A reversible response MOF-confined colorimetric sensor patch and its preparation method

Abstract

This invention discloses a reversible responsive MOF-confined colorimetric sensor patch and its preparation method, belonging to the field of aerogel-based colorimetric sensing technology. The sensor patch is composed of agarose, polyethylene glycol, and a UiO-66 / methyl red composite aerogel. Methyl red is anchored within the MOF through the nanopore confinement effect of UiO-66 and the coordination of zirconium cluster sites, forming UiO-66 / methyl red composite nanoparticles, which are interleaved within the porous network structure layers formed by hydrogen bonding cross-linking of agarose and polyethylene glycol. The preparation method includes: hydrothermal synthesis of UiO-66 / methyl red composite nanoparticles, mixing with polyethylene glycol, adding agarose to dissolve, and freeze-drying to form the final product. This patch exhibits properties such as resistance to dye leakage, resistance to temperature interference, reversible response, wide pH response, and rapid response, and can be used for pH detection in scenarios such as body fluids, environmental water samples, bacterial cultures, and wounds.

Description

Technical Field

[0001] This invention belongs to the field of aerogel-based colorimetric sensing technology, specifically relating to a reversible responsive MOF-confined colorimetric sensing patch and its preparation method. Background Technology

[0002] Rapid, in-situ, and visualized pH detection has significant application value in health monitoring, wound management, environmental assessment, and food safety. Traditional pH detection methods, such as potentiometry, while highly accurate, suffer from problems such as large instrument size, complex operation, and time-consuming testing, making it difficult to meet the demands for portable, real-time, and non-invasive detection. Colorimetric methods have gained widespread attention due to their intuitive response, lack of need for large equipment, and naked-eye recognition. Among them, colorimetric sensor patches, as a flexible wearable sensing platform, show great potential in areas such as sweat analysis and food freshness monitoring due to their low cost, good applicability, and non-invasiveness (e.g., CN113916871A).

[0003] Existing colorimetric sensor patches mostly employ pH indicators loaded onto polymer matrices (such as agarose, cellulose, gelatin, etc.) or fabric substrates through physical adsorption or direct doping. For example, CN119060416A loads anthocyanins into an aerogel porous network for pH detection, but the indicator binds to the matrix only through weak interactions, making it prone to leaching in liquid environments and causing signal drift. CN106706612B improves sensitivity by adjusting the pH of the immobilized solution, but does not fundamentally solve the problem of indicator anchoring stability.

[0004] In recent years, researchers have attempted to load indicators onto metal-organic frameworks (MOFs) to achieve confined anchoring using their high specific surface area and tunable pore structure (Zhang Yue et al., Research Progress on the Application of Dye-Loaded MOFs in Fluorescence Sensing). However, existing MOF / dye composite systems still have the following shortcomings: First, it is difficult to process MOFs loaded with dyes into flexible sensing patches, and there is a lack of strategies for composite with aerogel matrices; second, the dye anchoring mechanism is singular, and the stability against acid and alkali changes and long-term monitoring is insufficient; third, most systems focus on fluorescence detection, and there is relatively little research on reversible sensing patches based on colorimetric responses.

[0005] Therefore, developing a colorimetric sensor patch that combines anti-dye leakage, reversible response, resistance to temperature interference, wide pH response, and fast response has significant technical value and market prospects. Summary of the Invention

[0006] To address the technical problems of existing colorimetric sensing technologies, such as indicator leakage, irreversible response, poor temperature stability, narrow detection range, and difficulty in meeting the requirements of continuous monitoring and complex environmental applications, this invention provides a reversible responsive MOF-confined colorimetric sensing patch, its preparation method, and its applications. This sensing patch utilizes the dual effects of UiO-66 nanopore confinement and zirconium cluster coordination anchoring to stably fix methyl red within the MOF, inhibiting dye leaching. Simultaneously, a three-dimensional porous aerogel network formed by hydrogen bonding between agarose and polyethylene glycol enables rapid adsorption and mass transfer of the analyte liquid, thus achieving rapid, reversible, and temperature-resistant colorimetric detection over a wide pH range. Furthermore, the response range can be adjusted by regulating the polyethylene glycol content to meet diverse pH monitoring needs.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a colorimetric sensor patch with reversible response type MOF confinement.

[0009] The colorimetric sensing patch is composed of agarose (AG), polyethylene glycol (PEG), and UiO-66 / methyl red (MR) composite aerogel;

[0010] Methyl red is anchored inside the MOF through the nanopore confinement effect of UiO-66 and the coordination of zirconium cluster sites, forming UiO-66 / MR composite nanoparticles; the UiO-66 / MR composite nanoparticles are interleaved within the porous network structure sheets formed by hydrogen bonding between agarose and polyethylene glycol.

