SPR fiber-optic sensor, preparation method thereof and detection system

Abstract

The application discloses an SPR optical fiber sensor, a preparation method thereof and a detection system, wherein the SPR optical fiber sensor comprises: an optical fiber base with a removed optical fiber cladding; and a metal nanoparticle layer arranged on the optical fiber base, at least one section of the metal nanoparticle layer has a gradient change in particle size along an optical fiber axial direction. The application provides the SPR optical fiber sensor, and the sensitivity of the sensor is effectively enhanced and the detection range is expanded by arranging the metal nanoparticle layer with the gradient change in particle size along the optical fiber axial direction.

Description

Technical Field

[0001] This invention relates to the field of SPR fiber optic sensor technology, and more specifically, to an SPR fiber optic sensor, its fabrication method, and detection system. Background Technology

[0002] Surface plasmon resonance (SPR) is a novel detection method for studying the interaction between the surfaces of materials with different properties and incident light. SPR is an energy transfer effect that lies between the surface of a metallic layer and a dielectric layer.

[0003] With the deepening research on SPR sensing technology over the past few decades, researchers have developed SPR fiber optic sensors on optical fibers. When a beam of light propagates infinitely in the fiber core while satisfying the total internal reflection theorem, a portion of the light energy is transmitted into the cladding, forming an evanescent wave. This evanescent wave then enters the metal layer along the interface, causing the free electrons on the metal layer surface to move in a directional manner, forming a plasma wave. When the evanescent wave propagating along the interface meets certain phase-matching conditions, it will resonate with the plasma wave formed on the metal layer surface, ultimately causing a sharp attenuation of the energy propagating back into the fiber core, thus forming a resonance peak. Since the propagation distance of the evanescent wave in the metal medium is limited, the thickness of the metal layer must be set at the nanometer level to effectively utilize the SPR effect to detect changes in the medium above the metal. Taking the detection of the refractive index of the medium as an example, when the refractive index of the medium above the metal layer changes under certain conditions, the corresponding resonance conditions of the SPR effect will also change accordingly, resulting in a shift of the resonance peak in the transmission spectrum. By analyzing the shift of the resonance peak, performance parameters such as the sensitivity, detection accuracy, and quality factor of the sensor corresponding to the refractive index of the medium can be obtained. Therefore, it is widely used in various fields such as biomedicine, food safety, environmental monitoring, and chemical detection.

[0004] However, traditional fiber optic SPR (Self-Range Persistent Wave) sensors have very low sensitivity. In recent years, many researchers have been exploring methods to enhance fiber optic sensitivity. Sensitivity enhancement methods for fiber optic SPR sensors mainly fall into two categories: one involves modifying the fiber substrate structure, and the other involves enhancing sensitivity through film materials. For fiber optic SPR sensors, the evanescent wave penetrating the fiber core surface film and coupling with the sensing layer is fundamental to the sensor's operation. By designing different fiber substrate structures, the intensity of the evanescent wave can be effectively enhanced. Commonly used evanescent wave-enhanced fiber substrate structures include D-type, U-type, and tapered structures. Because optical fibers are inherently thin and fragile, modifying the substrate structure presents certain technical difficulties and challenges.

[0005] Once the type and shape of the optical fiber used as the sensor substrate are fixed, the film material in the sensing region becomes the most direct and important factor determining the sensor's performance. Researchers have attempted to enhance the performance of SPR fiber optic sensors by adding other film materials as auxiliary layers to the surface of metal films. When metal oxide films are used as auxiliary layers, they alter the electric field distribution in the sensing film, thereby enhancing the electric field strength and effectively improving the sensitivity of the fiber optic SPR sensor. Furthermore, researchers have discovered that coating the sensor surface with two-dimensional materials such as graphene can achieve highly sensitive measurements. These materials possess unique optical properties and good biocompatibility; due to their large specific surface area, they can bind more small biological molecules, improving the molecular binding efficiency at the sensor interface and effectively amplifying the SPR signal.

[0006] The two methods for enhancing sensitivity described above either involve modifying the optical fiber itself (substrate structure), which is costly, has poor repeatability, and is not conducive to large-scale applications; or optimizing the film material, which is cumbersome, complex, and costly. Ultimately, this results in low stability and reliability of surface plasmon resonance spectrometers built based on the aforementioned optical fiber sensors. Summary of the Invention

[0007] This invention aims to address one of the technical problems in related technologies to a certain extent. To this end, this invention proposes an SPR fiber optic sensor that effectively enhances the sensor's sensitivity and expands its detection range by setting a layer of metal nanoparticles with a gradient particle size along the fiber axis.

[0008] This invention also proposes a method for fabricating an SPR fiber optic sensor.

[0009] The present invention also proposes a detection system for an SPR fiber optic sensor.

[0010] The technical solution adopted by this invention is: to provide an SPR fiber optic sensor, comprising:

[0011] A section of fiber substrate with the fiber cladding removed;

[0012] A metal nanoparticle layer is disposed on an optical fiber substrate, wherein at least one section of the metal nanoparticle layer has a gradient in particle size along the optical fiber axis.

