Fast responding fluorescent dissolved oxygen sensing membrane, method of preparation and sensor

Abstract

This application relates to the field of sensor membrane technology, specifically a fast-response fluorescent dissolved oxygen sensing membrane, its preparation method, and its application. The method includes: performing low-temperature polycondensation of a mixture of fluorinated diamine and dianhydride with a polar solvent in an ice-water bath under a protective gas atmosphere to obtain a polyamic acid solution with a viscosity of 40-100 cP; adding 0.015 wt% of a fluorescent indicator and 0.15 wt% of inorganic ceramic particles to the solution, mixing thoroughly, and then coating the mixture onto the surface of a pretreated transparent substrate; forming a fluorescent layer through gradient heat treatment; and then sequentially coating a reflective layer and a light-shielding layer to obtain the sensing membrane. This application improves the high-temperature resistance, air permeability, and response speed of the sensing membrane.

Description

Technical Field

[0001] This application relates to the field of sensor membrane technology, specifically to a fast-response fluorescent dissolved oxygen sensing membrane, its preparation method, and a fluorescent dissolved oxygen sensor. Background Technology

[0002] Fluorescent dissolved oxygen sensing membranes detect dissolved oxygen concentration based on the fluorescence quenching effect of fluorescent substances on oxygen molecules, and are widely used in water quality monitoring, cell culture, fermentation process control, and other fields. Traditional sensing membranes often use cellulose acetate, polyethylene, polycarbonate, and other materials as matrices. These materials have limited permeability, resulting in slow response speeds and short lifespans. Therefore, improving the response speed of fluorescent dissolved oxygen sensing membranes is a problem that needs to be solved. Summary of the Invention

[0003] In view of the above problems, this application provides a fast-response fluorescent dissolved oxygen sensing membrane, a preparation method, and a fluorescent dissolved oxygen sensor, which improves the response speed of the sensing membrane.

[0004] According to one aspect of the embodiments of this application, a method for preparing a fast-response fluorescent dissolved oxygen sensing membrane is provided, comprising the following steps: Under a protective gas atmosphere and at 0-5°C, diamine and dianhydride are mixed with a polar solvent and subjected to a polycondensation reaction for 2-24 hours to obtain a polyamic acid solution. The viscosity of the solution is adjusted to 40-100 cP, wherein at least one of the diamine and dianhydride contains fluorine. Add 0.01-5% by weight of a fluorescent indicator and 0.1-5% by weight of inorganic ceramic particles to the polyamic acid solution, and mix evenly to obtain a coating solution; The coating liquid is applied to the surface of a transparent substrate, and a fluorescent layer is formed by gradient heat treatment. A reflective layer and a light-shielding layer are sequentially formed on the outside of the fluorescent layer to obtain the fluorescent dissolved oxygen sensing film.

[0005] In one alternative embodiment, the inorganic ceramic particles are selected from at least one of alumina, magnesium oxide, silicon dioxide, titanium oxide, zinc oxide, zirconium oxide, barium titanate, magnesium fluoride, or boehmite, and have an average particle size of 0.05-5 μm.

[0006] In one alternative embodiment, the diamine is selected from at least one of 4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, 2,2′-bis(trifluoromethyl)-4-diaminobiphenyl, and 1,3-bis(3-aminopropyl)tetramethyldisiloxane; and the dianhydride is selected from at least one of 4,4′-(hexafluoroisopropene)phthalic anhydride, 1,2,3,4-cyclobutanediol dianhydride, and pyromellitic dianhydride.

[0007] In one optional method, the coating liquid is applied to the surface of the transparent substrate by spin coating, and the spin coating parameters include: a first stage of 500 rpm for 10-30 s; and a second stage of 1000-9000 rpm for 30-90 s.

[0008] In one alternative approach, when forming the fluorescent layer via gradient heat treatment, the gradient heat treatment includes: heating to 80°C at a rate of 2-10°C / min and holding for 0.5-2 h; continuing to heat to 140-180°C and holding for 1-2 h; and then heating to 240-280°C and holding for 1-4 h.

[0009] In one alternative embodiment, the polymer matrix of the reflective layer is polytetrafluoroethylene or polyvinylidene fluoride, wherein 2-8 wt% of white pigment is dispersed therein; and the polymer matrix of the light-shielding layer is polytetrafluoroethylene or polyvinylidene fluoride, wherein 1-20 wt% of black pigment is dispersed therein.