[0011] In this invention, the anchoring mechanism of methyl red is as follows: the nanopores (pore size approximately 0.8-1.2 nm) of UiO-66 exert a spatial confinement effect on the methyl red molecule, restricting its configurational torsion; simultaneously, the Zr metal sites of UiO-66 form coordination bonds with the carboxyl groups in the methyl red molecule. This dual effect of spatial confinement and coordination anchoring effectively inhibits the leaching of methyl red molecules and maintains their structural stability in complex environments.

[0012] In this invention, agarose and polyethylene glycol form a cross-linked network through hydrogen bonds. Furthermore, the ether bonds of polyethylene glycol can compete with the azo groups in the methyl red molecule for hydrogen bonds, thereby regulating the protonation / deprotonation equilibrium of methyl red. By adjusting the content of polyethylene glycol, the response range of methyl red can be altered, achieving targeted regulation within different pH ranges.

[0013] In this invention, the porous network structure is a single-layer, interlaced structure with a porosity of 50%-85% and a pore size of 50-500 μm. This structure facilitates rapid adsorption and mass transfer of the liquid to be tested, thereby achieving a rapid response.

[0014] Secondly, the present invention provides a method for preparing the reversible responsive MOF-confined colorimetric sensor patch, comprising the following steps:

[0015] (1) Preparation of UiO-66 / MR composite nanoparticles: Zirconium source, terephthalic acid and methyl red were dissolved in N,N-dimethylformamide (DMF) / glacial acetic acid mixed solvent, and hydrothermally reacted at 100-140℃ for 8-24 hours. After centrifugation and washing, UiO-66 / MR composite nanoparticles were obtained.

[0016] (2) Preparation of UiO-66 / MR / PEG mixture: Disperse the UiO-66 / MR composite nanoparticles obtained in step (1) in an aqueous solution, add polyethylene glycol, and stir at 40-70℃ for 0.5-2 hours to obtain mixture A;

[0017] (3) Preparation of AG composite gel precursor: Add agarose to the mixture A obtained in step (2), heat and stir at 80-100℃ until completely dissolved to obtain mixture B;

[0018] (4) Freeze-drying molding: Inject the mixture B into the mold and freeze-dry for 12-48 hours to obtain the colorimetric sensor patch.

[0019] Further, in step (1), the mass ratio of methyl red to the total mass of the zirconium source and terephthalic acid is 1:5 to 1:12.

[0020] In a preferred embodiment, the mass ratio is 1:5 to 1:10. The reaction temperature is preferably 120°C, and the reaction time is preferably 12 hours.

[0021] Further, the amount of polyethylene glycol added in step (2) is 0.1-1 times the mass of UiO-66 / MR, and the molecular weight of the polyethylene glycol is 200-20000 Da.

[0022] Furthermore, the amount of agarose added in step (3) is 1%-3% of the total mass of mixture B. This range is reasonably determined based on the specific proportion (about 2%) in the embodiments of the present invention, which can ensure the mechanical strength and structural integrity of the aerogel, without reducing the porosity and response speed due to excessive agarose content.

[0023] It should be noted that although the ranges of the above process parameters are derived based on the specific conditions in the embodiments of the present invention (where the total mass ratio of methyl red to the zirconium source and terephthalic acid is approximately 1:8.7, the amount of PEG added is approximately 0.35 times, and the amount of agarose added is approximately 2%), those skilled in the art will understand that by appropriately adjusting the proportions of each component within the above ranges, an aerogel patch with a porous network structure and capable of achieving basic colorimetric sensing functions can still be formed. Therefore, the above ranges derived based on a single embodiment have reasonable technical foresight and should be considered to be covered by the scope of protection of the present invention.

[0024] Thirdly, the present invention provides the application of the colorimetric sensing patch in the preparation of products for pH detection.

[0025] Specifically, the colorimetric sensor patch can be used to prepare pH detection products for bodily fluids, including but not limited to portable rapid detection of bodily fluids such as human urine, blood, saliva, and sweat; it can be used to prepare pH detection products for environmental water samples, such as in-situ monitoring of water quality in rivers, lakes, industrial wastewater, and domestic sewage; it can be used to prepare pH monitoring products for bacterial culture processes, tracking the dynamic changes in pH during microbial growth and metabolism in real time to help determine the culture status; and it can also be used to prepare pH monitoring products for wounds, achieving non-invasive and continuous pH detection by attaching it to the wound surface, providing a visual reference for assessing the wound healing process.

