A high-sensitivity optical fiber SPR sensor and sensing system

Abstract

The utility model relates to biological sensing technology field, concretely relates to a kind of high sensitivity optical fiber SPR sensor and sensing system, the high sensitivity optical fiber SPR sensor, including optical fiber body (100);The optical fiber body (100) includes sensing area (110), gold film (120), indium tin oxide film (130), titanium dioxide film (140), input end and output end;In the cross-sectional direction of optical fiber SPR sensor, the sensing area (110) is covered in optical fiber body (100) surface, the gold film (120) is covered in sensing area (110) surface, the indium tin oxide film (130) is covered in gold film (120) surface, the titanium dioxide film (140) is covered in indium tin oxide film (130) surface;The sensing area (110) includes multimode optical fiber (111) sequentially fused, photonic crystal fiber (112) and multimode optical fiber (111), the sensor provided by the utility model compared with the existing only SPR optical fiber sensor with gold film has higher sensitivity, biological adsorption and chemical stability.

Description

Technical Field

[0001] This utility model relates to the field of biosensing technology, specifically to a high-sensitivity fiber optic SPR sensor and sensing system. Background Technology

[0002] Surface plasmon resonance (SPR) is a phenomenon that occurs at the interface between a metal film on the surface of an optical fiber and the external medium. When light is incident from an optically denser medium to an optically less dense medium, total internal reflection occurs, and some light passes through the less dense medium, forming a transmitted wave. Simultaneously, due to electromagnetic interference, the electron density distribution within the metal film becomes uneven, causing collective oscillations of electrons and forming a plasma wave. When the transmitted wave resonates with the surface plasma wave, the energy of the light is transferred to the surface plasma wave, resulting in the absorption of most of the incident light energy by the surface plasma wave, causing a sharp reduction in the energy of the reflected light. This resonance phenomenon creates a trough in the reflected light intensity response curve, corresponding to the resonance wavelength. Fiber optic SPR sensors utilize this resonance phenomenon to detect the properties of the external medium or analyze biomolecules in samples.

[0003] Fiber optic SPR sensors offer advantages such as simple fabrication, low cost, ease of miniaturization, and immunity to electromagnetic interference, leading to their widespread application in biological and chemical detection fields. Furthermore, fiber optics provide a larger sensing area, increasing sensitivity and reliability. The electromagnetic interference immunity of fiber optic SPR sensors also enhances their reliability in practical applications.

[0004] However, traditional fiber optic SPR sensors still have some limitations in terms of sensitivity, especially for the detection of low molecular weight biomolecules. Chinese patent CN221528427U discloses a sensing structure using a multimode fiber-single-mode fiber-multimode fiber, and by coating a gold film with a gallium sulfide film and gold nanorods, the sensitivity is increased to 5623 RIU / nm. However, this sensitivity is still insufficient to meet the high-precision requirements for trace biomolecule detection in industrial scenarios. Furthermore, the sensor's bioadsorption performance is insufficient, resulting in low capture efficiency for low molecular weight biomolecules. In addition, the chemical stability of the sensing interface needs improvement; performance degradation may occur in complex chemical environments or during long-term use, limiting its practical application under harsh conditions.

[0005] In view of the above, this utility model proposes a high-sensitivity fiber optic SPR sensor and sensing system, which can solve the problem of how to detect biomolecules with low relative molecular weight and maintain stable detection performance in complex biochemical environments. Utility Model Content

[0006] The first aspect of this utility model provides a high-sensitivity fiber optic SPR sensor, which includes an optical fiber body 100.

[0007] The optical fiber body 100 includes a sensing area 110, a gold film 120, an indium tin oxide film 130, a titanium dioxide film 140, an input end, and an output end;

[0008] In the cross-sectional direction of the fiber optic SPR sensor, the sensing area 110 covers the surface of the fiber optic body 100, the gold film 120 covers the surface of the sensing area 110, the indium tin oxide film 130 covers the surface of the gold film 120, and the titanium dioxide film 140 covers the surface of the indium tin oxide film 130.

[0009] The sensing area 110 includes a multimode fiber 111, a photonic crystal fiber 112, and another multimode fiber 111, which are sequentially fused together.

[0010] The second aspect of this utility model provides a sensing system, which includes the aforementioned fiber optic SPR sensor, broadband light source 200, and broadband spectrometer 300.