[0013] In existing technologies, the fabrication of SPR fiber optic sensors typically focuses on achieving the most uniform thickness and particle size of the metal nanoparticle layer to ensure stable sensing performance. Through in-depth research, the inventors discovered that if the particle size of the metal nanoparticle layer exhibits a gradient along the fiber axis, the sensor's sensitivity can be significantly improved, overcoming the industry's inherent understanding and technical biases regarding the uniformity design of metal nanoparticle layers. This innovative design effectively enhances the sensor's sensitivity and expands its detection range.

[0014] By adopting this design, the present invention provides a highly sensitive SPR fiber optic sensor with broad application potential in biological detection, chemical analysis and other high-precision sensing fields.

[0015] According to one embodiment of the present invention, the metal nanoparticle layer comprises one or more of gold, silver, copper, platinum, aluminum, titanium, and any combination thereof; the metal nanoparticle layer on the surface of the optical fiber core is mainly used to excite surface plasmon resonance. The metal nanoparticle layer interacts with the incident light to generate surface plasmon waves that are highly sensitive to changes in the refractive index of the external medium, thereby enhancing the sensitivity and detection limit of the sensor. Through the concentration effect of the local electromagnetic field, the metal nanoparticle layer can significantly improve the signal intensity.

[0016] According to one embodiment of the present invention, the larger particle size in the metal nanoparticle layer is 30-100 nm, and the smaller particle size is 10-60 nm; and / or

[0017] The ratio of the smaller particle size to the larger particle size in the metal nanoparticle layer is 1-6:10.

[0018] According to one embodiment of the present invention, the SPR fiber optic sensor further includes a single-layer dielectric layer or multiple dielectric layers with different refractive indices, wherein the metal nanoparticle layer is located above, below, or between multiple dielectric layers; the interference effect of the Fabry-Perot cavity of the dielectric layer is coupled with the local surface plasmon resonance effect of the metal nanoparticle layer, constructing a new characteristic peak in the near-infrared region of the spectrum, which can achieve high-sensitivity sensing and precisely adjust the position of the characteristic peak of the fiber optic sensor.

[0019] According to one embodiment of the present invention, the dielectric layer comprises a polymer, a metal, a metal oxide, silicon, or graphene. By adjusting the material of the dielectric layer, not only can the sensitivity of the sensor be optimized, but the position of the characteristic peaks can also be precisely adjusted to adapt to the needs of different detection objects and environments. For example, graphene has excellent conductivity and optical transparency, which can further enhance the sensor's response to electromagnetic fields, while metal oxides can provide a stable dielectric environment, improving the overall stability and durability of the sensor.

[0020] According to one embodiment of the present invention, the dielectric layer may be composed of any one or more of the following: parylene-C, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), silicon oxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3), titanium oxide (TiO2), or photoresist.

[0021] According to one embodiment of the present invention, a functional layer is provided on the surface of the metal nanoparticle layer.

[0022] According to one embodiment of the present invention, the functional layer includes one or more of polymer-based functional layers, metal oxide-based functional layers, biometric material-based functional layers, carbon-based material-based functional layers, and any combination thereof.

[0023] According to one embodiment of the present invention, the polymer-based functional layer comprises polyvinyl alcohol, polydimethylsiloxane, polystyrene, and polyamide; and / or

[0024] The metal oxide functional layer includes zinc oxide, indium tin oxide, aluminum oxide, and titanium oxide; and / or

[0025] The biometric material functional layer includes antibodies, DNA probes, and enzymes; and / or

[0026] The carbon-based material functional layers include graphene and carbon nanotubes; the metal oxide functional layers, such as zinc oxide (ZnO), indium tin oxide (ITO), aluminum oxide (Al2O3), and titanium oxide (TiO2), are known for their excellent photoelectric properties and transparency. They can further enhance the SPR effect, improving the sensor's sensitivity by increasing the dielectric constant and refractive index difference, and are particularly well-suited for photoelectric detection and gas sensing.

[0027] Biorecognition material functional layers, including antibodies, DNA probes, and enzymes, enable SPR fiber optic sensors to specifically recognize biomolecules, making them particularly suitable for biosensors and medical diagnostics. These materials can specifically bind to target molecules, thereby significantly altering the local refractive index and generating a distinct SPR signal response.

[0028] Carbon-based functional layers such as graphene and carbon nanotubes can greatly enhance the signal response of sensors and broaden their application range due to their excellent electrical conductivity and chemical sensitivity. Graphene also has excellent mechanical strength and surface activity, making it suitable for various functional applications in sensors.

[0029] According to one embodiment of the present invention, the optical fiber substrate structure includes a D-type structure, a U-type structure, a tapered structure, and a core mismatch structure; by changing the structure of the optical fiber substrate, the intensity of the evanescent wave can be effectively improved, which maximizes the coupling between the evanescent wave and the plasma wave, thereby further improving the sensitivity of the sensor.

