Optical feedback device and method for SERS detection based on hollow fiber

Abstract

This invention relates to an optical feedback device and method for SERS detection based on hollow optical fiber, belonging to the field of optical detection technology. It includes a hollow optical fiber device with an internally coated SERS structure and a solid optical fiber with a metal film at its end face for feedback. The solid optical fiber with the metal reflective film at its end face is coaxially nested within the hollow optical fiber with the internally coated SERS structure and can slide within it. The metal reflective film at the end face of the solid optical fiber is perpendicular to the axial direction and located within the hollow optical fiber with the internally coated SERS structure. Using this device to detect trace substances in liquid environments can reduce secondary pollution to the detection environment and can also perform three-dimensional Raman excitation and signal collection for trace substances widely distributed in liquid environments, providing a new technical method for the detection of pollutants in environmental water.

Description

Technical Field

[0001] This invention belongs to the field of nanophotonic device technology for environmental engineering and sensor technology. It constructs a spatial Raman spectroscopy feedback mechanism and structure to achieve bulk excitation and collection of Raman spectra, significantly enhancing the intensity of Raman spectral signals, thereby improving the detection sensitivity of target substances in liquids and providing a new technical method for the detection of pollutants in environmental water. Background Technology

[0002] Raman scattering spectroscopy can reveal the structural information of a substance, enabling its identification and content determination. However, its relatively weak intensity is not conducive to the identification and detection of trace substances. Surface-enhanced Raman scattering (SERS) is an effective method for detecting trace substances, widely used because it can efficiently enhance the Raman signal of a substance and provide structural information. For example, a two-dimensional metal groove array with an inverted pyramid shape, prepared by electron beam lithography combined with etching and sputtering, is a substrate used for SERS detection (Y. Lee, et al. ACS photonics 3(12), 2405-2412(2016)). Similar plasmonic nanostructures also have Raman enhancement effects. Since constructing two-dimensional planar Raman-enhanced structures sometimes cannot fully meet the requirements of Raman testing of low-concentration substances, some three-dimensional SERS substrates have also been reported. For example, SERS substrates with a gold / graphene / gold sandwich structure (M. Messina, at al. Phys. Chem. C 122(16), 9152-9161(2018)) and substrates with a three-dimensional Ni mesh structure as a carrier and adsorbed Ag nanoparticles (Z. Zhan, et al. Adv. Opt. Mater 4(12), 2021-2027(2016)).

[0003] To achieve real-time detection of trace amounts of substances in liquid environments, it is necessary to construct three-dimensionally distributed SERS "hot spots" in the liquid environment. When excitation light interacts with the analyte in the water environment, the SERS "hot spots" are stereo-enhanced. In this regard, Wang et al. proposed a microfluidic chip based on an Au@Ag / TiO2 NTs (Au core-Ag shell NPs and modified TiO2 nanotube arrays (NTs)) composite SERS substrate, which features three-dimensionally distributed SERS "hot spots" (C. Wang, et al. RSC Advances 6, 113115-113122 (2016)). Using a simple combination of tape lithography and anodizing, strip-shaped TiO2 NTs with regular pore structures were prepared on titanium foil. A simple self-assembly chemical deposition method was used to prepare Au@Ag NPs on the open surface and inner wall of the TiO2 NTs without causing blockage. The microfluidic chip exhibits good sensitivity to R6G molecules, capable of detecting a minimum concentration of R6G of 10⁻⁶. -10 M, the enhancement factor can reach 1.15×10 8 .

