Sensing probe assembly, flow control optical fiber sensing system and preparation method

Abstract

The invention discloses a sensing probe assembly, a fluidic optical fiber sensing system and a preparation method, and relates to the cross technical field of optical fiber sensing technology and microfluidic detection. One free end of a single-mode optical fiber in the sensing probe assembly is fixed to the outer wall of a first square capillary tube through ultraviolet curing glue, and a second square capillary tube is coaxially or parallelly inserted into an inner cavity of the first square capillary tube. A uniform air gap is formed between the inner wall of the first square capillary tube and the outer wall of the second square capillary tube, a microfluid channel is formed in the middle of the second square capillary tube, and broadband light beams emitted from the single-mode optical fiber are vertically incident. The micro-fluidic chip sequentially penetrates through the ultraviolet curing adhesive, the upper wall of the first square capillary tube, the air gap and the upper wall of the second square capillary tube, enters the micro-fluidic channel filled with liquid to be detected, then penetrates through the lower wall of the second square capillary tube and finally reaches the lower wall of the first square capillary tube. The probe has the advantages of high detection sensitivity, strong light beam coupling stability and the like.

Description

Technical Field

[0001] This invention relates to the field of cross-disciplinary technology of fiber optic sensing and microfluidic detection, and particularly to a sensing probe assembly, a fluidic fiber optic sensing system, and a method for its fabrication. Background Technology

[0002] With the rapid development of fields such as biomedicine, environmental monitoring, food safety, and drug development, the demand for highly sensitive, real-time, and in-situ detection of trace biochemical substances (such as proteins, antibody antigens, DNA, and heavy metal ions) is becoming increasingly urgent. Among numerous detection technologies, fiber optic biosensing technology has become a research hotspot in both academia and industry due to its unique advantages, including small size, resistance to electromagnetic interference, corrosion resistance, intrinsic safety, and ease of remote monitoring. In particular, fiber optic sensors based on the Fabry-Pérot (FP) interferometry principle are especially suitable for the precise measurement of physical quantities such as refractive index (RI) due to their compact structure, fast response speed, and high integrability.

[0003] Although traditional fiber optic FP sensors have achieved some applications, existing technical solutions still face a series of insurmountable bottlenecks and challenges when dealing with trace biological detection and microfluidic integration: Firstly, regarding sensor structure, circular capillary is currently the most commonly used material for constructing microfluidic fiber optic sensors. However, when a light beam emerges from a single-mode fiber and attempts to pass through the wall of a circular capillary, the curved outer and inner surfaces of the capillary generate a severe cylindrical lensing effect. This lensing effect causes severe defocusing or uncontrolled focusing of the incident beam, preventing most of the light energy from being reflected back to the fiber core along its original path, significantly reducing the contrast and signal-to-noise ratio of the interference fringes. Furthermore, due to the presence of the curved surface, the coupling alignment process between the fiber and the capillary is extremely sensitive to angle and position; even a tiny offset can cause the signal to disappear, greatly increasing the packaging difficulty and long-term stability risks of the device.

[0004] Secondly, to address the lensing effect of circular structures, some researchers have begun exploring the use of square capillary tubes. Square capillary tubes have naturally parallel, flat sidewalls that effectively maintain collimated beam propagation, eliminating the lensing effect and significantly improving signal quality. However, current square capillary sensors mostly employ a single-layer structure, forming a single FP cavity. According to the FP interference principle, the refractive index sensitivity of a single-cavity sensor is limited by its physical cavity length and operating wavelength, exhibiting a theoretical limit.

[0005] Finally, the optical vernier effect, as an emerging and highly efficient sensitization mechanism, utilizes the beat frequency envelope generated by the slight mismatch of the optical path difference through the cascaded superposition of two interference cavities, which can amplify the sensitivity by one or even two orders of magnitude. Currently, sensors utilizing the vernier effect are mostly manufactured using methods such as fiber misalignment fusion splicing or chemical etching taper. Although these methods can generate the vernier effect, they are difficult to integrate perfectly with microfluidics systems, and cannot simultaneously achieve "micro-liquid injection" and "structural robustness".