[0026] The above applications are all based on the wide pH response range, fast response, reversible use and good biocompatibility of the colorimetric sensor patch of the present invention, which can meet the needs of convenient, intuitive and real-time monitoring of pH value in different scenarios.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) Excellent resistance to dye leakage and temperature interference: Through the spatial confinement effect of MOF channels and the coordination anchoring effect of zirconium cluster sites, methyl red is stably fixed inside UiO-66, effectively inhibiting dye leaching and avoiding signal drift and potential biological toxicity. At the same time, methyl red is confined in the rigid channels of MOF, and its molecular configuration and acid-base balance are significantly reduced by temperature, so that the sensing patch maintains good detection stability in a wide temperature range (such as -40℃ to 70℃).

[0029] (2) Reversible response and wide pH monotonic response: Methyl red maintains its intrinsic protonation / deprotonation equilibrium in the confined system. Combined with the three-dimensional porous structure of the aerogel, a reversible cyclic response over a wide pH range is achieved, which can meet the needs of continuous monitoring. In addition, by adjusting the amount of polyethylene glycol added, the hydrogen bond competition between its ether bond and the azo group of methyl red can be changed, thereby adjusting the protonation / deprotonation equilibrium state of methyl red and achieving monotonic control of the response range of pH 3-10.

[0030] (3) Rapid response performance: The three-dimensional porous network structure of aerogel (porosity 50%-85%, pore size 50-500 μm) is conducive to the rapid adsorption and mass transfer of the liquid to be tested, so that the sensor patch can complete the color change response within a few seconds after contacting the liquid to be tested.

[0031] (4) The preparation process is simple and can be mass-produced: Methyl red is confined to the MOF channels by a one-step in-situ synthesis method. Combined with the overall molding freeze drying and punching process, the operation is simple, the batch uniformity is good, and it has good industrial production potential. Attached Figure Description

[0032] Figure 1 Image A shows scanning electron microscope (SEM) and transmission electron microscope (TEM) images of UiO-66 and UiO-66 / MR, while image B shows the surface morphology of three aerogels: AG, UiO-66 / MR / AG, and UiO-66 / MR / PEG / AG, as shown in the image.

[0033] Figure 2 A shows a comparison of the adsorption stability of methyl red by gel materials under different binding methods; B shows a schematic diagram of two binding methods between UiO-66 and methyl red; and C shows a schematic diagram of the large-scale preparation process of the sensor patch.

[0034] Figure 3 In the diagram, A represents the UV absorption spectrum of methyl red in solutions with different pH values; B represents the curve showing the change in the acid-base peak ratio of methyl red with pH; C represents the solid-state UV spectrum of the UiO-66 / MR / PEG / AG patch; D represents the curve showing the change in the acid-base peak ratio of the UiO-66 / MR / PEG / AG patch; E represents the solid-state UV spectrum of the UiO-66 / MR / AG patch; F represents the curve showing the change in the acid-base peak ratio of the UiO-66 / MR / AG patch; G represents the colorimetric performance of the two patches under different pH conditions; and H represents a scatter plot showing the change in the G / B values ​​of the two patches with pH.

[0035] Figure 4 Image A shows images of different composite gels in their dry state and after pH colorimetric analysis; Image B shows the statistical results of the response time of different composite gels to pH=3.

[0036] Figure 5Table A shows a comparison of the color stability of different materials (MR, UiO-66 / MR, UiO-66 / MR / PEG, UiO-66 / MR / AG, UiO-66 / MR / PEG / AG) within a temperature range of 25-95℃. Table B shows the UV absorption spectra of methyl red after treatment at different temperatures. Table C shows the changes in the acid-base peak ratio of the UiO-66 / MR / PEG / AG patch after treatment at different temperatures under pH=3.03, pH=6.37, and pH=9.38. Table DF shows the scatter plot and relative standard deviation (RSD) of the RGB values ​​of the UiO-66 / MR / PEG / AG patch after treatment at different temperatures under pH=9.38, pH=6.37, and pH=3.03.

[0037] Figure 6 A shows the pH dynamic response curves of the two patches, UiO-66 / MR / PEG / AG and UiO-66 / MR / AG; B shows the comparison of the dynamic response cycle monitoring data of the two patches; C shows the color change record of the UiO-66 / MR / PEG / AG patch during multiple cycles; D shows the stability statistics of the UiO-66 / MR / PEG / AG patch after multiple cycles; E shows the stability test results of the UiO-66 / MR / PEG / AG patch after long-term immersion in neutral solution (pH=7); F shows the colorimetric performance comparison of the UiO-66 / MR / PEG / AG patch after long-term immersion in water.

[0038] Figure 7 In the diagram, A represents the ultraviolet absorption spectra corresponding to the three color states of methyl red, B represents the solid ultraviolet absorption spectra of methyl red in various composite materials, C represents the schematic diagram of the deprotonation process of methyl red, and D represents the infrared spectra of various composite materials.

[0039] Figure 8 In the image, A is the colorimetric color difference graph of the UiO-66 / MR / PEG / AG composite gel pH detection sensor patch over bacterial culture time; B is the effect of the patch on bacterial growth density; and C is the effect of the patch on the bacterial growth environment.

