A silver-coated optical fiber Raman probe and its preparation method and application

Abstract

The present invention relates to the fields of materials, optics and environmental detection, and specifically to a silver-coated optical fiber Raman probe and a preparation method and application thereof, wherein methimazole is used as a Raman signal molecule to realize the detection of Cr(VI). The silver-coated optical fiber Raman probe of the present invention realizes ultra-sensitive detection of Cr(VI) and excellent antioxidant performance by functionalization with methimazole. The preparation method of the present invention has simple process, high sensitivity, good repeatability, good stability and good anti-interference. By adopting stannous chloride-assisted solvent thermal method, the morphology control of silver nanoparticles on the end face of the optical fiber and the strong interface adhesion between the optical fiber and the silver nanomaterial are realized. Specifically, the stannous chloride pretreatment process promotes the dense and uniform growth of silver nanoparticles on the end face of the optical fiber on the one hand, and enhances the interface adhesion between the optical fiber and the silver nanoparticles on the other hand. Ultra-sensitive detection of Cr(VI) and excellent antioxidant performance are realized by functionalization with methimazole.

Description

Technical Field

[0001] The invention relates to the fields of materials, optics and environmental detection, and in particular to a silver-plated optical fiber Raman probe and a preparation method and application thereof. Background Art

[0002] Hexavalent chromium ions are a major environmental pollutant with high carcinogenicity and mutagenicity. In recent years, the detection equipment for hexavalent chromium ions in water bodies is expensive, the sample pretreatment is complicated, and the test process is lengthy. Therefore, it is urgent to develop a rapid, highly sensitive, and low-cost biological detection technology. Compared with commonly used detection technologies such as ICP-OES, SERS has the advantages of rapid detection, high non-destructive sensitivity, and good specificity, and can be used in the field of environmental detection. Combining SERS technology with optical fiber can achieve highly sensitive, flexible, real-time, in-situ, long-distance, and low-loss detection, which has outstanding advantages in actual water body detection.

[0003] In order to obtain highly sensitive Cr(VI) detection technology, researchers have conducted a series of studies. In 2011, Sereshti et al. used ICP-OES to detect Cr(VI) with a concentration of 0.0044μmol / L. In 2015, Ravishankar et al. used electrochemical method to detect Cr(VI) with a concentration of 0.033μmol / L. In 2016, Vidal et al. used atomic absorption spectroscopy to detect Cr(VI) with a concentration of 0.058μmol / L. Compared with the above Cr(VI) detection technologies, SERS fiber optic sensors can not only realize simple, fast and highly sensitive Cr(VI) detection, but also have the advantages of flexible, real-time, in-situ, long-distance and low-loss detection, which greatly optimizes the Cr(VI) detection technology. At present, there is no public technology for detecting Cr(VI) with fiber optic probes or SERS fiber optic sensors. Summary of the invention

[0004] One of the purposes of the present invention is to provide a silver-coated optical fiber Raman probe, which uses methimazole functionalization to achieve ultra-high sensitivity and antioxidant properties for detecting objects to be detected, and provides a new idea and method for detecting pollutants in water bodies.

[0005] The second object of the present invention is to provide a method for preparing a silver-coated optical fiber Raman probe, which has a simple preparation process, good repeatability, good stability and good anti-interference performance.

[0006] A third object of the present invention is to provide an application of a silver-coated optical fiber Raman probe.

[0007] The solution adopted by the present invention to achieve one of the purposes is: a silver-plated optical fiber Raman probe, using methimazole as a Raman signal molecule to detect Cr (VI).

[0008] Preferably, the silver-plated optical fiber Raman probe comprises an optical fiber body, a silver-plated layer coated on the surface of the optical fiber body, and a methimazole functional layer adsorbed on the surface of the silver-plated layer.

[0009] The solution adopted by the present invention to achieve the second purpose is: a method for preparing the silver-coated optical fiber Raman probe, using stannous chloride sensitization-assisted solvothermal method combined with methimazole functionalization to prepare the silver-coated optical fiber probe.