[0006] In summary, there is a need to develop a microfluidic fiber optic sensor that can overcome the lens effect of circular capillary tubes, break through the sensitivity limit of single-cavity structures, and possess simple fabrication processes, high mechanical strength, and easy integration. The sensor structure based on double-layer nested square capillaries proposed in this invention is designed to address the aforementioned technical challenges. Summary of the Invention

[0007] The technical problem to be solved by the present invention is how to provide a sensing probe assembly with high detection sensitivity and strong beam coupling stability.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a sensing probe assembly, comprising: a single-mode optical fiber, an ultraviolet curable adhesive, a first square capillary, and a second square capillary. One free end of the single-mode optical fiber is fixed to the outer wall of the first square capillary by the ultraviolet curable adhesive. The second square capillary is coaxially or parallelly inserted into the internal cavity of the first square capillary. A uniform air gap is formed between the inner wall of the first square capillary and the outer wall of the second square capillary. A microfluidic channel is formed in the middle of the second square capillary. A broadband light beam emitted from the single-mode optical fiber is incident perpendicularly and passes through the ultraviolet curable adhesive, the upper wall of the first square capillary, the air gap, and the upper wall of the second square capillary in sequence, enters the microfluidic channel filled with the liquid to be measured, passes through the lower wall of the second square capillary, and finally reaches the lower wall of the first square capillary.

[0009] This invention also discloses a microfluidic fiber optic sensing system, including the aforementioned sensing probe assembly, and further including a broadband light source, a fiber optic circulator, a spectrometer, a computer, and a microfluidic pump system. The port of the fiber optic circulator is connected to the broadband light source, the port of the fiber optic circulator is connected to the sensing probe assembly, and the port of the fiber optic circulator is connected to the spectrometer. The microfluidic pump system is connected to the microfluidic channel of the sensing probe assembly via a conduit. The computer is connected to the spectrometer via an interface for real-time acquisition of spectral data and subsequent fast Fourier transform and vernier effect demodulation processing. Qualitative and quantitative sensing of the measured physical quantity or biochemical substance is achieved by tracking the drift of the low-frequency envelope in the reflection spectrum.

[0010] The present invention also discloses a method for preparing the aforementioned sensing probe assembly, comprising the following steps: S1, Prepare the first square capillary and the second square capillary; S2, insert the second square capillary into the internal cavity of the first square capillary, so that they remain coaxial or parallel in the first square capillary. S3. Place one end face of the single-mode fiber perpendicularly close to the center of the outer wall of the first square capillary, connect the broadband light source and the spectrum analyzer, turn on the broadband light source for real-time spectrum monitoring, and adjust the position so that the beam emitted by the single-mode fiber is optimally and perpendicularly coupled into the dual-cavity structure formed by the first square capillary and the second square capillary. S4. Keeping the relative positions of each component unchanged, fix the single-mode optical fiber to the contact interface of the first square capillary. Then, apply glue to seal the ends of the two capillary tubes. During this process, insert the microfluidic conduit with the matching outer diameter into both ends of the second square capillary tube and seal the interface with glue to form a complete microfluidic inlet and outlet channel.

[0011] The beneficial effects of adopting the above technical solution are as follows: 1) This invention introduces the optical vernier effect into the field of microfluidic fiber optic sensing. By using the series coupling of dual FP cavities, the signal of minute refractive index change is amplified by tens to hundreds of times, breaking through the physical limit of traditional single-cavity sensors, making it possible to detect low concentrations of biomolecules.

[0012] 2) This invention adopts a full-planar square capillary nested structure, which completely solves the inherent lens divergence effect of circular capillary, realizes collimated transmission and efficient coupling of beam, significantly improves the contrast of interference fringes, reduces the difficulty of alignment process, and enhances the long-term working stability of the device.

[0013] 3) The unique "air reference cavity + liquid sensing cavity" design of this invention endows the sensor with natural temperature-refractive index decoupling capability. By using the air cavity as a stable temperature reference, high-precision in-situ temperature compensation can be achieved without the need for an additional temperature sensor, solving the common temperature crosstalk problem in biological detection.

[0014] 4) Compared with existing technologies that rely on expensive femtosecond lasers or vacuum coating equipment, this invention only uses commercial standard capillaries, optical fibers and UV adhesives, and can be prepared through simple micro-assembly and dispensing processes, which greatly reduces production costs and technical barriers and facilitates large-scale promotion.