[0030] According to one embodiment of the present invention, the diameter of the fiber substrate from which the fiber cladding is removed is 100-1000 μm; and / or

[0031] The length of the fiber substrate from which the fiber cladding has been removed is 1-100 mm; and / or

[0032] The length of the fiber substrate without removing the fiber cladding is 10-200 mm; and / or

[0033] The fiber cladding is equipped with a connector.

[0034] According to one embodiment of the present invention, the connector includes SMA905, FC / PC, and quick-connect connectors; and / or

[0035] The thickness of the metal nanoparticle layer is 10-100 nm.

[0036] A method for fabricating an SPR fiber optic sensor as described above includes the following steps:

[0037] S1. Remove a section of the fiber cladding to expose the fiber substrate, and then clean it with a cleaning solution.

[0038] S2. A metal nanoparticle layer is deposited on the surface of the optical fiber substrate, and the particle size of at least one section of the metal nanoparticle layer varies in gradient along the optical fiber axis.

[0039] According to one embodiment of the present invention, in step S2, the coating process of the metal nanoparticle layer includes vacuum evaporation, magnetron sputtering, melt coating, electroless plating, and ion plating.

[0040] According to one embodiment of the present invention, in step S2, metal nanoparticle layers are prepared segment by segment, with the particle size increasing or decreasing between adjacent segments. Multiple metal nanoparticle layers are combined to form a segment of metal nanoparticle layer with a gradient change in particle size along the optical fiber axis. This layered coating technique not only enables precise control of metal nanoparticles of different sizes but also effectively constructs a metal nanoparticle layer with a gradient change in particle size along the optical fiber axis. This design can significantly enhance the performance of the SPR sensor, especially in terms of signal response and sensitivity.

[0041] According to an embodiment of the present invention, step S2 includes:

[0042] S1. Cut off one end of the optical fiber substrate to form a free end;

[0043] S2. Place the optical fiber substrate vertically with the free end facing upwards. Use magnetron sputtering to sputter a layer of metal nanoparticles onto the exposed portion of the optical fiber substrate. Magnetron sputtering, with its simplicity and high efficiency, is an ideal method for preparing metal nanoparticle layers.

[0044] A detection system includes a light source, a spectrometer, and any of the SPR fiber optic sensors described above. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the SPR fiber optic sensor in Embodiment 1 of the present invention;

[0047] Figure 2 This is a schematic diagram of the SPR fiber optic sensor in Embodiment 1 of the present invention;

[0048] Figure 3 This is a schematic diagram of the detection system in Embodiment 1 of the present invention;

[0049] Figure 4 The images show the spectra of the fiber optic SPR sensor in different glycerol aqueous solutions in Embodiment 1 of the present invention. The refractive indices of the glycerol aqueous solutions corresponding to the highest peaks in the spectra from top to bottom are 1.384, 1.357, 1.345, and 1.339, respectively.

[0050] Figure 5 This is the refractive index sensitivity fitting curve of the fiber optic SPR sensor in Embodiment 1 of the present invention;

[0051] Figure 6 The images show the SEM images of the front (a), middle (b), and rear (c) sections of the decladding portion of the fiber optic SPR sensor in Embodiment 1 of the present invention.

[0052] Figure 7 This is the refractive index sensitivity fitting curve of the fiber optic SPR sensor in Embodiment 2 of the present invention;

[0053] Figure 8 This is a schematic diagram of the SPR fiber optic sensor in Embodiment 3 of the present invention monitoring the binding of IgG in real time after chemical modification. The concentrations of IgG in the curves from top to bottom are 20, 10, 5, 2.5, and 1.25 μg / ml.

[0054] Figure 9 This is the standard curve of the IgG binding process in Example 3 of the present invention.

[0055] Explanation of the labels in the diagram:

[0056] 1. Connector; 2. Fiber cladding; 3. Fiber substrate; 4. Metal nanocoating; 5. Fiber probe; 6. Light source; 7. Spectrometer. Detailed Implementation

[0057] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0058] In this embodiment, SPR fiber optic sensors can be categorized into two types based on the light propagation path: linear transmission and reflective transmission. Linear transmission, also known as in-line transmission, typically refers to a sensing system that transmits the sensing signal via optical fiber to a remote location for processing and analysis. In this system, the optical fiber transmits the light signal, while the sensor and signal processing system are usually located at opposite ends of the fiber. This allows the sensor to remotely monitor and measure changes in target physical quantities, such as temperature, pressure, deformation, and vibration, without direct contact with the object being measured, thus achieving non-contact measurement.

[0059] A reflective fiber optic sensor, also known as a terminal reflective sensor, has a metal nanocoating coated on the end of an optical fiber, forming a reflective surface at the tip. This sensor utilizes the interference effect of reflected light for measurement. When the refractive index of the analyte changes, the SPR resonance condition also changes accordingly, resulting in a shift in the resonant wavelength, which is reflected in a change in the intensity of the reflected light. By detecting the change in the intensity of the reflected light, information about the refractive index of the analyte can be obtained.