[0040] Figure 9 A shows the color difference diagram of the patch in simulated urine after spiking; B shows the effect curve of ammonium ion concentration on solution pH; C shows the change data of patch color difference ED value with simulated solution pH; D shows the colorimetric and color difference diagrams of the patch on real urine of different volunteers; E shows the statistical analysis of patch color difference ED value corresponding to different volunteers; and F shows the accuracy comparison of pH value predicted by the two patches with the actual pH value. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0042] After reading the contents disclosed in this invention, those skilled in the art can make appropriate adjustments or substitutions to the process parameters of the methods and applications described in this invention without departing from the spirit and scope of this invention. Such obvious adjustments, substitutions or combinations should be included within the protection scope of this invention.

[0043] Unless otherwise specified, the materials, reagents, instruments and testing methods used in the following embodiments can be obtained commercially or prepared, operated and implemented with reference to conventional methods disclosed in the art.

[0044] It should be noted that all technical parameters described in this document as numerical ranges (such as temperature, ratio, time, content, etc.) should be understood as encompassing all possible sub-ranges and specific numerical points within that range, regardless of whether the specific numerical value or sub-range is explicitly listed. Unless otherwise specified, the technical terms used in this document have the meanings commonly understood by those skilled in the art.

[0045] Example 1: A reversible response MOF-confined colorimetric sensor patch

[0046] This embodiment provides a reversible, MOF-confined colorimetric pH sensing patch and its preparation method. The patch utilizes the confinement effect of the metal-organic framework UiO-66 on the pH indicator methyl red (MR), and combines it with polyethylene glycol (PEG)-modified agarose (AG) aerogel as a carrier, achieving a wide-range, reversible, and rapid colorimetric response to pH. The specific preparation steps are as follows:

[0047] (1) Preparation of UiO-66 / MR composite nanomaterials:

[0048] Prepare a mixed stock solution by adding 88 mL of N,N-dimethylformamide (DMF) and 12 mL of glacial acetic acid (HAc) to a 100 mL beaker. Weigh 34.9 mg of zirconium tetrachloride and 24.9 mg of terephthalic acid into a 20 mL heat-resistant vial, add 8 mL of the above DMF (HAc) mixed stock solution and 2 mL of a 4 mg / mL methyl red (MR) DMF / HAc solution, and sonicate until the solid particles are completely dissolved and the solution becomes transparent. Place the transparent mixed solution in a 120 °C oven and heat for 12 h. After the reaction is complete, allow it to cool naturally to room temperature and remove the vial. Sonicate the solution in the vial to homogenize it, transfer it to a 50 mL centrifuge tube, centrifuge at 9500 r / min for 5 min, and wash once with deionized water to obtain UiO-66 / MR composite nanomaterials.

[0049] (2) Preparation of UiO-66 / MR / PEG mixture:

[0050] Take 1 mL of UiO-66 / MR composite nanoparticle suspension with a concentration of 170 mg / mL and centrifuged and place it in a 20 mL glass bottle. Add 0.75 mL of polyethylene glycol (PEG) solution with a concentration of 0.08 g / mL and deionized water as solvent. After mixing, stir in a water bath at 50℃ for 1 hour to obtain mixture A.

[0051] (3) Preparation of AG composite gel precursor:

[0052] Weigh 60 mg of agarose (AG) powder into a 20 mL glass bottle, add 1 mL of deionized water, and heat and stir on a 95°C hot plate until completely dissolved. Add the mixture A obtained in step (2) dropwise into the hot agarose solution and continue stirring for 3 minutes to mix it evenly, to obtain mixture B.

[0053] (4) Freeze-drying and shaping:

[0054] Mixture B was taken out with a pipette and dropped into a mold that had been preheated on a heating plate. After dropping, it was quickly transferred to liquid nitrogen for freezing and shaping. After freezing for 10 minutes, it was placed in a freeze dryer and freeze-dried for 4 hours to obtain the UiO-66 / MR / PEG / AG composite aerogel material, which is the reversible responsive MOF-confined colorimetric sensor patch.

[0055] Example 2

[0056] This embodiment provides a colorimetric pH detection sensor patch for comparison, the preparation method of which is basically the same as that in Example 1, except that polyethylene glycol (PEG) is not added. The specific preparation steps are as follows:

[0057] (1) Preparation of UiO-66 / MR composite nanomaterials: Same as step (1) in Example 1.