[0004] Kang et al. proposed a novel method for real-time preparation of surface-enhanced Raman scattering (SERS) substrates. This method involves forming Ag anion clusters in a capillary via laser reduction, while probe molecules (aromatic amines, aromatic thiols, or phenolic compounds) dissolved in the solution during the reduction process can simultaneously be detected as Raman signals (Y. Kang, et al. Microchemical Journal 137, 15-21 (2018)). This method allows for the simultaneous preparation of silver nanoparticle clusters and the acquisition of SERS signals, completing Raman signal collection within seconds. However, this method has the drawback of easily introducing secondary contamination of the test liquid environment into the nanoparticle clusters. Summary of the Invention

[0005] Based on the above problems and background technology, this invention proposes a bulk-enhanced Raman spectroscopy testing device and method for substance identification and trace detection in a liquid environment using a hollow optical fiber with an internally plated metal nano-Raman enhancement structure. Compared with a pure solution system without an optical feedback device, after the excitation light is incident on the test solution, it is confined within the core of the hollow optical fiber in the test solution, thereby enhancing the Raman spectrum through enhanced light-matter interaction. The three-dimensional Raman spectroscopy feedback mechanism of the hollow optical fiber can be achieved by constructing a metal nano-Raman enhancement structure on the inner wall of the capillary.

[0006] This invention discloses an optical feedback device based on SERS detection using hollow optical fiber, characterized in that it includes a hollow optical fiber device with an internally plated SERS structure (attached). Figure 1A solid optical fiber with a metal film feedback at its end face and a metal reflective film feedback at its end face are coaxially nested inside a hollow optical fiber with an inner SERS structure, and can slide in the hollow optical fiber with an inner SERS structure. The metal reflective film at the end face of the solid optical fiber is perpendicular to the axial direction and located inside the hollow optical fiber with an inner SERS structure.

[0007] The SERS structure consists of metal nanospheres fixed to the inner surface of a hollow optical fiber.

[0008] Furthermore, the metal nanospheres are formed into a thin film and fixed to the inner surface of the hollow optical fiber. In the thin film, there are gaps between the metal nanospheres. The diameter of the metal nanospheres is preferably 50-150 nm. The metal nanospheres and the metal reflective film material are all made of any one of the following metal materials that have high reflectivity to the visible-near infrared: gold, silver, aluminum, copper, etc.

[0009] The fabrication method of a hollow optical fiber device with an internally plated SERS structure includes the following steps:

[0010] (1) Clean the hollow optical fiber with acetone and ethanol respectively by ultrasonic cleaning for later use;

[0011] (2) Preparation of metal nanoparticles:

[0012] A solution of the metal salt corresponding to the metal nanoparticles is added to a toluene solution containing tetraoctylammonium bromide while stirring the solution. Preferably, each 1-2 g of tetraoctylammonium bromide corresponds to 60-100 mL of toluene solvent, 0.2-0.5 g of metal salt, and 1-3 mL of water. After the metal salt is completely dissolved, a reducing agent capable of reducing the metal salt to a metal is added and stirred to reduce the metal. Once the chemical reaction is complete, stirring is stopped to obtain a colloidal solution. The colloidal solution is separated to remove the aqueous phase, and the organic phase is removed by vacuum distillation. Methanol is added to the viscous liquid containing the metal particles, causing the metal particles to precipitate. The metal particles are then separated from the solution to obtain metal particles coated with tetraoctylammonium bromide.

[0013] (3) Disperse the metal particles obtained in step (2) in an organic solvent to prepare a metal colloidal solution;

[0014] (4) Hollow optical fiber filled with metal particles

[0015] Using capillary force, the metal particle colloidal solution in step (3) is adsorbed into the hollow optical fiber, and then the metal nanoparticle colloidal solution in the hollow optical fiber is discharged, so that the metal nanoparticle colloidal solution hangs on the wall of the hollow optical fiber and is dried by air.

[0016] Repeat the above steps (4) to create an environment on the inner wall of the optical fiber that is easy to adsorb metal nanoparticles. After the last adsorption of the colloidal solution of metal nanoparticles, the colloidal solution will no longer be discharged from the optical fiber.

[0017] The optical fiber filled with the colloidal solution of metal particles in the above steps is placed on a heating plate at 110℃-120℃. As the solvent evaporates, it carries away the excess metal particles that are not attached to the inner wall of the optical fiber and is ejected from both ends of the optical fiber. The remaining metal particles are attached to the inner wall of the hollow optical fiber.

[0018] (5) Further heat treatment to form the SERS structure on the inner wall of the optical fiber.