[0010] Preferably, the steps include:

[0011] (1) Fiber sensitization pretreatment: The optical fiber to be treated is immersed in a stannous chloride aqueous solution for sensitization treatment;

[0012] (2) Preparing a precursor solution: preparing a soluble silver salt solution and a sodium bicarbonate solution, adding a surfactant to the stirred soluble silver salt solution, and after the surfactant is dissolved, pouring the sodium bicarbonate solution into the solution and mixing the mixture evenly;

[0013] (3) Solvothermal method for preparing silver-coated optical fiber: the optical fiber is placed in a prepared precursor solution, sealed, and reacted at a certain temperature until complete, thus obtaining a silver-coated optical fiber;

[0014] (4) Methimazole functionalization: The prepared silver-coated optical fiber is immersed in a certain concentration of methimazole Brittan-Robinson (BR) buffer solution with a halide salt added thereto, taken out after functionalization is completed, washed to remove the residue, and dried under an inert atmosphere to obtain the silver-coated optical fiber Raman probe.

[0015] Preferably, in step (1), the concentration of the stannous chloride aqueous solution is 0-2 wt %.

[0016] Preferably, in step (2), the soluble silver salt is silver nitrate; the surfactant is polyvinyl pyrrolidone, polyethylene glycol or hexadecyl ammonium bromide; wherein the molar ratio of the surfactant to the soluble silver salt is 0-16:1, the molar ratio of the soluble silver salt to sodium bicarbonate is 1-2:1, and the concentration of the soluble silver salt is 0.01-1 mol / L.

[0017] Preferably, in step (3), the reaction temperature is 120-220°C.

[0018] Preferably, in step (4), the concentration of methimazole is 10 -7 –0.1mol / L, the functionalization time is 10min-2h, the concentration of halide salt is 0-1mol / L, and the pH value of BR buffer solution is 2-7.

[0019] Preferably, in step (4), the halide salt is at least one of sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide and potassium iodide.

[0020] The solution adopted by the present invention to achieve the third purpose is: application of a silver-coated optical fiber Raman probe, and applying the silver-coated optical fiber Raman probe to a SERS optical fiber Raman sensor.

[0021] The present invention has the following advantages and beneficial effects:

[0022] The silver-plated optical fiber Raman probe of the present invention realizes ultra-sensitive detection of Cr(VI) and excellent antioxidant performance by using methimazole functionalization.

[0023] The preparation method of the present invention has simple process, high sensitivity, good repeatability, good stability and good anti-interference performance. By adopting stannous chloride-assisted solvent thermal method, the morphology control of silver nanoparticles on the end face of optical fiber and the strong interface adhesion between optical fiber and silver nanomaterials are realized. Specifically, the stannous chloride pretreatment process promotes the dense and uniform growth of silver nanoparticles on the end face of optical fiber on the one hand, and enhances the interface adhesion between optical fiber and silver nanoparticles on the other hand. By adopting methimazole functionalization, ultra-sensitive detection of Cr(VI) and excellent antioxidant performance are realized.

[0024] The SERS fiber optic sensor prepared by the silver-coated fiber Raman probe of the present invention can realize flexible, real-time, in-situ, long-distance, and low-loss detection, and can be applied to detection in the environment and other fields. Compared with the traditional Cr(VI) detection technology, the SERS fiber optic sensor of the present invention is non-destructive and rapid, without the need for complex sample pretreatment and lengthy detection reagents, and realizes simple, rapid, and ultra-high sensitivity detection, broadens the detection technology applicable to Cr(VI), and greatly optimizes the convenience and sensitivity of detection. The SERS fiber optic sensor of the present invention has ultra-high sensitivity and can detect concentrations of 10 -11 mol / L and above Cr(VI), excellent antioxidant, repeatability and anti-interference properties, suitable for environmental testing field. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the SERS optical fiber sensor of the present invention;

[0026] Figure 2 The SERS optical fiber sensor in Example 1 of the present invention detects 10 -5 mol / L-10 -11 Surface enhanced Raman scattering spectra of mol / L Cr(VI) solution;

[0027] Figure 3 This is a UV-visible absorption spectrum of the reaction solution of the silver-plated optical fiber probe in Example 2 of the present invention;

[0028] Figure 4 This is the SEM spectrum of the silver-coated optical fiber probe at 5 μm scale in Example 3 of the present invention;

