Optical fiber-based doxycycline concentration detection method

Abstract

The invention discloses an optical fiber-based doxycycline concentration detection method. A used device comprises a broadband light source, a single-mode optical fiber, a polarization controller, a flow cell, a TFBG-SPR sensor and a spectrum analyzer. Firstly, a broadband light source emits light with the wavelength range of 1420-1620 nm, the polarization state of the light is adjusted to a P state through a polarization controller, then a sensing probe modified by a doxycycline molecularly imprinted film prepared through a copolymerization cross-linking method is used, and finally a spectrum is formed on a spectrum analyzer. The imprinted film modified on the surface of the optical fiber can be combined with doxycycline molecules to cause change of the refractive index, drifting of a transmission spectrum is shown on an optical spectrum analyzer, and rapid, accurate and trace detection of the concentration of the doxycycline is realized by comparing the relationship between the concentration of different doxycycline solutions and the drifting of the transmission spectrum. The invention provides a novel method which is simple in structure, high in accuracy and quick in response for measuring the concentration of doxycycline, and has very important potential application value in the aspects of environmental pollution, food health monitoring and the like.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and specifically to a method for detecting doxycycline concentration based on a gold-plated tilted fiber grating combined with a doxycycline imprinted thin film. Background Technology

[0002] Doxycycline is one of the most widely used veterinary antibiotics in animal husbandry, and its residues may induce increased bacterial resistance, affecting human and animal health.

[0003] Doxycycline, a tetracycline antibiotic composed of β-diester groups, possesses potent antibacterial activity, low price, and stable efficacy, making it an effective alternative to penicillin antibiotics. However, the widespread use of doxycycline has also brought several potential problems. For example, doxycycline residues can affect water quality and may cause potential changes to the ecosystem; prolonged exposure of aquatic organisms to these residues may lead to increased drug resistance, thereby affecting their growth and reproduction. Excessive use of doxycycline in animal production may allow the drug to enter the food chain and accumulate in the human body, causing liver damage, allergic reactions, and gastrointestinal diseases, posing a threat to public health.

[0004] Currently, the most commonly used methods for detecting doxycycline residues in food or solutions include: microbiological methods, immunoassay, liquid chromatography, liquid chromatography-tandem mass spectrometry, electrochemiluminescence, and fluorescence labeling. However, these methods have drawbacks such as high requirements for environmental conditions and equipment, high cost, and complex sample pretreatment processes, making it difficult to meet practical application needs for doxycycline concentration detection.

[0005] In recent years, fiber optic sensors have demonstrated great application potential in many fields such as biomedicine and chemical detection due to their advantages of high accuracy, fast detection speed, strong resistance to electromagnetic interference, and high sensitivity.

[0006] As a type of fiber optic grating, TFBG possesses high sensitivity, high robustness, and low loss due to its unique fiber structure design, making it widely applicable in the fields of physical quantity, chemical substance, and biological detection.

[0007] On the other hand, the application of molecularly imprinted polymers in drug-specific recognition has been significantly enhanced. In particular, through sophisticated polymer preparation techniques, it is possible to design imprinted materials with high selectivity and specificity. These materials can form strong interactions with target molecules, thus playing an important role in various analyses and detections.

[0008] The combination of fiber optic sensors and imprinted polymers makes it possible to achieve specific identification of veterinary drugs. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this study proposes a trace doxycycline sensor based on a combination of molecular imprinting technology and TFBG-SPR. Surface plasmon resonance is excited by sputtering a 50 nm thick gold film onto a tilted fiber Bragg grating, and then coating the gold film with a doxycycline molecularly imprinted polymer with specific recognition function, thereby achieving specific detection of doxycycline. The specific steps include: S1. Fabrication of tilted fiber gratings and sputtering of gold films; S2. Preparation and modification of doxycycline molecularly imprinted polymers; Connection of S3, broadband light source (1), polarization controller (2), TFBG-SPR sensor (5), and spectrometer (6); S4, doxycycline concentration and specificity detection.

[0010] The tilted fiber Bragg grating in step S1 is etched using a phase mask. After fabrication, it is placed in a magnetron sputtering deposition chamber for gold film deposition, ultimately depositing a gold film with a thickness of about 50 nm on the surface of the tilted fiber Bragg grating.

[0011] In step S2, doxycycline recognition sites are pre-designed in the synthesized polymer structure by using acrylamide, itaconic acid, N,N′-methylenebisacrylamide, ammonium persulfate, and doxycycline, thereby forming a "molecular template" with high selectivity and high affinity, leaving a "mold cavity" with complementary shape and chemical properties for selectively recognizing the target molecule doxycycline.

