Probe type optical fiber SPR sensor based on microsphere structure

Abstract

The invention provides a probe type optical fiber SPR (Surface Plasmon Resonance) sensor system based on a microsphere structure. The probe type optical fiber SPR sensor is characterized in that the probe type optical fiber SPR sensor is composed of a broadband light source, a spectrograph, a broadband circulator and a microballoon structure probe type optical fiber SPR sensor, the microballoon structure probe type optical fiber SPR sensor is formed by welding a multimode optical fiber with a section of single-mode optical fiber, and the single-mode optical fiber at the welding position of the multimode optical fiber and the single-mode optical fiber is prepared into the microballoon structure; the nano-silver film is deposited on the surface of the single-mode optical fiber, the polydimethylsiloxane film and the polyvinyl alcohol film are coated section by section along the outer surface of the nano-silver film, and the nano-gold film is plated on the end face of the tail end, so that the temperature parameter and the humidity parameter can be simultaneously measured in various sensing application scenes. The device is simple in structure, flexible and compact, and can be widely applied to the optical fiber sensing application fields of chemistry, biology, medicine, life science and the like.

Description

(1) Technical Field

[0001] The present invention relates to a probe-type fiber optic SPR sensor based on a microsphere structure, which can be used for simultaneous measurement of temperature and humidity parameters in biochemical sensing application scenarios, and can be widely applied to fiber optic sensing application fields such as chemistry, biology, medicine, and life sciences, belonging to the fiber optic sensing technology field. (2) Background Art

[0002] Surface Plasmon Resonance (SPR) refers to the phenomenon that when P-polarized light undergoes total internal reflection at the interface between a prism and a metal thin film, when the frequency of the incident light matches the resonance frequency of the surface plasmon wave, part of the beam energy is transferred to the free electrons in the metal to form a surface plasmon resonance wave, resulting in a significant decrease in the intensity of the reflected light and forming an SPR resonance valley phenomenon. Due to the high sensitivity of this phenomenon to changes in the external refractive index, SPR technology has been widely applied in many fields such as chemistry, biology, medicine, and life sciences for highly sensitive detection and analysis.

[0003] SPR sensors can achieve the sensing function by depositing sensitive materials on the fiber end face, side polishing, or fused biconical taper. Common types of optical fibers include single-mode fibers, multi-mode fibers, hollow fibers, and special fibers. Although fiber optic SPR sensors are compact and easy to integrate, due to the fixed structure of the fiber core of most sensors, it is difficult to modulate its inherent resonance wavelength externally, resulting in certain limitations in sensitivity. In contrast, prism-type SPR sensors can change the resonance wavelength by adjusting the incident angle, thereby improving sensitivity. However, prism-type SPR sensor systems have the problems of large volume and high cost, which limit their wide promotion in practical applications.

[0004] Patent CN202410911895.8 discloses an arc-shaped plastic fiber optic SPR sensor and its preparation method. By cutting a certain thickness in the middle of the optical fiber with a blade, heating it with an alcohol lamp, the cut part by the blade is drawn into an arc-shaped sensing area, and a 50-nm-thick silver nano-film is deposited on the arc surface of the sensing area. This invention can generate resonance absorption peaks at different wavelength positions in the output spectrum, and the whole system has the advantage of high sensitivity to refractive index. However, this sensor requires the use of flame heating during preparation, which has a relatively high risk.

[0005] Patent CN202410938243.3 discloses an L-shaped structure dual-channel plastic optical fiber surface plasmon resonance sensor and its preparation method. The L-shaped sensor mainly uses the high-temperature hot pressing method to hot press D-shaped structures on two mutually perpendicular surfaces of the plastic optical fiber respectively, then coats nano silver films on the two sensing surfaces, and coats the temperature-sensitive material PDMS on one of the surfaces. This invention utilizes the different sensitivities of the SPR sensor to refractive index and temperature, and can generate two resonance absorption peaks at different wavelength positions in the output spectrum, forming two surface plasmon resonance sensing channels. The whole system has the advantages of high sensitivity to refractive index and compact structure. However, the preparation process of this sensor is complex, and the transmission structure limits the convenience of use.

[0006] Patent CN202310582906.8 discloses a multi-side polished temperature-compensated SPR sensor based on multimode fiber. The multi-side polished temperature-compensated SPR sensor based on multimode fiber effectively reduces the uncertainty caused by temperature during refractive index measurement, ensuring the stability of measurement. However, it cannot meet the requirements of high-sensitivity measurement.