[0015] 5) The inner quartz capillary of this invention directly serves as a microfluidic channel, possessing excellent chemical inertness and biocompatibility, and requiring very little sample volume, making it highly suitable for integration into a microfluidic chip (Lab-on-a-Chip) system for real-time, dynamic biochemical analysis. Attached Figure Description

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 This is a schematic diagram of the cross-sectional structure of the probe described in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the longitudinal cross-sectional optical path principle of the probe described in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the microfluidic fiber optic sensing system described in Embodiment 2 of the present invention. Figure 4 This is a schematic diagram of the fabrication process of the probe described in Embodiment 3 of the present invention; Figure 5 This is a schematic diagram of the vernier effect spectral principle in Embodiment 3 of the present invention.

[0018] Wherein: 1: Single-mode optical fiber; 2: UV-curable adhesive; 3: First square capillary; 4: Second square capillary; 5: Air gap; 6: Microfluidic channel; 7: Broadband light source; 8: Fiber circulator; 9: Spectrometer; 10: Computer; 11: Microfluidic pump system; 12: Sensing probe assembly; 13: High-frequency interference fringes; 14: Low-frequency envelope; 15: Wavelength shift of the envelope peak; L1: Physical cavity length of the air gap; L2: Physical cavity length of the microfluidic channel. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0021] Example 1 like Figure 1 and Figure 2As shown in the figure, an embodiment of the present invention discloses a sensing probe assembly. The sensing probe assembly 12 adopts a novel nested square capillary structure, mainly including a single-mode optical fiber 1, a UV-curable adhesive 2, a first square capillary (outer tube) 3, and a second square capillary (inner tube) 4. One free end of the single-mode optical fiber 1 is fixed to the outer wall of the first square capillary 3 by the UV-curable adhesive 2. The second square capillary 4 is coaxially or parallelly inserted into the internal cavity of the first square capillary 3, forming a uniform air gap 5 between the inner wall of the first square capillary 3 and the outer wall of the second square capillary 4. A microfluidic channel 6 is formed in the middle of the second square capillary 4.

[0022] Preferably, both the first square capillary 3 and the second square capillary 4 are made of high-purity fused silica glass, which has an extremely low coefficient of thermal expansion (approximately 5.5 × 10⁻⁷ / ℃) and good optical transmittance. This significantly reduces the impact of ambient temperature changes on the thermal deformation of the sensor's geometry, improving the stability of the reference signal. Simultaneously, the flat outer and inner surfaces of the square capillary naturally eliminate the lens divergence effect of the circular capillary, allowing the beam emitted from the single-mode fiber to propagate and reflect in a collimated state between the multilayer interfaces. This significantly improves the contrast ratio and signal-to-noise ratio (SNR) of the echo signal, reducing the technological difficulty of fiber alignment and coupling.

[0023] In this embodiment, the inner side length of the first square capillary 3 is approximately 452 μm, and the outer side length is approximately 650 μm; the outer side length of the second square capillary 4 is approximately 200 μm, and the inner side length (i.e., the width of the microfluidic channel 6) is approximately 100 μm. This size range ensures extremely low sample consumption at the nanoliter to microliter level, suitable for the detection of expensive or scarce biological samples, while avoiding excessive fluid resistance or clogging problems caused by excessively narrow channels. Simultaneously, the size of the outer tube is adjusted accordingly to the size of the inner tube and the required vernier matching conditions, ensuring a compact structure and high mechanical strength.

[0024] The second square capillary tube 4 is coaxially or parallelly inserted into the internal cavity of the first square capillary tube 3. Due to the difference in size design, a uniform air gap 5 with a thickness of approximately 126 μm is formed between the inner wall of the first square capillary tube 3 and the outer wall of the second square capillary tube 4. The end face of the single-mode fiber 1 is cut flat with a high-precision cleaver, and can be ground and polished if necessary, and then placed perpendicular to the center of a flat outer wall of the first square capillary tube 3. The single-mode fiber 1 is fixed to the outer wall of the first square capillary tube 3 by a refractive index-matched or low-shrinkage UV-curable adhesive 2, which ensures the stability of the mechanical connection and effectively reduces Fresnel reflection loss between the fiber end face and the outer wall of the capillary tube.