[0058] (2) Preparation of UiO-66 / MR / AG composite aerogel:

[0059] Take 1 mL of a 170 mg / mL, centrifuged UiO-66 / MR composite nanoparticle suspension and place it in a 20 mL glass bottle. Stir for 1 hour in a 50°C water bath. Separately weigh 60 mg of agarose (AG) powder and add 1 mL of deionized water to a 20 mL glass bottle. Heat and stir on a 95°C hot plate until completely dissolved. Add the stirred UiO-66 / MR suspension dropwise to the hot agarose solution and continue stirring for 3 minutes to mix thoroughly. Then, use a pipette to remove the mixture and drop it into a mold preheated on a hot plate. After the drop is complete, quickly transfer it to liquid nitrogen for freeze-drying. After freezing for 10 minutes, freeze-dry for 4 hours to obtain the UiO-66 / MR / AG composite aerogel material, which is a PEG-free colorimetric sensor patch for comparison.

[0060] Comparative Example

[0061] This comparative example provides several control samples for performance comparison, as follows:

[0062] Pure agarose aerogel (AG): 60 mg of agarose was dissolved in 1 mL of deionized water, heated to dissolve, and then freeze-dried to obtain the agarose aerogel. It was used to verify the intrinsic properties of the substrate material.

[0063] Pure methyl red solution (MR): Methyl red is dissolved in deionized water to prepare a suitable concentration for comparing the performance of free indicators.

[0064] Pure UiO-66 nanoparticles (UiO-66): prepared according to step (1) of Example 1 but without the addition of methyl red, used to verify the basic properties of MOF substrate materials.

[0065] UiO-66 / MR composite nanoparticles (UiO-66 / MR): These are the composite nanoparticles prepared in step (1) of Example 1, used to verify the effect of MOF confinement on methyl red.

[0066] UiO-66 / MR / PEG composite material (UiO-66 / MR / PEG): Take 1 mL of UiO-66 / MR composite nanoparticle suspension with a concentration of 170 mg / mL, add 0.75 mL of PEG solution with a concentration of 0.08 g / mL (PEG mass is 0.35 times the mass of UiO-66 / MR), mix well, stir at 50℃ for 1 hour, and then freeze-dry directly (without adding agarose) to verify the interaction between PEG and methyl red and the necessity of agarose aerogel matrix.

[0067] AG adsorption methyl red material (AG adsorption dye group): Methyl red is mixed with agarose and then freeze-dried to verify the leakage of physical adsorption.

[0068] UiO-66 / AG post-adsorption methyl red material (UiO-66 / AG post-adsorption dye group): First, a blank UiO-66 / AG aerogel was prepared, and then immersed in methyl red solution to allow the dye to be physically adsorbed, which was used to compare the leakage difference between post-adsorption and one-step synthesis methods.

[0069] One-step in-situ synthesis of UiO-66 / MR / AG material (one-step in-situ synthesis of UiO-66 / MR group): namely, the UiO-66 / MR / AG composite aerogel without PEG prepared in Example 2, used to verify the advantages of the one-step in-situ synthesis method.

[0070] Example of effect

[0071] To verify the various performance characteristics of the colorimetric sensing patch described in this invention, the sensing patches prepared in Examples 1 and 2, as well as the control samples in the comparative examples, were tested as follows.

[0072] 1. Microscopic morphological characterization

[0073] To investigate whether the introduction of methyl red (MR) affects the crystal structure of UiO-66 and the three-dimensional porous network morphology of aerogels with different components, the microstructure of the materials was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 1 The results from the A-coating assay show that UiO-66 exhibits a regular octahedral crystal morphology. The UiO-66 / MR composite material loaded with MR maintains a complete crystal structure with clear lattice fringes, indicating that MR is successfully confined within the MOF channels without disrupting its crystal framework. To further compare the differences in channel structure among the three aerogels, SEM characterization was performed on AG, UiO-66 / MR / AG, and UiO-66 / MR / PEG / AG, and the results are as follows. Figure 1As shown in Figure B, all three aerogels form a three-dimensional porous network structure. Among them, the UiO-66 / MR / PEG / AG aerogel with added PEG has a more uniform pore size distribution and better pore connectivity, indicating that the introduction of PEG helps to improve the dispersion of the precursor and optimize the ice crystal growth behavior during the freeze-drying process.

[0074] 2. Dye leakage resistance and potential for large-scale preparation

[0075] To evaluate the effect of MOF confinement on suppressing methyl red dye leakage and the feasibility of large-scale fabrication of the sensor patch, a dye leakage comparison experiment and a perforation fabrication test were conducted.