[0010] In one alternative embodiment, the fluorescent indicator is a ruthenium polypyridine complex or a platinum porphyrin complex.

[0011] According to another aspect of the present application, a fast-response fluorescent dissolved oxygen sensing membrane prepared by the method described in any of the above embodiments is provided.

[0012] According to another aspect of the embodiments of this application, a fluorescent dissolved oxygen sensor is provided, the fluorescent dissolved oxygen sensor including the above-described fast-response fluorescent dissolved oxygen sensing membrane.

[0013] This application embodiment uses fluorinated dianhydride and / or fluorinated diamine as raw materials for the synthesis of the sensing membrane, enabling the prepared sensing membrane to withstand high-temperature sterilization. Low-temperature polycondensation is performed in a protective gas atmosphere at 0-5°C to control the formation of a regular prepolymer structure of polyamic acid. Subsequently, inorganic ceramic particles are introduced to construct micro- and nano-scale porous channels in the polymer matrix to improve oxygen diffusion efficiency. Gradient heat treatment then gradually solidifies the polyamic acid to form a stable fluorescent layer resistant to high temperatures. Finally, a reflective layer and a light-shielding layer are sequentially integrated to enhance the signal and isolate interference. Through the above methods, the response speed of the sensing membrane is improved, as well as its long-term stability and detection reliability under high humidity, acid / alkali, or complex optical environments are enhanced, comprehensively solving the problems of slow response and poor environmental adaptability of traditional fluorescent dissolved oxygen sensing membranes.

[0014] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Detailed Implementation

[0015] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0016] This application provides a method for preparing a fast-response fluorescent dissolved oxygen sensing membrane, comprising the following steps: Under a protective gas atmosphere and at 0-5°C, diamine and dianhydride are mixed with a polar solvent and subjected to a polycondensation reaction for 2-24 hours to obtain a polyamic acid solution. The viscosity of the solution is adjusted to 40-100 cP, wherein at least one of the diamine and dianhydride contains fluorine. Add 0.01-5% by weight of fluorescent indicator and 0.1-5% by weight of inorganic ceramic particles to a polyamic acid solution, and mix thoroughly to obtain a coating solution; The coating liquid is applied to the surface of a transparent substrate, and a fluorescent layer is formed by gradient heat treatment. A reflective layer and a light-shielding layer are sequentially formed on the outside of the fluorescent layer to obtain a fluorescent dissolved oxygen sensing film.

[0017] By using fluorinated dianhydrides and / or fluorinated diamines as raw materials for the synthesis of the sensing membrane, the prepared sensing membrane can withstand high-temperature sterilization. Low-temperature polycondensation is performed in a protective gas atmosphere at 0-5℃ to control the formation of a regular prepolymer structure of polyamic acid. Subsequently, inorganic ceramic particles are introduced to construct micro- and nano-scale porous channels in the polymer matrix to improve oxygen diffusion efficiency. Gradient heat treatment then gradually solidifies the polyamic acid to form a stable fluorescent layer resistant to high temperatures. Finally, a reflective layer and a light-shielding layer are integrated sequentially to enhance the signal and isolate interference. Through these methods, the response speed of the sensing membrane is improved, as well as its long-term stability and detection reliability under high humidity, acid / alkali, or complex optical environments are enhanced, comprehensively solving the problems of slow response and poor environmental adaptability of traditional fluorescent dissolved oxygen sensing membranes.

[0018] In some embodiments, the inorganic ceramic particles are selected from at least one of aluminum oxide, magnesium oxide, silicon dioxide, titanium oxide, zinc oxide, zirconium oxide, barium titanate, magnesium fluoride, or boehmite, and have an average particle size of 0.05-5 μm.

[0019] The aforementioned inorganic ceramic particles possess high hardness, high thermal stability, and chemical inertness. Controlling their average particle size within the range of 0.05-5 μm ensures good dispersion in polyamic acid solutions, preventing severe agglomeration. After film formation, these particles act as rigid support points within the polymer matrix, effectively enhancing the film's elastic modulus and mechanical strength, such as scratch resistance. Simultaneously, the micro- and nano-scale pores formed at the particle-polymer interface create additional oxygen diffusion channels, significantly increasing the film's specific surface area and permeability, thus enabling rapid response. This particle size range balances the reinforcing effect with the film's optical uniformity, avoiding light scattering or film defects caused by excessively large particles.