[0029] Figure 5 The oxidation resistance of the SERS optical fiber sensor in Example 4 of the present invention;

[0030] Figure 6 is the repeatability of the SERS optical fiber sensor in Example 5 of the present invention;

[0031] Figure 7 The anti-interference performance of the SERS optical fiber sensor in Example 6 of the present invention;

[0032] In the figure: a silver-coated optical fiber probe (1), a laser (2), a first signal transmission device (3), a microscope objective (4), a filter and a second signal transmission device (5), a signal collection device (6), and a computer (7). DETAILED DESCRIPTION

[0033] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0034] Embodiment 1:

[0035] A silver-coated optical fiber Raman probe, the preparation method of which comprises the following steps:

[0036] 1) Fiber sensitization pretreatment: The quartz optical fiber with a flat end face, clean and dry was immersed in a 0.2 wt% stannous chloride aqueous solution for 3 minutes for sensitization treatment.

[0037] 2) Prepare precursor solution: prepare 30 ml of 0.067 mol / L silver nitrate solution and 30 mL of 0.04 mol / L sodium bicarbonate solution. After the silver nitrate is completely dissolved, add 1.776 g of polyvinyl pyrrolidone, stir evenly, then add the completely dissolved sodium bicarbonate solution and continue stirring until uniform.

[0038] 3) Preparation of silver-coated optical fiber by solvent thermal method: Pour the prepared precursor solution into a polytetrafluoroethylene autoclave, put in the optical fiber, seal the container, and react at 140°C for 1 hour. After the reaction is completed and cooled naturally, take out the optical fiber.

[0039] 4) Methimazole functionalization: The prepared silver-coated optical fiber was immersed in a 0.1 mol / L methimazole BR (Brittan-Robinson) buffer solution (pH=3) added with 0.075 mol / L sodium chloride for 40 min. After the functionalization was completed, it was taken out, the residual solution was rinsed with distilled water, and then dried under argon to obtain a silver-coated optical fiber Raman probe for storage.

[0040] The silver-coated optical fiber Raman probe prepared in Example 1 is used to prepare a SERS optical fiber sensor, such as Figure 1 As shown, the SERS fiber optic sensor specifically includes: a silver-coated fiber optic probe (1), a laser (2), a first signal transmission device (3), a microscope objective lens (4), a filter and a second signal transmission device (5), a signal collection device (6), and a computer (7). The laser light emitted by the laser (2) passes through the first signal transmission device (3) and reaches the microscope objective lens (4), and then is emitted to the proximal end face of the silver-coated fiber optic probe (1). After the incident laser light reaches the distal end face loaded with silver nanoparticles through the optical fiber, it interacts with the substances adsorbed on the surface of the silver nanoparticles, and the collected SERS signal is transmitted back to the microscope objective lens (4) through the same optical fiber, and then reaches the signal collection device (6) through the filter and the second signal transmission device (5), and the detected SERS spectrum is displayed by the computer (7).

[0041] The SERS optical fiber sensor was immersed in 10 -5 mol / L、10 -6 mol / L、10 -7 mol / L、10 -8 mol / L、10 -9 mol / L、10 -10 mol / L and 10 -11 After soaking in mol / L Cr(VI) solution for 30 min, the sensor was taken out and the SERS spectra of the sensor before and after soaking were tested.

[0042] Figure 2 The SERS optical fiber sensor test 10 in this embodiment 1 -5 mol / L-10 -11 Surface enhanced Raman scattering spectra of mol / L Cr(VI) solution, both at 1363 cm -1 There is a strong absorption peak at the center, indicating that the SERS fiber optic sensor has excellent surface enhanced Raman scattering performance.

[0043] Embodiment 2:

[0044] A silver-coated optical fiber Raman probe, the preparation method of which comprises the following steps:

[0045] 1) Fiber sensitization pretreatment: The quartz optical fiber with a flat end face, clean and dry was immersed in a 0.1 wt% stannous chloride aqueous solution for 1 min for sensitization treatment.

[0046] 2) Prepare precursor solution: prepare 30 ml of 0.01 mol / L silver nitrate solution and 30 mL of 0.01 mol / L sodium bicarbonate solution. After the silver nitrate is completely dissolved, add 3.552 g of polyvinyl pyrrolidone, stir evenly, then add the completely dissolved sodium bicarbonate solution and continue stirring until uniform.