[0025] Combination Figure 2As shown in the optical path diagram, the broadband beam emitted from the single-mode fiber 1 is incident perpendicularly, passing sequentially through the UV-curable adhesive 2, the upper wall of the first square capillary 3, the air gap 5, and the upper wall of the second square capillary 4, entering the microfluidic channel 6 filled with the liquid to be tested, then passing through the lower wall of the second square capillary 4, and finally reaching the lower wall of the first square capillary 3. Since all four sides of the square capillary are optical planes, the beam does not experience the cylindrical lens effect inherent in traditional circular capillary channels when passing through the various media, thus maintaining good collimation. In the above optical path, the beam undergoes Fresnel reflection at each interface where the refractive index changes abruptly (especially the interfaces on both sides of the air gap 5 and the microfluidic channel 6). These reflected beams return along the original path to the single-mode fiber 1, superimposing within the fiber core and resulting in multi-beam interference. In this design, the air gap 5 forms a Fabry-Perot (FP) reference cavity with a physical cavity length of L1 (approximately 126 μm), containing air (refractive index nair ≈ 1.0). The microfluidic channel 6 forms an FP sensing cavity with a physical cavity length of L2 (approximately 100 μm), containing the analyte liquid (refractive index nliquid ≈ 1.33). Alternatively, the optical lengths of the air cavity and the liquid cavity can be made extremely small. Under these conditions, the free spectral ranges (FSR) of the high-frequency interference fringes in the reflection spectrum are extremely close, and the resulting beat frequency envelope has a large amplification factor (M). Theoretically, this can increase the refractive index sensitivity of the sensor to over 10000 nm / RIU, thereby enabling effective detection of trace biochemical substances.

[0026] The probe possesses inherent dual-parameter self-compensation characteristics. The reference cavity, formed by an air gap, is not in contact with the liquid being measured; its optical cavity length is only affected by thermal expansion and thermo-optical effects caused by ambient temperature, and is insensitive to changes in the refractive index of the liquid. The sensing cavity, formed by a microfluidic channel, is affected by both ambient temperature and the liquid's refractive index. Based on this characteristic, this invention utilizes the sensitivity matrix method for signal demodulation. By establishing a system of two linear equations containing the characteristic wavelength drifts of the air cavity and the liquid cavity, and introducing temperature and refractive index sensitivity coefficients, and by solving the inverse matrix, the cross-interference error caused by temperature fluctuations can be accurately deducted while calculating changes in the liquid's refractive index, achieving high-precision in-situ temperature-compensated measurement.

[0027] The inner wall surface of the microfluidic channel can be biofunctionalized to achieve specific detection of certain biomarkers (such as proteins, antibodies, viruses, DNA sequences, etc.). Specific modification methods include, but are not limited to: silanizing the quartz inner wall using a silane coupling agent (such as APTES) to introduce active groups such as amino or carboxyl groups; and covalently immobilizing specific antibodies or aptamers on the inner wall of the microfluidic channel using a cross-linking agent (such as glutaraldehyde). When specific antigens flow through the channel, the antigen-antibody binding reaction changes the thickness and effective refractive index of the biolayer on the inner wall of the channel, thereby altering the optical path of the sensing cavity. Combined with the above vernier sensitization mechanism, label-free detection of extremely low concentrations of biomolecules can be achieved.

[0028] Furthermore, the sensing probe can be cascaded or connected in parallel with multiple nested units having different cavity length parameters, or multiple independent sensing areas can be constructed at different locations within the same inner tube. Combined with wavelength division multiplexing (WDM) or space division multiplexing techniques, it can simultaneously detect multiple different biochemical substances or achieve distributed multi-point sensing, greatly expanding the sensor's application potential in complex biological fluid analysis. Further optimization of this technical solution involves equipping the computer in the signal acquisition and processing module with dedicated demodulation algorithm software. This algorithm not only includes conventional peak tracking algorithms but also integrates Fast Fourier Transform (FFT) and bandpass filtering algorithms. By performing an FFT on the acquired complex superimposed spectrum, the spectral components corresponding to the air cavity, liquid cavity, and mixing cavity can be separated in the spatial frequency domain. Then, the independent spectra of each sub-cavity are reconstructed using Inverse Fourier Transform (IFFT). This optimized scheme allows for the independent and accurate extraction of phase or wavelength information of the reference cavity and sensing cavity even under imperfect vernier effects or overly complex spectra, greatly improving the robustness and accuracy of signal demodulation.

