High-sensitivity and rapid microstructure polymer optical fiber tetracycline sensor and preparation method thereof

Abstract

The invention provides a novel micro-structure polymer optical fiber tetracycline sensor based on C3N4-MIL-53 sensitive material modification, which can realize low-cost, high-sensitivity and rapid detection of tetracycline concentration in water. The optical fiber probe is characterized in that the optical fiber probe is composed of a side-cast area and a microgroove area, and the surface of the side-cast area is sequentially coated with a layer of Canadian resin and a C3N4-MIL-53 sensitive film. Through the microgroove structure, most of light transmitted by the optical fiber can be concentrated in a specific angle range for transmission, so that the intensity of evanescent waves is effectively enhanced, and the sensitivity of the sensor is improved. The C3N4-MIL-53 sensitive material is adopted for modification, and the specific adsorption effect of the C3N4-MIL-53 sensitive material on tetracycline is utilized, so that the rapid, high-sensitivity and high-selectivity detection function of the sensor on the concentration of tetracycline in water is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical fiber sensing technology and chemical analysis, and particularly relates to a high-sensitivity and rapid microstructure polymer optical fiber tetracycline sensor and a preparation method thereof. BACKGROUND

[0002] Antibiotics, as effective drugs for treating bacterial infections, play an important role in the field of clinical medicine. However, these substances have environmental persistence and biodegradation characteristics, and their extensive use has caused multiple environmental problems: on the one hand, it pollutes the ecological environment of water bodies, and on the other hand, it promotes the production of superbugs and drug-resistant strains, posing a major threat to human health and ecological safety. There are many types of antibiotics, among which tetracycline antibiotics are widely used due to their broad-spectrum antibacterial properties. After entering the human body, it is difficult to be absorbed, and most of it will be discharged into sewage, which is one of the main pollutants in the water environment. Therefore, the detection and research of tetracycline (TC) in the water environment has important value for maintaining the ecological environment of water bodies.

[0003] Researchers at home and abroad have carried out a lot of research work on tetracycline detection. For example, Chinese invention patent application No. 202510672645.8 "A ratio type fluorescent probe for specifically detecting tetracycline antibiotics and its preparation and application" provides a gallium germanate zinc nanoprobe modified by amino, citric acid and europium, which can specifically bind to tetracycline antibiotics. The sensor has two different fluorescence emission intensities, realizes different color changes under ultraviolet light, and completes the quantitative detection of tetracycline by comparing different colors and tetracycline concentrations. For example, Chinese invention patent application No. 202310052160.X "A molecularly imprinted photoelectrochemical sensor based on CDs@PCN-224 nanocomposite material and its use" provides a preparation method of a nanocomposite material (CDs@PCN-224) of in-situ synthesized porphyrin-based metal organic framework (PCN-224) and carbon quantum dots (CDs), and a photoelectrochemical sensor constructed based on the material combined with molecular imprinting technology for quantitative detection of tetracycline. Common tetracycline detection methods now include colorimetric method, fluorescence spectroscopy, photoelectrochemical detection method, etc. However, these methods generally have limitations such as complicated operation, high detection cost, etc. For example, colorimetric method requires multiple chemical color development reactions, fluorescence spectroscopy relies on label modification, and electrochemical electrodes are easily contaminated and need to be modified regularly. In addition, these methods generally have problems such as time-consuming and complex consumables in the sample pretreatment stage. Therefore, it is of great practical significance to provide a high-sensitivity, low-cost and simple tetracycline detection method.