[0047] 3) Preparation of silver-coated optical fiber by solvent thermal method: Pour the prepared precursor solution into a polytetrafluoroethylene autoclave, put in the optical fiber, seal the container, and react at 120°C for 24 hours. After the reaction is completed and cooled naturally, take out the optical fiber.

[0048] 4) Methimazole functionalization: The prepared silver-coated optical fiber was immersed in 10% sodium bromide solution. -7 mol / L methimazole BR (Brittan-Robinson) buffer solution (pH=2) for 10 min. After functionalization, the probe was taken out and the residual solution was rinsed with distilled water. The probe was dried under argon to obtain a silver-coated optical fiber Raman probe for storage.

[0049] The silver-coated optical fiber Raman probe prepared in Example 2 was used to prepare the same SERS optical fiber sensor as in Example 1. The obtained SERS optical fiber sensor was immersed in the Cr(VI) solution to be tested for 10 minutes, then taken out, and the SERS spectra of the sensor before and after immersion were tested.

[0050] The SERS optical fiber sensor obtained in Example 2 has a layer of metallic luster on the end and side surfaces, and can detect a concentration of 10 -6 Cr(VI) solution with concentration of mol / L or above.

[0051] Figure 3 This is the UV-visible absorption spectrum of the silver-plated optical fiber reaction solution in Example 2 of the present invention. It can be seen from the figure that the resonance peak of the sample is at 420nm, indicating that silver nanoparticles exist in the sample.

[0052] Embodiment 3:

[0053] A method for preparing a silver-coated optical fiber Raman probe comprises the following steps:

[0054] 1) Optical fiber sensitization pretreatment: A clean and dry quartz optical fiber with a tapered end face is immersed in a 2 wt% stannous chloride aqueous solution for 2 minutes for sensitization treatment.

[0055] 2) Prepare the precursor solution: prepare 30 ml of 0.5 mol / L silver nitrate solution and 30 mL of 1 mol / L sodium bicarbonate solution. After the silver nitrate is completely dissolved, add 0 g of polyvinyl pyrrolidone, stir evenly, then add the completely dissolved sodium bicarbonate solution and continue stirring until uniform.

[0056] 3) Preparation of silver-coated optical fiber by solvent thermal method: Pour the prepared precursor solution into a polytetrafluoroethylene autoclave, put in the optical fiber, seal the container, and react at 160°C for 8 hours. After the reaction is completed and cooled naturally, take out the optical fiber.

[0057] 4) Methimazole functionalization: The prepared silver-coated optical fiber was immersed in 10 - 6 mol / L methimazole BR (Brittan-Robinson) buffer solution (pH=4) for 20 min. After functionalization, the probe was taken out, the residual solution was rinsed with distilled water, and then dried under argon to obtain a silver-coated optical fiber Raman probe for storage.

[0058] The silver-coated optical fiber Raman probe prepared in Example 3 was used to prepare the same SERS optical fiber sensor as in Example 1. The obtained SERS optical fiber sensor was immersed in the Cr(VI) solution to be tested for 20 minutes, then taken out, and the SERS spectra of the sensor before and after immersion were tested.

[0059] The SERS optical fiber sensor obtained in Example 3 has a layer of metallic luster on the end and side surfaces, and can detect a concentration of 10 -7 Cr(VI) solution with concentration of mol / L or above.

[0060] Figure 4 This is a SEM image of the end face of the silver-plated optical fiber probe at a scale of 5 μm in Example 3 of the present invention. As can be seen from the image, spherical silver nanoparticles grow on the end face of the optical fiber, and the average grain size is 75 nm.

[0061] Embodiment 4:

[0062] A silver-coated optical fiber Raman probe, the preparation method of which comprises the following steps:

[0063] 1) Fiber sensitization pretreatment: The sapphire fiber with a flat end face, clean and dry was immersed in a 0 wt% stannous chloride aqueous solution for 4 minutes for sensitization treatment.