[0020] In some embodiments, the diamine is selected from at least one of 4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, 2,2′-bis(trifluoromethyl)-4-diaminobiphenyl, and 1,3-bis(3-aminopropyl)tetramethyldisiloxane; the dianhydride is selected from at least one of 4,4′-(hexafluoroisopropene)phthalic anhydride, 1,2,3,4-cyclobutanediol dianhydride, and pyromellitic dianhydride.

[0021] By ensuring that at least one of the diamine and dianhydride contains fluorine, a fluorinated monomer is introduced, reducing the dielectric constant of the polymer and increasing the free volume of the molecules. This not only enhances the film's permeability to accelerate response but also endows the polymer matrix with good hydrophobicity, chemical stability, and high-temperature resistance (able to withstand temperatures above 280°C for extended periods), enabling the sensing membrane to adapt to high-temperature sterilization and complex chemical environments. The specific monomers mentioned above possess moderate reactivity and good solubility, which is beneficial for forming polyamic acid precursors with controllable molecular weight distribution at low temperatures.

[0022] In some embodiments, the coating method for applying the coating liquid to the surface of the transparent substrate is spin coating, and the spin coating parameters include: a first stage rotation speed of 500 rpm and a time of 10-30 s; and a second stage rotation speed of 1000-9000 rpm and a time of 30-90 s.

[0023] By employing spin coating and optimizing the parameters of the two stages mentioned above, it is possible to accurately and reproducibly prepare films with uniform thickness and no defects. The first stage (low speed) ensures that the coating solution is fully spread on the substrate surface and eliminates large air bubbles; the second stage (high speed) adjusts the film thickness to the ideal range (approximately 10-50 μm) by precisely controlling the centrifugal force, achieving extremely high in-plane uniformity. Precise control of the film thickness ensures consistent response speed and fluorescence signal intensity.

[0024] In some embodiments, when forming a fluorescent layer by gradient heat treatment, the gradient heat treatment includes: heating to 80°C at 2-10°C / min and holding for 0.5-2 h; continuing to heat to 140-180°C and holding for 1-2 h; and then heating to 240-280°C and holding for 1-4 h.

[0025] In gradient heat treatment, the first step (80℃) primarily achieves gentle and complete solvent evaporation, preventing pinholes or cracks caused by rapid solvent evaporation. The second step (140-180℃) promotes partial imidization of polyamic acid, initially shaping the film and enhancing its mechanical strength. The third step (240-280℃) completes full imidization, forming a highly stable polyimide ring structure. Gradual heating avoids thermal stress concentration, ensuring good adhesion between the film and the substrate and the integrity of the internal structure.

[0026] In some embodiments, the polymer matrix of the reflective layer is polytetrafluoroethylene or polyvinylidene fluoride, wherein 2-8 wt% of white pigment is dispersed therein; the polymer matrix of the light-shielding layer is polytetrafluoroethylene or polyvinylidene fluoride, wherein 1-20 wt% of black pigment is dispersed therein.

[0027] The reflective and light-shielding layers use polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) as the matrix, exhibiting excellent chemical compatibility and similar coefficients of thermal expansion with the fluorinated polyimide fluorescent layer, forming a strong and stable interlayer bond. PTFE / PVDF itself possesses excellent chemical inertness, hydrophobicity, and weather resistance, providing ultimate protection for the internal fluorescent layer and significantly improving the long-term stability of the sensing membrane in humid, acidic, alkaline, or organic solvent environments. The white pigment (such as TiO2) in the reflective layer efficiently reflects excitation light and emits fluorescence, enhancing the effective light signal and improving detection sensitivity. The black pigment in the light-shielding layer almost completely absorbs ambient stray light, greatly reducing optical background noise and improving the signal-to-noise ratio and measurement accuracy.

[0028] In some embodiments, the fluorescent indicator is a ruthenium polypyridine complex or a platinum porphyrin complex.

[0029] Ruthenium polypyridine complexes (such as Ru(dpp)3²) + Platinum porphyrin complexes (such as PtOEP) are validated, highly oxygen-sensitive fluorescent probes. They exhibit high fluorescence quantum yields, good photostability, and a well-defined fluorescence lifetime quenching relationship with oxygen concentration. These indicators can be effectively embedded or dispersed in a polyimide matrix to form a uniform, stable sensitive layer.