[0004] Optical fiber sensor (OFS) has the characteristics of small size, chemical corrosion resistance, and immunity to electromagnetic interference, and is suitable for measurement applications in various special environments. Compared with quartz optical fiber, polymer optical fiber is made of high polymer polymer, which has the advantages of light weight, excellent bendability, large core diameter, easy operation and low manufacturing cost. The sensor system constructed by using polymer optical fiber has higher strain tolerance and simple operation. In addition, polymer materials are easy to be combined with organic substances, and have good biocompatibility, which has great potential in the field of biosensing. Now there are researchers at home and abroad combining fiber optic sensors and tetracycline detection, such as: non-patent literature Shrivastav A M, Mishra S K, Gupta B D. Localized and propagating surface plasmon resonance based fiber optic sensor for the detection of tetracycline using molecular imprinting [J]. (Materials Research Express, 2015, 2 (3):035007) published in 2015, using multimode optical fiber as the carrier, by coating silver film on the bare core, silver nanoparticles (size 10-30nm) synthesized by hydrothermal method and tetracycline template molecular imprinting film (MIP film), a tetracycline detection sensor is constructed, which realizes the detection of tetracycline with a concentration of 10 -8 M-10 -5 M Concentration detection, and low cost, fast response, which provides a feasible path for tetracycline fiber sensing detection. But the existing technology has insufficient anti-interference ability to interference substances in complex matrix, relies on plasmon resonance wavelength shift detection, and has high cost, and the silver film and silver nanoparticle coating are easy to be corroded in the detection environment containing chemical substances, resulting in insufficient long-term stability. According to the above-mentioned deficiencies, the microgroove structure is designed to enhance the evanescent wave intensity, and by using the high-efficiency selective adsorption ability of C3N4-MIL-53 sensitive material to tetracycline, high-sensitivity, high-selectivity, rapid-response tetracycline detection is realized. SUMMARY

[0005] The application provides a side-polished micro-groove structure polymer optical fiber, and a fiber sensor for tetracycline detection is realized by adopting C3N4-MIL-53 sensitive material on the fiber. The micro-groove structure in the fiber sensor of the application can enhance the evanescent wave intensity and improve the sensitivity of the sensor. The C3N4-MIL-53 material adopted in the application has a strong adsorption effect on tetracycline, which can cause changes in the dielectric constant and the refractive index of the C3N4-MIL-53 film, change the depth of the evanescent wave, and further change the output light intensity of the polymer optical fiber, so that the detection of the external tetracycline concentration can be realized by monitoring the change of the output light intensity of the polymer optical fiber.

[0006] The polymer optical fiber comprises a side-polished structure and a micro-groove structure, which comprises a polished area and a series of micro-grooves with the same interval. The polished area is prepared by a wheel type fiber polishing machine, and the series of micro-grooves with the same interval are prepared by a hot pressing method. A layer of Canadian resin film and a layer of C3N4-MIL-53 film are coated on the polished area of the plastic optical fiber in sequence.

[0007] The application comprises:

[0008] 1. The application provides a preparation method of a side-polished micro-groove structure polymer optical fiber tetracycline sensor, which has the advantages of simple preparation process, high sensitivity, label-free, fast response and low cost.

[0009] 2. The application improves the sensitivity of the sensor by adopting a micro-structure optical fiber. The optical fiber used in the application is a step-type polymer optical fiber with a diameter of 1mm, a cladding thickness of 10um, a numerical aperture of 0.5, and a core and cladding material of PMMA and fluorinated polymer, respectively. A region with a length L of 25mm and a depth D of 400um is polished on the surface of the polymer optical fiber. Twelve micro-grooves with an interval of 2mm and an angle alpha of 60 degrees are made directly below the side-polished region, and the micro-groove depth d is 120um.

[0010] 3. The application coats a layer of Canadian resin and a layer of C3N4-MIL-53 sensitive film on the surface of the side-polished region of the optical fiber probe in sequence, so that the optical fiber has the sensing function of tetracycline.

[0011] The working principle of the application is as follows: when the incident light enters the polymer optical fiber at a certain angle, it is transmitted into the Canadian resin film through the micro-groove structure, and then evanescent waves are generated at the junction of the Canadian resin film and the C3N4-MIL-53 film. The energy of the evanescent wave decays exponentially along the vertical direction of the junction surface of the Canadian resin film and the C3N4-MIL-53 film, and the effective penetration depth d p as shown in the following formula.

[0012]

[0013] At this time, n1 and n2 are the refractive indices of the Canadian resin film and the C3N4-MIL-53 film, respectively, and the incident angle θ of the transmitted light at the interface after passing through the microgroove (ignoring the influence of the fiber cladding) can be expressed as the following formula,

[0014] n3 and n4 are the refractive indices of the core and the medium in the microgroove structure region (i.e. the external medium), respectively, and β is the incident angle of the transmitted light at the microgroove structure.

