Preparation method of optical fiber LSPR (Localized Surface Plasmon Resonance) sensor based on gold nanocrystal modification

Abstract

The invention discloses a preparation method of an optical fiber LSPR sensor based on gold nanocrystal modification, and belongs to the technical field of optical fiber sensing. The method comprises the following steps: removing a cladding layer of an optical fiber, soaking the optical fiber in a piranha solution to modify hydroxyl, and preparing a hydrophilic optical fiber; and uniformly and compactly assembling the gold nanoparticles on the surface of the optical fiber by using a liquid-liquid interface self-assembly technology by taking the gold nanoparticles coated with polyvinylpyrrolidone (PVP) as an assembly unit to obtain the optical fiber LSPR sensor. According to the invention, the problems of poor distribution uniformity, tedious preparation process, poor signal repeatability and the like of gold nanoparticles modified on the optical fiber by using a traditional method at present are solved, and the purpose of further improving the sensing performance is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a method for preparing an optical fiber LSPR sensor based on gold nanocrystal modification. Background Art

[0002] In recent years, with the development of metal nanomaterials and nanostructure processing technology, LSPR sensors have been widely used in clinical medicine, environmental testing, disease diagnosis, food safety and other fields due to their advantages such as label-free detection, good biocompatibility and high sensitivity. LSPR is an optical phenomenon produced when incident light interacts with metal nanoparticles smaller than the incident wavelength. Its properties strongly depend on the type, size, shape, detection environment and spacing between particles of the metal nanomaterial. Different from traditional LSPR sensing technology, fiber optic LSPR sensing technology has the advantages of strong stability, strong anti-interference ability and real-time monitoring of multiple analytes, which has attracted more and more attention from researchers in the field of biosensing.

[0003] Generally, the preferred techniques for modifying gold nanoparticles on the surface of optical fibers are usually chemical bond modification and electrostatic adsorption. Although these methods can deposit a certain amount of gold nanoparticles on the surface of optical fibers, they require complex processing steps, are time-consuming, and the distribution uniformity and assembly density of gold nanoparticles are difficult to control. Therefore, in order to improve on-site rapid analysis based on optical fiber sensing, it is crucial to study the effect of the uniform arrangement of gold nanoparticles on the performance of optical fiber LSPR sensors and design optical fiber LSPR sensors with high sensitivity, high stability and high reproducibility, thereby promoting the development of optical fiber LSPR sensors in the fields of biosensing, virus detection and environmental detection. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of poor uniformity of distribution of gold nanoparticles modified on optical fiber by traditional methods and complicated preparation process, and proposes a preparation method of optical fiber LSPR sensor based on gold nanocrystal modification.

[0005] A preparation method of an optical fiber LSPR sensor modified with gold nanocrystals is characterized by preparing gold nanoparticles coated with hexadecyltrimethylammonium chloride (CTAC), and then exchanging its ligands to obtain gold nanoparticles coated with polyvinylpyrrolidone (PVP). The gold nanoparticles are used as assembly units, and the gold nanoparticles are assembled uniformly and densely on the surface of the optical fiber by liquid-liquid interface self-assembly technology to obtain an optical fiber LSPR sensor.

[0006] The gold nanoparticles described in the present invention are marked as Au NPs.

[0007] The hexadecyltrimethylammonium chloride described in the present invention is marked as CTAC.

[0008] The polyvinyl pyrrolidone described in the present invention is marked as PVP.

[0009] If not otherwise specified, the solutions described in the present invention are all aqueous solutions.