[0064] 2) Prepare precursor solution: prepare 30 ml of 0.05 mol / L silver nitrate solution and 30 mL of 0.05 mol / L sodium bicarbonate solution. After the silver nitrate is completely dissolved, add 2 g of polyvinyl pyrrolidone, stir evenly, then add the completely dissolved sodium bicarbonate solution and continue stirring until uniform.

[0065] 3) Preparation of silver-coated optical fiber by solvent thermal method: Pour the prepared precursor solution into a polytetrafluoroethylene autoclave, put in the optical fiber, seal the container, and react at 220°C for 1 hour. After the reaction is completed and cooled naturally, take out the optical fiber.

[0066] 4) Methimazole functionalization: The prepared silver-coated optical fiber was immersed in 10 -3 mol / L methimazole BR (Brittan-Robinson) buffer solution (pH=5) for 30 min. After functionalization, the probe was taken out and the residual solution was rinsed with distilled water. The probe was dried under argon to obtain a silver-coated optical fiber Raman probe for storage.

[0067] The silver-coated optical fiber Raman probe prepared in Example 4 was used to prepare the same SERS optical fiber sensor as in Example 4. The obtained SERS optical fiber sensor was immersed in the Cr(VI) solution to be tested for 60 minutes, then taken out, and the SERS spectra of the sensor before and after immersion were tested.

[0068] The SERS optical fiber sensor obtained in Example 4 has a layer of metallic luster on the end and side surfaces, and can detect a concentration of 10 -6 Cr(VI) solution with concentration of mol / L or above.

[0069] Figure 5 The SERS spectra of the SERS optical fiber sensor in Example 4 of the present invention after being placed in the air for 0 days and 14 days are shown. The peak intensity of the SERS spectrum changes by 36%, showing good stability.

[0070] Embodiment 5:

[0071] A silver-coated optical fiber Raman probe, the preparation method of which comprises the following steps:

[0072] 1) Fiber sensitization pretreatment: The photonic crystal fiber with a flat end face, clean and dry is immersed in a 1 wt% stannous chloride aqueous solution for 30 minutes for sensitization treatment.

[0073] 2) Prepare the precursor solution: prepare 30 ml of 1 mol / L silver nitrate solution and 30 mL of 1.5 mol / L sodium bicarbonate solution. After the silver nitrate is completely dissolved, add 0.132 g of polyethylene glycol, stir evenly, then add the completely dissolved sodium bicarbonate solution and continue stirring until uniform.

[0074] 3) Preparation of silver-coated optical fiber by solvent thermal method: Pour the prepared precursor solution into a polytetrafluoroethylene autoclave, put in the optical fiber, seal the container, and react at 180°C for 12 hours. After the reaction is completed and cooled naturally, take out the optical fiber.

[0075] 4) Methimazole functionalization: The prepared silver-coated optical fiber was immersed in 10 -3mol / L methimazole BR (Brittan-Robinson) buffer solution (pH=5) for 30 min. After functionalization, the probe was taken out and the residual solution was rinsed with distilled water. The probe was dried under argon to obtain a silver-coated optical fiber Raman probe for storage.

[0076] The silver-coated optical fiber Raman probe prepared in Example 5 was used to prepare the same SERS optical fiber sensor as in Example 1. The obtained SERS optical fiber sensor was immersed in the Cr(VI) solution to be tested for 60 minutes, then taken out, and the SERS spectra of the sensor before and after immersion were tested.

[0077] The SERS optical fiber sensor obtained in Example 5 has a layer of metallic luster on the end and side surfaces, and can detect a concentration of 10 -8 Cr(VI) solution with concentration of mol / L or above.

[0078] Figure 6 This is a repeatability test of the SERS optical fiber sensor in Example 5 of the present invention. The peak shapes and intensities of the SERS spectra detected by the six optical fiber sensors are similar, showing excellent repeatability.

[0079] Embodiment 6:

[0080] A silver-coated optical fiber Raman probe, the preparation method of which comprises the following steps:

[0081] 1) Fiber sensitization pretreatment: The quartz optical fiber with a flat end face, clean and dry was immersed in a 1.2 wt% stannous chloride aqueous solution for 15 minutes for sensitization treatment.

