substrate disclosed by the invention is high in sensitivity and good in signal uniformity.

Description

Technical Field

[0001] The present invention belongs to the field of Raman detection technology, relates to a magnetic field induced Raman enhancement substrate, and in particular to a magnetoelectric composite SERS substrate based on P(VDF-TrFE) and a preparation method and application thereof. Background Art

[0002] Surface-enhanced Raman spectroscopy (SERS) has developed into a powerful detection and analysis technique, thanks to its specificity and highly sensitive detection of target molecules. Precious metal nanostructures such as gold, silver, and copper exhibit a strong SERS effect, making them a popular material for SERS substrate development. However, once a single precious metal substrate is prepared, its SERS performance is fixed and unadjustable, resulting in poor universality and hindering subsequent practical applications.

[0003] Piezoelectric materials can convert mechanical energy into electrical energy. Research has combined piezoelectric FF-PNTs with silver nanoparticles to create FF-PNTs / Ag composites, and has used piezoelectric SERS detection of 4-ABT molecules. The SERS signal from a bent substrate is over ten times higher than that from an extended substrate. However, mechanical deformation of these composite substrates during Raman testing can easily cause the laser to lose focus, hindering in situ SERS detection. Furthermore, the Raman signal enhancement factor needs to be further optimized. Therefore, the currently constructed FF-PNTs / Ag substrates are not suitable for use in complex environments. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the present invention proposes a magnetoelectric composite SERS substrate based on P(VDF-TrFE) and its preparation method and application. Among them, CoFe2O4 is a ferromagnetic material, and P(VDF-TrFE) is a ferroelectric material, which also has piezoelectric properties and has significant electrical output characteristics under the action of force. By applying an external magnetic field and utilizing the magnetoelectric coupling effect, the stress generated by CoFe2O4 acts on P(VDF-TrFE), changing the spontaneous polarization intensity of P(VDF-TrFE), thereby adjusting the localized surface plasmon resonance effect of surface Ag, and ultimately achieving a significant improvement in the SERS signal of adsorbed molecules. The long-distance application of the magnetic field will not affect the focusing of the incident laser, which is beneficial to in-situ SERS detection in a real environment.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE), comprising the following steps:

[0007] CoFe2O4 nanoparticles and graphene oxide powder (commercial GO powder) were mixed with N,N-dimethylformamide, and then P(VDF-TrFE) powder was added and mixed to obtain a mixed solution;

[0008] Casting the mixed solution onto a substrate surface, drying, and annealing the mixture to obtain a CoFe2O4 / GO / P(VDF-TrFE) thin film;

[0009] Silver nanoparticle arrays (AgNPs arrays) were deposited on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film to obtain the P(VDF-TrFE)-based magnetoelectric composite SERS substrate (i.e., Ag / CoFe2O4 / GO / P(VDF-TrFE)).

[0010] The second technical solution of the present invention is a magnetoelectric composite SERS substrate (abbreviated as: SERS substrate) based on P(VDF-TrFE) prepared according to the above preparation method.

[0011] The third technical solution of the present invention is a SERS sensor, comprising the above-mentioned magnetoelectric composite SERS substrate based on P(VDF-TrFE).

[0012] A fourth technical solution of the present invention is a SERS sensor system, comprising the above-mentioned SERS sensor.

[0013] The present invention discloses the following technical effects:

[0014] The present invention provides a magnetoelectric composite SERS substrate based on P(VDF-TrFE), which has an Ag / CoFe2O4 / GO / P(VDF-TrFE) composite structure, wherein CoFe2O4 nanoparticles generate stress on P(VDF-TrFE) under the action of a magnetic field, causing P(VDF-TrFE) to generate a piezoelectric potential, and the generated potential can regulate the SERS signal intensity; the large-area, high-quality, uniformly distributed AgNPs array provides stability for signal collection; an external magnetic field can regulate the SERS performance of the substrate without directly contacting the substrate, which is beneficial to in-situ signal enhancement; the SERS substrate of the present invention has high sensitivity and good signal uniformity.

[0015] The present invention adopts mature hydrothermal synthesis technology and vacuum thermal deposition technology, and has the advantages of low cost, simple operation, high repeatability and easy batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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.

[0017] Figure 1 This is a scanning electron microscope image of the SERS substrate prepared in Example 2.

[0018] Figure 2 This is the Fourier near-infrared transform spectrum of the SERS substrate prepared in Example 2.

[0019] Figure 3 This is the electrical signal of the SERS substrate prepared in Example 2.

[0020] Figure 4 This is the magnetic field response Raman spectrum of the SERS substrate prepared in Example 2.