[0029] Example 2 See Figure 3As shown in the figure, this invention also discloses a microfluidic fiber optic sensing system based on nested square capillary vernier sensitization. This system mainly comprises a broadband light source 7, a fiber optic circulator 8, a spectrometer 9, a computer 10, a microfluidic pump system 11, and a core sensing probe assembly 12. In the specific experimental setup, the broadband light source 7 preferably uses a C+L band amplified spontaneous emission (ASE) light source, with an output spectral range covering 1528 nm to 1603 nm and an output power stability better than 0.01 dB, ensuring clear interference fringes can be excited over a wide spectral range. The fiber optic circulator 8 is a low insertion loss single-mode fiber optic circulator, with port 1 connected to the broadband light source 7, port 2 connected to the sensing probe assembly 12, and port 3 connected to the spectrometer 9. The resolution of the spectrometer 9 is set to 0.02 nm, and the number of sampling points is set to a high value to accurately record dense high-frequency interference fringes and low-frequency vernier envelopes. The microfluidic pump system 11 includes a high-precision syringe pump and a microfluidic conduit, which is connected to the microfluidic channel 6 of the sensing probe assembly 12 via the conduit. It can precisely control the injection and washing of the test liquid at a flow rate from 0.1 μL / min to 100 μL / min. The computer 10 is connected to the spectrometer 9 via a GPIB interface for real-time acquisition of spectral data and subsequent Fast Fourier Transform (FFT) and vernier effect demodulation processing.

[0030] Example 3 See Figure 4 As shown, this embodiment of the invention also discloses a method for preparing the sensing probe assembly described in Embodiment 1, specifically including the following steps: Step A, Material Preparation and Cleaning. Cut a first square capillary tube 3 and a second square capillary tube 4 with a length of about 3 cm to 5 cm, remove the polymer coating at both ends, and immerse them in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 15 minutes each to thoroughly remove surface oil and impurities. Then place them in a clean oven to dry for later use.

[0031] Step B, Nested Assembly. The cleaned first square capillary tube 3 is fixed on the stage. The second square capillary tube 4 is held in place by a high-precision six-dimensional micromanipulation platform. Under real-time monitoring with a long working distance microscope (CCD), the inner tube 4 is carefully inserted into the internal cavity of the outer tube 3. The position of the inner tube 4 is fine-tuned by adjusting the X and Y axis knobs of the micromanipulation platform, ensuring it remains as coaxial or parallel as possible within the outer tube 3, avoiding direct contact between the tube walls and causing friction or stress.

[0032] Step C, Fiber Coupling and Alignment. Strip the coating from one end of the single-mode fiber 1 and cut it flat, then fix it on another three-dimensional adjustment frame. Position the fiber end face perpendicularly close to the center of the outer wall of the first square capillary 3, connect the broadband light source 7 and the spectrometer 9, and turn on the light source for real-time spectral monitoring. Finely adjust the fiber's position (X, Y, Z axes) and angle (θ angle), and observe the waveform changes on the spectrometer 9. When the maximum contrast (extinction ratio) is observed in the reflection spectrum, and clear, regular vernier envelope characteristics are observed (such as...), the fiber will be aligned. Figure 5 When the high-frequency stripe 13 and low-frequency envelope 14 are shown, it indicates that the beam has been optimally vertically coupled into the dual-cavity structure, at which point the displacement stage is locked.

[0033] Step D: Dispensing and Curing. Keeping the relative positions of all components unchanged, carefully apply a small amount of UV-curable adhesive 2 to the interface between the single-mode optical fiber 1 and the first square capillary tube 3. Irradiate with a 365 nm UV LED point light source for 60 to 120 seconds to ensure complete curing, thus firmly fixing the optical fiber. Subsequently, seal the ends of the two capillaries with adhesive. During this process, microfluidic conduits (such as PEEK tubes or quartz capillaries) with matching outer diameters should be pre-inserted into both ends of the second square capillary tube 4, and the interfaces should be sealed with adhesive to form a complete microfluidic inlet and outlet channel, preventing liquid leakage. Finally, anneal the prepared sensor assembly in a 60°C constant temperature oven for 2 hours to release the internal stress generated by adhesive curing and improve the long-term stability and temperature characteristics of the sensor.