[0076] To verify the immobilization stability of methyl red under different binding methods, three comparative experiments were set up: the AG adsorption dye group, the UiO-66 / AG post-adsorption dye group, and the one-step in-situ synthesized UiO-66 / MR group. The dyes were soaked in water for 12 h and then centrifuged for observation. The results are as follows: Figure 2 As shown in Figure A: the first two groups showed obvious decolorization, and the supernatant was red; while the dye in the UiO-66 / MR group synthesized by the one-step method did not fall off, and the supernatant was clear. Figure 2 Figure B illustrates the difference between the two binding methods: in the post-adsorption method, the dye only adheres to the MOF surface and is easily desorbed; in the one-step synthesis method, methyl red is confined in situ within the MOF channels and does not detach even after long-term storage. Therefore, it can be concluded that the UiO-66 / MR composite material prepared by the one-step in-situ synthesis method can effectively immobilize methyl red by utilizing the spatial confinement effect of the MOF channels, significantly suppressing dye leakage and ensuring the long-term signal stability of the sensing patch.

[0077] To evaluate the mass production capability of this patch, a fabrication and testing process combining integral molding, freeze-drying, and perforation was employed. The specific steps were as follows: large-size composite gel sheets were prepared, freeze-dried for shaping, and then perforated uniformly using a 5 mm punch to obtain a large number of small patches of uniform size. The results are as follows... Figure 2 As shown in Figure C, this process is simple to operate, allowing for the one-time molding and processing of large-sized gel substrates. Subsequent cutting can efficiently obtain uniform patches, and the process is simple and controllable. Therefore, this composite gel sensing patch has good potential for large-scale preparation and can meet the needs of industrial mass production.

[0078] 3. Wide pH range colorimetric performance

[0079] To investigate the colorimetric response and detection range of the sensor patch under different pH conditions, a series of standard solutions with pH 2-12 were prepared using BR buffer solution. The ultraviolet absorption spectra and colorimetric performance of the sensor patches prepared in Example 1 (UiO-66 / MR / PEG / AG) and Example 2 (UiO-66 / MR / AG) were characterized.

[0080] To clarify the spectral variation of methyl red, the ultraviolet absorption spectra of methyl red solutions under different pH conditions were measured. The results are as follows: Figure 3 As shown in Figure A: as the pH increases from 2 to 12, a characteristic absorption peak is observed at approximately 528 nm under acidic conditions (pH 2-4); under alkaline conditions (pH 6-12), the 420 nm peak becomes the main peak. Figure 3 B shows the acid-base peak ratio (A) 528 / A 408 The typical S-shaped response with pH indicates that methyl red has a significant pH-dependent color change in the pH range of 2-10.

[0081] To verify whether methyl red retains its pH-responsive characteristics in the MOF confinement system, solid-state UV spectroscopy characterization was performed on the two patches. The results are as follows: Figure 3 As shown in the CF diagram, the solid-state UV spectra of both patches exhibit pH-dependent changes similar to those in the solution system, with the acid-base peak ratio showing a good S-shaped response with pH, ​​confirming that methyl red retains its intrinsic pH response characteristics in the MOF confinement system.

[0082] To evaluate the color changes and detection range of the two patches, the color changes of the patches after adding solutions of different pH values ​​were recorded, and the RGB values ​​were extracted for quantitative analysis. The results are as follows: Figure 3 As shown in G and H: After adding solutions of different pH values, the colorimetric signals of the two patches (UiO-66 / MR / PEG / AG and UiO-66 / MR / AG) showed obvious monotonic changes with different solution pH values. Nonlinear fitting was performed on the G / B-pH of the two patches, and the nonlinear curves showed a typical S-shaped response. The fitting equations are as follows:

[0083] UiO-66 / MR / PEG / AG: y = 0.095 + 2.11 / [1 + (8.58 / x) 12.84 ] 0.22 ;

[0084] UiO-66 / MR / AG: y = 0.024 + 2.95 / [1 + (6.65 / x) 3.33 ] 3.3 .

[0085] Therefore, it can be concluded that both patches can achieve visualization and quantitative detection of solution pH. Example 1 shows higher response sensitivity in the acidic range, while Example 2 shows higher response sensitivity in the alkaline range. Both patches have the potential to broaden the overall pH detection range and improve practical application adaptability.

[0086] 4. Response time test

[0087] To compare the response rates of different composite gels to pH changes and the effect of dye distribution on response time, the color change response time of each sample to a solution at pH=3 was measured. The results are as follows: Figure 4 As shown, both UiO-66 / MR / PEG / AG and UiO-66 / MR / AG patches can complete the color response within a few seconds, achieving a response speed in the second range. At the same time, it was found that the more uniform the dye distribution in the gel and the better the pore connectivity, the shorter the response time. It was concluded that the introduction of PEG helps to shorten the response time.

[0088] 5. Temperature stability test

[0089] To evaluate the applicability of the sensing patch over a wide temperature range and the effect of temperature on the detection signal, the UiO-66 / MR / PEG / AG patch prepared in Example 1 and the control materials (MR, UiO-66 / MR, UiO-66 / MR / PEG, UiO-66 / MR / AG) were treated at different temperatures from 25°C to 95°C, and the color changes and ultraviolet absorption spectra were recorded. The UiO-66 / MR / PEG / AG patch was also placed in pH solutions at different temperatures, and the colorimetric signals of the patch at different pH values ​​were recorded.