[0019] The optical fiber with internally plated metal particles from step (4) is further placed in a muffle furnace for high-temperature annealing at 400℃-600℃. The surface modifier of the metal nanoparticles is removed, and simultaneously, the metal particles are further melted on the inner wall surface of the optical fiber to form a relatively large metal nanosphere structure with certain gaps. (See...) Figure 3 .

[0020] The application of an optical feedback device based on hollow fiber SERS detection involves excitation light entering from one end of a hollow fiber and then into a hollow fiber with an inner SERS enhancement structure placed in the test liquid. The excitation light is reflected multiple times by the inner SERS enhancement structure, resulting in efficient Raman scattering. The excitation light, after being focused multiple times, reaches the metal film at the end face of the solid fiber and is reflected back into the liquid inside the hollow fiber core. It is then reflected multiple times again by the metal film on the inner wall of the hollow fiber, resulting in multiple focusing. As a result, the intensity of the Raman spectral signal is significantly improved. The axial direction of the excitation light is parallel to the central axis of the hollow fiber, forming a converging excitation beam.

[0021] This device is used for the detection of trace or ultra-trace amounts of target substances in test solutions. The test solution can be any size of water body, aqueous solution, or non-aqueous liquid sample. It can be used for environmental water quality testing in the laboratory, or it can be combined with other devices to form a detection device that is inserted into the water body for detection. The analyte can be any biological or chemical molecule in any liquid at different concentrations, such as the red dye Rhodamine 6G in alcohol, or toxic organic pollutants in Haihe River water.

[0022] Advantages and features of this invention

[0023] 1) This invention assembles metal nanoparticles onto the inner wall of a capillary, thereby constructing a three-dimensionally distributed SERS-enhanced "hot spot".

[0024] 2) This invention enables stereoscopic excitation of Raman spectra of substances in liquid environments, significantly enhancing the Raman signal. It overcomes the limitation of existing methods where the interaction between excitation light and the analyte on the enhancement substrate is confined to a planar plane.

[0025] 3) This invention can detect trace amounts and low concentrations of substances.

[0026] 4) This device is simple to prepare, can be reused, greatly reduces environmental pollution, and can also reduce costs.

[0027] 5) This device is widely applicable to various testing environments, such as laboratory testing and the detection of target objects in water environments such as rivers, lakes and seas. Attached Figure Description

[0028] Figure 1 A cross-sectional schematic diagram of a hollow optical fiber device with an internally plated SERS structure.

[0029] (1) corresponds to the 3D diagram of the hollow fiber feedback device with internally plated SERS structure; (2) corresponds to the optical path diagram of the convergent excitation beam.

[0030] A: Hollow and solid fiber substrates; C (solid line): Converging excitation beam; E: Metal nanoparticle structure.

[0031] Figure 2 A cross-sectional schematic diagram of a hollow fiber optic device with a solid fiber optic cable with an inner metal-coated SERS structure and a metal-coated end-face feedback.

[0032] (1) corresponds to the 3D diagram of the hollow fiber device with a SERS structure nested with an inner metal-coated SERS structure and end-face metal film feedback solid fiber; (2) corresponds to the optical path diagram of the convergent excitation beam.

[0033] A: Hollow and solid optical fiber substrates; B: Metal thin film; C (solid line): Converging excitation beam; D (dashed line): Excitation light reflected back to the incident end.

[0034] Figure 3 SEM image of the SERS structure on the inner wall of the hollow optical fiber.

[0035] Figure 4 Raman spectroscopy results of rhodamine alcohol solution when there is a metallic SERS structure on the inner wall of the hollow optical fiber.

[0036] Figure 5 Raman spectra of R6G ethanol solutions of different concentrations measured by hollow optical fibers with silver nanoparticle SERS structure on the inner wall. Detailed Implementation

[0037] The present invention will be further described below with reference to specific implementation examples, but the present invention is not limited to the following embodiments.

[0038] Example 1: Implementation of SERS structure inside hollow optical fiber

[0039] (1) Clean the hollow optical fiber with an inner diameter of 600 μm once with acetone and ethanol for later use.