[0015] According to the above formula, it can be seen that the incident angle θ is affected by α, β, n3 and n4. Under the condition of the same β, θ decreases with the increase of α (0°≤α≤90°), which in turn leads to the increase of d p That is, the polymer optical fiber with microgroove structure (α=60°) can effectively enhance the evanescent wave intensity compared with the polymer optical fiber without microgroove (α=0°). The effective penetration depth d p of the evanescent wave increases with the increase of the refractive index n2 of the C3N4-MIL-53 film, which leads to the weakening of the output light intensity of the polymer optical fiber. In addition, when the C3N4-MIL-53 adsorbs tetracycline, it will cause the dielectric constant and the refractive index of the film to increase, which will lead to the increase of the effective penetration depth d p of the evanescent wave, and in turn lead to the weakening of the output light intensity of the polymer optical fiber. Therefore, by using a side-polished microgroove polymer optical fiber combined with a specific sensitive film, an evanescent wave type polymer optical fiber tetracycline sensor can be designed, and the detection of external tetracycline can be realized by monitoring the change of the light intensity at the output end of the polymer optical fiber.

[0016] C3N4-MIL-53 is a new material composed of graphite phase carbon nitride (C3N4) and metal organic framework material MIL-53 (Fe), which has excellent physical and chemical properties. C3N4 has high specific surface area and rich surface functional groups such as amino and hydroxyl groups, while MIL-53 is known for its highly ordered pore structure and adjustable pore size. The composite structure of C3N4-MIL-53 forms a multi-level porous network structure through π-π stacking, hydrogen bonding and electrostatic interaction, which provides an ideal physical and chemical environment for efficient adsorption of tetracycline. In addition, the photocatalytic properties of C3N4 and the metal active sites of MIL-53 synergistically enhance the adsorption capacity of the material for tetracycline. The combination of the two not only enhances the mechanical stability and chemical stability of the material, but also improves its adsorption performance.

[0017] The adsorption process of tetracycline on C3N4-MIL-53 involves a synergistic effect of multiple intermolecular forces. Specifically, a pi-pi stacking interaction occurs between the aromatic ring structure in the tetracycline molecule and the conjugated pi system of C3N4, constituting the main adsorption driving force. At the same time, functional groups such as hydroxyl, amino and carbonyl in the tetracycline molecule can form coordination bonds or intermolecular hydrogen bonds with the metal nodes (such as Fe3+) in MIL-53. In addition, the negative charge on the surface of the material and the positive charge area in the tetracycline molecule are further enhanced by electrostatic attraction. In summary, C3N4-MIL-53 enhances the capture capacity of tetracycline through multiple synergistic mechanisms and also exhibits good selectivity.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] 1. The microstructured polymer optical fiber tetracycline sensor of the present application has the advantages of simple structure, low cost, long-term use, good stability and the like.

[0020] 2. The microstructured polymer optical fiber tetracycline sensor of the present application uses C3N4-MIL-53 as a sensitive material to achieve rapid, high-sensitivity and high-selectivity detection of tetracycline

[0021] 3. The microstructured polymer optical fiber tetracycline sensor of the present application effectively enhances the evanescent wave intensity and the sensitivity of the sensor by utilizing the microgroove structure, and has important application value in the field of optical fiber sensing. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a preparation schematic diagram of the microstructured polymer optical fiber tetracycline sensor of the present application;

[0023] Figure 2 is a structural schematic diagram of the microstructured polymer optical fiber tetracycline sensor of the present application;

[0024] Figure 3 is a schematic diagram of the optical fiber sensing and detection system built by the present application;

[0025] Figure 4 is a sensitive response curve of the microstructured polymer optical fiber tetracycline sensor;

[0026] Figure 5 is a test result of the influence of groove depth on the microstructured polymer optical fiber tetracycline sensor;

[0027] Figure 6 is a response time curve of the microstructured polymer optical fiber tetracycline sensor;

[0028] Figure 7 is a test result of the influence of C3N4-MIL-53 film thickness on the performance of the sensor;

[0029] Figure 8 is the test result of sensor selectivity; DETAILED DESCRIPTION

[0030] The specific implementation of the present application will be further described in detail below in combination with the drawings.