[0007] In order to overcome the deficiencies of the above prior technologies, the present invention discloses a probe-type SPR sensor based on a microsphere structure. By melting and processing at the fiber fusion joint to form a microsphere structure, the beam diffraction effect is significantly enhanced, and the sensitivity is improved. At the same time, by changing the physical size of the microsphere structure, the resonant wavelength can be flexibly modulated, overcoming the problem that the inherent resonant wavelength of the fiber SPR sensor is difficult to adjust. In addition, this sensor is compactly designed, and the probe-type structure has broader application potential and portability. (III) Summary of the Invention

[0008] The purpose of the present invention is to provide a probe-type fiber SPR sensor with a microsphere structure that is compact, flexible, and can be mass-produced, for solving the problems existing in the prior art.

[0009] The present invention is implemented as follows:

[0010] The probe-type fiber SPR sensor system with a microsphere structure of this invention consists of a broadband light source, a spectrometer, a broadband circulator, and a probe-type fiber SPR sensor with a microsphere structure. The probe-type fiber SPR sensor with a microsphere structure is composed of a section of multimode fiber fused with a section of single-mode fiber. The single-mode fiber at the fusion joint of the single-mode fiber and the multimode fiber is prepared into a microsphere structure, and the end of the single-mode fiber is coated with nano gold film. After the microsphere structure of the single-mode fiber, nano silver film is deposited on part of the surface, and polydimethylsiloxane film and polyvinyl alcohol film are coated segment by segment along the outer surface of the nano silver film, for realizing the simultaneous measurement of temperature parameters and humidity parameters. This design integrates the transmission, induction, and reflection of light, and can meet the applications in multiple scenarios.

[0011] Figure 1 And Figure 2 Figure 1 shows the working principle diagram of the probe-type fiber optic SPR sensor based on the microsphere structure.

[0012] As Figure 1 shown, first, the broadband light from the broadband light source 1 is coupled into the single-mode fiber 3. After passing through the broadband circulator 4, the broadband light is simultaneously coupled into the core of the microsphere-structured single-mode fiber through the multimode fiber 6, and part of the light enters the cladding of the microsphere-structured single-mode fiber. The probe-type fiber optic SPR sensor with a microsphere structure consists of three parts: the first part is the multimode fiber, which is used to introduce the broadband light source into the sensor system; the second part is the single-mode fiber with a microsphere structure. By fabricating the single-mode fiber into a microsphere structure, the beam diffraction effect is enhanced to improve the sensitivity. At the same time, by changing the physical size of the microsphere structure, the resonant wavelength can be flexibly modulated, overcoming the inherent shortcoming of the resonant wavelength of the fiber optic SPR sensor; the third part is the single-mode fiber with a nano-silver film coated with a segmented polydimethylsiloxane film and a polyvinyl alcohol film on the surface and a nano-gold film coated on the tail end, enabling the SPR sensor to simultaneously measure the temperature parameter and the humidity parameter, and making the light return along the original optical path to form a probe structure.

[0013] As Figure 2 shown, the broadband light source is introduced into the sensor through the multimode fiber 21. The larger core diameter of the multimode fiber ensures the stable transmission of light. When the light enters the microsphere-structured single-mode fiber 22 from the multimode fiber, due to the mismatch of the core diameters, part of the light enters the cladding of the single-mode fiber and undergoes total internal reflection at the interface between the cladding and the air. During this process, the beam diffraction effect is enhanced when the light passes through the microsphere-structured single-mode fiber. Subsequently, when it comes into contact with the surface of the nano-silver film 25 coated with a polydimethylsiloxane film 23 and a polyvinyl alcohol film 24, the SPR phenomenon is excited, and the SPR optical signal is transmitted along the single-mode fiber, reflected by the nano-gold film at the tail end, and then transmitted back to the spectrometer 2 along the original optical path.

[0014] Surface plasmon resonance (SPR) is a physical phenomenon of the interaction between light and free electrons on the metal surface. When light waves enter from the optical fiber and generate an evanescent wave on the surface of the metal film, if its wave vector satisfies the phase matching condition with the surface plasmon wave (SPW) of the metal surface, resonance will occur, resulting in strong absorption of light energy at a specific wavelength, thus forming an obvious absorption valley in the reflection spectrum. This resonant wavelength is extremely sensitive to the refractive index of the surrounding medium. Therefore, by monitoring the change in the resonant wavelength, precise detection of environmental parameters can be achieved.