[0010] The preparation method of the optical fiber LSPR sensor based on gold nanocrystal modification described in the present invention comprises the following steps: (1) Preparation of Au NPs by seed-mediated growth method: 2-2.5 mL of 0.1 M CTAC solution was mixed with 5-20 μL of 10 nm gold nanosphere seed solution, followed by the addition of 130-150 μL of 0.1 M ascorbic acid (AA) solution. After the reactants were completely dissolved, 2-2.5 mL of 0.5×10 −3 M HAuCl4 solution, react at 25-30°C for 15-20 min, centrifuge at 5500-6000rpm for 10-15 min; then disperse the precipitate into 0.5-1 mL, 1% PVP ethanol solution, centrifuge at 5500-6000rpm for 10-15 min, and disperse the precipitate in 0.5-1 mL ethanol to obtain Au NPs ethanol solution, which is stored at 4°C; (2) Preparation of fiber LSPR sensor: Mix 100~300 μL of the Au NPs ethanol solution prepared in step (1) with 1.5~2.5 mL of dichloromethane, then add 3.5~4.5 mL of ultrapure water and shake vigorously for 30~50 seconds. Then slowly add 700~900 μL of n-hexane. At this time, a uniform gold nanoparticle film is formed at the liquid-liquid interface. After slowly removing the n-hexane, the nanoparticle film can be directly transferred to the optical fiber to prepare the fiber LSPR sensor.

[0011] Further, 2~2.5 mL, 200×10 −3 Mix 40-60 μL of 0.1 M hexadecyltrimethylammonium chloride solution with 40-60 μL of CTAB-coated gold nanoclusters solution, then add 1.5-3 mL of 0.1 M ascorbic acid solution. After the reactants are completely dissolved, add 2-2.5 mL of 0.5×10 −3 M HAuCl4 solution, react at 25-30°C for 15-20 minutes, then centrifuge at 14000-15500 rpm for 20-40 minutes and resuspend in 1-2 mL, 20×10 -3 In M CTAC solution, a gold nanosphere seed solution was obtained; Further, 0.3-0.4 g of hexadecyltrimethylammonium bromide was weighed and dissolved in 4-6 mL of water and gently stirred at 25-30 °C. 4-6 mL of 0.5 mM HAuCl4 solution was added to the above solution, and then 0.5-0.8 mL of 10×10 −3 M NaBH4 solution, stirred vigorously for 1.5-3.0 min, and placed at 25-30 °C for 2-5 h to ensure complete reaction, to obtain a CTAB-coated gold nanocluster solution.

[0012] Principle of the invention: The invention takes improving the sensitivity and repeatability of optical fiber LSPR sensing detection as the starting point, combines the advantages of optical fiber real-time sensing, and creatively proposes to use Au NPs as assembly units and utilize liquid-liquid interface self-assembly technology to prepare optical fiber LSPR sensors, thereby solving the problems of poor distribution uniformity of gold nanoparticles modified on optical fibers using traditional methods and complicated preparation processes, and prepares an optical fiber LSPR sensor uniformly modified with gold nanoparticles.

[0013] Beneficial effects of the present invention: (1) The gold nanoparticles assembled on the optical fiber are densely arranged and evenly distributed, which can effectively improve the detection repeatability; (2) The gold nanoparticles assembled on the optical fiber have regular hot spots, which can significantly enhance the LSPR sensing performance; (3) The obtained gold nanoparticles can reach the nanoscale, with an average size of about 35 nm and a uniform particle size distribution.

[0014] The present invention utilizes liquid-liquid interface self-assembly technology to make the gold nanoparticles assembled on the optical fiber densely arranged and evenly distributed, effectively improving the detection sensitivity. More importantly, there are regular hot spots between the gold nanoparticles, further improving the repeatability of the detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The following is an abstract of the present invention.

[0016] Figure 2 TEM image of the gold nanoparticles obtained in Example 1 of the present invention; Figure 2 As shown, the average particle size of the gold trioctahedron is about 35 nm.

[0017] Figure 3 This is a scanning electron microscope image (optical fiber surface) of the optical fiber LSPR sensor obtained in Example 3 of the present invention; Figure 3 As shown, the optical fiber is evenly covered with a layer of gold trioctahedron.