[0031] Before the preparation of the side-polished micro-slot structure polymer optical fiber, the preparation of C3N4-MIL-53 is completed. First, MIL-53(Fe) is synthesized by a solvothermal method. 10 mmol of FeCl3·6H2O, an equimolar amount of terephthalic acid (H2BDC), and an appropriate amount of C3N4 are dissolved in 50 mL of N,N-dimethylformamide (DMF) solvent. To promote the complete dissolution and mixing of the raw materials, the mixed solution is placed in an ultrasonic cleaning instrument and kept under ultrasonic oscillation for more than 12 hours. After mixing uniformly, the reaction solution is transferred to the inner liner of a 100 mL polytetrafluoroethylene reaction kettle, and a stainless steel high-pressure reaction kettle is installed and sealed. The reaction is carried out at a constant temperature of 150°C for 24 hours. After the reaction is terminated, the system is cooled to ambient temperature, and solid-liquid separation is achieved by centrifugation. To purify the product, the precipitate is washed with DMF and methanol alternately for two times each to completely remove residual reactants and organic impurities. The washed product is dried in a vacuum drying box for 12 h. Finally, the dried composite material is ground into fine powder for use. To facilitate the subsequent coating of the sensitive film, the obtained C3N4-MIL-53 powder is dispersed in an ethanol solution to form a uniform dispersion system.

[0032] Referring to Figure 1 (a)-(d), are schematic diagrams of the preparation process of the microstructure polymer optical fiber tetracycline sensor, mainly including side polishing, hot pressing, and coating of Canada resin solution and C3N4-MIL-53, etc.

[0033] Referring to Figure 1(a) is the preparation of the side-polishing region, which is prepared as follows: first, a wheel-type optical fiber polishing device is used to prepare the side-polishing structure of the polymer optical fiber, which can prepare polymer optical fibers with different side-polishing lengths and side-polishing depths. During the side-polishing process, 800 grit sandpaper is first pasted on the surface of the rotating grinding wheel using double-sided tape, and the polymer optical fiber is supported and fixed using a special optical fiber support and a fiber winding disc. Then, the parameters are set by the computer, the grinding wheel rotation button is turned on, and the side-polishing process is started. The rotating grinding wheel is controlled to move back and forth along the optical fiber axis. It is worth noting that the speed of the grinding wheel is particularly critical: too low a speed will result in low processing efficiency, while too high a speed may cause uneven processing surface, or even cause the optical fiber to be excessively thinned in some areas and fail. To monitor the polishing quality in real time, the system is equipped with a microscopic observation device, which can observe the side-polishing effect of the polymer optical fiber in real time and accurately measure the remaining diameter of the optical fiber after side-polishing to evaluate the polishing depth. After polishing, the polishing surface needs to be polished for 5 minutes using aluminum oxide polishing paste with polishing cloth to improve the surface roughness, and then the residual paste on the surface of the optical fiber is wiped clean. Preferably, the optical fiber used in the experiment has a diameter of 1 mm, a side-polishing length of 25 mm, and a side-polishing depth of 400 µm.

[0034] Referring to Figure 1 (b) is a schematic diagram of the preparation of a micro-groove structure on the opposite side of the polished surface of the polymer optical fiber by a hot-pressing process. First, the polished surface of the polymer optical fiber is fixed with the polished surface facing down using adhesive tape. Then, the micro-groove mold is heated to 80°C using a heating platform, and then the heated mold is precisely positioned on the surface of the optical fiber. The mold is smoothly pressed down by rotating the iron block knob clockwise at a uniform speed. This pressure state needs to be maintained for 5 minutes, and then the demolding process is completed after cooling. It should be noted that the mold temperature must be strictly controlled within a reasonable range. Too high a temperature will cause the surface material of the optical fiber to melt, thereby affecting the forming effect of the micro-groove. To obtain micro-grooves with different depths, the rotation angle of the knob can be adjusted. After the grooving is completed, the grooving effect can be observed and the groove depth can be measured by a microscopic imaging system. Finally, the polymer optical fiber with the side-polished micro-groove structure is ultrasonically cleaned and dried to prepare for the subsequent sensitive film coating process. Preferably, the micro-groove structure has a pitch of 2 mm, a micro-groove angle α of 60°, a micro-groove depth d of 120 μm, and a number of 12.

