Synergistic enhanced SERS substrate as well as preparation method and application thereof

Abstract

The invention provides a micro optical fiber-metal nanoparticle-two-dimensional material synergistically enhanced SERS (Surface Enhanced Raman Scattering) substrate, and belongs to the field of nano materials and the field of Raman spectrum detection. The synergistically-enhanced Raman-enhanced substrate provided by the invention is composed of a micro-optical fiber on which a two-dimensional material grows and surface-deposited metal nanoparticles. The preparation method of the substrate comprises the following steps: growing the two-dimensional material on the surface of the drawn micro-optical fiber by using a chemical vapor deposition method. Charge transfer between the two-dimensional material and to-be-detected molecules can realize chemical enhancement of Raman signals. According to the present invention, the micro-optical fiber is adopted to regulate the local plasmon of the metal nanoparticles so as to achieve the electromagnetic enhancement of the Raman signal of the molecule to be detected, and the micro-optical fiber is adopted as the growth carrier of the two-dimensional material so as to increase the interaction between the two-dimensional material and the signal light, such that the strong chemical enhancement effect is obtained; the Raman enhanced substrate is low in cost and good in enhancement effect, and has important application value in the fields of analytical chemistry, nano materials, Raman spectrum detection and the like.

Description

Technical Field

[0001] The present invention relates to a Raman enhancement substrate, specifically to a SERS substrate with synergistic enhancement of microfiber-metal nanoparticles-two-dimensional materials, belonging to the fields of nanomaterials and Raman spectroscopy detection. Background Art

[0002] Raman spectroscopy is an important modern spectroscopic technique. Its excellent analytical performance of being fast, simple, repeatable, non-destructive, and qualitative and quantitative makes it a powerful tool for analyzing and studying molecular structures and configurations, determining the symmetry of crystal structures, studying defects and impurities in solids, environmental pollutants, biomolecules, and the microstructures of industrial materials. However, the Raman spectral lines are weak, which limits its application. Surface Enhanced Raman Scattering (SERS) was first discovered by Fleishmann et al. in 1974 and is divided into two types: electromagnetic enhancement and chemical enhancement. The principle of electromagnetic enhancement is that when the frequency of the incident light is close to the surface plasmon frequency of the metal and the light intensity is strong enough, localized surface plasmons (LSPs) will be generated on the metal surface, causing the light intensity to reach a very high value near the particle surface, thereby significantly enhancing the intensity of Raman scattering. Chemical enhancement is the enhancement generated by charge transfer between the substrate and the molecule to be detected, and its enhancement factor is relatively weak. Generally, physical enhancement plays a major role, but the contribution of chemical enhancement is also indispensable. The discovery of this technology solves the problem of weak Raman scattering spectral lines and is widely used in various fields such as biomedicine and environmental detection.

[0003] In recent years, the surface-enhanced Raman scattering (SERS) technology has developed rapidly, and various SERS substrates have been invented. To date, the SERS technology has been relatively mature, and there are already Raman enhancement substrates capable of detecting single molecules. The problem faced by the current SERS technology is that it is difficult to achieve sufficient high SERS enhancement solely relying on chemical enhancement, and a high enhancement factor of electromagnetic enhancement is required. Electromagnetic enhancement mainly comes from the local surface plasmons resonance (LSPR) of metal nanoparticles or nanostructures. The intensity of LSPR is the strongest between adjacent metal nanoparticles or at the vertices of sharp metal nanostructures, which is called "hot spots". Increasing the density of "hot spots" is an effective way to enhance the electromagnetic enhancement effect. To obtain a sufficient number of "hot spots", a large amount of metal nanoparticles or metal nanostructures need to be used, resulting in a relatively high manufacturing cost of the SERS substrate. For example, the SERS chip fabricated with a large amount of gold nanoparticles and aged gold nanowires in Patent CN119534425A, and the SERS substrate fabricated by adsorbing a large amount of silver nanoparticles on an organic material framework in Patent CN119470392A, etc. Therefore, there is a need for a Raman enhancement substrate with low cost and strong enhancement effect. Summary of the Invention

[0004] To solve the above problems, the purpose of the present invention is to provide a SERS substrate with synergistic enhancement of microfiber-metal nanoparticles-two-dimensional materials.