[0011] The beneficial effects of this invention are as follows: The fiber optic SPR sensor provided by this invention is based on indium tin oxide-sensitized photonic crystal fiber SPR, forming a sensing region composed of a multimode fiber-photonic crystal fiber-multimode fiber fusion splicing. The high carrier mobility of indium tin oxide can significantly enhance the surface plasmon resonance effect, and its high conductivity can regulate the electromagnetic field distribution, effectively improving the sensitivity of the sensor. The biocompatibility of titanium dioxide can greatly improve the adsorption capacity for biomolecules, and its surface hydroxyl groups provide active sites for bioprobe modification, making it particularly suitable for capturing low-concentration biomarkers. The through-hole structure design of the photonic crystal fiber constrains the light field through the refractive index gradient formed by the open holes, enhancing the interaction between the evanescent field and the analyte. At the same time, the circular through holes maintain structural stability, thereby improving the detection resolution. The multimode-photonic crystal-multimode fiber fusion splicing structure further amplifies the SPR signal through the mode coupling effect. Combining the electric field enhancement characteristics of indium tin oxide and the bio-interface function of titanium dioxide, the sensitivity, selectivity and stability are synergistically improved. Compared with existing SPR fiber optic sensors with only a gold film, this invention has higher sensitivity, bioadsorption and chemical stability. Attached Figure Description

[0012] Figure 1 This is a cross-section of the fiber optic SPR sensor of this invention. Figure 1 .

[0013] Figure 2 This is a cross-section of the fiber optic SPR sensor of this invention. Figure 2 .

[0014] Figure 3 This is a schematic diagram of the sensing system of this utility model.

[0015] Figure 4 This is the SPR reflectance spectrum of this utility model. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0017] In the description of this utility model, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0018] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0019] According to the instruction manual Figure 1 It is understood that the present invention provides an optical fiber SPR sensor including an optical fiber body 100;

[0020] The optical fiber body 100 includes a sensing area 110, a gold film 120, an indium tin oxide film 130, a titanium dioxide film 140, an input end, and an output end.

[0021] In this invention, indium tin oxide has a wide spectral response, which enables it to effectively absorb and emit light signals in the visible and near-infrared spectral ranges, thereby effectively improving the sensitivity and detection range of the fiber optic SPR sensor.

[0022] According to the instruction manual Figure 2It can be seen that, in the cross-sectional direction of the fiber optic SPR sensor, the sensing area 110 covers the surface of the fiber body 100, the gold film 120 covers the surface of the sensing area 110, the indium tin oxide film 130 covers the surface of the gold film 120, and the titanium dioxide film 140 covers the surface of the indium tin oxide film 130.

[0023] In this invention, the outermost titanium dioxide film 140 utilizes its abundant hydroxyl groups and biocompatibility to enhance the adsorption efficiency of biomolecules, resulting in higher sensitivity, bioadsorption, and chemical stability compared to existing SPR fiber optic sensors that only have a gold film.

[0024] The optical fiber body 100 includes a multimode optical fiber 111, a photonic crystal optical fiber 112, and the multimode optical fiber 111, which are fused together in sequence.

[0025] Preferably, the photonic crystal fiber and the multimode fiber have the same radius, which is 7500-7700nm.

[0026] The photonic crystal fiber 112 has eight through holes 113 distributed circumferentially along the axis of the photonic crystal fiber 112 in a cross-sectional direction parallel to the sensing region 110.

[0027] The multimode fiber 111 has a central air hole with a radius of 6500-7000nm, which fully exposes the through hole 113 of the photonic crystal fiber 112.

[0028] Of the through holes 113, in the cross-sectional direction parallel to the sensing area 110, the two through holes 113 that pass through the cross-sectional diameter are elliptical through holes, and the remaining through holes 113 are circular through holes.

[0029] In this utility model, as shown in the appendix to the specification... Figure 2 The aforementioned specific structure, in which the through-hole 113 in the X-axis direction is elliptical and the remaining through-holes 113 are circular, can effectively compress the mode field and enhance the evanescent field intensity. The through-hole 113 structure of the photonic crystal fiber achieves directional compression of the mode field through the elliptical through-hole in the X-axis direction, thereby enhancing the evanescent field, while the circular through-hole maintains the mechanical stability of the structure.