[0018] Figure 4For the optical fiber LSPR sensor obtained in Example 3 of the present invention, the resonance wavelength of the LSPR absorption peak changes from 687.81 nm to 699.33 nm at different refractive indices, resulting in a red shift phenomenon. According to the refractive index sensitivity calculation formula, the average refractive index sensitivity is 190.20 nm / RIU and the maximum refractive index sensitivity is 311.04 nm / RIU. DETAILED DESCRIPTION

[0019] Example 1: Preparation of gold nanoparticles (Au NPs) (1) Preparation of 3 nm gold nanocluster solution: Weigh 0.365 g of hexadecyltrimethylammonium bromide (CTAB) and dissolve it in 5 mL of water. Stir gently at 27 °C. Add 5 mL of 0.5 mM chloroauric acid solution (HAuCl4) to the above solution, and then quickly add 0.6 mL of 10×10 −3 M sodium borohydride solution (NaBH4), stirred for 2 min, and placed at 27 °C for 3 h to ensure the complete reaction, to obtain a CTAB-coated gold nanocluster solution.

[0020] (2) Preparation of 10 nm gold nanosphere seed solution: 2 mL, 200×10 −3 50 μL of CTAB-coated gold nanocluster solution was mixed with 50 μL of hexadecyltrimethylammonium chloride solution (CTAC) obtained in step (1), and then 1.5 mL of 0.1 M ascorbic acid solution (AA) was added. After the reactants were completely dissolved, 2 mL of 0.5×10 -3 M HAuCl4 solution was reacted at 27°C for 15 min, then centrifuged at 14500 rpm for 30 min and resuspended in 1 mL, 20×10 -3 A gold nanosphere seed solution with a particle size of 10 nm was obtained in the M CTAC solution.

[0021] (3) Preparation of Au NPs: Mix 2 mL of 0.1 M CTAC solution with 5 μL of the 10 nm gold nanosphere seed solution obtained in step (2), then add 130 μL of 0.1 M AA solution. After the reactants are completely dissolved, add 2 mL of 0.5×10 −3 M HAuCl4 solution, react at 27 °C for 15 min, centrifuge at 6000 rpm for 15 min, then disperse the precipitate into 0.5 mL of 1% polyvinyl pyrrolidone (PVP) ethanol solution, centrifuge at 6000 rpm for 15 min, and disperse the precipitate in 0.5 mL of ethanol to obtain AuNPs ethanol solution, which was stored at 4 °C.

[0022] Example 2: Preparation of hydroxyl-functionalized optical fiber First, the optical fiber was cut into 35 cm long segments, and the 2 cm cladding in the middle of the optical fiber was removed with a knife as the sensing area. Then the optical fiber was immersed in piranha solution (H2SO4:H2O2=4:1, volume ratio) for 2 hours, then rinsed with water and dried to modify the hydroxyl groups on the optical fiber.

[0023] Example 3: Preparation and detection of optical fiber LSPR sensor (1) Preparation of optical fiber LSPR sensor: The gold nanoparticles prepared in Example 1 are used as assembly units and are densely and evenly assembled on the optical fiber treated in Example 2 using liquid-liquid interface self-assembly technology. Au NPs with weak negative charge are evenly assembled on the hydroxyl-functionalized optical fiber surface.

[0024] (2) Preparation of sucrose samples In order to analyze the change of LSPR peak of gold nanoparticle-based optical fiber LSPR sensor with refractive index, sucrose samples 1 with different concentrations were prepared and used as test liquids for refractive index sensing experiments together with ultrapure water.