[0082] 2) Prepare the precursor solution: prepare 30 ml of 0.2 mol / L silver nitrate solution and 30 mL of 0.3 mol / L sodium bicarbonate solution. After the silver nitrate is completely dissolved, add 1.2 g of hexadecyl ammonium bromide, stir evenly, then add the completely dissolved sodium bicarbonate solution and continue stirring until uniform.

[0083] 3) Preparation of silver-coated optical fiber by solvent thermal method: Pour the prepared precursor solution into a polytetrafluoroethylene autoclave, put in the optical fiber, seal the container, and react at 200°C for 4 hours. After the reaction is completed and cooled naturally, take out the optical fiber.

[0084] 4) Methimazole functionalization: The prepared silver-coated optical fiber was immersed in a 0.1 mol / L methimazole BR (Brittan-Robinson) buffer solution (pH=7) added with 0.075 mol / L sodium iodide to obtain a silver-coated optical fiber Raman probe, which was then stored.

[0085] The silver-coated optical fiber Raman probe prepared in Example 6 was used to prepare the same SERS optical fiber sensor as in Example 6. The obtained SERS optical fiber sensor was immersed in the Cr(VI) solution to be tested for 30 minutes, then taken out, and the SERS spectra of the sensor before and after immersion were tested.

[0086] The SERS optical fiber sensor obtained in Example 6 has a layer of metallic luster on the end and side surfaces, and can detect a concentration of 10 -7 Cr(VI) solution with concentration of mol / L or above.

[0087] Figure 7 This is a test of the anti-interference property of the SERS optical fiber sensor in Example 6 of the present invention. When other interfering ions with a concentration 100 times that of Cr(VI) were added, the SERS spectrum intensity remained almost unchanged, showing good anti-interference property.

[0088] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A silver-coated optical fiber Raman probe, characterized in that: Methimazole is used as a Raman signal molecule to detect Cr(VI); the silver-coated optical fiber Raman probe comprises an optical fiber body, a silver-coated layer coated on the surface of the optical fiber body, and a methimazole functional layer adsorbed on the surface of the silver-coated layer; The silver-coated optical fiber Raman probe can detect concentrations of 10 -11 Cr(VI) of mol / L and above, The method adopts stannous chloride sensitization-assisted solvothermal method and methimazole functionalization to prepare a silver-coated optical fiber Raman probe; the method comprises the following steps: (1) Fiber sensitization pretreatment: Immerse the optical fiber to be treated in a stannous chloride aqueous solution for sensitization treatment; (2) Preparing a precursor solution: preparing a soluble silver salt solution and a sodium bicarbonate solution, adding a surfactant to the stirred soluble silver salt solution, and after the surfactant is dissolved, pouring the sodium bicarbonate solution into the solution and mixing evenly; (3) Preparation of silver-coated optical fiber by solvent thermal method: Place the optical fiber in the prepared precursor solution, seal it, and react it at a certain temperature until it is complete, thus obtaining the silver-coated optical fiber; (4) Methimazole functionalization: The prepared silver-coated optical fiber is immersed in a 0.1 mol / L methimazole-containing Brittan-Robinson buffer solution with 0.075 mol / L sodium chloride added thereto, the pH of the buffer solution being 3, and the immersion time being 40 min. After the functionalization is completed, the optical fiber is taken out, washed to remove the residue, and dried in an inert atmosphere to obtain the silver-coated optical fiber Raman probe.

2. The silver-coated optical fiber Raman probe according to claim 1, characterized in that: In the step (1), the concentration of the stannous chloride aqueous solution is 0-2 wt %.

3. The silver-coated optical fiber Raman probe according to claim 1, characterized in that: In the step (2), the soluble silver salt is silver nitrate; the surfactant is polyvinyl pyrrolidone, polyethylene glycol or hexadecyl ammonium bromide; wherein the molar ratio of the surfactant to the soluble silver salt is 0-16:1, the molar ratio of the soluble silver salt to sodium bicarbonate is 1-2:1, and the concentration of the soluble silver salt is 0.01-1 mol / L.

4. The silver-coated optical fiber Raman probe according to claim 1, characterized in that: In the step (3), the reaction temperature is 120-220°C.

5. An application of a silver-coated optical fiber Raman probe, characterized in that: The silver-coated optical fiber Raman probe according to any one of claims 1 to 4 is applied to a SERS optical fiber Raman sensor.

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