[0090] Depend on Figure 5 As shown in Figure A, the pure MR solution exhibits significant discoloration or fading at high temperatures; while the MOF-confined composite materials such as UiO-66 / MR, UiO-66 / MR / PEG, UiO-66 / MR / AG, and UiO-66 / MR / PEG / AG maintain good color stability at different temperatures, with the UiO-66 / MR / PEG / AG patch showing the least color change with temperature. To further quantify the effect of temperature on the spectral characteristics of methyl red, the ultraviolet absorption spectra after treatment at different temperatures were measured. The results are as follows: Figure 5 As shown in Figure B: the characteristic absorption peak positions and intensities of methyl red remained basically consistent at various temperatures, with no significant drift or attenuation. The UiO-66 / MR / PEG / AG patch was placed in buffer solutions at pH=3.03, pH=6.37, and pH=9.38, respectively, and its acid-base peak ratio was measured after treatment at different temperatures. The results are as follows... Figure 5 As shown in Figure C: Under the three pH conditions, the acid-base peak ratio of the patch fluctuates little with temperature changes, exhibiting good temperature insensitivity.

[0091] To quantitatively evaluate the temperature stability of the patch color, the RGB values ​​of the UiO-66 / MR / PEG / AG patch were extracted at different temperatures, and the relative standard deviation (RSD) was calculated. The results are as follows: Figure 5As shown in the diagram: at pH=9.38, the RSD of the R value is 1.17%, and the RSD of the B value is 2.5%; at pH=6.37, the RSD of the R value is 0.96%, and the RSD of the B value is 1.39%; at pH=3.03, the RSD of the R value is 0.36%, and the RSD of the B value is 1.98%. The RSD values ​​under all conditions are less than 3%, indicating that the color signal of the patch exhibits high consistency across different temperatures.

[0092] Therefore, it can be concluded that the UiO-66 / MR / PEG / AG composite gel sensing patch prepared by the present invention has good temperature stability in a wide temperature range of -40℃ to 70℃, and the color signal fluctuates little with temperature changes, making it suitable for pH monitoring in variable temperature environments.

[0093] 6. Long-term monitoring performance and dynamic response characteristics

[0094] To verify the reversible response capability and long-term stability of the sensor patch, continuous pH cycle control test and long-term immersion test were conducted.

[0095] Test steps: (1) Dynamic response test: Fix the composite gel patch to the beaker wall, add buffer solution with pH=2.5, first add 9 M NaOH solution dropwise to adjust the pH from 2.5 to 10, then add 1 M HCl solution dropwise to adjust the pH back to 2.3, and record the color change of the patch in real time. (2) Cyclic stability test: Repeat the above acid-base cycle operation multiple times, and record the G / B value of the patch after each cycle. (3) Long-term immersion test: Immerse the patch in a neutral solution (pH=7.13) for a long time, and take it out periodically to test its color signal.

[0096] like Figure 6 As shown in Figures A and B, the color change of both patches is synchronized with the pH change during the continuous rise and fall of pH, and both can track the continuous change of solution pH in real time, demonstrating good dynamic response characteristics. Figure 6 The results of C and D show that the G / B value response curves of the UiO-66 / MR / PEG / AG patch basically overlapped after multiple acid-base cycles, and it still maintained good response performance, exhibiting reversible response characteristics. Figure 6 The results of E and F indicate that the colorimetric performance of the patch did not significantly decrease after long-term immersion in a neutral solution, and the color response was basically consistent with that of a fresh patch.

[0097] Therefore, it can be concluded that the composite gel sensing patch prepared by the present invention has good long-term stability and reversible cycle capability, which can meet the reusability requirements in continuous monitoring scenarios.

[0098] 7. Spectroscopic analysis to verify interactions

[0099] To verify the structural state of methyl red in the composite material and the interaction between the gel and MOF, solid-state ultraviolet and infrared spectroscopy characterization was performed.