[0025] (3) Detection of optical fiber LSPR sensor The optical fiber LSPR sensor obtained in step (1) was placed in a microfluidic chip, and then sucrose samples 1 of different concentrations were added to the microfluidic chip in sequence, while the optical signal in the spectrometer was recorded. The refractive index of sucrose aqueous solutions of different concentrations was measured using the Abbe refractive index, and the refractive index range was found to be between 1.33 and 1.42. Figure 3 As shown in the figure, as the refractive index of the test liquid increases, the resonance wavelength of the LSPR absorption peak changes from 687.81 nm to 699.33 nm, resulting in a red shift. According to the refractive index sensitivity calculation formula, the average refractive index sensitivity is 190.20 nm / RIU and the maximum refractive index sensitivity is 311.04nm / RIU.

Claims

1. A method for preparing an optical fiber LSPR sensor modified with gold nanocrystals, the steps of which are as follows: (1) Preparation of Au NPs using the seed growth method: 2–2.5 mL of 0.1 M hexadecyltrimethylammonium chloride solution was mixed with 5–20 μL of 10 nm gold nanosphere seed solution, followed by the addition of 130–150 μL of 0.01 M ascorbic acid solution. After the reactants were completely dissolved, 2–2.5 mL of 0.5 × 10 −3 M HAuCl4 solution, react at 25-30°C for 15-20 min, centrifuge at 5500-6000 rpm for 10-15 min; then disperse the precipitate into 0.5-1 mL, 1% PVP ethanol solution, centrifuge at 5500-6000 rpm for 10-15 min, and disperse the precipitate in 0.5-1 mL ethanol to obtain Au NPs ethanol solution, which is stored at 4°C; (2) Preparation of hydroxyl-functionalized optical fiber using piranha solution: First, cut the optical fiber into 35 cm long segments, and use a knife to remove the 2 cm cladding in the middle of the optical fiber as the sensing area. Then soak the dried optical fiber in piranha solution for 1 to 3 hours, rinse with water and dry, so that hydroxyl groups are modified on the surface of the optical fiber, and then rinse with water and dry for use; (3) Preparation of optical fiber LSPR sensor: The gold nanoparticles prepared in Example 1 are used as assembly units, and are densely and uniformly assembled on the optical fiber treated in Example 2 using liquid-liquid interface self-assembly technology. The Au NPs with weak negative charge are uniformly assembled on the surface of the hydroxyl-functionalized optical fiber, thereby preparing an optical fiber LSPR sensor modified with gold nanoparticles; in, Au NPs are gold nanoparticles, and PVP is polyvinyl pyrrolidone.

2. A method for preparing a gold nanocrystal-modified optical fiber LSPR sensor according to claim 1, characterized in that: 2~2.5 mL, 200×10 −3 Mix 40-60 μL of 0.1 M hexadecyltrimethylammonium chloride solution with 40-60 μL of hexadecyltrimethylammonium bromide-coated gold nanoclusters solution, then add 1.5-3 mL of 0.1 M ascorbic acid solution. After the reactants are completely dissolved, add 2-2.5 mL of 0.5×10 −3 M HAuCl4 solution, react at 25-30°C for 15-20 minutes, then centrifuge at 14000-15500 rpm for 20-40 minutes and resuspend in 1-2 mL, 20×10 -3 M CTAC solution to obtain gold nanosphere seed solution.

3. A method for preparing a gold nanocrystal-modified optical fiber LSPR sensor according to claim 2, characterized in that: Weigh 0.3-0.4 g of hexadecyltrimethylammonium bromide and dissolve it in 4-6 mL of water. Stir gently at 25-30 °C. Add 4-6 mL of 0.5 mM HAuCl4 solution to the above solution, and then quickly add 0.5-0.8 mL of 10×10 −3 M NaBH4 solution, stirred vigorously for 1.5-3.0 min, and placed at 25-30 °C for 2-5 h to ensure complete reaction, to obtain a hexadecyltrimethylammonium bromide-capped gold nanocluster solution.

4. An optical fiber LSPR sensor modified with gold nanocrystals, characterized in that: The method is prepared by any one of claims 1 to 3.

5. A method for preparing a gold nanocrystal-modified optical fiber LSPR sensor according to claim 4.

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