[0021] Figure 5 In situ collected SERS spectra of dopamine molecules in aqueous solution when the SERS substrate prepared in Example 2 is subjected to magnetic field intensities of (a) 0 and (b) 700 Oe, respectively. DETAILED DESCRIPTION

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] Magnetoelectric thin films are unique materials that can effectively convert magnetic energy into electrical energy and have been widely used in medical prosthetics. However, current research has not yet applied magnetoelectric thin films to Raman spectroscopy to study the effect of applied magnetic fields on their SERS performance.

[0028] The first aspect of the present invention provides a method for preparing a magnetoelectric composite SERS substrate (magnetic field induced Raman enhancement substrate) based on P(VDF-TrFE), comprising the following steps:

[0029] CoFe2O4 nanoparticles and graphene oxide powder (commercial GO powder) were mixed with N,N-dimethylformamide, and then P(VDF-TrFE) powder was added and mixed to obtain a mixed solution;

[0030] Casting the mixed solution onto a substrate surface, drying, and annealing the mixture to obtain a CoFe2O4 / GO / P(VDF-TrFE) thin film;

[0031] Silver nanoparticle arrays (AgNPs arrays) are deposited on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film to obtain the P(VDF-TrFE)-based magnetoelectric composite SERS substrate.

[0032] In a preferred embodiment of the present invention, the mass ratio of the CoFe2O4 nanoparticles to the graphene oxide powder is (2-10):1; the mass ratio of the graphene oxide powder to the P(VDF-TrFE) powder is 1:100-150.

[0033] In the present invention, the mass ratio of CoFe2O4 nanoparticles and graphene oxide to P(VDF-TrFE) powder should not be too high, otherwise the transmittance of the substrate will be reduced, which is not conducive to in situ SERS detection.

[0034] In a preferred embodiment of the present invention, the mass volume ratio of the graphene oxide powder to the N,N-dimethylformamide is 10 mg:8.5 ml.

[0035] In a preferred embodiment of the present invention, the drying temperature is 60° C. and the drying time is 12 hours; and the annealing temperature is 120° C. and the drying time is 2 hours.

[0036] In a preferred embodiment of the present invention, the deposition method is evaporation, specifically vacuum evaporation coating, magnetron sputtering coating or ion plating; the thickness of the AgNPs array is 25nm. During evaporation, the evaporation source is a silver rake with a purity of 99.99%, and the vacuum is evacuated to 8×10 -6 After the current was controlled at a rate of Torr, a layer of AgNPs array was deposited on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film.

[0037] Before evaporating the AgNPs array on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film, a layer of AAO mask was covered on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film.

[0038] In a preferred embodiment of the present invention, the CoFe2O4 nanoparticles are prepared by a hydrothermal synthesis method. Specifically, the preparation method comprises the following steps:

[0039] Mixing the cobalt source and the iron source with ethylene glycol, and then adding sodium acetate and a stabilizer to obtain a precursor solution;

[0040] Performing a hydrothermal reaction on the precursor solution to obtain the CoFe2O4 nanoparticles;

[0041] The stabilizer is cetyltrimethylammonium bromide or polyethylene glycol.

[0042] In a preferred embodiment of the present invention, the cobalt source is cobalt dichloride hexahydrate; the iron source is ferric chloride hexahydrate; the ratio of the cobalt source, iron source, ethylene glycol, sodium acetate, and stabilizer is 2.5 mmol: 5 mmol: 40 ml: 3.6 g: 1 g; the hydrothermal reaction temperature is 200°C and the reaction time is 8 hours. After the hydrothermal reaction is completed, the product obtained by the hydrothermal reaction is further washed.

[0043] In the above preparation method, the mixing method is ultrasound, mechanical stirring or magnetic stirring; the present invention does not specifically limit the ultrasonic power, mechanical stirring or magnetic stirring speed, and the ultrasonic power and stirring speed commonly used by those skilled in the art can be used.

[0044] The second aspect of the present invention provides a P(VDF-TrFE)-based magnetoelectric composite SERS substrate (abbreviated as: SERS substrate) prepared according to the above preparation method.

[0045] The SERS substrate of the present invention comprises GO, CoFe2O4 nanoparticles, P(VDF-TrFE) and an AgNPs array, wherein GO and CoFe2O4 are embedded in the interior of the P(VDF-TrFE) film; and the AgNPs array is coated on the surface of the P(VDF-TrFE) film. The presence of CoFe2O4 / GO / P(VDF-TrFE) can effectively convert magnetic energy into electrical energy under the action of an external magnetic field, and the generated electric potential can regulate the SERS signal intensity. The large-area, high-quality, uniformly distributed AgNPs array provides stability for signal acquisition. The AgNPs array is adsorbed on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film, which can significantly enhance the sensitivity of SERS. The method of the present invention has a simple process, high repeatability, and is easy to mass-produce. It can provide an excellent Raman enhancement effect while saving costs, greatly promoting the application and promotion of SERS substrates in practice.