[0012] Specifically, the amide group of acrylamide and the carboxyl group of itaconic acid react with the hydroxyl and amide groups of doxycycline, respectively, to form hydrogen bonds. Ammonium persulfate, acting as a free radical initiator, decomposes at 60°C into sulfate free radicals, which attack the carbon-carbon and carbon-oxygen double bonds in acrylamide, itaconic acid, and N,N′-methylenebisacrylamide, generating acrylamide, itaconic acid, and N,N′-methylenebisacrylamide living free radicals that initiate polymerization with the corresponding monomers, forming polymer chains. N,N′-methylenebisacrylamide acts as a crosslinking agent, copolymerizing with the functional monomers acrylamide and itaconic acid through carbon-carbon and carbon-oxygen double bonds to form a three-dimensional network structure that fixes the tetracyclic skeleton of doxycycline in space, ultimately forming a doxycycline-imprinted polymer. Prolonged immersion in deionized water can disrupt the hydrogen bonds between the template molecule doxycycline and the functional monomers acrylamide and itaconic acid, removing doxycycline and forming imprinted cavities, thus achieving specific recognition of doxycycline.

[0013] In step S3, the broadband light source (1), polarization controller (3), TFBG-SPR sensor (5), and spectrometer (6) are connected as follows: the broadband light source (1) is connected to the left end of the polarization controller (3) through a single-mode optical fiber (2), the polarization controller (3) is connected to the TFBG-SPR sensor (5), the TFBG-SPR sensor (5) is fixed in the flow cell (4), and the right end is connected to the spectrometer (6); the broadband light source (1) is used to provide light source, the polarization controller (3) is used to adjust p-state polarization, the flow cell (4) is used to add the doxycycline solution to be tested, and the spectrometer (6) is used to monitor and record the spectral changes; when the doxycycline imprinted film modified on the surface of TFBG-SPR (5) combines with the doxycycline in the solution to be tested, the refractive index changes, which is manifested as a shift in the transmission spectrum on the spectrometer (6). By comparing the relationship between different doxycycline concentrations and the transmission spectrum shift, the concentration of doxycycline can be detected.

[0014] Preferably, the wavelength of the broadband light source (1) is 1420-1620 nm.

[0015] The concentrations of doxycycline detected in step S4 were adjusted to: 0.1 μg / mL, 0.2 μg / mL, 0.3 μg / mL, 0.4 μg / mL, 0.5 μg / mL, 0.6 μg / mL, 0.7 μg / mL, 0.8 μg / mL, 0.9 μg / mL, and 1 μg / mL.

[0016] The biomolecules included in the specific detection in step S4 are: oxytetracycline hydrochloride, cephalexin, chloramphenicol, and antipyrine.

[0017] The working principle of the trace doxycycline sensor based on molecular imprinting technology combined with TFBG-SPR prepared in this invention is as follows: When light waves enter an optical fiber and are completely reflected by the fiber sidewalls, the tilted fiber grating can also excite evanescent surface plasmon resonance waves on the gold surface. When the p-polarized component of the light enters the gold film, the free electrons of the gold film interact with the p-polarized component of the light to generate plasma. At the interface between the optical fiber and the gold film, plasma vibration forms surface plasmon waves. When the horizontal component of the evanescent wave vector matches the wave vector of the surface plasmon wave and energy transfer occurs, the evanescent wave and the surface plasmon wave resonate, generating surface plasmon resonance. Light energy near the resonance wavelength is absorbed, resulting in a resonance valley in the output spectrum. The sensitive film on the surface of the tilted fiber grating absorbs doxycycline from the test solution, causing a change in the local refractive index, and the resonance valley and resonance wavelength also change. Therefore, the concentration of doxycycline can be inferred by monitoring the shift of the resonance wavelength.

[0018] In summary, this invention provides a TFBG-SPR sensor capable of specifically detecting doxycycline concentration. This sensor is based on the fact that imprinted molecular thin films can specifically bind to doxycycline, changing the effective refractive index and causing a shift in the transmission spectrum, thereby enabling the detection of doxycycline. It has advantages such as simple structure, low detection limit, and fast response time.