[0040] (2) Preparation of silver nanoparticles:

[0041] Add an aqueous solution of silver nitrate to a toluene solution containing tetraoctylammonium bromide while stirring the solution. The mass of tetraoctylammonium bromide is 1.5 g, the volume of toluene solvent is 80 mL, the mass of silver nitrate is 0.32 g, and the volume of water is 2 mL.

[0042] After the silver nitrate has completely dissolved, add 20 mL of sodium borohydride aqueous solution with a concentration of 0.37 mol / L. Stop stirring after 5 min, and the chemical reaction is complete.

[0043] The colloidal solution was separated to remove the aqueous phase, and the organic phase was removed by vacuum distillation. Methanol was added to the black viscous liquid containing silver nanoparticles, and the silver nanoparticles precipitated. The silver nanoparticles were separated from the solution, and after the remaining solvent was completely evaporated, silver nanoparticles coated with tetraoctylammonium bromide were obtained.

[0044] (3) Disperse the silver nanoparticles prepared in step (2) in acetone to prepare a silver nanoparticle colloidal solution with a concentration of 80 mg / mL;

[0045] (4) Hollow optical fiber filled with silver nanoparticles

[0046] Using capillary force, the metal nanoparticle colloidal solution in step (3) is adsorbed into the hollow optical fiber, and then the filled metal nanoparticle colloidal solution is discharged.

[0047] Repeat the above steps to create an environment on the inner wall of the optical fiber that is conducive to the adsorption of metal nanoparticles. After the last adsorption of the colloidal solution of metal nanoparticles, the colloidal solution is not discharged from the optical fiber.

[0048] The optical fiber filled with the silver nanoparticle colloidal solution in the above steps is placed on a heating plate at 110°C. As the solvent evaporates, it carries away the excess metal nanoparticles that are not attached to the inner wall of the optical fiber and is ejected from both ends of the optical fiber. The remaining metal nanoparticles are attached to the inner wall of the hollow optical fiber.

[0049] (5) Further heat treatment to form the SERS structure on the inner wall of the optical fiber.

[0050] The optical fiber with internally deposited metal nanoparticles from step (4) was further placed in a muffle furnace for high-temperature annealing at 400°C. The surface modifier of the metal nanoparticles was removed, and simultaneously, the metal nanoparticles further melted on the inner wall surface of the optical fiber to form a relatively large metal nanosphere structure with certain gaps. (See...) Figure 3 .

[0051] Example 2: Comparison of Raman spectra of R6G ethanol solutions with SERS structures of silver nanoparticles on the inner wall

[0052] Hollow optical fibers with silver nanoparticle SERS structures deposited on their inner walls were placed in a concentration of 10... -3Rhodamine 6G was excited to Raman signal using a 785 nm excitation source in an ethanol solution with an excitation light output power of 100 mW and an integration time of 1 s. The resulting enhanced Raman spectrum of Rhodamine 6G is shown below. Figure 4 As shown by the thin line. Simultaneously, pure silica optical fibers with equal inner diameter lengths are placed in a concentration of 10... -3 The Raman signal measured for a 6g mol / L rhodamine ethanol solution is as follows: Figure 4 As shown by the thick line, the Raman signal of the same concentration of Rhodamine 6G molecules in alcohol solution is significantly enhanced by the SERS structure of silver nanoparticles.

[0053] Example 3: Raman spectroscopy results of R6G ethanol solutions of different concentrations measured from hollow optical fibers with silver nanoparticle SERS structures on their inner walls.

[0054] Hollow optical fibers with silver nanoparticle SERS structures deposited on their inner walls were placed in different concentrations of 10. -6 The Raman signal of rhodamine 6G in an alcoholic solution was excited using a 785 nm excitation source with an excitation light output power of 100 mW and an integration time of 1 s. The enhanced Raman spectrum of the resulting rhodamine 6G in an alcoholic solution is shown below. Figure 5 As shown in the figure. With decreasing concentration of the 6g rhodamine ethanol solution, the effects are sequentially as follows: Figure 5 Curves (1), (2), and (3) show that the Raman enhancement signal of Rhodamine 6G measured by the hollow optical fiber with a SERS structure and silver nanoparticles coated on the inner wall gradually weakens. The lowest concentration of Rhodamine 6G ethanol solution that can be detected is 10. -6 mol / L.