[0060] Combination Figure 2 As shown, in a linear transmission SPR fiber optic sensor, a localized surface plasmon resonance (LSPR) structure is fixed to the side of the optical fiber, while the outer surface of the fiber serves as the sensing region. The device at the other end of the fiber receives the transmitted optical signal. Within the sensing region, light interacting with the nanostructure excites the LSPR effect, causing a change in the intensity or wavelength of the transmitted light, which is detected by the receiver.

[0061] Combination Figure 1 As shown, in a reflective SPR fiber optic sensor, incident light enters from only one end and is reflected by the receiving end face of the fiber coupler. The LSPR-active nanostructure is fixed to the outer surface of the fiber end face or near the probe tip. The receiver is responsible for acquiring and analyzing the reflected signal data to determine changes in intensity or wavelength of the reflected light. Through these two structures, FOLSPR can efficiently detect various environmental changes, providing flexible options for sensing applications.

[0062] D-type fiber substrates remove the cladding on one side of the fiber using a side-jetting process, exposing the fiber core and thus enabling evanescent field leakage. Its main advantages lie in the smooth sensing area, which facilitates uniform film deposition on the fiber surface, enhancing the SPR effect, and also allows for the addition of sensitizing layers and the attachment of biomolecules.

[0063] The U-shaped fiber substrate is formed by partially removing the fiber cladding and then bending it under heat to create a U-shaped structure, thus completing the fabrication of the sensing region. When the light signal enters the sensing region, the incident angle decreases, and the penetration depth of the light increases, thereby enhancing the evanescent field effect and improving the sensitivity of the sensor.

[0064] Tapered fiber substrates are created by heating and stretching ordinary optical fibers using a carbon dioxide laser to form a tapered region. Through tapering, the core and cladding diameters of the fiber gradually decrease, allowing the evanescent field to penetrate the cladding and extend into the external medium, thereby enhancing the interaction between the fiber and the external environment.

[0065] Grating-type fiber substrates effectively excite the SPR effect by incorporating gratings into the fiber core to generate periodic refraction. Common grating types include uniform fiber Bragg gratings, tilted fiber Bragg gratings, eccentric fiber Bragg gratings, maximum-angle tilted fiber gratings, and long-period fiber gratings. By adjusting parameters such as the grating tilt angle, grating pitch, and eccentricity, these grating structures can couple light waves of specific wavelengths from the fiber core to the cladding, achieving optimized detection of specific sensing signals. Different types of fiber grating structures can be designed and adjusted for different application scenarios to improve sensor performance and sensitivity.

[0066] Example 1

[0067] This embodiment discloses an SPR fiber optic sensor.

[0068] like Figure 3 As shown, a schematic diagram of an optical fiber surface plasmon resonance (SPR) sensor detection system is provided, including: a fabricated optical fiber probe 5, a light source 6, and a spectrometer 7. The SPR optical fiber sensor used in this embodiment is as follows: Figure 1 As shown, the system includes: an optical fiber substrate with a diameter of 100-1000 μm (without the cladding removed), an optical fiber substrate with a length of 1-100 mm (without the cladding removed), and an optical fiber substrate with a length of 10-200 mm (without the cladding removed). The optical fiber cladding is equipped with a connector. An optical fiber probe is positioned between the light source and the spectrometer. The optical fiber probe is connected to the light source via an optical fiber. Light emitted from the light source is transmitted to the optical fiber probe through the intermediate optical fiber. Within the optical fiber probe, light is continuously reflected before reaching the sensing area. The signal generated by the reaction between the optical fiber probe and the analyte is received by the spectrometer.

[0069] Specifically, the cladding removal process using a fiber probe involves physical sputtering to form a gold film on the fiber surface, with the gold film particle size exhibiting a gradient along the fiber axis. When light emitted from the light source propagates infinitely through the fiber core under the law of total internal reflection, a portion of the light energy is transmitted into the cladding, forming an evanescent wave that enters the gold layer along the interface. This evanescent wave then causes the free electrons on the gold layer surface to move in a directional manner, forming a plasma wave. When the evanescent wave propagating along the interface meets certain phase-matching conditions, it resonates with the plasma wave formed on the metal layer surface, ultimately causing a dramatic attenuation of the energy propagating back into the fiber core. After receiving the signal, the spectrometer detects the resonance peak in the spectrum.

[0070] Specifically, in this embodiment, the optical fiber probe has a diameter of 0.43 mm, a sensor area of ​​6 mm, and an optical fiber length of 35 mm. The fabrication steps are as follows:

[0071] (a) Fiber cladding removal: Take a complete, untreated fiber and use Miller pliers to remove 6 mm of the cladding to expose the fiber core as the sensor area.

[0072] (b) Fiber pretreatment: The fiber with the cladding removed is sonicated with ultrapure water and acetone for 5 minutes in sequence. After the fiber is removed, it is rinsed with ultrapure water and left to stand for 5 minutes to remove the moisture on the surface of the fiber.

