SPR optical fiber sensor and preparation method and detection system thereof

Abstract

The invention discloses an SPR (Surface Plasmon Resonance) optical fiber sensor as well as a preparation method and a detection system thereof, and the SPR optical fiber sensor comprises a section of optical fiber substrate without an optical fiber cladding; the metal nanoparticle layer is arranged on the optical fiber substrate, and the particle size of at least one section of the metal nanoparticle layer is changed in a gradient mode in the axial direction of the optical fiber. According to the SPR optical fiber sensor provided by the invention, the sensitivity of the sensor is effectively enhanced and the detection range of the sensor is expanded by arranging the metal nanoparticle layer of which the particle size is in gradient change along the axial direction of the optical fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of SPR optical fiber sensors, and more specifically to an SPR optical fiber sensor and a preparation method and a detection system thereof. Background Art

[0002] Surface Plasmon Resonance (SPR) is a novel detection method for studying the interaction between the surface of materials with different properties and incident light. SPR is an energy transfer effect between the surface of a metal layer and a dielectric.

[0003] With the in-depth study of SPR sensing technology in the past few decades, researchers have come up with the development of SPR fiber sensors on optical fibers. When a beam of light satisfies the total reflection theorem in the optical fiber core and propagates infinitely in the optical fiber, a portion of the light energy will be transmitted into the cladding to form an evanescent wave and enter the metal layer along the interface, thereby causing the directional movement of free electrons on the surface of the metal layer to form 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 surface of the metal layer, eventually causing the energy propagated back to the optical fiber core to be drastically attenuated, thereby forming a resonance peak. Since the propagation distance of the evanescent wave in the metal medium is limited, the thickness of the metal layer can only be set at the nanometer level to effectively utilize the SPR effect to detect the degree of change in the metal upper layer medium. Taking the detection medium refractive index as an example, when the refractive index of the upper layer medium of the metal layer changes under certain conditions, the corresponding resonance condition of the SPR effect will also change accordingly, resulting in the shift of the resonance peak in the transmission spectrum. By analyzing the offset of the resonance peak, the performance parameters of the sensor such as sensitivity, detection accuracy, quality factor, etc. corresponding to the refractive index of the medium can be obtained. Therefore, it is widely used in various fields such as biomedicine, food safety and environmental testing, and chemical testing.

[0004] However, the sensitivity of traditional fiber SPR is very low. In recent years, many scientific researchers are exploring ways to enhance the sensitivity of optical fibers. The methods for enhancing the sensitivity of fiber SPR optical fiber sensors are mainly divided into two categories: one is about the change of the optical fiber substrate structure, and the other is the sensitivity enhancement of the film material. For fiber SPR optical fiber sensors, the evanescent wave penetrates the film layer on the surface of the fiber core and couples with the sensing layer, which is the basis for the operation of the sensor. By designing different optical fiber substrate structures, the intensity of the evanescent wave can be effectively enhanced. The commonly used evanescent wave enhanced optical fiber substrate structures mainly include D-type structure, U-type structure, tapered structure, etc. Since the structure of the optical fiber itself is relatively thin and easy to break, there are certain technical difficulties and challenges in the process of changing the base structure.

[0005] When the type and shape of the optical fiber used as the sensor substrate are fixed, the film material in the sensing area becomes the most direct and important factor in determining the performance of the sensor. Researchers have tried to add other film materials as auxiliary film layers on the surface of the metal film to improve the performance of the SPR fiber sensor. When the metal oxide film is used as an auxiliary film layer, it changes the electric field distribution in the sensing film layer, so that the electric field strength is correspondingly enhanced, and thus the sensitivity of the optical fiber SPR fiber sensor can be effectively improved. In addition, researchers have found that coating two-dimensional materials such as graphene on the surface of the sensor can achieve high-sensitivity measurements. This type of material has unique optical properties and good biocompatibility. Because of its large specific surface area, it can bind more small biological molecules, improve the molecular binding efficiency of the sensor interface, and effectively amplify the SPR signal.