[0030] Compared to a fiber optic SPR sensor with a single gold film, the gold film 120 and the indium tin oxide film 130 exhibit stronger electron transfer, enhancing the electric field strength between the film layers and effectively strengthening the plasma wave. This, in turn, enhances the SPR signal and improves the sensor's sensitivity. During measurement, the surface of the gold film 120 can couple with the plasmon polaritons generated by the indium tin oxide film 130 to increase the electric field strength, thereby further improving the sensor's sensitivity.

[0031] The major axis of the elliptical through-hole 113 is 3185-3215 nm, the minor axis is 2385 nm-2415 nm, and the aspect ratio is 1.32-1.35:1.

[0032] The diameter of the circular through-hole 113 is 2780-2820 nm.

[0033] The distance between the center of the optical fiber body 100 and the center of the through hole 113 is 4990-5010 nm.

[0034] The photonic crystal fiber is fabricated by stacking and pulling.

[0035] In one specific embodiment, firstly, a quartz tube with a purity ≥99.999% is used as the substrate. A femtosecond laser precision drilling system is used to process one central circular through-hole, eight peripheral circular through-holes, and one X-axis elliptical through-hole. The center of all through-holes is strictly controlled to be within the 4990-5010 nm range from the center of the fiber body 100. A real-time laser ranging system is used for closed-loop control during the drilling process. Then, in Class... In a Class 100 cleanroom, pre-fabricated quartz tubes were assembled in a hexagonal close-packed structure. A helium-neon laser interferometer with a wavelength of 632.8 nm was used for positioning, ensuring the positional accuracy of each through-hole reached ±50 nm. After assembly, the tubes were encapsulated and fixed with quartz rods. Finally, the preform was placed in a drawing tower and drawn at a constant speed of 0.2 m / min at an environment of 1945-1955℃. Through-hole deformation was monitored in real time using a high-speed CCD imaging system with a sampling frequency of 1 kHz, and the traction tension was dynamically adjusted to 0.5-1.2 N using a PID control system. The final through-hole deformation rate was less than 0.5%, completing the fabrication of the photonic crystal fiber. The entire fabrication process was carried out in a cleanroom environment of 22.9-23.1℃ and 40-50% humidity, ensuring that the fiber's geometric parameters and optical performance achieved attenuation loss of <0.3 dB / km at a wavelength of 1550 nm and a nonlinear coefficient of <18 W. -1 ·km -1 Design requirements.

[0036] The titanium dioxide film 140 is fixed to the surface of the indium tin oxide film 130 by particle assembly.

[0037] Specifically, the particle assembly includes:

[0038] First, the optical fiber sensing area, coated with indium tin oxide film 130 and gold film 120, was immersed in 0.1M NaOH solution for 30 minutes to form a negatively charged hydroxylated layer on its surface. Then, it was immersed in 0.01M polydiallyldimethylammonium chloride (PDDA) solution for 20 minutes to form a positively charged polymer layer on the surface of the sensing area. The treated optical fiber was then immersed in TiO2 nanosol with a particle size of 22-28 nm and a concentration of 0.5wt% at pH=3.5. Through electrostatic adsorption, the negatively charged TiO2 nanoparticles with a Zeta potential of -32mV were combined with the PDDA modification layer. After immersion for 60 minutes, the fiber was finally annealed in a nitrogen environment at 450℃ for 2 hours to form sintered neck connections between the TiO2 nanoparticles and to form Ti-O-In chemical bonds with the substrate.

[0039] The length ratio of the multimode fiber 111, the photonic crystal fiber 112, and the multimode fiber 111 is 1:1-3:1-2. The thickness ratio of the gold film 120, the indium tin oxide film 130, and the titanium dioxide film 140 is 1:0.9-1.1:0.9-1.1.

[0040] The sensing area 110 is formed by sequentially fusing 5-10mm multimode fiber 111, 10-15mm photonic crystal fiber 112 and 5-10mm multimode fiber 111 after removing the coating layer.

[0041] Specifically, cut two 250-350mm multimode optical fibers 111, and use fiber stripping pliers to remove 5mm of the coating from the ends of the two multimode optical fibers 111 to expose the cladding. Use special lens cleaning paper dipped in a small amount of alcohol solution to clean the treated multimode optical fibers 111, and then use a fiber optic cleaver to cut off the excess part of the end where the coating was removed, leaving a 5mm portion of the removed coating.