[0005] The present invention provides a SERS substrate with synergistic enhancement of microfiber-metal nanoparticles-two-dimensional materials, having the following characteristics: the SERS substrate with synergistic enhancement of microfiber-metal nanoparticles-two-dimensional materials comprises a microfiber, a monolayer two-dimensional material grown on the surface of the microfiber, and metal nanoparticles adsorbed on the surface of the monolayer two-dimensional material.

[0006] The cross-section of the microfiber can be regarded as a whispering gallery microcavity. Through the strong coupling between the microfiber whispering gallery microcavity and metal nanoparticles, the local surface plasmons of the metal nanoparticles can be regulated, reducing the linewidth of the scattering spectrum of the local surface plasmons and increasing the peak intensity, and electromagnetic enhancement of the Raman signal of the molecule to be detected can be achieved. Using the microfiber as the substrate for growing two-dimensional materials can modulate their optoelectronic properties. With the help of evanescent wave coupling technology, the interaction intensity between the two-dimensional material and the signal light can be increased. At the same time, the micron-scale size of the microfiber gives it extremely high flexibility, making it convenient to be integrated into complex optical systems, and the microfiber is simple to prepare and has a low cost. Therefore, using the microfiber as the substrate for growing two-dimensional materials and transferring gold nanoparticles onto the surface of the grown two-dimensional materials can combine the chemical enhancement brought by the two-dimensional materials with the electromagnetic enhancement of the surface plasmons brought by the metal nanoparticles for synergistic enhancement. Under the action of the above factors, a relatively high SERS enhancement effect can be obtained with only a single metal nanoparticle, which not only improves the SERS signal intensity but also enhances the stability and reproducibility of the SERS substrate, and greatly reduces the cost of the SERS substrate.

[0007] The present invention also provides a preparation method for a SERS substrate with synergistic enhancement of microfiber-metal nanoparticles-two-dimensional materials, mainly including the following steps:

[0008] S1: Microfiber preparation: Cut a section of standard single-mode quartz fiber, use a wire stripper to remove the coating of a part of the quartz fiber, and clean the part where the coating is removed with an alcohol cotton swab; after using a heat source to heat and remove the coating part, stretch both ends of the fiber, and the heated part will gradually become thinner until it breaks. By adjusting the stretching speed and heating time, the required microfiber is pulled out;

[0009] S2: Growing a single layer of two-dimensional material on the surface of the microfiber:

[0010] S21: Dip the microfiber prepared in step S1 into a transition metal salt solution and then put it into the quartz tube of a tube furnace. Connect a washing bottle filled with a liquid-phase sulfur source to the inlet end of the quartz tube. When argon is introduced into the inlet end of the washing bottle, the liquid-phase sulfur source in the washing bottle can be brought into the quartz tube from the inlet end of the quartz tube by the argon;

[0011] S22: Seal both ends of the quartz tube, check the airtightness of the quartz tube and the washing bottle, and evacuate the inside of the quartz tube and the washing bottle to vacuum;

[0012] S23: Open the inlet end of the quartz tube, introduce argon into the inlet end of the washing bottle until the air pressure in the quartz tube is 0.9 mPa - 1.1 mPa, then open the outlet end of the quartz tube, continue to introduce argon into the washing bottle and let it flow out from the outlet end of the quartz tube to keep the air pressure in the quartz tube within the range of 0.9 mPa - 1.1 mPa. The tube furnace is heated to 800 °C - 900 °C at a rate of 15 °C / min - 25 °C / min, held for 8 min - 10 min, and then cooled naturally to obtain a single-layer two-dimensional material grown on the surface of the microfiber;

[0013] S3: Spot-apply metal nanoparticles: Fix the microfiber with the grown single-layer two-dimensional material on the fiber fixing rack and tighten it, and spot-apply the metal nanoparticles onto the surface of the microfiber with a pipette to form a synergistic Raman enhancement substrate.

[0014] In step S1, the diameter of the pulled microfiber is 1 μm - 5 μm.

[0015] In step S2, the liquid-phase sulfur source is dodecanethiol, and the transition metal salt solution is sodium molybdate solution; the flow rate of the introduced argon is 40 sccm - 60 sccm.

[0016] In step S2, the microfiber is subjected to plasma treatment for 30 s - 60 s before being dipped into the transition metal salt solution to improve the hydrophilicity of the microfiber surface.

[0017] In step S2, after the microfiber is dipped into the transition metal salt solution, it is placed in the quartz tube of the tube furnace. Specifically: Place the microfiber dipped in the transition metal salt solution at the bottom of an inverted alumina boat, and then press a glass sheet above the microfiber to form a microfiber placement device, and place the microfiber placement device in the quartz tube.