[0006] The above two methods of enhancing sensitivity either modify the optical fiber itself (substrate structure), which is costly and has poor repeatability, making it unfavorable for large-scale applications; or optimize the film material, which is cumbersome and complex and costly. Ultimately, the surface plasmon resonance spectrometer based on the above optical fiber sensor has low stability and reliability. Summary of the invention

[0007] The present invention aims to solve one of the technical problems in the related art to a certain extent. To this end, the present invention proposes an SPR optical fiber sensor, which effectively enhances the sensitivity of the sensor and expands its detection range by providing a metal nanoparticle layer with a gradient particle size along the axial direction of the optical fiber.

[0008] The invention also provides a method for preparing the SPR optical fiber sensor.

[0009] The invention also provides a detection system of the SPR optical fiber sensor.

[0010] The technical solution adopted by the present invention is: to provide an SPR optical fiber sensor, comprising:

[0011] A length of optical fiber substrate from which the optical fiber cladding has been removed;

[0012] The metal nanoparticle layer is arranged on the optical fiber substrate, and the particle size of at least one section of the metal nanoparticle layer changes gradually along the axial direction of the optical fiber.

[0013] In the prior art, the preparation of SPR optical fiber sensors usually aims to make the thickness and particle size of the metal nanoparticle layer as uniform as possible to achieve a stable sensing effect. Through in-depth research, the inventors found that if the particle size of the metal nanoparticle layer changes in a gradient along the optical fiber axis, the sensitivity of the sensor can be significantly improved, breaking through the industry's inherent cognition and technical prejudice on the uniformity design of the metal nanoparticle layer. This innovative design can effectively enhance the sensitivity of the sensor and expand its detection range.

[0014] By adopting this design, the present invention provides a highly sensitive SPR optical fiber sensor, which has wide 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 includes 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 the surface plasmon resonance effect. The metal nanoparticle layer interacts with the incident light to generate a surface plasmon wave that is highly sensitive to the refractive index change 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 strength.

[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 optical fiber sensor also includes a single dielectric layer or multiple dielectric layers with different refractive indices, and the metal nanoparticle layer is located in the upper layer, lower layer or between the multiple dielectric layers of the dielectric layer; the interference effect of the Fabry-Perot cavity of the dielectric layer is coupled with the localized surface plasma resonance effect of the metal nanoparticle layer, and a new characteristic peak is constructed in the near-infrared region of the spectrum, which can achieve high-sensitivity sensing and accurately adjust the characteristic peak position of the optical fiber sensor.

[0019] According to one embodiment of the present invention, the dielectric layer includes polymers, metals, metal oxides, silicon, and graphene; by adjusting the material of the dielectric layer, not only can the sensitivity of the sensor be optimized, but also the position of the characteristic peak can be accurately adjusted to meet 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 and improve the overall stability and durability of the sensor.

[0020] According to an embodiment of the present invention, the dielectric layer can be made of poly(monochloro-p-xylene) (Parylene-C), poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ), titanium oxide (TiO2 ) or any one or more of 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 a polymer-based functional layer, a metal oxide-based functional layer, a biometric material-based functional layer, a carbon-based material-based functional layer, and any combination thereof.

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

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

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

[0026] The carbon-based material functional layer includes graphene and carbon nanotubes; the metal oxide functional layer includes zinc oxide (ZnO), indium tin oxide (ITO), aluminum oxide (Al 2 O 3 ) and titanium oxide (TiO 2 ), are known for their excellent photoelectric properties and transparency. They can further enhance the SPR effect, improve the sensitivity of the sensor by increasing the dielectric constant and refractive index difference, and have good applications in photoelectric detection and gas sensing.

[0027] Functional layers of biorecognition materials include antibodies, DNA probes, and enzymes, which enable SPR optical fiber sensors to specifically recognize biological molecules and are particularly suitable for biosensors and medical diagnosis. These materials can specifically bind to target molecules, thereby significantly changing the local refractive index and generating a significant SPR signal response.

[0028] Carbon-based material functional layers such as graphene and carbon nanotubes can greatly enhance the signal response capability of sensors and broaden their application range due to their excellent conductivity and chemical sensitivity. Graphene also has excellent mechanical strength and surface activity, making it suitable for a variety of 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 optical fiber substrate after removing the optical fiber cladding is 100-1000 μm; and / or

[0031] The length of the optical fiber substrate after removing the optical fiber cladding is 1-100 mm; and / or

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

[0033] The optical fiber cladding is provided with a connector.