[0019] The beneficial effects of this invention are as follows: First, a thin gold film is deposited on the surface of a tilted fiber grating to excite the SPR effect. Then, a molecularly imprinted thin film with specific recognition of doxycycline is coated onto the gold film surface. The molecularly imprinted thin film prepared using doxycycline as a template molecule enhances the selectivity of the tilted fiber grating for doxycycline. Furthermore, the precise binding of doxycycline molecules to the "imprinted cavity" on the sensor surface causes a local change in the refractive index of the sensor surface, thereby achieving highly sensitive detection of doxycycline. The sensor has a dynamic detection range of 0.1-1 μg / mL, a response time of 5 minutes, and a detection limit of 0.0323 μg / mL, which is half that of current similar doxycycline sensors. Undoubtedly, this sensor, as a doxycycline sensor with an extremely low detection limit and fast response speed, has significant potential application value in environmental pollution and food health monitoring. Attached Figure Description

[0020] Figure 1 A schematic diagram of an experimental setup for doxycycline sensing TFBG-SPR spectral measurement.

[0021] Figure 2 Transmission spectra of the TFBG-SPR sensor in doxycycline solutions of different concentrations.

[0022] Figure 3 Specific response diagram of the TFBG-SPR sensor for doxycycline detection. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments:

[0024] Example 1: Fabrication of tilted fiber Bragg grating and sputtering of gold film.

[0025] In this embodiment, see Figure 1First, a 1cm photosensitive fiber (51) was fused into a single-mode fiber, and the fiber structure was placed in a reactor at 15.2 MPa and 20°C, where hydrogen was injected for 14 days of hydrogen loading treatment. Then, the hydrogen-loaded fiber structure was placed in front of a phase mask with an 8° tilt angle, and a precision displacement stage was used to write high-energy pulsed ultraviolet laser light generated by a frequency-doubled argon-ion laser onto the photosensitive fiber in the fiber structure through the phase mask. Finally, the prepared tilted fiber grating was annealed in a constant temperature oven at 120°C for 12 hours to release the residual hydrogen in the photosensitive fiber. The prepared tilted fiber grating was then cleaned with anhydrous alcohol and placed in a magnetron sputtering deposition chamber for gold film deposition, ultimately depositing a gold film with a thickness of approximately 50nm on the surface of the tilted fiber grating.

[0026] Example 2: Preparation and modification of doxycycline molecularly imprinted polymers.

[0027] In this embodiment, the preparation and modification of the molecularly imprinted polymer that specifically binds to doxycycline are carried out through the following steps: a) Weigh 0.096g of doxycycline and dissolve it in 1.5ml of deionized water, then shake to mix and form solution 1; b) Weigh 0.71g of acrylamide, 0.39g of itaconic acid and 0.044g of N,N′-methylenebisacrylamide as crosslinking agents, add them to solution 1, and sonicate for 30 minutes to form solution 2; c) Weigh 0.05g of ammonium persulfate as a free radical initiator and add it to solution 2. Sonicate for 15 minutes to form solution 3. d) The solution 3 was sealed and placed on a heating platform and heated in a 60°C water bath for 1 hour to prepare doxycycline molecularly imprinted hydrosol. e) Clean the optical fiber with deionized water and anhydrous alcohol to ensure that dust and stains are removed from the surface of the optical fiber and that the surface of the optical fiber is kept clean and dry. Then, use an immersion method to allow the doxycycline molecularly imprinted hydrosol to adhere to the tilted fiber grating. f) After drying the tilted fiber grating with the doxycycline molecularly imprinted hydrosol film in a drying oven at 60°C for 2 hours, a thermal polymerization reaction is initiated again to firmly assemble the sensitive film onto the tilted fiber grating. g) Soak it in deionized water for 12 hours to remove the template molecule doxycycline from the sensitive membrane, leaving an imprint cavity with complementary shape and chemical properties for selective recognition of doxycycline.

[0028] Example 3: Construction of the detection platform.

[0029] In this embodiment, see Figure 1The detection platform is composed of a single-mode optical fiber (2) connecting a broadband light source (1), a polarization controller (3), a TFBG-SPR sensor (5) placed in a flow cell (4), and a spectrometer (6). The broadband light source (1) has a wavelength range of 1420-1620 nm and is used to provide light. The polarization controller (3) is used to obtain a greater stripe contrast. The flow cell (4) is used to add the doxycycline solution to be tested. The spectrometer (6) is used to monitor and record the spectral changes. When the doxycycline imprinted film modified on the surface of the TFBG-SPR (5) combines with the doxycycline in the solution to be tested, the refractive index changes, which is manifested as a shift in the transmission spectrum on the spectrometer (6). By comparing the relationship between different doxycycline concentrations and the transmission spectrum shift, the concentration of doxycycline can be detected.