[0030] The present application will be described in detail below through specific embodiments and comparative examples. All transparent substrates (PET, glass, etc.) used in the embodiments and comparative examples must undergo rigorous cleaning to remove surface contaminants and ensure coating adhesion and uniformity. The cleaning steps are as follows: ultrasonic cleaning in ultrapure water, ethanol, and acetone sequentially for 5-10 minutes, followed by nitrogen drying before use.

[0031] Example 1 (1) Under a nitrogen atmosphere, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane (fluorinated diamine) and 4,4′-(hexafluoroisopropene) phthalic anhydride (fluorinated dianhydride) were added to N,N-dimethylformamide (DMF) at a molar ratio of 1:1. The mixture was placed in an ice-water bath to maintain the reaction temperature at 0-2℃ and stirred for 4 hours to obtain a polyamic acid solution. The viscosity of the solution was measured using a rotational viscometer and adjusted to 70±2 cP by adding DMF.

[0032] (2) Add 1.5% by mass of the fluorescent indicator Ru(dpp)3² to the above solution. + A uniform coating solution was obtained by magnetically stirring (tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II)) and 2.0% hydrophilic silica particles with an average particle size of 0.1 μm, followed by ultrasonic dispersion for 30 minutes.

[0033] (3) The coating solution was spin-coated onto the pretreated quartz glass substrate (2.5 cm × 2.5 cm, 0.2 mm thick) using a spin-coating method. The spin-coating parameters were: 500 rpm for 20 seconds in the first stage and 3000 rpm for 60 seconds in the second stage. The coated substrate was then placed in a temperature-controlled oven and subjected to gradient heat treatment under a nitrogen atmosphere: the temperature was increased to 80°C at a rate of 5°C / min and held for 1 hour to allow the solvent to evaporate fully; then the temperature was increased to 160°C at the same rate and held for 1 hour to promote partial imidization; finally, the temperature was increased to 260°C and held for 2 hours to complete the imidization and curing of the fluorescent layer. The thickness of the fluorescent layer was controlled at 25 ± 3 μm.

[0034] (4) A reflective layer was coated on the outside of the fluorescent layer using a blade coating method. The reflective layer slurry was made of polytetrafluoroethylene (PTFE) emulsion and 5 wt% titanium dioxide (TiO2, average particle size 0.5 μm). After coating, it was dried at 80°C for 24 hours to form a reflective layer with a thickness of about 40 μm.

[0035] (5) A light-shielding layer is then coated on the outside of the reflective layer. The light-shielding layer slurry is made of PTFE emulsion mixed with 10 wt% conductive carbon black. After coating, it is dried at 80°C for 24 hours to form a light-shielding layer with a thickness of about 80 μm. Finally, a fluorescent dissolved oxygen sensing film with a three-layer structure is obtained.

[0036] In this embodiment, perfluorinated diamines and dianhydrides were polymerized at low temperatures, effectively controlling the molecular weight distribution of polyamic acid and forming a regular prepolymer structure. Added nano-silica particles, as inorganic fillers, were uniformly dispersed in the polymer matrix. These rigid particles not only provided physical reinforcement, improving the membrane's mechanical strength (scratch resistance), but more importantly, they formed micro- and nano-scale pores and tortuous channels within the membrane. These pores significantly increased the membrane's effective specific surface area, providing more and faster diffusion paths for oxygen molecules, thereby directly improving the sensor's response speed. Simultaneously, the PTFE-based reflective and light-shielding layers exhibited excellent chemical inertness, hydrophobicity, and light-shielding effects, effectively protecting the internal fluorescent layer, reducing external environmental interference, and improving the sensor's long-term stability and signal-to-noise ratio in complex media (such as bio-fermentation broth).

[0037] Example 2 The difference between Example 2 and Example 1 is that the inorganic ceramic particles were replaced with monoclinic zirconium oxide (ZrO2) with an average particle size of 0.5 μm, and the amount added was 1.5% of the mass of the polyamic acid solution. Zirconia has higher hardness and chemical stability.

[0038] In Example 2, the introduction of zirconia particles, in addition to providing an antireflective effect similar to silica, further enhances the durability of the sensing membrane in high-temperature or corrosive environments due to their higher thermal stability and chemical inertness. The moderate increase in particle size (0.5 μm) helps to form a more stable micron-scale pore structure within the membrane, avoiding potential severe agglomeration of nanoparticles, thereby achieving a better balance between permeability and mechanical strength.