[0046] A third aspect of the present invention provides a SERS sensor comprising the above-mentioned P(VDF-TrFE)-based magnetoelectric composite SERS substrate.

[0047] A fourth aspect of the present invention provides a SERS sensor system, comprising the above-mentioned SERS sensor.

[0048] 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.

[0049] The commercial GO powder used in the examples of the present invention was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. with a purity of >99% and a density of 1.9 g / cm 3 .

[0050] The P(VDF-TrFE) powder used in the examples of the present invention was obtained from Beijing Inokai Technology Co., Ltd., and the TrFE content was 30 mol%.

[0051] The double-channel anodic aluminum oxide (AAO) mask used in the embodiment of the present invention has an aperture of 70 nm, a hole center distance of 125 nm, and a film thickness of 300 nm.

[0052] 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.

[0053] The "room temperature" mentioned in the present invention, unless otherwise specified, refers to 20-30°C.

[0054] Example 1

[0055] This embodiment provides a method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE), the steps are as follows:

[0056] (1) Preparation of CoFe2O4 nanoparticle precursor solution:

[0057] Using a 1 / 10,000 balance, weigh 2.5 mmol of cobalt dichloride hexahydrate and 5 mmol of ferric chloride hexahydrate into a container. Use a pipette to inject 40 ml of ethylene glycol into the container containing the mixed powder. The mixture is then magnetically stirred at room temperature for 1 hour. Then, 3.6 g of sodium acetate and 1 g of hexadecyltrimethylammonium bromide are added and stirring is continued for 4 hours to obtain a precursor solution.

[0058] (2) Transfer of precursor solution:

[0059] Use a pipette to transfer the precursor solution prepared in step (1) into a 50ml hydrothermal reactor.

[0060] (3) Heat treatment to obtain CoFe2O4 nanoparticles:

[0061] The hydrothermal reactor from step (2) was placed in a thermostat and heated to 200°C, where it was maintained at that temperature for 8 hours. The thermostat was then naturally cooled to room temperature. The black powder was removed from the hydrothermal reactor and washed three times with ethanol and then with deionized water, respectively, to obtain CoFe2O4 nanoparticles.

[0062] (4) Preparation of CoFe2O4 / GO / P(VDF-TrFE) thin film:

[0063] Weigh 10 mg of commercial GO powder and 20 mg of CoFe2O4 nanoparticles obtained in step (3) using a 1 / 10,000 balance and place them in a container. Use a pipette to take 8.5 ml of N,N-dimethylformamide and inject it into the container containing the mixed powder. Then, ultrasonicate the mixture for 2 hours at room temperature, then add 1 g of P(VDF-TrFE) powder, and ultrasonicate and mechanically stir for 2 hours and 8 hours at room temperature, respectively, to obtain a uniform mixed solution. Pour 1 mL of the mixed solution into a 1×1 cm 2 The surface of the silicon wafer was placed in a constant temperature oven and dried at 60°C for 12 hours, and then annealed at 120°C for 2 hours to crystallize the film to obtain a CoFe2O4 / GO / P(VDF-TrFE) thin film.

[0064] (5) Preparation of Ag / CoFe2O4 / GO / P(VDF-TrFE) thin film:

[0065] The surface of the CoFe2O4 / GO / P(VDF-TrFE) film obtained in step (4) was covered with a double-channel anodic aluminum oxide (AAO) mask. It was then placed in a vacuum thermal evaporation coating device. The evaporation source used a silver rake with a purity of 99.99%. The vacuum was evaporated to 8×10 -6 After evaporation at a controlled current rate of Torr, a layer of silver with a thickness of about 25 nm was deposited on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film. AAO was removed using high-temperature tape to finally obtain a magnetoelectric composite SERS substrate based on P(VDF-TrFE), which was denoted as Ag / CoFe2O4 / GO / P(VDF-TrFE).

[0066] Example 2

[0067] The only difference from Example 1 is that the amount of CoFe2O4 nanoparticles added in step (4) is 50 mg, and the remaining steps and parameters are the same as those in Example 1.

[0068] Example 3

[0069] The only difference from Example 1 is that the amount of CoFe2O4 nanoparticles added in step (4) is 100 mg, and the remaining steps and parameters are the same as those in Example 1.