[0042] The error in cutting length is within ±0.5mm.

[0043] The length of the sensing area 110 is 20 mm.

[0044] The thickness ratio of the gold film (120), the indium tin oxide film (130), and the titanium dioxide film (140) is 1:0.9-1.1:0.9-1.1.

[0045] The thickness of the gold film 120 is 45-55 nm.

[0046] The gold film 120, when within a specific thickness range, can achieve electromagnetic waves of a certain wavelength with the same frequency as the surface plasma waves generated on the surface of the gold film 120, thereby exciting the surface discrete element resonance and realizing the sensing function of this sensor. When the thickness of the gold film 120 is too low, its charge transfer efficiency will decrease, and if its thickness is too high, it will affect the sensitivity and quality factor of the sensor. When its thickness is between 45-55nm, it can meet the usage requirements.

[0047] Preferably, the thickness of the gold film 120 is 50 nm.

[0048] In this invention, when the thickness of the gold film 120 is 50nm, the sensor can ensure high sensitivity while also maintaining a high quality factor.

[0049] The thickness of the indium tin oxide film 130 is 45-55 nm.

[0050] When the thickness of the indium tin oxide film 130 is set to 45nm to 55nm, the sensitivity and quality factor of the sensor can ensure the normal use of the sensor.

[0051] Preferably, the thickness of the indium tin oxide film 130 is 50 nm.

[0052] In this invention, the technical effect achieved in the experiment is best when the thickness of the indium tin oxide film 130 is 50nm. When the thickness of the indium tin oxide film 130 is 50nm, the sensor can ensure high sensitivity while also maintaining a high quality factor.

[0053] The titanium dioxide film 140 has a thickness of 45-55 nm.

[0054] The thickness range of the titanium dioxide film 140 enables the optimal plasmon coupling effect, balancing transmittance, conductivity, and bioadsorption.

[0055] Preferably, the titanium dioxide film 140 has a thickness of 50 nm.

[0056] In this invention, when the thickness of the titanium dioxide film 140 is 50 nm, this thickness range can achieve the best plasmon coupling effect and balance transmittance, conductivity and bioadsorption.

[0057] As per the instruction manual Figure 3 As shown, the second aspect of this utility model provides a sensing system, including the aforementioned high-sensitivity fiber optic SPR sensor, broadband light source 200, and broadband spectrometer 300.

[0058] The broadband light source 200 has a visible light spectrum and is connected to the input end of the fiber optic SPR sensor.

[0059] The broadband spectrometer 300 is connected to the output end of the fiber optic SPR sensor. The broadband spectrometer 300 includes a data interface, through which it is connected to an external computer.

[0060] The fiber optic SPR sensor has an input end connected to a broadband light source 200 with a visible light spectrum, and an output end connected to a broadband spectrometer 300. The broadband spectrometer 300 is connected to an external computer via a data interface. The fiber optic SPR sensor is placed in the solution to be tested.

[0061] Example 1

[0062] As shown in the attached diagram of the instruction manual. Figure 2 As shown, a high-sensitivity fiber optic SPR sensor includes an optical fiber body 100.

[0063] The optical fiber body 100 includes a sensing area 110 formed by sequentially welding a multimode fiber 111, a photonic crystal fiber 112, and another multimode fiber 111. The photonic crystal fiber 112 is 10mm long, the multimode fibers 111 at both ends are 5mm long, and the total length of the sensing area 110 is 20mm.

[0064] The surface of the sensing area 110 consists of a gold film 120 with a thickness of 45nm to 55nm, an indium tin oxide film 130 with a thickness of 45nm to 55nm, and a titanium dioxide film 140 with a thickness of 45nm to 55nm, arranged sequentially from the inside to the outside. The titanium dioxide film 140 is fixed on the surface of the indium tin oxide film 130 by a particle assembly method. When the thickness of the gold film 120, the indium tin oxide film 130, and the titanium dioxide film 140 is 50nm, a high quality factor is achieved while ensuring high sensitivity.