[0034] The fabrication method of the sensor probe employs an all-fiber physical assembly process, avoiding expensive femtosecond laser etching or chemical etching steps. Specifically, it includes: selecting matching inner and outer square capillaries; inserting the inner tube into the outer tube under a micro-operating system; monitoring the reflection spectrum in real time using a broadband light source and spectrometer; and finding the optimal coupling point with the highest interference fringe contrast and most obvious envelope characteristics by adjusting the relative position of the single-mode fiber and the sidewall of the outer tube; subsequently, rapidly encapsulating the fiber contact point and both ends of the capillary tube using a low-shrinkage UV-curable adhesive. This process is simple, highly controllable, and has a high yield. Furthermore, the UV adhesive used can be a refractive index-matching adhesive to further reduce Fresnel reflection loss on the primary surface.

[0035] See Figure 5The diagram illustrates the spectral principle of the vernier effect-based sensitization method of this invention. This invention utilizes the optical vernier effect generated by the aforementioned dual-cavity structure for sensitization. When a broadband optical signal enters the sensing probe assembly 12, two sets of interfering light waves generated by the air reference cavity (L1) and the liquid sensing cavity (L2) are superimposed. Through precise design, the optical path length of the air reference cavity (OPLref≈nairL1) is made similar to, but not equal to, the optical path length of the liquid sensing cavity (OPLsens≈nliquidL2) (e.g., L1≈126μm, L2≈100μm, nliquid≈1.33). At this time, dense high-frequency interference fringes 13 appear in the spectrum. The amplitude of these fringes is modulated by a low-frequency envelope 14, forming a typical vernier interference pattern. When the refractive index of the liquid in the microfluidic channel 6 changes slightly, the optical path of the sensing cavity changes, causing a slight displacement of the high-frequency interference fringes 13. According to the vernier amplification principle, this minute displacement is significantly amplified by the amplification factor $M$, manifesting as a huge wavelength shift of the low-frequency envelope peak $15$. By tracking the amount of envelope peak shift, refractive index detection with a sensitivity of over 10000 nm / RIU can be achieved, far exceeding that of traditional single-cavity sensors.

[0036] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Unless otherwise specified, an element defined by the phrase "comprising..." or "including..." does not exclude the presence of additional elements in the process, method, article, or terminal device that includes said element. Additionally, in this document, "greater than," "less than," "exceeding," etc., are understood to exclude the stated number; "above," "below," "within," etc., are understood to include the stated number.

[0037] Although the above embodiments have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the above descriptions are merely embodiments of the present invention and do not limit the scope of patent protection of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A sensing probe assembly characterized by It comprises: Single-mode optical fiber (1), ultraviolet curing glue (2), first square capillary (3) and second square capillary (4), one free end of single-mode optical fiber (1) is fixed to the outer wall of the first square capillary (3) through ultraviolet curing glue (2), the second square capillary (4) is coaxially or parallelly inserted into the internal cavity of the first square capillary (3), a uniform air gap (5) is formed between the inner wall of the first square capillary (3) and the outer wall of the second square capillary (4), the middle part of the second square capillary (4) forms a microfluidic channel (6), the broadband light beam emitted from the single-mode optical fiber (1) is vertically incident, and sequentially passes through the ultraviolet curing glue (2), the upper wall of the first square capillary (3), the air gap (5), the upper wall of the second square capillary (4), enters the microfluidic channel (6) filled with the liquid to be measured, and then passes through the lower wall of the second square capillary (4) and finally reaches the lower wall of the first square capillary (3).

2. The sensing probe assembly of claim 1, wherein: The air gap (5) constitutes a Fabry-Perot reference cavity with a physical cavity length of L1, and the medium in the cavity is air; the microfluidic channel (6) constitutes a Fabry-Perot sensing cavity with a physical cavity length of L2, and the medium in the cavity is the liquid to be measured.

3. The sensing probe assembly of claim 1, wherein: The first square capillary 3 and the second square capillary (4) are both made of high-purity fused quartz glass.

4. The sensing probe assembly of claim 3, wherein: The inner side length of the first square capillary 3 is 452 μm, and the outer side length is 650 μm; the outer side length of the second square capillary 4 is about 200 μm, and the inner side length is 100 μm.