[0073] (c) Deposition of the gold film: Using an ion sputtering apparatus, the pretreated optical fiber was placed vertically on the fixture inside the sputtering machine, covered with a glass tube, and the vent valve was tightened. The thickness of the sputtered film on the optical fiber surface was adjusted by controlling the deposition time and deposition current. A deposition current of 15 mA and a deposition time of 20 s were set for gold film sputtering. After deposition, the optical fiber probe was removed for subsequent experiments.

[0074] Detection of analyte refractive index sensitivity based on SPR fiber optic sensor: The refractive index of the solution was adjusted by mixing glycerol and ultrapure water in different volume ratios. Glycerol aqueous solutions with refractive indices of 1.333, 1.339, 1.345, 1.357, and 1.384 were used for detection by the SPR fiber optic sensor provided in this invention, resulting in changes in the resonance wavelength, as shown in the spectrum. Figure 4 As shown, the refractive indices of the highest peaks in the spectrum, from top to bottom, are 1.384, 1.357, 1.345, and 1.339, respectively. The sensor's sensitivity can be calculated using the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to different refractive indices of the analyte at the resonant wavelength, and Δn is the difference in refractive indices of the analyte. Its refractive index sensitivity fitting curve is shown below. Figure 5As shown, based on the slope of the fitted curve, the sensitivity of the fiber optic SPR sensor of this invention is 3369 nm / RIU. To investigate the deposition of gold particles on the fiber surface, SEM testing was performed on the fiber with the gold layer fabricated. The gold particles on the fiber probe surface are shown in the figure. Figure 6 As shown, the gold particle size in the front (a), middle (b), and rear (c) sections of the fiber optic probe sensing region exhibits a gradient change along the fiber optic axis. For each section, multiple points were taken to calculate the average gold particle size. The average gold particle size in the front (a) section is 47.16 nm, in the middle (b) section it is 39.42 nm, and in the rear (c) section it is 29.75 nm.

[0075] In some other embodiments, the fiber length is 10-200 mm, preferably 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm or 70 mm. The cladding stripping length using Miller clamps is 10-100 mm, preferably 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm or 100 mm.

[0076] In some other embodiments, the metal nanoparticle layer is replaced by pure metals such as silver, copper, platinum, aluminum, or titanium instead of the gold film in this embodiment. In some other embodiments, the metal nanoparticle layer is replaced by any combination of silver, copper, platinum, aluminum, and pure titanium instead of the gold film in this embodiment.

[0077] In other embodiments, several dielectric layers are disposed on the optical fiber substrate. The interference effect of the Fabry-Perot cavity in the dielectric layers is coupled with the localized surface plasmon resonance effect of the gold nanoparticles, constructing a new characteristic peak in the near-infrared region of the spectrum. This enables high-sensitivity sensing and allows for precise adjustment of the characteristic peak position of the optical fiber sensor. This is prior art, as clearly described in the specific implementation of CN115855883A, and therefore will not be elaborated further.

[0078] Example 2

[0079] A schematic diagram of a fiber optic surface plasmon resonance sensor detection system is provided, including: a fabricated fiber optic probe 5, a light source 6, and a spectrometer 7. The fiber optic probe is positioned between the light source and the spectrometer. The fiber optic probe is connected to the light source via an optical fiber. Light emitted from the light source is transmitted to the fiber optic probe through the intermediate optical fiber, and reaches the sensing area through continuous reflection within the fiber optic probe. The signal generated by the reaction between the fiber optic probe and the analyte is received by the spectrometer.

[0080] Specifically, the cladding removal process of the fiber probe involves physical sputtering to form a gold film on the fiber surface, with the gold film particle size exhibiting a gradient along the fiber axis. A TiO2 thin film is then coated onto the gold film surface using an dip-coating method. The gold layer is positioned between the fiber core and the TiO2 dielectric layer. The addition of the TiO2 dielectric layer further enhances the SPR effect, improving the sensitivity of the SPR fiber sensor by increasing the dielectric constant and refractive index difference.

[0081] Furthermore, in some other embodiments, a layer of pure silver, pure copper, pure platinum, pure aluminum, or pure titanium is pre-sputtered between the optical fiber surface and the gold film, which together with the gold film form a metal nanoparticle layer.

[0082] Specifically, in this embodiment, the optical fiber probe has a diameter of 0.43 mm, a sensor area of ​​6 mm, and an optical fiber length of 35 mm. The fabrication steps are as follows:

[0083] (a) Fiber cladding removal: Take a complete, untreated fiber and use Miller pliers to remove 6 mm of the cladding to expose the fiber core as the sensor area.

[0084] (b) Fiber pretreatment: The fiber with the cladding removed is sonicated with ultrapure water and acetone for 5 minutes in sequence. After the fiber is removed, it is rinsed with ultrapure water and left to stand for 5 minutes to remove the moisture on the surface of the fiber.

[0085] (c) Deposition of the gold film: Using an ion sputtering apparatus, the pretreated optical fiber was placed vertically on the fixture inside the sputtering machine, covered with a glass tube, and the vent valve was tightened. The thickness of the sputtered film on the optical fiber surface was adjusted by controlling the deposition time and deposition current. A deposition current of 15 mA and a deposition time of 20 s were set for gold film sputtering. After deposition, the optical fiber probe was removed for subsequent experiments.