[0065] As shown in the attached diagram of the instruction manual. Figure 3 As shown, the sensing system formed by the above-mentioned high-sensitivity fiber optic SPR biosensor includes an indium tin oxide-sensitized photonic crystal fiber SPR sensor with multimode fiber 111 as the optical path. Its input end is connected to a broadband light source 200 with a visible light spectrum, and its output end is connected to a broadband spectrometer 300. The broadband spectrometer 300 is connected to an external computer through a data interface. The indium tin oxide-sensitized photonic crystal fiber SPR sensor is placed in the solution to be detected.

[0066] The fabrication method of the above-mentioned fiber optic SPR sensor includes the following steps:

[0067] (1) Fabrication of optical fiber body 100

[0068] First, a quartz tube with a purity ≥99.999% was used as the substrate. Eight peripheral circular through-holes (2800nm ​​in diameter) were drilled using a femtosecond laser precision drilling system. Two of these through-holes (113) passing through the diameter of the sensing area 110 are elliptical (major axis 3200nm, minor axis 2400nm). The distance between the center of all through-holes and the fiber axis was strictly controlled within 5000nm. A real-time laser ranging system was used for closed-loop control during the drilling process. Then, in a Class 100 cleanroom, the processed quartz tubes were assembled in a hexagonal close-packed structure. A helium-neon laser interferometer with a wavelength of 632.8nm was used for positioning, ensuring the positional accuracy of each through-hole reached ±50nm. After assembly, the tubes were encapsulated and fixed using high-purity quartz rods. Finally, the preform was placed in a drawing tower and drawn at a constant speed of 0.2 m / min under precise temperature control at 1950℃. The through-hole deformation was monitored in real time using a high-speed CCD imaging system with a sampling frequency of 1 kHz, and the traction tension was dynamically adjusted to 0.8 N using a PID control system to ensure that the final through-hole deformation rate was less than 0.5%, thus completing the fabrication of the photonic crystal fiber. Then, two 300 mm multimode fibers 111 were cut, and 30 mm of the coating structure was stripped from the ends of each fiber using fiber strippers to expose the cladding. The treated multimode fibers 111 were cleaned with a small amount of alcohol solution using lens paper, and then the excess coating was removed from the ends using a fiber cleaver, leaving a 5 mm section with the coating removed. Subsequently, the photonic crystal fiber 112 is connected to the processed multimode fiber 111 on both sides using a fiber optic wiping machine, resulting in a sensing area 110 formed by wiping the 5mm multimode fiber 111 (with the coating removed), the 10mm photonic crystal fiber 112, and the 5mm multimode fiber 111 in sequence. The total length of the sensing area 110 is 20mm.

[0069] (2) Sputtered gold film 120

[0070] Gold films 120 were sputtered on both sides of the sensor. The prepared sensor was then placed in a vacuum ion beam sputtering instrument to deposit gold films 120 on the sensor surface. The current of the vacuum ion beam sputtering instrument was 8mA, the time was 90 seconds, and the thickness of the gold film 120 was 50nm.

[0071] (3) Sputtering of indium tin oxide film 130

[0072] Indium tin oxide (ITO) films 130 were sputtered onto the gold film. The prepared sensor was then placed in a vacuum ion beam sputtering instrument to deposit ITO films 130 on the sensor surface. The current of the vacuum ion beam sputtering instrument was 10 mA, the time was 120 seconds, and the thickness of the ITO film 130 was 50 nm.

[0073] (4) Fixing the titanium dioxide film at 140

[0074] First, the optical fiber sensing area with an indium tin oxide film 130 was immersed in a 0.1M NaOH solution for 30 minutes to form a negatively charged hydroxylated layer on its surface. Then, it was immersed in a 0.01M polydiallyldimethylammonium chloride (PDDA) solution for 20 minutes to form a positively charged polymer layer on the surface of the sensing area. The treated optical fiber was then immersed in a TiO2 nanosol with a pH of 3.5, a particle size of 25 nm, and a concentration of 0.5 wt%. The negatively charged TiO2 nanoparticles with a Zeta potential of -32 mV were bonded to the PDDA modification layer through electrostatic adsorption for 60 minutes. Finally, it was annealed in a nitrogen atmosphere at 450℃ for 2 hours to form sintered neck connections between the TiO2 nanoparticles and to form Ti-O-In chemical bonds with the substrate.

[0075] The refractive index of a liquid was measured using the bulk fiber SPR sensor prepared above.