5. A microfluidic optical fiber sensing system comprising a sensing probe assembly (12) according to any one of claims 1 to 4, characterized in that: The system further comprises a broadband light source (7), a fiber optic circulator (8), a spectrum analyzer (9), a computer (10) and a microfluidic pump system (11), the port 1 of the fiber optic circulator (8) is connected with the broadband light source (7), the port 2 of the fiber optic circulator (8) is connected with the sensing probe assembly (12), and the port 3 of the fiber optic circulator (8) is connected with the spectrum analyzer (9); the microfluidic pump system (11) is connected with the microfluidic channel (6) of the sensing probe assembly (12) through a conduit, and the computer (10) is connected with the spectrum analyzer (9) through an interface, for real-time acquisition of spectrum data and subsequent fast Fourier transform and vernier effect demodulation processing, and the drift of the low-frequency envelope in the reflected spectrum is tracked to realize qualitative and quantitative sensing of the physical quantity or biochemical substance to be measured.

6. A method of manufacturing a sensor probe assembly as claimed in any one of claims 1-4, characterized in that It comprises the following steps: S1, preparing the first square capillary (3) and the second square capillary (4); S2, inserting the second square capillary (4) into the internal cavity of the first square capillary (3) to keep it coaxial or parallel in the first square capillary (3); S3, vertically approaching the center position of the outer side wall of the first square capillary (3) with one end face of the single-mode optical fiber (1), connecting the broadband light source (7) and the spectrum analyzer (9), turning on the broadband light source (7) for real-time spectrum monitoring, and adjusting the position to make the light beam emitted from the single-mode optical fiber (1) be best vertically coupled into the double-cavity structure composed of the first square capillary (3) and the second square capillary (4). S4, keep the relative position of each component unchanged, fix the single-mode optical fiber (1) to the contact interface of the first square capillary (3); then, seal the two ends of the two capillaries by dispensing glue, in this process, the outer diameter matched microfluidic conduit is inserted into the two ends of the second square capillary (4) in advance, and the interface is sealed with glue to form a complete microfluidic inlet and outlet channel.

7. The method of claim 6, wherein The step S1 specifically comprises: The first square capillary (3) and the second square capillary (4) with a length of 3-5 cm are cut, the polymer coating at both ends is removed, and the capillaries are sequentially immersed in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 15 minutes to remove surface oil stains and impurities, and then dried in a clean oven for standby.

8. The method of claim 6, wherein The step S2 specifically comprises: The cleaned first square capillary (3) is fixed on the stage, the second square capillary (4) is clamped by the high-precision six-dimensional micro-manipulation platform, the second square capillary (4) is inserted into the internal cavity of the first square capillary (3) under the real-time monitoring of the long working distance microscope, the position of the second square capillary (4) is fine-tuned by adjusting the X and Y axis knobs of the micro-manipulation platform, so that the second square capillary (4) is kept coaxial or parallel in the first square capillary (3), and direct contact of the tube wall is avoided to cause friction or stress.

9. The method of claim 6, wherein The step S3 specifically comprises: One end of the single-mode optical fiber (1) is stripped and cut flat and fixed on another three-dimensional adjusting frame; the end face of the optical fiber is vertically close to the center position of the outer side wall of the first square capillary (3), the broadband light source (7) and the spectrum analyzer (9) are connected, the broadband light source (7) is turned on for real-time spectrum monitoring; the position and angle of the single-mode optical fiber (1) are finely adjusted, and the waveform change on the spectrum analyzer (9) is observed; when the contrast in the reflected spectrum is maximum and the clear and regular vernier envelope feature is observed, it indicates that the light beam has been best vertically coupled into the double-cavity structure, and the displacement table is locked at this time.

10. The method of claim 6, wherein The step S4 specifically comprises: The relative position of each component in the sensing probe assembly is kept unchanged, and a small amount of ultraviolet curing glue (2) is added at the contact interface of the single-mode optical fiber (1) and the first square capillary (3), and a wavelength of 365 nm ultraviolet LED point light source is used for irradiation for 60-120 seconds to make it completely cured, so that the optical fiber is firmly fixed; Then, the two ends of the two capillaries are sealed by dispensing glue, in this process, the outer diameter matched microfluidic conduit is inserted into the two ends of the second square capillary (4) in advance, and the interface is sealed with glue to form a complete microfluidic inlet and outlet channel; Finally, the prepared sensor assembly is placed in a 60℃ constant temperature oven for annealing treatment for 2 hours.

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