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

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

[0036] A method for preparing any of the above-mentioned SPR optical fiber sensors comprises the following steps:

[0037] S1, remove a section of optical fiber cladding to expose the optical fiber base, and clean it with a cleaning solution;

[0038] S2. A metal nanoparticle layer is plated on the surface of the optical fiber substrate, wherein the particle size of at least one section of the metal nanoparticle layer changes in a gradient along the axial direction of the optical fiber.

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

[0040] According to one embodiment of the present invention, in step S2, the metal nanoparticle layer is prepared section by section, the particle size of each adjacent metal nanoparticle layer increases or decreases, and multiple metal nanoparticle layers are combined to form a metal nanoparticle layer with a particle size gradient along the axial direction of the optical fiber; this layered coating technology can not only achieve precise control of metal nanoparticles of different particle sizes, but also effectively construct a metal nanoparticle layer with a particle size gradient along the axial direction of the optical fiber. This design can significantly enhance the performance of the SPR sensor, especially in terms of signal response and sensitivity.

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

[0042] S1, cutting 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 of the optical fiber substrate facing upwards, and use magnetron sputtering to sputter a layer of metal nanoparticles on the exposed part of the optical fiber substrate. Use magnetron sputtering to sputter a layer of metal nanoparticles on the exposed part of the optical fiber substrate. Magnetron sputtering is an ideal choice for preparing metal nanoparticle layers due to its simplicity and high efficiency.

[0044] A detection system comprises a light source, a spectrum analyzer and any one of the above-mentioned SPR optical fiber sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 Schematic diagram of the structure of the SPR optical fiber sensor in Example 1 of the present invention;

[0047] Figure 2 Schematic diagram of the structure of the SPR optical fiber sensor in Example 1 of the present invention;

[0048] Figure 3 Schematic diagram of the structure of the detection system in Example 1 of the present invention;

[0049] Figure 4 Spectra of the optical fiber SPR sensor in Example 1 of the present invention in different glycerol aqueous solutions, the refractive indices of the glycerol aqueous solutions corresponding to the highest peaks in the spectrum are 1.384, 1.357, 1.345, and 1.339 from top to bottom;

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

[0051] Figure 6 The SEM images of the front end (a), middle (b), and rear end (c) of the uncladding portion of the optical fiber SPR sensor in Example 1 of the present invention;

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

[0053] Figure 8 Schematic diagram of the SPR optical fiber sensor in Example 3 of the present invention for real-time monitoring of IgG binding after chemical modification, in which the concentrations of IgG from top to bottom are 20, 10, 5, 2.5, and 1.25 μg / ml, respectively;

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

[0055] Description of the numbers in the figure:

[0056] 1. Connector; 2. Optical fiber cladding; 3. Optical fiber substrate; 4. Metal nano-coating; 5. Optical fiber probe; 6. Light source; 7. Spectrometer. DETAILED DESCRIPTION

[0057] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0058] In this embodiment, the SPR fiber optic sensor can be divided into two types according to the propagation path of light: linear transmission type and reflective type. Among them, the linear transmission type is also called online transmission type, which usually refers to a sensing system that transmits the sensing signal to the remote end through an optical fiber for processing and analysis. In this system, the optical fiber assumes the function of transmitting the optical signal, and the sensor and the signal processing system are usually located at both ends of the optical fiber. In this way, the sensor can remotely monitor and measure changes in target physical quantities, such as temperature, pressure, deformation, and vibration, without directly contacting the measurement object, thereby achieving non-contact measurement.

[0059] Reflective fiber optic sensor, also known as terminal reflective sensor, has a metal nanocoating applied to the terminal of the optical fiber to form a reflective surface at the end. The sensor uses the interference effect of reflected light for measurement. When the refractive index of the substance to be measured changes, the SPR resonance condition will also change accordingly, resulting in a shift in the resonance wavelength, which is reflected in the change in the intensity of the reflected light. By detecting the change in the intensity of the reflected light, the refractive index information of the substance to be measured can be obtained.