[0076] As shown in the attached diagram of the instruction manual. Figure 4 As shown, the gallium sulfide-enhanced fiber optic SPR sensor of this application was sequentially immersed in solutions with refractive indices of 1.33061, 1.34012, 1.35010, 1.36002, 1.37001, 1.37992, 1.38004, 1.39000, and 1.40002 to obtain transmission spectrum curves. By performing linear fitting on the above measurement results, the sensitivity of the sensor can be obtained as 9661.90 nm / RIU, and the linearity is 0.99.

[0077] The fiber optic SPR biosensor provided by this invention overcomes the limitations of existing technologies in detecting low concentrations and low molecular weight biomolecules through structural design and material optimization. This sensor can maintain stable detection performance in complex biochemical environments, achieving high-precision and high-reliability detection of trace biomarkers, and meeting the stringent requirements of modern biomedical testing and environmental monitoring.

[0078] Finally, it should be noted that the above specific embodiments are intended to illustrate the technical solution of this utility model and do not constitute any limitation on this utility model. Those skilled in the art should fully understand that modifications to the technical solutions described in the foregoing embodiments or equivalent substitutions for any part or all of the technical features are entirely feasible. Such modifications or substitutions, as long as they do not deviate from the protection scope defined by the claims of this utility model, should be considered reasonable extensions of this utility model.

Claims

1. A high-sensitivity fiber optic SPR sensor, characterized in that, Includes the fiber body (100); The optical fiber body (100) includes a sensing area (110), a gold film (120), an indium tin oxide film (130), a titanium dioxide film (140), an input end, and an output end; In the cross-sectional direction of the fiber optic SPR sensor, the sensing area (110) covers the surface of the fiber body (100), the gold film (120) covers the surface of the sensing area (110), the indium tin oxide film (130) covers the surface of the gold film (120), and the titanium dioxide film (140) covers the surface of the indium tin oxide film (130). The sensing area (110) includes a multimode fiber (111), a photonic crystal fiber (112), and a multimode fiber (111) fused together in sequence.

2. The fiber optic SPR sensor according to claim 1, characterized in that, The photonic crystal fiber (112) has the same radius as the multimode fiber (111), which is 7500-7700nm.

3. The fiber optic SPR sensor according to claim 1, characterized in that, The photonic crystal fiber (112) has eight through holes (113) circumferentially distributed along the axis of the photonic crystal fiber (112) in a cross-sectional direction parallel to the sensing region (110). The multimode optical fiber (111) has a central air hole with a radius of 6500-7000 nm.

4. The fiber optic SPR sensor according to claim 3, characterized in that, The distance between the center of the optical fiber body (100) and the center of the through hole (113) is 4990-5010 nm.

5. The fiber optic SPR sensor according to claim 3, characterized in that, Of the through holes (113), in the cross-sectional direction parallel to the sensing area (110), the two through holes (113) that pass through the diameter of the cross-section are elliptical through holes, and the remaining through holes (113) are circular through holes.

6. The fiber optic SPR sensor according to claim 5, characterized in that, The major axis of the elliptical through-hole (113) is 3185-3215 nm, the minor axis is 2385 nm-2415 nm, and the aspect ratio is 1.32-1.35:1; The diameter of the circular through hole (113) is 2780-2820 nm.

7. The fiber optic SPR sensor according to claim 1, characterized in that, The length ratio of the multimode fiber (111), the photonic crystal fiber (112), and the multimode fiber (111) is 1:1-3:1-2.

8. The fiber optic SPR sensor according to claim 1, characterized in that, The length of the sensing area (110) is 20-35 mm; The thickness ratio of the gold film (120), the indium tin oxide film (130), and the titanium dioxide film (140) is 1:0.9-1.1:0.9-1.

1.

9. A sensing system, characterized in that, Includes the fiber optic SPR sensor, broadband light source (200), and broadband spectrometer (300) as described in any one of claims 1-8.

10. The sensing system according to claim 9, characterized in that, The broadband light source (200) has a visible light spectrum and is connected to the input end of the fiber optic SPR sensor. The output end of the fiber optic SPR sensor body (100) is connected to the broadband spectrometer (300), the broadband spectrometer (300) is connected to an external computer through a data interface, and the fiber optic SPR sensor is placed in the solution to be detected.

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