Claims

1. An optical feedback device based on hollow fiber SERS detection, characterized in that, The device includes a hollow optical fiber device with an internal SERS structure and a solid optical fiber with a metal film feedback at the end face. The solid optical fiber with a metal reflective film feedback at the end face is coaxially nested inside the hollow optical fiber with an internal SERS structure and can slide in the hollow optical fiber with an internal SERS structure. The metal reflective film at the end face of the solid optical fiber is perpendicular to the axial direction and located inside the hollow optical fiber with an internal SERS structure. The SERS structure consists of metal nanospheres fixed to the inner surface of a hollow optical fiber; the metal nanospheres form a thin film fixed to the inner surface of the hollow optical fiber, and there are gaps between the metal nanospheres in the film; both the metal nanospheres and the metal reflective film material are made of any one of gold, silver, aluminum, or copper metal materials with high reflectivity to the visible-near infrared.

2. The optical feedback device based on hollow fiber SERS detection according to claim 1, characterized in that, The diameter of the metal nanospheres is 50-150 nm.

3. A method for preparing an optical feedback device based on hollow fiber SERS detection as described in any one of claims 1-2, characterized in that, The fabrication of a hollow optical fiber device with an internally plated SERS structure includes the following steps: (1) Clean the hollow optical fiber with acetone and ethanol respectively by ultrasonic cleaning for later use; (2) Preparation of metal nanoparticles: Add a solution of the metal salt corresponding to the metal nanoparticles to a toluene solution containing tetraoctylammonium bromide, while stirring the solution. For every 1-2 g of tetraoctylammonium bromide, the corresponding volume of toluene solvent is 60-100 mL, the corresponding mass of the metal salt is 0.2-0.5 g, and the corresponding volume of water is 1-3 mL. After the metal salt is completely dissolved, add a reducing agent that can reduce the metal salt to the metal and stir to reduce it. Once the chemical reaction is complete, stop stirring to obtain a colloidal solution. The colloidal solution was separated to remove the aqueous phase, and the organic phase was removed by vacuum distillation. Methanol was added to the viscous liquid containing metal particles, and the metal particles precipitated. The metal particles were then separated from the solution to obtain metal particles coated with tetraoctylammonium bromide. (3) Disperse the metal particles obtained in step (2) in an organic solvent to prepare a metal colloidal solution; (4) Hollow optical fiber filled with metal particles Using capillary force, the metal particle colloidal solution in step (3) is adsorbed into the hollow optical fiber, and then the metal nanoparticle colloidal solution in the hollow optical fiber is discharged, so that the metal nanoparticle colloidal solution hangs on the wall of the hollow optical fiber and is dried by air. Repeat the above steps (4) to create an environment on the inner wall of the optical fiber that is easy to adsorb metal nanoparticles. After the last adsorption of the colloidal solution of metal nanoparticles, the colloidal solution will no longer be discharged from the optical fiber. The optical fiber filled with the colloidal solution of metal particles in the above steps is placed on a heating plate at 110℃-120℃. As the solvent evaporates, it carries away the excess metal particles that are not attached to the inner wall of the optical fiber and is ejected from both ends of the optical fiber. The remaining metal particles are attached to the inner wall of the hollow optical fiber. (5) Further heat treatment to form the SERS structure on the inner wall of the optical fiber The optical fiber with internally plated metal particles in step (4) is further placed in a muffle furnace and subjected to high-temperature annealing at 400℃-600℃. The surface modifier of the metal nanoparticles is removed, and at the same time, the metal particles are further melted on the inner wall surface of the optical fiber to form a relatively large metal nanosphere structure with certain gaps.

4. The application of the optical feedback device based on hollow optical fiber SERS detection as described in any one of claims 1-2, for the detection of trace or ultra-trace target substances in the test solution, wherein the test solution is a water body, aqueous solution or non-aqueous liquid sample of any size.

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