[0060] Combination Figure 2 As shown in the figure, in the linear transmission SPR fiber sensor, the localized surface plasmon resonance (LSPR) structure is fixed on the side of the optical fiber, and the outer surface of the optical fiber is used as the sensing area. The device at the other end of the optical fiber is responsible for receiving the transmitted light signal. In the sensing area, the light interacting with the nanostructure will excite the LSPR effect, causing a change in the intensity or wavelength of the transmitted light, which will be detected by the receiver.

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

[0062] The D-type optical fiber substrate removes the cladding on one side of the optical fiber through a side-throwing process to expose the fiber core, thereby achieving the leakage of the evanescent field. Its main advantage is that the sensing area is smooth, which is conducive to the uniform deposition of the film layer on the optical fiber surface, enhancing the generation of the SPR effect, and facilitating the addition of the sensitization layer and the attachment of biological molecules.

[0063] The U-shaped fiber substrate is formed by partially removing the fiber cladding and bending it under heat to form a U-shaped structure to complete the preparation of the sensing area. When the light signal enters the sensing area, the incident angle decreases and the penetration depth of the light increases, thereby strengthening the evanescent field effect and improving the sensitivity of the sensor.

[0064] The taper fiber substrate is formed by heating and stretching ordinary optical fiber with a carbon dioxide laser to form a tapered area. Through taper, the core and cladding diameters of the optical fiber are gradually reduced, allowing the evanescent field to pass through the cladding and expand to the external medium, thereby enhancing the interaction between the optical fiber and the external environment.

[0065] The grating-type optical fiber substrate produces periodic refraction by writing a grating in the optical fiber core, thereby effectively stimulating the SPR effect. Common grating types include uniform fiber Bragg grating, tilted fiber Bragg grating, eccentric fiber Bragg grating, extremely large angle tilted fiber grating and long period fiber grating. These grating structures can couple light waves of specific wavelengths from the core to the cladding by adjusting the grating's inclination angle, grating pitch, eccentricity and other parameters, thereby achieving optimized detection of specific sensing signals. Different types of fiber Bragg grating structures can be designed and adjusted for different application scenarios to improve the performance and sensitivity of the sensor.

[0066] Embodiment 1

[0067] In this embodiment, an SPR optical fiber sensor is disclosed.

[0068] like Figure 3 As shown in FIG. 1 , a schematic diagram of the structure of an optical fiber surface plasmon resonance sensor detection system is provided, including: a prepared 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 1As shown, it includes: a fiber substrate with a diameter of 100-1000μm after removing the fiber cladding, a fiber substrate with a length of 1-100mm after removing the fiber cladding, a fiber substrate with a length of 10-200mm without removing the fiber cladding, and the fiber cladding is provided with a connector. The fiber optic probe is arranged between the light source and the spectrometer. The fiber optic probe needs to be connected to the light source through an optical fiber, and the light emitted from the light source is transmitted to the fiber optic probe through the middle optical fiber, and reaches the sensing area through continuous reflection in the fiber optic probe. The signal generated by the fiber optic probe through the reaction with the substance to be measured is received by the spectrometer.

[0069] Specifically, the fiber optic probe removes the cladding through physical sputtering, and forms a layer of gold film on the surface of the optical fiber, and the particle size of the gold film changes gradiently along the axial direction of the optical fiber. When the light emitted by the light source satisfies the total reflection theorem in the optical fiber core and propagates infinitely in the optical fiber, a part of the light energy will be transmitted into the cladding to form an evanescent wave and enter the gold layer along the interface, thereby causing the free electrons on the surface of the gold layer to move in a directional manner to form 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 surface of the metal layer, eventually causing the energy propagated back to the optical fiber core to attenuate sharply. After the spectrometer receives the signal, the electronic device detects the resonance peak formed in the spectrum.

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

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

[0072] (b) Fiber pretreatment: The fiber with the cladding removed was ultrasonically treated with ultrapure water and acetone for 5 min in sequence. The fiber was taken out and rinsed with ultrapure water and allowed to stand for 5 min to remove moisture from the fiber surface.

[0073] (c) Deposition of gold film: Using an ion sputtering apparatus, the pre-treated optical fiber is placed vertically on the fixture in the sputtering coating machine, covered with a glass tube, and the air release valve is tightened. The thickness of the film sputtered on the optical fiber surface is adjusted by controlling the coating time and coating current. The coating current is set to 15mA and the coating time is set to 20s for sputtering of the gold film. After the coating is completed, the optical fiber probe is taken out for subsequent experiments.