[0086] (d) Preparation of TiO2 sol: First, prepare 50 mL of 4% acetic acid solution using 99.5% acetic acid; weigh 250 mg of chitosan powder using a balance and add it to 50 mL of 4% acetic acid solution, then stir with a magnetic stirrer at room temperature until the chitosan is completely dissolved; next, weigh 50 mg of TiO2 nanoparticles and slowly add them to the chitosan solution, then stir magnetically at room temperature for 2 h to form TiO2 sol.

[0087] (e) TiO2 dielectric layer preparation: The gold-plated fiber SPR sensing probe was immersed in TiO2 sol for 5 min, then the lifting device was manually rotated to pull the fiber probe up within a certain time, and dried at room temperature for 10 min; the fiber SPR sensor was rinsed with deionized water for 1 min, pulled out and dried at room temperature for 10 min; the same dip-coating process was completed using 4% polyacrylic acid solution instead of TiO2 sol; it was then soaked in deionized water for 1 min and dried at room temperature for 20 min. After deposition, the sensing probe was placed in a vacuum drying oven at 60℃ for 2 h, at which point the deposition of the TiO2 thin film was completed.

[0088] Sensitivity detection of analyte refractive index based on SPR fiber optic sensor: The refractive index of the solution is adjusted by mixing glycerol and ultrapure water in different volume ratios. Glycerol aqueous solutions with refractive indices of 1.333, 1.339, 1.345, 1.357, and 1.384 are used for detection by the SPR fiber optic sensor provided in this invention, causing changes in the resonant wavelength, thus achieving high sensitivity and real-time detection. The sensor sensitivity can be obtained by the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to different refractive indices of the analyte at the resonant wavelength, and Δn is the difference in refractive index of the analyte. The refractive index sensitivity fitting curve is shown below. Figure 7 As shown, based on the slope of the fitted curve, the sensitivity of the fiber optic SPR sensor of the present invention can be determined to be 4635 nm / RIU. Compared with the sensitivity of 3369 nm / RIU of the fiber optic SPR sensor obtained in Example 1, the addition of the TiO2 dielectric layer increases the sensitivity of the fiber optic SPR sensor.

[0089] In some other embodiments, the titanium dioxide dielectric layer in this embodiment is replaced by any one or more of poly(p-chloroxylene), polydimethylsiloxane, polymethyl methacrylate, silicon oxide, silicon nitride, aluminum oxide, and photoresist.

[0090] Example 3

[0091] In this embodiment, the SPR fiber optic sensor of this patented invention is used to detect immunoglobulins. The steps are as follows:

[0092] (a) Fiber cladding removal: Take a complete, untreated fiber and use Miller pliers to remove 6 mm of the cladding to expose the fiber core as the sensor area.

[0093] (b) Fiber pretreatment: The fiber with the cladding removed is sonicated with ultrapure water and acetone for 5 minutes in sequence. After the fiber is removed, it is rinsed with ultrapure water and left to stand for 5 minutes to remove the moisture on the surface of the fiber.

[0094] (c) Deposition of gold film: Using an SBC-12 miniature ion sputtering system, the pretreated optical fiber was placed vertically on the fixture inside the sputtering coating machine, the glass tube was covered, and the vent valve was tightened. The coating thickness was adjusted by controlling the coating time and coating current. The coating current was set to 15mA and the coating time to 20s.

[0095] (d) Construction of the SPR fiber optic sensor system: To study the sensing performance of the SPR fiber optic sensor proposed in this invention, a fiber optic SPR sensor system was constructed. The light source used in the system was a D2600 tungsten lamp from Hangzhou Jingfei Technology Co., Ltd., with a working wavelength range of 350nm to 950nm. The coated fiber optic probe was immersed in an aqueous glycerol solution with a refractive index variation of 1.333-1.384. After reflection by the reflective layer at the fiber end face, the light waves were collected by a spectrometer (FLA5300 70μm, wavelength range: 350-1100nm). The SPR spectral curves were obtained by data analysis using the 2023 Jingfei Spectral Testing and Analysis Software V6.64.3.157 developed by Hangzhou Jingfei Technology Co., Ltd.

[0096] (e) SPR sensor sensitivity testing: The refractive index of the solution was adjusted by mixing glycerol and ultrapure water in different volume ratios. Glycerol aqueous solutions with refractive indices of 1.333, 1.339, 1.345, 1.357, and 1.384 were used in the SPR fiber optic sensor provided by this invention for detection, resulting in changes in the resonant wavelength. The sensor sensitivity can be obtained by the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to different refractive indices of the analyte at the resonant wavelength, and Δn is the difference in refractive index of the analyte.