[0015] To achieve the measurement of temperature and humidity dual parameters, two functional polymer films are segmented and coated on the surface of the nano-silver film: the temperature-sensitive material polydimethylsiloxane and the humidity-sensitive material polyvinyl alcohol. The refractive index of polydimethylsiloxane changes with the increase of temperature, resulting in a blue shift of the resonance wavelength; during the moisture absorption process of polyvinyl alcohol, volume expansion and refractive index change occur, thus causing a red shift of the SPR resonance wavelength. The two respectively regulate different resonance valleys of the SPR signal, making it show a good decoupling response to environmental temperature and humidity changes. By monitoring the position changes of the two characteristic resonance valleys in the reflection spectrum and establishing a sensitivity matrix model between the response wavelength and temperature and humidity, the simultaneous quantitative measurement of environmental temperature and relative humidity can be accurately achieved.

[0016] In summary, the probe-type fiber optic SPR sensor with a microsphere structure of the present invention overcomes the deficiencies of traditional SPR sensors in terms of sensitivity, resonant wavelength modulation ability, and system volume by combining the fiber optic transmission characteristics, surface plasmon resonance effect of the microsphere structure, and reflection enhancement mechanism. The entire sensing system structure has the advantages of high sensitivity, small volume, and simple preparation process, and is suitable for various application scenarios such as medical diagnosis, biochemical detection, and environmental monitoring. (IV) BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To illustrate the present invention more clearly, the drawings required for the present invention will be briefly introduced below.

[0018] Figure 1 It is a schematic diagram of a probe-type fiber optic SPR sensor system based on a microsphere structure. Among them, 1 is a broadband light source, 2 is a spectrometer, 3 is an optical fiber, 4 is a broadband circulator, 5 is a probe-type fiber optic SPR sensor with a microsphere structure, 6 is a multimode optical fiber, and 7 is a single-mode optical fiber with a microsphere structure.

[0019] Figure 2 It is a structural diagram of a probe-type fiber optic SPR sensor based on a microsphere structure. 21 is a multimode optical fiber, 22 is a single-mode optical fiber with a microsphere structure, 23 is a polydimethylsiloxane film, 24 is a polyvinyl alcohol film, 25 is a nano-silver film, and 26 is a nano-gold film.

[0020] Figure 3 It is a cross-sectional view of the multimode optical fiber and single-mode optical fiber selected for the probe-type fiber optic SPR sensor based on a microsphere structure. 31 is a multimode optical fiber, 32 is a single-mode optical fiber, 33 is the core of the multimode optical fiber, and 34 is the core of the single-mode optical fiber.

[0021] Figure 4 It is an experimental flow chart of a probe-type fiber optic SPR sensor based on a microsphere structure. 41 is a broadband light source, 42 is a spectrometer, 43 is a broadband circulator, 44 is an injection pump, 45 is a sensing area, 46 is a probe-type fiber optic SPR sensor with a microsphere structure, 47 is a waste liquid pool, and 48 is a computer.

[0022] Figure 5 It is the spectrogram of the response of the probe-type fiber optic SPR sensor based on the microsphere structure to the change in the surrounding refractive index. (V) Specific implementation manners

[0023] In order to more clearly clarify the purpose and technical advantages of the present invention, the specific implementation of the present invention will be described in detail below. This description will show various aspects of the embodiments of the present invention. Through the specific analysis of the embodiments, readers will more intuitively grasp the technical characteristics of the present invention and its application value in the field of fiber optic sensing.

[0024] The geometric dimensions of the single-mode fiber selected in this example are as follows: the cladding diameter is 125 μm, the core diameter is 9 μm, and the numerical aperture of the core is 0.12; the geometric dimensions of the multi-mode fiber are as follows: the cladding diameter is 125 μm, the core diameter is 105 μm, and the numerical aperture of the core is 0.22.

[0025] In this invention, a fiber optic with a microsphere structure is prepared by using a fiber optic four-electrode fused taper system. First, the multi-mode fiber and the single-mode fiber are precisely fusion spliced. Subsequently, the coating is mechanically stripped at a position 2 cm away from the melting point on the single-mode fiber section, and the bare fiber area is accurately fixed at the center of the double electrodes; the melting power of the electrodes is set to 65 W and the time is 15 s. The two electrodes are heated by synchronous discharge and the motors on both sides are controlled to push the fiber bidirectionally towards the center at a constant rate, so that the molten area shrinks into a sphere, and the particle size of the microsphere is precisely regulated by adjusting the number of melting cycles; after the sphere is formed, a 2-cm bare fiber area on the right side is reserved as the sensing and transmission area, and finally a probe-type fiber optic SPR sensor with a microsphere structure is formed.