[0074] Detection of the refractive index sensitivity of the analyte based on the SPR optical fiber sensor: The refractive index of the solution is adjusted by mixing glycerol and ultrapure water in different volume ratios, and glycerol aqueous solutions with refractive indices of 1.333, 1.339, 1.345, 1.357, and 1.384 are respectively used for the detection of the SPR optical fiber sensor provided by the present invention, resulting in a change in the resonance wavelength. The spectrum is shown in FIG. Figure 4 As shown in the figure, the refractive index of the highest peak in the spectrum is 1.384, 1.357, 1.345, and 1.339 from top to bottom. The sensitivity of the sensor can be obtained by the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to the object with different refractive index at the resonance wavelength, and Δn is the refractive index difference of the object to be measured. The refractive index sensitivity fitting curve is shown in Figure 5 As shown in the figure, according to the slope of the fitting curve, it can be concluded that the sensitivity of the optical fiber SPR sensor of the present invention is 3369nm / RIU. In order to explore the deposition of gold particles on the optical fiber surface, the optical fiber prepared with the gold layer was subjected to SEM test. The gold particles on the surface of the optical fiber probe are as follows: Figure 6 As shown in the figure, the gold particle size at the front end (a), middle (b), and rear end (c) of the optical fiber probe sensing area changes gradually along the optical fiber axis. In each part, the average value of the gold particle size is calculated by taking multiple points. The average particle size of the gold particles at the front end (a) is 47.16nm, the average particle size of the gold particles in the middle (b) is 39.42nm, and the average particle size of the gold particles at the rear end (c) is 29.75nm.

[0075] In some other embodiments, the optical fiber length is 10-200 mm, preferably 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm or 70 mm. The length of the cladding stripped by Miller pliers 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 silver, copper, platinum, aluminum or titanium metal instead of the gold film in this embodiment. In some other embodiments, the metal nanoparticle layer is replaced by any combination of pure silver, copper, platinum, aluminum and titanium metal instead of the gold film in this embodiment.

[0077] In some other embodiments, a plurality of dielectric layers are arranged on the optical fiber substrate, and the interference effect of the Fabry-Perot cavity of the dielectric layer is coupled with the localized surface plasmon resonance effect of the gold nanoparticles, and a new characteristic peak is constructed in the near-infrared region of the spectrum, which can realize high-sensitivity sensing and accurately adjust the characteristic peak position of the optical fiber sensor. This is a prior art, as clearly described in the specific implementation in CN115855883A, so it will not be elaborated.

[0078] Embodiment 2

[0079] A schematic diagram of the structure of an optical fiber surface plasmon resonance sensor detection system is provided, comprising: a prepared optical fiber probe 5, a light source 6, and a spectrometer 7. The optical fiber probe is arranged between the light source and the spectrometer. The optical fiber probe needs to be connected to the light source through an optical fiber, and the light emitted from the light source is transmitted to the optical fiber probe through the intermediate optical fiber, and reaches the sensing area through continuous reflection in the optical fiber probe. The optical fiber probe generates a signal by reacting with the substance to be tested, and the signal is received by the spectrometer.

[0080] Specifically, the optical fiber probe removes the cladding layer by physical sputtering, and forms a gold film on the surface of the optical fiber, and the particle size of the gold film changes gradually along the axial direction of the optical fiber. A layer of TiO 2 Thin film, gold layer in the fiber core and TiO 2 In the middle of the dielectric layer, TiO 2 The addition of the dielectric layer further enhances the SPR effect and improves the sensitivity of the SPR fiber optic 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-magnetron sputtered between the optical fiber surface and the gold film, and they together with the gold film constitute a metal nanoparticle layer.

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

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

[0084] (b) Fiber pretreatment: The fiber with the cladding removed was ultrasonically treated with ultrapure water and acetone for 5 min in sequence. The fiber was taken out and rinsed with ultrapure water and allowed to stand for 5 min to remove moisture from the fiber surface.