[0097] (f) Preparation of the carboxylated dextran functional layer: The gold-coated optical fiber was placed in a centrifuge tube, and 5 mM 11-mercaptoundecanoic acid was added. The reaction was carried out at 40 °C for 30 min, resulting in the formation of a mercaptoalcohol layer on the surface. This facilitates further modification while sealing the surface to reduce non-specific adsorption. The optical fiber was removed from the centrifuge tube and washed with 80% ethanol solution and ultrapure water to remove residual solution. It was then allowed to stand for 5 min to remove moisture from the fiber surface. The mercaptoalcohol-linked optical fiber was placed in a new centrifuge tube, and 0.6 M epichlorohydrin solution was added. The reaction was carried out at room temperature for 4 h, resulting in the formation of epoxy groups on the surface. The fiber was then removed, rinsed with ethanol and ultrapure water, and allowed to stand for 5 min to remove moisture from the fiber surface. The dried optical fiber was then placed in a 0.3 g / mL dextran solution and reacted at room temperature for 20 h, resulting in the formation of a dextran layer on the gold film surface via covalent bonds. The fiber was then removed, washed with ultrapure water, and allowed to stand for 5 min to remove moisture from the fiber surface. The dextran-modified optical fiber was placed in a new centrifuge tube, and 1M bromoacetic acid solution was added. The tube was then incubated with shaking at room temperature for 16 hours to carboxylate the dextran attached to the chip surface. After removal, the fiber was washed with ultrapure water and allowed to stand for 5 minutes to remove moisture from the fiber surface, thus completing the modification process.

[0098] Analyte (IgG) detection: Activation buffer solution, 50 mM N-hydroxysuccinimide (NHS), and 200 mM 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were mixed at a volume ratio of 1:1. The modified fiber optic SPR probe was reacted in the mixture for 30 min. The activated fiber optic SPR probe was then immersed in 200 μg / ml Protein A (sodium acetate buffer, 0.01 M, pH = 4.5) solution and the sensing area was completely immersed at room temperature for 10 min. The shift in resonance wavelength was observed. Once the ligand immobilization process reached stability, the fiber optic probe was immersed in the analyte. The IgG molecules in the analyte specifically bound to the Protein A immobilized on the fiber optic surface, causing a change in the refractive index around the fiber optic probe, and consequently shifting the resonance wavelength in the spectrum. Figure 8 This is a schematic diagram of the SPR fiber optic sensor of the present invention monitoring IgG binding in real time after chemical modification. Figure 9 It is the standard curve for the IgG binding process.

[0099] In this embodiment, the carboxylated dextran functional layer belongs to the category of biorecognition material functional layers, more specifically, it is a type of antibody recognition material functional layer. In other embodiments, polyvinyl alcohol, polydimethylsiloxane, polystyrene, polyamide, zinc oxide, indium tin oxide, aluminum oxide, titanium oxide, DNA probes, enzymes, graphene, or carbon nanotubes are used instead of the IgG antibody functional layer in this embodiment.

[0100] Comparative Example 1

[0101] like Figure 3 The diagram illustrates a fiber optic surface plasmon resonance sensor detection system, comprising: a fabricated fiber optic probe 5, a light source 6, and a spectrometer 7. The fiber optic probe is positioned between the light source and the spectrometer. The fiber optic probe is connected to the light source via an optical fiber. Light emitted from the light source is transmitted to the fiber optic probe through the intermediate optical fiber, and after continuous reflection within the probe, reaches the sensing area. The signal generated by the reaction between the fiber optic probe and the analyte is received by the spectrometer.

[0102] Specifically, the optical fiber probe used in this comparative example has a diameter of 0.43 mm, a sensor area of ​​6 mm, and an optical fiber length of 35 mm. The steps for gold film deposition on the optical fiber surface are as follows:

[0103] (a) Fiber cladding removal: Take a complete, untreated fiber and use Miller pliers to remove 6 mm of the cladding to expose the fiber core as the sensor area.

[0104] (b) Fiber pretreatment: The fiber with the cladding removed is sonicated with ultrapure water and acetone for 5 minutes in sequence. After the fiber is removed, it is rinsed with ultrapure water and left to stand for 5 minutes to remove the moisture on the surface of the fiber.

[0105] (c) Gold film deposition on the fiber optic surface: Place the pretreated fiber flat on the stage of the SBC-12 miniature ion sputtering instrument, ensuring the entire sensing area and the target are at the same height. Cover with the glass tube and tighten the vent valve. Set the deposition current to 15mA and the deposition time to 20s. Rotate the fiber flat inside the sputtering instrument to deposit the gold film, ensuring that gold particles uniformly cover the fiber sensing area.

[0106] Sensitivity detection of analyte refractive index based on SPR fiber optic sensor: The refractive index of the solution was adjusted by mixing glycerol and ultrapure water in different volume ratios. Glycerol aqueous solutions with refractive indices of 1.333, 1.339, 1.345, 1.357, and 1.384 were used for detection by the SPR fiber optic sensor. The sensor sensitivity can be obtained by the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to different refractive indices of the analyte at the resonant wavelength, and Δn is the difference in refractive index of the analyte. Under the condition that the gold particles on the fiber surface are uniform, the sensitivity of the SPR fiber optic sensor is 157 nm / RIU.