[0026] After the fiber optic is fusion spliced well, the surface of the single-mode fiber is immersed in a SnCl2 glycerol solution with a molecular concentration of 0.2% for about 10 minutes, and then rinsed clean with distilled water to clean the fiber optic surface. Next, Tollens' reagent is prepared. 3 mL of 0.1 mol / L silver nitrate solution is poured into a 10-mL beaker, and dilute ammonia water is added dropwise with stirring until the brown precipitate completely dissolves. Then 1.4 mL of 0.8 mol / L potassium hydroxide solution is added. If the precipitate appears again, continue to add ammonia water until it dissolves, and finally Tollens' reagent is obtained. Take out part of Tollens' reagent and prepare a 1:5 dilution with distilled water to obtain a thinner silver nano-film. The diluted Tollens' reagent is poured into 5 mL of 0.05 mol / L glucose solution, the position of the fiber optic is adjusted, and it is immersed in the solution for 10 minutes. After taking out the fiber optic, it is rinsed and dried with distilled water. Finally, the surface of the fiber optic after silver plating treatment is coated with a polydimethylsiloxane film and a polyvinyl alcohol film section by section.

[0027] The end of the optical fiber is thoroughly cleaned with isopropyl alcohol and deionized water, and the surface is activated by low-power plasma treatment. Then, the optical fiber is fixed in a vacuum deposition device, and a 300-nm nanogold film is deposited on its end by magnetron sputtering technology to achieve a reflection effect, enabling the sensor to form a probe structure.

[0028] A probe-type fiber optic SPR sensor based on a microsphere structure provided by an embodiment of the present invention can simultaneously and sensitively measure the temperature and humidity of the natural environment.

[0029] As described above, only the preferred embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art makes various modifications and changes to the present invention according to the spirit and scope of the present invention, and they should all be included in the protection scope of the claims of the present invention.

Claims

1. A probe-type fiber optic SPR sensor system based on a microsphere structure, characterized in that: The system consists of a broadband light source, a broadband circulator, a spectrometer, and a probe-type fiber optic SPR sensor with a microsphere structure. The probe-type fiber optic SPR sensor with a microsphere structure is formed by splicing a multimode fiber to a single-mode fiber. The single-mode fiber at the splicing point of the multimode fiber and the single-mode fiber is fabricated into a microsphere structure. A nano silver film is deposited on the surface of the single-mode fiber, and a polydimethylsiloxane film and a polyvinyl alcohol film are coated segmentally along the outer surface of the nano silver film to form a surface plasmon resonance (SPR) sensitive probe for realizing the temperature and humidity measurement of the sensor. A nano gold film is deposited on the end face of the tail of the single-mode fiber to achieve effective beam reflection.

2. The probe-type fiber optic SPR sensor based on a microsphere structure according to claim 1, characterized in that: Fabricating the single-mode fiber at the splicing point of the multimode fiber and the single-mode fiber into a microsphere structure enhances the beam diffraction effect, improves the sensitivity of the sensor to the detection parameters, realizes high-precision sensing measurement, and at the same time maintains low loss, ensuring the efficiency and stability of signal transmission.

3. The probe-type fiber optic SPR sensor based on a microsphere structure according to claim 1, wherein: Depositing a nano silver film on the surface of the single-mode fiber produces a stronger evanescent wave when the surface plasmon resonance phenomenon occurs compared with the traditional nano gold film, and is more sensitive to environmental parameter changes.

4. The probe-type optical fiber SPR sensor based on a microsphere structure according to claim 1, wherein: By depositing a nano silver film on the surface of the single-mode fiber and coating a polydimethylsiloxane film and a polyvinyl alcohol film segmentally along the outer surface of the nano silver film, the SPR sensor can measure the temperature and humidity parameters simultaneously.

5. The probe-type fiber optic SPR sensor based on a microsphere structure according to claim 1, wherein: A nano gold film with a thickness of 300 nm is deposited on the end face of the tail of the single-mode fiber, realizing the effective reflection of the sensing signal.

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