[0018] In step S3, the metal nanoparticles are gold nanospheres with a diameter of about 80 nm.

[0019] After the substrate prepared by the present invention is immersed in the solution of the substance to be measured, the charge transfer between the two-dimensional material and the substance to be measured and the local surface plasmon of the metal nanoparticles can achieve synergistic Raman enhancement.

[0020] Functions and effects of the invention

[0021] According to the method provided by the present invention, after growing a two-dimensional material on the surface of the drawn microfiber, metal nanoparticles are transferred onto the surface of the two-dimensional material, and a Raman enhancement substrate with a synergistic enhancement effect can be fabricated. The microfiber can regulate the local surface plasmons of the metal nanoparticles, thereby achieving electromagnetic enhancement of the Raman signals of the molecules to be detected. At the same time, the microfiber serves as a growth carrier for the two-dimensional material, increasing the interaction between the two-dimensional material and the signal light, and obtaining a stronger chemical enhancement effect. The method of the present invention is simple and low-cost, combining the chemical enhancement brought by the two-dimensional material and the electromagnetic enhancement of the surface plasmons brought by the metal nanoparticles to form a synergistic enhancement, overcoming the problems of unstable electromagnetic enhancement alone and poor enhancement effect of chemical enhancement alone, and having broad application prospects in the field of nanomaterials and Raman spectroscopy detection. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of the present invention.

[0023] Figure 2 It is a diagram of the two-dimensional material growth device of the present invention.

[0024] Figure 3 It is a schematic diagram of the microfiber placement device in the present invention.

[0025] Figure 4 It is an optical microscope photograph of a monolayer molybdenum disulfide sheet on the microfiber.

[0026] Figure 5 It is an SEM photograph of the metal nanoparticles on the surface of the monolayer molybdenum disulfide on the microfiber.

[0027] Figure 6 It is the Raman scattering spectrum of the monolayer molybdenum disulfide sheet on the microfiber.

[0028] Figure 7 It is the photoluminescence spectrum of the monolayer molybdenum disulfide sheet on the microfiber.

[0029] Figure 8 It is a comparison of the Raman enhancement effects of molybdenum disulfide achieved after placing metal nanoparticles on the monolayer molybdenum disulfide sheet on the microfiber.

[0030] Figure 9 It is a comparison of the Raman enhancement effects of the Raman enhancement substrate composed of the microfiber-metal nanoparticle composite structure and the two-dimensional material on the R6G fluorescent dye.

[0031] Description of the reference numerals: 1 - microfiber, 2 - metal nanoparticles, 3 - two-dimensional material, 4 - glass slide, 5 - alumina boat, 6 - wash bottle, 7 - quartz tube, 8 - tube furnace Detailed Embodiments

[0032] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The raw materials, reagents or devices used in the embodiments and comparative examples can be obtained from conventional commercial channels or by existing technical methods without special instructions. Unless otherwise specified, the test or measurement methods are conventional methods in this field.

[0033] Figure 1 This is a schematic diagram of the present invention. On the microfiber 1, two-dimensional material 3 grows on the surface, and metal nanoparticles 2 are placed on the surface of the two-dimensional material 3. Through the synergistic effect of the electromagnetic enhancement of the localized surface plasmon of the metal nanoparticles regulated by the microfiber and the chemical enhancement of the two-dimensional material, a Raman enhancement substrate with synergistic enhancement of the microfiber-metal nanoparticle composite structure and the two-dimensional material is obtained.