[0085] (c) Deposition of gold film: Using an ion sputtering apparatus, the pre-treated optical fiber is placed vertically on the fixture in the sputtering coating machine, covered with a glass tube, and the air release valve is tightened. The thickness of the film sputtered on the optical fiber surface is adjusted by controlling the coating time and coating current. The coating current is set to 15mA and the coating time is set to 20s for sputtering of the gold film. After the coating is completed, the optical fiber probe is taken out for subsequent experiments.

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

[0087] (e)TiO 2 Dielectric layer preparation: immerse the gold-coated optical fiber SPR sensing probe into the TiO 2 The fiber optic probe was placed in the sol for 5 min, and then the lifting device was manually rotated to pull the fiber optic probe within a certain period of time and dried at room temperature for 10 min. The fiber optic SPR sensor was rinsed with deionized water for 1 min, pulled out and dried at room temperature for 10 min. A 4% polyacrylic acid solution was used to replace TiO 2 Sol completed the same dip coating process; soaked in deionized water for 1 min and dried at room temperature for 20 min. After the deposition was completed, the sensor probe was placed in a vacuum drying oven at 60 ° C for 2 h. At this time, the TiO 2 Deposition of thin films.

[0088] Detection of the refractive index sensitivity of the analyte based on the SPR optical fiber sensor: By mixing glycerol and ultrapure water in different volume ratios to adjust the refractive index of the solution, glycerol aqueous solutions with refractive indices of 1.333, 1.339, 1.345, 1.357, and 1.384 are respectively used for the detection of the SPR optical fiber sensor provided by the present invention, resulting in changes in the resonant wavelength, which can achieve high sensitivity and real-time detection. The sensitivity of the sensor can be derived from the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to the objects to be tested with different refractive indices at the resonant wavelength, and Δn is the difference in the refractive index of the object to be tested. The refractive index sensitivity fitting curve is as follows: Figure 7 As shown in FIG. 1 , according to the slope of the fitting curve, it can be concluded that the sensitivity of the optical fiber SPR sensor of the present invention is 4635 nm / RIU. Compared with the sensitivity of the optical fiber SPR sensor obtained in Example 1 of 3369 nm / RIU, TiO 2 The addition of the dielectric layer increases the sensitivity of the fiber-optic SPR sensor.

[0089] In some other embodiments, any one or more of poly(monochloroparaxylene), polydimethylsiloxane, poly(methyl methacrylate), silicon oxide, silicon nitride, aluminum oxide, and photoresist are used to replace the titanium dioxide dielectric layer in this embodiment.

[0090] Embodiment 3

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

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

[0093] (b) Fiber pretreatment: The fiber with the cladding removed was ultrasonically treated with ultrapure water and acetone for 5 min in sequence. The fiber was taken out and rinsed with ultrapure water and allowed to stand for 5 min to remove moisture from the fiber surface.

[0094] (c) Deposition of gold film: Using SBC-12 small ion sputtering instrument, the pre-treated optical fiber is placed vertically on the fixture in the sputtering coating machine, covered with a glass cylinder, and the air release valve is tightened. The coating time and coating current are controlled to adjust the thickness of the film layer, and the coating current is set to 15mA and the coating time is set to 20s.

[0095] (d) Construction of SPR fiber sensor system: In order to study the sensing performance of the SPR fiber sensor proposed in the present invention, a fiber SPR sensor system was built. The light source used in the system is a D2600 tungsten light source from Hangzhou Jingfei Technology Co., Ltd., with an operating wavelength range of 350nm to 950nm. The coated fiber probe is immersed in a glycerol aqueous solution with a refractive index change of 1.333-1.384. After the light wave is reflected by the fiber end face reflection layer, it is collected by a spectrometer (FLA5300 70μm, band: 350-1100nm). Data analysis was performed using the 2023 Jingfei spectral test analysis software V6.64.3.157 developed by Hangzhou Jingfei Technology Co., Ltd. to obtain the SPR spectrum curve.

[0096] (e) Test of the sensitivity of the SPR sensor: By mixing glycerol and ultrapure water in different volume ratios to adjust the refractive index of the solution, 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 optical fiber sensor provided by the present invention, resulting in changes in the resonance wavelength. The sensitivity of the sensor can be obtained by the following formula: S = Δλ / Δn, where Δλ is the wavelength difference corresponding to the different refractive index objects to be measured at the resonance wavelength, and Δn is the refractive index difference of the object to be measured.