[0107] By comparing Comparative Example 1 and Example 1, the sensitivity of the fiber optic SPR sensor was improved.

[0108] In the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0109] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An SPR fiber optic sensor, characterized in that, include: A section of fiber substrate with the fiber cladding removed; A metal nanoparticle layer is disposed on an optical fiber substrate, and at least one section of the metal nanoparticle layer has a gradient in particle size along the optical fiber axis, which effectively enhances the sensitivity of the sensor. The fabrication method of the SPR fiber optic sensor includes the following steps: S1. Remove a section of the fiber cladding to expose the fiber substrate, and then clean it with a cleaning solution. S2. A metal nanoparticle layer is deposited on the surface of the optical fiber substrate, and the particle size of at least one section of the metal nanoparticle layer varies with a gradient along the optical fiber axis. Specifically, the deposition of the gold film layer is carried out using an ion sputtering instrument. The pretreated optical fiber is placed vertically on the fixture inside the sputtering coating machine, covered with a glass tube, and the vent valve is tightened. The thickness of the film layer sputtered on the surface of the optical fiber is adjusted by controlling the coating time and coating current. The coating current is set to 15mA and the coating time to 20s for sputtering the gold film. The gold particle size in the front (a), middle (b), and rear (c) sections of the fiber optic probe sensing area varies with gradient along the fiber axis. The average gold particle size is calculated from multiple points in each section. The average gold particle size in the front (a) section is 47.16 nm, in the middle (b) section it is 39.42 nm, and in the rear (c) section it is 29.75 nm.

2. The SPR fiber optic sensor according to claim 1, characterized in that: It also includes a single-layer dielectric layer or multiple dielectric layers with different refractive indices, wherein the metal nanoparticle layer is located above, below, or between multiple dielectric layers.

3. The SPR fiber optic sensor according to claim 2, characterized in that: The dielectric layer includes polymers, metals, metal oxides, silicon, and graphene.

4. The SPR fiber optic sensor according to claim 3, characterized in that: The dielectric layer includes any one or more of poly(p-chloroxylene), polydimethylsiloxane, polymethyl methacrylate, silicon oxide, silicon nitride, aluminum oxide, titanium oxide, and photoresist.

5. An SPR fiber optic sensor according to claim 1, characterized in that: The surface of the metal nanoparticle layer is provided with a functional layer.

6. The SPR fiber optic sensor according to claim 5, characterized in that: The functional layer includes one or more of the following: polymer functional layer, metal oxide functional layer, biometric material functional layer, and carbon-based material functional layer.

7. An SPR fiber optic sensor according to claim 6, characterized in that: The polymer functional layer includes polyvinyl alcohol, polydimethylsiloxane, polystyrene, and polyamide; and / or The metal oxide functional layer includes zinc oxide, indium tin oxide, aluminum oxide, and titanium oxide; and / or The biometric material functional layer includes antibodies, DNA probes, and enzymes; and / or The carbon-based material functional layer includes graphene and carbon nanotubes.

8. An SPR fiber optic sensor according to claim 1, characterized in that: The optical fiber substrate structure includes D-type structure, U-type structure, tapered structure and core mismatch structure.

9. An SPR fiber optic sensor according to claim 1, characterized in that: The diameter of the fiber substrate from which the fiber cladding has been removed is 100-1000 μm; and / or The length of the fiber substrate from which the fiber cladding has been removed is 1-100 mm; and / or The length of the fiber substrate without removing the fiber cladding is 10-200 mm; and / or The fiber cladding is equipped with a connector.

10. An SPR fiber optic sensor according to claim 9, characterized in that: The connectors include SMA905, FC / PC, and quick-connect connectors; and / or The thickness of the metal nanoparticle layer is 10-100 nm.

11. A method for fabricating an SPR fiber optic sensor according to any one of claims 1-10, characterized in that, Includes the following steps: S1. Remove a section of the fiber cladding to expose the fiber substrate, and then clean it with a cleaning solution. S2. A metal nanoparticle layer is deposited on the surface of the optical fiber substrate, and the particle size of at least one section of the metal nanoparticle layer varies with a gradient along the optical fiber axis. Specifically, the deposition of the gold film layer is carried out using an ion sputtering instrument. The pretreated optical fiber is placed vertically on the fixture inside the sputtering coating machine, covered with a glass tube, and the vent valve is tightened. The thickness of the film layer sputtered on the surface of the optical fiber is adjusted by controlling the coating time and coating current. The coating current is set to 15mA and the coating time to 20s for sputtering the gold film. The gold particle size in the front (a), middle (b), and rear (c) sections of the fiber optic probe sensing area varies with gradient along the fiber axis. The average gold particle size is calculated from multiple points in each section. The average gold particle size in the front (a) section is 47.16 nm, in the middle (b) section it is 39.42 nm, and in the rear (c) section it is 29.75 nm.

12. A detection system, characterized in that: It includes a light source, a spectrometer, and the SPR fiber optic sensor as described in any one of claims 1-10.

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