[0039] Example 3 The difference between Example 3 and Example 1 is that the polymerization reaction in step (1) is carried out in an ice-water bath at 5±1℃ and the reaction time is extended to 8 hours.

[0040] In Example 3, the polymerization temperature was strictly controlled within the low-temperature range of 0-5°C. The low-temperature environment significantly reduced the polymerization rate of the diamine and dianhydride, resulting in a more gradual and controllable growth of the polyamic acid chains. This facilitates the formation of polymers with narrower molecular weight distribution and more uniform structure. In subsequent film formation and heat treatment processes, a dense-porous composite structure with more uniform pore size distribution and fewer internal defects can be generated, enabling the sensing membrane to respond quickly and stably.

[0041] Example 4 The difference between Example 4 and Example 1 is that the diamine used is a mixture of 4,4'-diaminodiphenylmethane (non-fluorinated) and 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane (fluorinated) (molar ratio 1:1), and the dianhydride used is still 4,4′-(hexafluoroisopropene) phthalic anhydride (fluorinated).

[0042] In Example 4, the introduction of some non-fluorinated diamine monomers can moderately adjust the polarity, solubility and chain segment flexibility of the polymer while maintaining the high temperature resistance of the polyimide matrix. This helps to optimize the compatibility between the polyimide matrix and inorganic ceramic particles and fluorescent dyes, promotes more uniform dispersion of each component, and further improves the overall uniformity and performance reproducibility of the film.

[0043] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no inorganic ceramic particles are added.

[0044] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the polymerization reaction in step (1) was carried out at room temperature of 25°C.

[0045] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the polymer matrix of the reflective layer and the light-shielding layer uses epoxy resin instead of polytetrafluoroethylene.

[0046] Comparative Example 4 (1) Under a nitrogen atmosphere, cellulose acetate and N,N-dimethylformamide were mixed evenly and stirred at 60°C for 1 hour to carry out the polymerization reaction. N,N-dimethylformamide was added continuously to adjust the viscosity of the solution to 70 cP. The mass percentage of cellulose acetate was 10% and the mass percentage of N,N-dimethylformamide was 90%.

[0047] (2) Add 1.5 wt% of the metal pyridine indicator to the solution and mix well to obtain a mixed solution.

[0048] (3) Coat the mixed solution onto a 2mm thick glass surface and cure it at high temperature in a nitrogen atmosphere for 2 hours at 50°C.

[0049] (4) Allow to cool naturally to room temperature.

[0050] In Comparative Example 4, cellulose acetate was used as the matrix, no inorganic particles were added, and the polymerization and film-forming temperatures were carried out according to conventional processes.

[0051] The fluorescent dissolved oxygen sensing membranes prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to system performance tests. The specific test methods are as follows: Response time test: The sensing membrane was placed in a dynamic dissolved oxygen testing system, which could rapidly switch the test solution from a saturated oxygen concentration (approximately 8.5 mg / L, 25°C) to an oxygen-free environment (by bubbling nitrogen). The time required for the fluorescence intensity to recover to 90% of its steady-state value (T90) was recorded using a high-sensitivity fluorescence detection system equipped with a photomultiplier tube as the response time. Each sample was tested 5 times and the average value was taken.

[0052] Mechanical strength testing: The elastic modulus and hardness of the fluorescent layer surface were measured using a nanoindenter. A scratch tester was used to scratch the film surface with a constant load (10 mN) and a moving speed (10 μm / s), and the critical load at which obvious rupture occurred was observed and recorded.

[0053] High temperature and chemical resistance tests: The sensing membrane was placed in a 280℃ oven for 1 hour, and after cooling, the appearance changes were observed and the response time was tested again. The sensing membrane was immersed in hydrochloric acid solution (pH=3), sodium hydroxide solution (pH=10), and 70% ethanol solution for 24 hours respectively. After being removed, cleaned, and dried, its fluorescence retention rate was tested.

[0054] The test results are shown in Table 1: Table 1

[0055] The test results above show that: Response speed: The response times of all embodiments were shorter than those of the comparative examples, and significantly better than those of the traditional cellulose acetate membrane (Comparative Example 4), demonstrating the effectiveness of inorganic ceramic particles and low-temperature polymerization in constructing rapid oxygen diffusion channels. Comparative Example 1 (without particles) had the slowest response, followed by Comparative Example 2 (room temperature polymerization), indicating a synergistic effect between inorganic ceramic particles and low-temperature polymerization.