[0097] (f) Preparation of carboxylated dextran functional layer: Place the gold-coated optical fiber in a centrifuge tube, add 5 mM 11-mercapto-undecanol, and react at 40°C for 30 min. Connect the mercapto-alkanol on the surface to facilitate further modification and seal the surface to reduce nonspecific adsorption. Take out the optical fiber from the centrifuge tube and wash it with 80% ethanol solution and ultrapure water to remove the residual solution on the surface. Let it stand for 5 min to remove the moisture on the surface of the optical fiber. Place the optical fiber connected with mercapto-alkanol in a new centrifuge tube, add 0.6 M epichlorohydrin solution, and react at room temperature for 4 h to generate epoxy groups on the surface. Then take it out and rinse it with ethanol and ultrapure water and let it stand for 5 min to remove the moisture on the surface of the optical fiber. Place the dried optical fiber in a 0.3 g / mL dextran solution and react at room temperature for 20 h. Modify a layer of dextran on the gold film surface by covalent bonding. Then take it out and wash it with ultrapure water. Let it stand for 5 min to remove the moisture on the surface of the optical fiber. Place the optical fiber modified with dextran into a new centrifuge tube, add 1M bromoacetic acid solution, and incubate at room temperature for 16 hours to carboxylate the dextran connected to the chip surface. After taking it out, wash it with ultrapure water and let it stand for 5 minutes to remove the moisture on the optical fiber surface, and the modification is completed.

[0098] Analyte (IgG) detection: Mix the activation buffer solution, 50mM N-hydroxysuccinimide (NHS) and 200mM 1-ethyl-(3-dimethylaminopropyl) carbodiimide (EDC) in a volume ratio of 1:1, and react the modified fiber SPR probe in the mixture for 30 minutes. Put the activated fiber SPR probe into 200μg / ml Protein A (sodium acetate buffer, 0.01M, pH=4.5) solution, completely immerse the sensing area for 10 minutes at room temperature, and observe the shift of the resonance wavelength. When the ligand fixation process reaches stability, the fiber probe is immersed in the analyte, and the IgG molecules in the analyte will specifically bind to the Protein A fixed on the surface of the optical fiber, causing the refractive index around the fiber probe to change, and the resonance wavelength in the spectrum will also move accordingly. Figure 8 It is a schematic diagram of the SPR optical fiber sensor of the present invention for real-time monitoring of IgG binding after chemical modification. Fig. 9 is the standard curve of IgG binding process.

[0099] In this embodiment, the carboxylated dextran functional layer is a type of biological recognition material functional layer, more specifically, an antibody recognition material functional layer. In some other embodiments, the IgG antibody functional layer in this embodiment is replaced by polyvinyl alcohol, polydimethylsiloxane, polystyrene, polyamide, zinc oxide, indium tin oxide, aluminum oxide, titanium oxide, DNA probe, enzyme, graphene or carbon nanotubes.

[0100] Comparative Example 1

[0101] like Figure 3 As shown, a schematic diagram of the structure of a fiber optic surface plasmon resonance sensor detection system is provided, including: a prepared fiber optic probe 5, a light source 6, and a spectrometer 7. The fiber optic probe is arranged between the light source and the spectrometer. The fiber optic probe needs to be connected to the light source through an optical fiber, and the 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 in the fiber optic probe. The signal generated by the fiber optic probe through the reaction with the substance to be tested 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, an optical fiber length of 35 mm, and the steps for plating the gold film on the optical fiber surface are as follows:

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

[0104] (b) Fiber pretreatment: The fiber with the cladding removed was ultrasonically treated with ultrapure water and acetone for 5 min in sequence. The fiber was taken out and rinsed with ultrapure water and allowed to stand for 5 min to remove moisture from the fiber surface.

[0105] (c) Gold film coating on the optical fiber surface: Place the pretreated optical fiber flat on the stage of the SBC-12 small ion sputtering instrument, keep the entire sensing area and the target at the same height, cover with a glass tube, and tighten the air release valve. Set the coating current to 15mA and the coating time to 20s. Place the optical fiber flat in the sputtering instrument and rotate to coat the gold film so that the gold particles on the surface evenly cover the optical fiber sensing area.