[0035] Referring to Figure 1 (c) and (d) are schematic diagrams of the coating process of Canadian resin and C3N4-MIL-53 material. As shown in Figure 1 (c), a small amount of Canadian resin solution is first added to the polished area, and then a cylindrical doctor blade is used to uniformly coat the resin along the axial direction, so that a uniform thin film of Canadian resin covers the polished surface. Then, as shown in Figure 1(d) as shown, the C3N4-MIL-53 solution was added dropwise on the surface of the Canada balsam film in a stepwise manner, and the solution was evenly spread in the resin area by slightly shaking the probe. After natural air drying, a uniform C3N4-MIL-53 film was formed on the surface of the Canada balsam. To ensure the repeatability of the experiment, a micropipette was used to strictly control the amount of the two solutions during the preparation of the probe. The coated probe was placed in a constant temperature drying oven and treated at 80°C for 12h. The temperature and drying time of the equipment can be accurately controlled. Preferably, the thickness of the C3N4-MIL-53 film is 26 µm.

[0036] Figure 2 The structure of the microstructured polymer optical fiber tetracycline sensor probe of the application is shown in the schematic diagram. It is characterized by being composed of a polished region and a microgroove region. The length of the polished region is 25 mm, and the depth is 400 µm. A layer of Canada balsam and a C3N4-MIL-53 sensitive film are coated on the surface of the side-polished region in turn. The microgroove structure is composed of 12 microgrooves with a pitch of 2 mm and an angle α of 60°. The microgroove depth d is 120 µm.

[0037] Referring to Figure 3 The optical fiber sensing system of the application is shown in the schematic diagram.

[0038] In the experimental device, the optical fiber adapters are used at both ends of the optical fiber probe to connect the halogen light source (Ideaoptics HL2000, wavelength range: 360-2500 nm) and the spectrum analyzer (Ocean Optics USB2000+, wavelength range: 200-850 nm), respectively. For the convenience of experimental testing, the polymer optical fiber sensing probe is fixed in the culture dish using adhesive tape, and the spectrum analyzer is connected to the computer for real-time monitoring and recording of the transmission spectrum.

[0039] Referring to Figure 4 (a)-(c) are the tetracycline response results of the bare optical fiber, the probe coated only with a layer of Canada balsam, and the probe coated with a layer of Canada balsam and a layer of C3N4-MIL-53 sensitive material, respectively.

[0040] From Figure 4 (a), it can be seen that the uncoated probe has no response to different concentrations of tetracycline. From Figure 4 (b), it can be seen that the probe coated with Canada balsam has a small and irregular spectral shift change to different concentrations of tetracycline, which can be ignored. From Figure 4(c) It can be seen that the Canadian resin and C3N4-MIL-53 coated probes have a significant response to tetracycline, and the intensity of the transmission spectrum decreases with the increase of tetracycline concentration. This shows that C3N4-MIL-53 adsorbs tetracycline, resulting in a decrease in the output light intensity of the polymer optical fiber. Therefore, the sensor can realize the detection of tetracycline concentration.

[0041] Referring to Figure 5 , the experimental results of tetracycline detection of different micro-groove depth probes coated with Canadian resin and C3N4-MIL-53 films, the thickness of C3N4-MIL-53 film is 26 μm.

[0042] From Figure 5 (a) and Figure 5 (b) it can be seen that in the concentration range of 0-100 ppm, both structures of the probe have good sensing response to tetracycline, compared with the probe with groove depth of 0 μm. As shown in Figure 4 (c), the spectral intensity decreases more obviously with the increase of micro-groove depth, which shows that the optical fiber probes with groove depth of 88 μm and 120 μm have higher response sensitivity to tetracycline. And from Figure 5 (c) and (d), it can be seen that the sensitivity of the probe increases with the increase of micro-groove depth, but too large micro-groove depth will also cause the device to be easily damaged and too large transmission loss. In addition, in the tetracycline concentration range of 5-20 ppm, the relative change amount of tetracycline concentration and output light intensity There is a linear fitting relationship with high fitting degree. At this time, the sensitivity of the probe is -0.00155 ppm -1 , and the detection limit is 0.005 ppm.