[0034] Figure 2 This is a diagram of the two-dimensional material growth device of the present invention. First, the microfiber is subjected to plasma treatment for about 60 s to improve its surface performance, and then the microfiber is immersed in a sodium molybdate solution of 1.46 mg / ml -1 . Four microfibers 1 are placed at a certain interval at the bottom of the inverted alumina boat 5, so that the tip of the microfiber 1 extends out about 2 mm. A glass sheet 4 is placed on the microfiber 1 for fixation to form a microfiber placement device. The fiber placement device is placed in the quartz tube 7 of the tube furnace 8. A washing bottle 6 filled with 1-dodecanethiol is connected to one end of the quartz tube 7 through which gas is introduced. When argon is introduced into the washing bottle 6 from the inlet end of the washing bottle 6, the argon can bring the liquid-phase sulfur source in the washing bottle 6 into the quartz tube 7 from the inlet end of the quartz tube 7. After all the experimental raw materials and equipment are placed, the two ends of the quartz tube 7 are sealed, the airtightness of the quartz tube 7 and the washing bottle 6 is checked, and the inside of the quartz tube 7 and the washing bottle 6 is pumped to vacuum; then the inlet end of the quartz tube 7 is opened, argon is introduced from the inlet end of the washing bottle 6, the argon flow rate is 200 sccm until the pressure in the quartz tube 7 is 1 mPa, then the outlet end of the quartz tube 7 is opened, and argon is continuously introduced into the washing bottle 6 and vented from the outlet end of the quartz tube 7; subsequently, the introduced argon gas flow is adjusted to 40 sccm, and the vented gas volume is adjusted to keep the pressure in the quartz tube 7 at 1 mPa. The tube furnace 8 is heated to 840 °C at a rate of 20 °C / min and maintained at 840 °C for 60 min. During this process, molybdenum disulfide is deposited on the surface of the microfiber 1. The tube furnace 8 is turned off and cooled naturally. When the temperature drops to room temperature, the fiber is taken out to obtain a fiber with molybdenum disulfide on its surface.

[0035] As Figure 3 shown, the microfiber 1 is placed at the bottom of the inverted alumina boat 5, and a glass sheet 4 is placed above the microfiber 1 for fixation.

[0036] As Figure 4As shown in the figure, the light-colored area in the figure is molybdenum disulfide grown on the surface of the optical fiber. This indicates that the molybdenum disulfide on the optical fiber with molybdenum disulfide on its surface prepared by this embodiment is clearly visible, indicating that this method has successfully achieved the growth of monolayer molybdenum disulfide on the surface of the optical fiber.

[0037] As Figure 5 shown, the figure shows metal nanoparticles placed on the surface of the microfiber.

[0038] As Figure 6 shown, the figure shows Figure 4 the Raman spectrum of molybdenum disulfide in 1 , and the spacing between the in-plane vibration peak and the out-of-plane vibration peak is less than 20 cm-

[0039] Figure 7 This is the photoluminescence spectrum of the monolayer molybdenum disulfide sheet on the microfiber. The position of its emission peak is at 694 nm and the emission is strong, indicating that the molybdenum disulfide grown on the surface of the optical fiber is monolayer.

[0040] According to the method for growing monolayer two-dimensional materials on the surface of an optical fiber involved in this embodiment, the drawn microfiber is placed in a tube furnace and adjusted to a suitable growth program, and large-area and high-quality two-dimensional materials can be synthesized on the surfaces of microfibers with different diameters. The preparation method of this embodiment is simple and low-cost, and two-dimensional materials can be grown on the surfaces of microfibers with diameters ranging from 1 μm to 5 μm. The surface quality of the two-dimensional materials on the prepared microfibers is good, and it has important potential application values in the fields of nonlinear optics, optoelectronics, etc.

[0041] Figure 8 This is the comparison of the Raman enhancement effect achieved after placing metal nanoparticles on the monolayer molybdenum disulfide sheet on the microfiber. After placing the metal nanoparticles, affected by the electromagnetic enhancement of the local surface plasmons brought by the metal nanoparticles, the intensity of the Raman peak of molybdenum disulfide is enhanced.

[0042] Figure 9 This is the comparison of the Raman enhancement effect of the Raman enhancement substrate composed of the microfiber-metal nanoparticle composite structure and two-dimensional materials on the R6G fluorescent dye. The Raman enhancement substrate is immersed in the diluted R6G fluorescent dye solution. Only chemical enhancement can be obtained at the molybdenum disulfide without metal nanoparticles, while synergistic enhancement can be obtained at the molybdenum disulfide with metal nanoparticles. It can be seen that the Raman peak after synergistic enhancement is significantly higher than the Raman peak of chemical enhancement.

[0043] Functions and effects of the embodiment

[0044] The Raman enhancement substrate synergistically enhanced by microfiber-metal nanoparticles-2D materials prepared according to this embodiment grows 2D materials on the surface of the microfiber and then transfers metal nanoparticles onto the 2D materials. The preparation method of this embodiment is simple and low-cost. Under the regulation of the strong evanescent field of the micro-nano fiber, the synergistic effect of the electromagnetic enhancement brought by metal nanoparticles and the chemical enhancement brought by 2D materials enables a single gold nanoparticle to also have sufficient Raman enhancement effect, greatly reducing the production cost and having broad application prospects in the field of nanomaterials and the field of Raman spectroscopy detection.