[0070] Comparative Example 1

[0071] The only difference from Example 2 is that the addition of 10 mg of commercial GO powder in step (4) is omitted, and the remaining steps and parameters are the same as those in Example 2. Figure 2 It can be seen that compared with the SERS substrate with 10 mg of commercial GO powder added in Example 2, when 10 mg of commercial GO powder is not added, the SERS substrate at 850, 1288 and 1400 cm -1 The absorption peak at α is weaker, indicating a lower piezoelectric phase content.

[0072] Figure 1 The scanning electron microscope image of the SERS substrate prepared in Example 2 shows that a large area of ​​uniform AgNPs array is tightly attached to the surface of the CoFe2O4 / GO / P(VDF-TrFE) film. The average diameter of the AgNPs is about 75 nm, showing a uniform size distribution within the range of 75±0.2 nm.

[0073] Figure 2 This is the Fourier near-infrared transform spectrum of the SERS substrate prepared in Example 2, at 773 cm -1 The low α-phase absorption peaks at 850, 1288, and 1400 cm -1 The high β-phase absorption peak at 100 nm proves that the substrate has strong piezoelectric properties.

[0074] Figure 3 The electrical signal of the SERS substrate prepared in Example 2, with a current response of up to 20 nA, further proves that the substrate can generate excellent electrical output under the action of an external magnetic field.

[0075] Figure 4 The magnetic field response Raman spectrum of the SERS substrate prepared in Example 2 proves that the SERS signal of the adsorbed molecules can be further enhanced under the action of an external magnetic field.

[0076] Figure 5 The SERS spectra of dopamine molecules in aqueous solution collected in situ for the SERS substrate prepared in Example 2 at magnetic field strengths of (a) 0 and (b) 700 Oe, respectively. When a magnetic field of 700 Oe is applied, the detection limit of the substrate for dopamine is reduced to 10 - 6 M, showing the great development potential of magnetic field-assisted SERS enhancement technology in the field of sensitive detection of neurotransmitters in situ.

[0077] 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 method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE), characterized in that: The following steps are involved: CoFe2O4 nanoparticles and graphene oxide powder were mixed with N,N-dimethylformamide, and then P(VDF-TrFE) powder was added and mixed to obtain a mixed solution; Casting the mixed solution onto a substrate surface, drying, and annealing the mixture to obtain a CoFe2O4 / GO / P(VDF-TrFE) thin film; A silver nanoparticle array is deposited on the surface of the CoFe2O4 / GO / P(VDF-TrFE) film to obtain the P(VDF-TrFE)-based magnetoelectric composite SERS substrate.

2. The method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE) according to claim 1, characterized in that: The mass ratio of the CoFe2O4 nanoparticles to the graphene oxide powder is (2-10):1; the mass ratio of the graphene oxide powder to the P(VDF-TrFE) powder is 1:100-150.

3. The method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE) according to claim 1, characterized in that: The mass volume ratio of the graphene oxide powder to the N,N-dimethylformamide is 10 mg: (5-10) ml.

4. The method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE) according to claim 1, characterized in that: The drying temperature is 50-60° C. and the time is 12 hours; the annealing temperature is 100-120° C. and the time is 2 hours.

5. The method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE) according to claim 1, characterized in that: The deposition is specifically carried out by vacuum evaporation coating method, magnetron sputtering coating method or ion plating method; the thickness of the silver nanoparticle array is 25nm.

6. The method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE) according to claim 1, characterized in that: The preparation method of the CoFe2O4 nanoparticles comprises the following steps: Mixing the cobalt source and the iron source with ethylene glycol, and then adding sodium acetate and a stabilizer to obtain a precursor solution; Performing a hydrothermal reaction on the precursor solution to obtain the CoFe2O4 nanoparticles; The stabilizer is cetyltrimethylammonium bromide or polyethylene glycol.

7. The method for preparing a magnetoelectric composite SERS substrate based on P(VDF-TrFE) according to claim 6, characterized in that: The cobalt source is cobalt dichloride hexahydrate; the iron source is ferric chloride hexahydrate; the ratio of the cobalt source, iron source, ethylene glycol, sodium acetate and stabilizer is 2.5mmol:5mmol:40ml:3.6g:1g; the temperature of the hydrothermal reaction is 200°C and the time is 8 hours.

8. A magnetoelectric composite SERS substrate based on P(VDF-TrFE) prepared according to the preparation method according to any one of claims 1 to 7.

9. A SERS sensor, characterized in that: Including the P(VDF-TrFE)-based magnetoelectric composite SERS substrate as described in claim 8.

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

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