[0043] Referring to Figure 6 , the response time test results of the sensor to different concentrations of tetracycline solution, the groove depth of the probe is 120 μm.

[0044] It can be seen that the sensor has a fast response speed when it is used for tetracycline sensing experiment, which is less than 20 s.

[0045] Referring to Figure 7 , the experimental results of the influence of different C3N4-MIL-53 film thickness on tetracycline detection.

[0046] From Fig. 7(a) and Figure 7(b)It can be seen that the tetracycline sensitivity of the probe first increases and then decreases with the increase of the thickness of C3N4-MIL-53 film, and the sensitivity of the probe with a film thickness of 26 μm is the highest. The reason is that with the increase of the thickness of C3N4-MIL-53 film, the more tetracycline is adsorbed, which leads to the increase of the refractive index of C3N4-MIL-53 film, thereby improving the sensitivity of the probe. However, with the further increase of the thickness of C3N4-MIL-53 film, the interaction of light and sensitive film is reduced, thereby reducing the sensitivity of the probe.

[0047] Referring to Figure 8 For the experimental results of the response of the sensor to different antibiotic solutions, the concentration of the analyte solution used in the experiment is 100 ppm.

[0048] From Figure 8 It can be seen that the sensor has high sensitivity to tetracycline, and low sensitivity to other antibiotics. Therefore, the sensor can realize selective recognition of tetracycline molecules.

Claims

1. A microstructured polymer optical fiber sensor for tetracycline detection, characterized in that: The optical fiber sensing probe is composed of a side-polishing structure and a micro-groove structure. The surface of the side-polishing structure is coated with a layer of Canadian resin and a C3N4-MIL-53 sensitive film in sequence.

2. The optical fiber used in the microstructure polymer optical fiber sensor for tetracycline detection according to claim 1 is a step-type polymer optical fiber with a diameter of 1 mm, a cladding thickness of 10 μm, a numerical aperture of 0.5, and a core and cladding material of PMMA and fluorinated polymer, respectively; the probe comprises a side-polishing region with a polishing length L of 25 mm and a polishing depth D of 400 μm, and 12 micro-grooves with a pitch of 2 mm and an angle α of 60°.

3. The C3N4-MIL-53 sensitive material used in the microstructure polymer optical fiber sensor for tetracycline detection according to claim 1 is a novel material composed of graphite-phase carbon nitride (C3N4) and metal organic framework material MIL-53 (Fe), and has excellent physical and chemical properties. The photocatalytic properties of C3N4 and the metal active sites of MIL-53 synergistically enhance the adsorption capacity of tetracycline; the π-π stacking interaction between the aromatic ring structure in the tetracycline molecule and the conjugated π system of C3N4 constitutes the main adsorption driving force; the functional groups such as hydroxyl, amino and carbonyl in the tetracycline molecule can form coordination bonds or intermolecular hydrogen bonds with the metal nodes in MIL-53; the negative charge on the surface of the material and the positive charge region in the tetracycline molecule are further enhanced by electrostatic attraction.

4. The side-polishing structure according to claim 1 is prepared by a computer-controlled wheel side-polishing machine, and the polished surface is polished with an alumina polishing paste and a polishing cloth after polishing.

5. The preparation method of the C3N4-MIL-53 sensitive film according to claim 1 comprises the following steps: firstly, a small amount of Canadian resin solution is added to the side-polishing region, and a cylindrical scraper is used to uniformly coat the resin along the axial direction to form a Canadian resin film; then, the C3N4-MIL-53 solution is added to the resin surface in multiple times, the solution is uniformly diffused by slightly shaking the probe, and the C3N4-MIL-53 film is formed after natural air drying; finally, the coated probe is placed in a constant-temperature drying oven and treated at 80℃ for 12 h.

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