[0056] Mechanical strength: The elastic modulus and critical scratch load of the examples were higher than those of comparative examples 1-3, indicating that the addition of inorganic particles had a significant reinforcing and toughening effect. Example 2, using zirconia particles, exhibited the best mechanical properties.

[0057] Temperature and chemical resistance: The response time of the examples showed minimal change after high-temperature treatment, and the performance showed almost no degradation after chemical resistance testing, indicating that using fluorinated polyimide as the matrix and combining it with a PTFE protective layer improved the product's stability. Comparative Example 3, which used epoxy resin as the protective layer, swelled in the chemical solution, resulting in a significant performance degradation. The cellulose acetate membrane of Comparative Example 4 was completely unable to withstand high temperatures.

[0058] This application presents a fluorescent dissolved oxygen sensing membrane that combines rapid response, excellent mechanical strength, and environmental stability by introducing specific inorganic ceramic particles into a fluorinated polyimide matrix and employing a low-temperature controllable polymerization process. Its response speed is more than twice that of traditional materials, its mechanical properties are significantly enhanced, and it can withstand high-temperature sterilization and various chemical environments. This greatly expands the application prospects of fluorescent dissolved oxygen sensing technology in harsh environments, such as online bioreactor monitoring, deep-sea exploration, or chemical process control.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a fast-response fluorescent dissolved oxygen sensing membrane, characterized in that, Includes the following steps: Under a protective gas atmosphere and at 0-5°C, diamine and dianhydride are mixed with a polar solvent and subjected to a polycondensation reaction for 2-24 hours to obtain a polyamic acid solution. The viscosity of the solution is adjusted to 40-100 cP, wherein at least one of the diamine and dianhydride contains fluorine. Add 0.01-5% by mass of a fluorescent indicator and 0.1-5% by mass of inorganic ceramic particles to the polyamic acid solution, and mix thoroughly to obtain a coating solution; The coating liquid is applied to the surface of a transparent substrate, and a fluorescent layer is formed by gradient heat treatment. A reflective layer and a light-shielding layer are sequentially formed on the outside of the fluorescent layer to obtain the fluorescent dissolved oxygen sensing film.

2. The method according to claim 1, characterized in that, The inorganic ceramic particles are selected from at least one of aluminum oxide, magnesium oxide, silicon dioxide, titanium oxide, zinc oxide, zirconium oxide, barium titanate, magnesium fluoride, or boehmite, with an average particle size of 0.05-5 μm.

3. The method according to claim 1, characterized in that, The diamine is selected from at least one of 4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, 2,2′-bis(trifluoromethyl)-4-diaminobiphenyl, and 1,3-bis(3-aminopropyl)tetramethyldisiloxane; the dianhydride is selected from at least one of 4,4′-(hexafluoroisopropene)phthalic anhydride, 1,2,3,4-cyclobutanediol dianhydride, and pyromellitic dianhydride.

4. The method according to claim 1, characterized in that, The coating method when the coating liquid is applied to the surface of the transparent substrate is spin coating. The spin coating parameters include: first stage rotation speed of 500 rpm, time of 10-30 s; second stage rotation speed of 1000-9000 rpm, time of 30-90 s.

5. The method according to claim 1, characterized in that, When forming a fluorescent layer through gradient heat treatment, the gradient heat treatment includes: heating to 80℃ at 2-10℃ / min and holding for 0.5-2 h; continuing to heat to 140-180℃ and holding for 1-2 h; and then heating to 240-280℃ and holding for 1-4 h.

6. The method according to claim 1, characterized in that, The polymer matrix of the reflective layer is polytetrafluoroethylene or polyvinylidene fluoride, wherein 2-8 wt% white pigment is dispersed therein; the polymer matrix of the light-shielding layer is polytetrafluoroethylene or polyvinylidene fluoride, wherein 1-20 wt% black pigment is dispersed therein.

7. The method according to claim 1, characterized in that, The fluorescent indicator is a ruthenium polypyridine complex or a platinum porphyrin complex.

8. A fast-response fluorescent dissolved oxygen sensing membrane prepared by the method of any one of claims 1-7.

9. A fluorescent dissolved oxygen sensor, characterized in that, It includes the fluorescent dissolved oxygen sensing membrane as described in claim 8.

10. The application of the fluorescent dissolved oxygen sensing membrane according to claim 8 in environmental monitoring, biomedical detection or industrial process control.

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