Claims

1. A synergistically enhanced SERS substrate, characterized in that, Including: A microfiber, which serves as a substrate to support and promote the growth of two-dimensional materials, so as to enhance the interaction between the two-dimensional materials and the signal light; A single-layer two-dimensional material, which grows on the surface of the microfiber to provide a chemical enhancement effect; Metal nanoparticles, which are uniformly adsorbed on the surface of the single-layer two-dimensional material, and whose local surface plasmon resonance is regulated by the microfiber to achieve electromagnetic enhancement of the Raman signal of the molecule to be detected; Wherein, the chemical enhancement effect of the two-dimensional material is combined with the electromagnetic enhancement effect of the metal nanoparticles, which improves the SERS signal intensity and also enhances the stability and reproducibility of the SERS substrate.

2. A preparation method of a synergistically enhanced SERS substrate, characterized in that, It mainly includes the following steps: S1: Microfiber preparation: Cut a section of standard single-mode quartz fiber, use a wire stripper to remove the coating of a part of the quartz fiber, and clean the part without the coating with an alcohol swab; after using a heat source to heat and remove the coating part, stretch both ends of the fiber, and the heated part will gradually become thinner until it breaks. By adjusting the stretching speed and heating time, the required microfiber is pulled out; S2: Growth of a single-layer two-dimensional material on the surface of the microfiber: S21: After dipping the microfiber prepared in step S1 into a transition metal salt solution and then putting it into the quartz tube of a tube furnace, connect a washing bottle filled with a liquid-phase sulfur source to the inlet end of the quartz tube. When argon is introduced into the inlet end of the washing bottle, the liquid-phase sulfur source in the washing bottle can be brought into the quartz tube from the inlet end of the quartz tube by argon; S22: Seal both ends of the quartz tube, check the airtightness of the quartz tube and the washing bottle, and evacuate the inside of the quartz tube and the washing bottle to vacuum; S23: Open the inlet end of the quartz tube, introduce argon into the inlet end of the washing bottle until the air pressure in the quartz tube is 0.9 mPa - 1.1 mPa, then open the outlet end of the quartz tube, continue to introduce argon into the washing bottle and let it flow out from the outlet end of the quartz tube, so that the air pressure in the quartz tube is kept within the range of 0.9 mPa - 1.1 mPa. The tube furnace is heated to 800 °C - 900 °C at a rate of 15 °C / min - 25 °C / min, held for 8 min - 10 min, and cooled naturally, thus obtaining a single-layer two-dimensional material grown on the surface of the microfiber; S3: Spot coating of metal nanoparticles: Fix the microfiber with a single-layer two-dimensional material grown on it on a fiber fixing rack and tighten it, and spot coat the metal nanoparticles onto the surface of the microfiber with a pipette gun to form a synergistic Raman enhancement substrate.

3. The preparation method of a synergistically enhanced SERS substrate according to claim 2, characterized in that, In step S1, the diameter of the prepared microfiber is 1 μm - 5 μm.

4. The preparation method of a synergistically enhanced SERS substrate according to claim 2, wherein, In step S2, the liquid-phase sulfur source is dodecanethiol, the transition metal salt solution is sodium molybdate solution, and the flow rate of the introduced argon is 40 sccm - 60 sccm.

5. The preparation method of a synergistically enhanced SERS substrate according to claim 2, wherein, In step S2, before dipping the microfiber into the transition metal salt solution, it also includes a step of plasma treating the microfiber for 30 s - 60 s to improve the hydrophilicity of the microfiber surface.

6. The preparation method of a synergistically enhanced SERS substrate according to claim 2, characterized in that, In step S2, after the microfiber is dipped into the transition metal salt solution, it is placed into the quartz tube of the tube furnace. Specifically, the microfiber dipped with the transition metal salt solution is placed at the bottom of an inverted alumina boat, and then a piece of glass is pressed above the microfiber to form a microfiber placement device, and the microfiber placement device is placed into the quartz tube of the tube furnace.

7. The preparation method of a synergistically enhanced SERS substrate according to claim 2, wherein, In step S3, the metal nanoparticles are gold nanospheres with a diameter of about 80 nm.

8. Application of the SERS substrate prepared by the preparation method of a synergistically enhanced SERS substrate according to any one of claims 2-7 in Raman spectroscopy detection.

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