[0030] Example 4: Detection of doxycycline concentration and specificity.

[0031] Doxycycline solution and specificity tests were performed. All drug solutions were prepared with deionized water.

[0032] Doxycycline concentration detection: The TFBG-SPR sensor modified with doxycycline molecularly imprinted film was placed in the flow cell (4), and doxycycline solutions of different concentrations were prepared using deionized water, with concentrations of 0.1 μg / mL, 0.2 μg / mL, 0.3 μg / mL, 0.4 μg / mL, 0.5 μg / mL, 0.6 μg / mL, 0.7 μg / mL, 0.8 μg / mL, 0.9 μg / mL, and 1 μg / mL. Deionized water was added to the flow cell (4), and the initial spectrum was recorded using a spectrometer (6). Then, doxycycline solution was added to the flow cell (4) and allowed to stand. The transmission spectrum was then recorded using the spectrometer (6). After detection, the liquid in the flow cell (4) was drained, and deionized water was introduced to rinse the fiber optic surface and the flow cell (4). Then, another test solution was added, and the operation was repeated to complete the spectral acquisition. Transmission spectra of doxycycline solutions of different concentrations were obtained, and differential fitting was performed. Intensity difference and fitting curves were plotted, and the detection limit was calculated. Figure 2 As shown.

[0033] Specificity detection: 0.5 μg / mL solutions of oxytetracycline hydrochloride, cephalexin, chloramphenicol, and antipyrine were prepared respectively. First, the transmission spectrum of the TFBG-SPR sensor in anhydrous ethanol was measured. The optical fiber was rinsed multiple times with deionized water. The test solutions were added to the flow cell and allowed to stand. The transmission spectra were then recorded using a spectrometer (6). After detection, the liquid in the flow cell (4) was drained, and deionized water was introduced to rinse the surface of the optical fiber and the flow cell (4). Different test solutions were added sequentially, and the above steps were repeated to evaluate the specificity of the TFBG-SPR sensor for different drugs, such as… Figure 3 As shown.

[0034] The embodiments described above provide a detailed explanation of the technical solution of the present invention, but the scope of protection of this disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for detecting doxycycline concentration based on optical fiber, characterized in that: The detection device consists of a broadband light source (1), a single-mode fiber (2), a polarization controller (3), a flow cell (4), a TFBG-SPR sensor (5), and a spectrometer (6); the broadband light source (1) is connected to the input end of the polarization controller (3) through the single-mode fiber (2); the output end of the polarization controller (3) is connected to the left end of the TFBG-SPR sensor (5), and the right end of the TFBG-SPR sensor (5) is connected to the spectrometer (6); The fabrication steps of the TFBG-SPR sensor (5) are as follows: First, hydrogen is loaded onto the photosensitive fiber (51) and then a tilted fiber grating (52) with a tilt angle of 8 degrees is formed by ultraviolet etching and annealing. Then, the tilted fiber grating (52) is placed in a magnetron sputtering deposition chamber and a gold film with a thickness of 50 nm is deposited on its surface. A doxycycline molecular imprinted film (53) is prepared by copolymer crosslinking and then modified onto the gold film on the surface of the fiber. The preparation steps of the doxycycline molecularly imprinted film (53) are as follows: a doxycycline molecularly imprinted polymer is synthesized by using acrylamide, itaconic acid, N,N′-methylenebisacrylamide, ammonium persulfate and doxycycline, and coated onto the surface of the tilted fiber grating (52) to form a sensitive film. Then, the template molecule doxycycline in the sensitive film is removed by soaking in deionized water, leaving an imprinted cavity with complementary shape and chemical properties for selective recognition of doxycycline, thus forming the doxycycline molecularly imprinted film (53). The steps of the fiber-optic doxycycline concentration detection method are as follows: First, fix the TFBG-SPR sensor (5) in the flow cell (4), then add the doxycycline test solution to the flow cell (4). The doxycycline binds to the doxycycline molecularly imprinted film (53) modified on the surface of the TFBG-SPR sensor (5). The light emitted by the broadband light source (1) passes through the TFBG-SPR sensor (5) and the transmission spectrum is recorded on the spectrometer (6). The flow cell (4) is cleaned with deionized water. The data recorded on the spectrometer (6) are fitted with doxycycline solutions of different concentrations added to the flow cell (4) to obtain the relationship between different doxycycline concentrations and transmission spectrum drift, thereby realizing the detection of doxycycline concentration.

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