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

[0107] By comparing Comparative Example 1 with Example 1, the sensitivity of the optical fiber SPR sensor is improved.

[0108] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0109] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A SPR optical fiber sensor, characterized in that: include: A length of optical fiber substrate from which the optical fiber cladding has been removed; The metal nanoparticle layer is arranged on the optical fiber substrate, and the particle size of at least one section of the metal nanoparticle layer changes gradually along the axial direction of the optical fiber.

2. A SPR optical fiber sensor according to claim 1, characterized in that: The metal nanoparticle layer includes one or more of gold, silver, copper, platinum, aluminum, titanium and any combination thereof.

3. A SPR optical fiber sensor according to claim 1, characterized in that: The larger particle size of the metal nanoparticle layer is 30-100 nm, and the smaller particle size is 10-60 nm; and / or The ratio of the smaller particle size to the larger particle size in the metal nanoparticle layer is 1-6:

10.

4. A SPR optical fiber sensor according to claim 1, characterized in that: It also includes a single dielectric layer or multiple dielectric layers with different refractive indices, and the metal nanoparticle layer is located on the upper layer, the lower layer or between the multiple dielectric layers.

5. A SPR optical fiber sensor according to claim 4, characterized in that: The dielectric layer includes polymer, metal, metal oxide, silicon and graphene.

6. A SPR optical fiber sensor according to claim 5, characterized in that: The dielectric layer includes any one or more of poly(monochloroparaxylene), poly(dimethylsiloxane), poly(methyl methacrylate), silicon oxide, silicon nitride, aluminum oxide, titanium oxide, and photoresist.

7. A SPR optical fiber sensor according to claim 1, characterized in that: A functional layer is provided on the surface of the metal nanoparticle layer.

8. An SPR optical fiber sensor according to claim 7, characterized in that: The functional layer includes one or more of a polymer functional layer, a metal oxide functional layer, a biometric material functional layer, a carbon-based material functional layer and any combination thereof.

9. A SPR optical fiber sensor according to claim 8, characterized in that: The polymer functional layer includes polyvinyl alcohol, polydimethylsiloxane, polystyrene and polyamide; and / or The metal oxide functional layer comprises zinc oxide, indium tin oxide, aluminum oxide and titanium oxide; and / or The bio-recognition material functional layer includes antibodies, DNA probes and enzymes; and / or The carbon-based material functional layer includes graphene and carbon nanotubes.

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

11. An SPR optical fiber sensor according to claim 1, characterized in that: The diameter of the optical fiber substrate after removing the optical fiber cladding is 100-1000 μm; and / or The length of the optical fiber substrate after removing the optical fiber cladding is 1-100 mm; and / or The optical fiber substrate without removing the optical fiber cladding has a length of 10-200 mm; and / or The optical fiber cladding is provided with a connector.

12. An SPR optical fiber sensor according to claim 10, 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.

13. A method for preparing the SPR optical fiber sensor according to any one of claims 1 to 12, characterized in that: The following steps are involved: S1, remove a section of optical fiber cladding to expose the optical fiber base, and clean it with a cleaning solution; S2. A metal nanoparticle layer is plated on the surface of the optical fiber substrate, wherein the particle size of at least one section of the metal nanoparticle layer changes in a gradient along the axial direction of the optical fiber.

14. The preparation method according to claim 13, characterized in that: In step S2 , the coating process of the metal nanoparticle layer includes vacuum evaporation, magnetron sputtering, melt coating, chemical plating and ion plating.

15. The preparation method according to claim 14, characterized in that: In step S2, metal nanoparticle layers are prepared section by section, the particle sizes of two adjacent metal nanoparticle layers increase or decrease, and multiple metal nanoparticle layers are combined to form a metal nanoparticle layer with a particle size gradient along the axial direction of the optical fiber.

16. The preparation method according to claim 14, characterized in that: Step S2 includes: S1, cutting off one end of the optical fiber substrate to form a free end; S2. Place the optical fiber substrate vertically with the free end of the optical fiber substrate facing upward, and use magnetron sputtering to sputter a layer of metal nanoparticles on the exposed part of the optical fiber substrate.

17. A detection system, characterized in that: The invention comprises a light source, a spectrum analyzer and the SPR optical fiber sensor according to any one of claims 1 to 12.

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