[0100] The results are as follows Figure 7 As shown in Figures A and B, the characteristic absorption peaks of methyl red in composite materials such as UiO-66 / MR, UiO-66 / MR / AG, and UiO-66 / MR / PEG / AG are basically consistent with those in the solution system, confirming that methyl red can still maintain its intrinsic pH response characteristics in the MOF confinement system. Agarose is a highly polar medium, and the methyl red quinone cationic structure also has high polarity. In the UiO-66 / MR / AG patch, methyl red exists in the acidic structure, thus exhibiting higher response sensitivity to the alkaline pH range. PEG changes the existence form of methyl red by constructing a low-polarity microenvironment and reconstructing the hydrogen bond network, causing methyl red to become dominant in the basic structure in the UiO-66 / MR / PEG / AG composite patch, thereby achieving a highly sensitive response to the acidic pH range. Figure 7 The diagram in C illustrates the deprotonation process of methyl red as pH increases, transforming it from a quinone cation structure and a protonated azo structure to an azo anion structure. Figure 7 Infrared spectroscopy of the medium-density spectroscopy (MDS) shows that UiO-66 / MR maintains good structural integrity during the composite process. The spectra reveal a clear, hierarchical superposition of characteristic absorption peaks among the components in the composite material, while subtle changes in peak position suggest physical encapsulation and hydrogen bonding interactions between AG and PEG. The MDS fully records the evolution of the material from UiO-66 / MR framework construction to polymer modification and then to multi-component hierarchical functionalization, providing reliable molecular-level evidence for the multi-level structural design of the material. Therefore, it can be concluded that methyl red retains its intrinsic pH-responsive characteristics in the MOF-confined system, and the functions of each component are synergistically maintained.

[0101] 8. Applicability in bacterial culture systems

[0102] To evaluate the suitability and biocompatibility of the sensor patch in a biological culture system, the patch was placed in an E. coli culture medium, and color changes and bacterial growth were monitored. Results are as follows: Figure 8 As shown in Figure A: the color of the patch changes regularly with increasing culture time, which can reflect the changes in pH of the culture medium in real time. Figure 8 Results B and C showed that the presence of the patch did not significantly inhibit bacterial growth, indicating that the patch has good biocompatibility and can be used for pH monitoring in microbial culture systems without interfering with normal bacterial activity.

[0103] 9. Applicability of human urine pH testing

[0104] To verify the applicability of the sensing patch in real biological fluid samples, it was applied to pH detection in simulated urine and real human urine.

[0105] Simulated urine testing: To evaluate the patch's response characteristics in complex bodily fluid environments, the patch was spiked and analyzed in simulated urine at different pH values. Results are as follows: Figure 9 As shown in Figures A and C: the color difference ED value of the patch in simulated urine shows a good S-shaped response relationship with pH, ​​indicating that the patch maintains a stable colorimetric response capability in the simulated urine matrix. Figure 9 The study further confirmed the effect of ammonium ion concentration on solution pH, providing a reference for urine pH testing.

[0106] Real urine testing: To verify the effectiveness of the patch on real samples, the patch was applied to real urine samples from different volunteers. Results are as follows: Figure 9 As shown in D and E: the patch has a clear distinguishing effect on the colorimetric response of real urine from different volunteers, and the color difference ED value can effectively reflect the pH difference of different urine samples.

[0107] Accuracy Assessment: To quantify the detection accuracy of the patches, the predicted pH values ​​of the two patches were compared with the actual pH values. Results are as follows: Figure 9 As shown in Figure F: the pH values ​​predicted by the two patches have a high degree of consistency with the actual pH values, with small deviations.

[0108] Therefore, it can be concluded that the composite gel pH detection sensor patch prepared by the present invention exhibits good detection accuracy and stability in both simulated urine and real human urine samples, and has good application prospects in the field of portable body fluid pH detection.

[0109] In summary, the composite gel-based pH sensing patch prepared in this invention, by immobilizing methyl red indicator through MOF confinement effect and combining it with a PEG / AG aerogel three-dimensional network structure, achieves pH colorimetric detection with a wide pH range (3-10), rapid response (seconds), good temperature stability (-40℃ to 70℃), reversible cyclic response, and good biocompatibility. It has broad application prospects in environmental monitoring, biological culture, and clinical body fluid detection.

Claims

1. A reversible response MOF-confined colorimetric sensor patch, characterized in that, The colorimetric sensing patch is composed of agarose, polyethylene glycol, and UiO-66 / methyl red composite aerogel; Methyl red is anchored inside the MOF through the nanopore confinement effect of UiO-66 and the coordination effect of zirconium cluster sites, forming UiO-66 / methyl red composite nanoparticles; the UiO-66 / methyl red composite nanoparticles are interleaved within the porous network structure sheets formed by hydrogen bonding of agarose and polyethylene glycol.

2. The colorimetric sensor patch according to claim 1, characterized in that, The anchoring mechanism of methyl red in UiO-66 / methyl red is as follows: the nanopores of UiO-66 produce a spatial confinement effect on methyl red molecules, while the Zr metal sites of UiO-66 form coordination bonds with the carboxyl groups of methyl red.

3. The colorimetric sensor patch according to claim 1, characterized in that, The agarose and polyethylene glycol form a cross-linked network through hydrogen bonds. The ether bonds of polyethylene glycol compete with the azo groups of methyl red through hydrogen bonds to regulate the protonation / deprotonation balance of methyl red.

4. The colorimetric sensor patch according to claim 1, characterized in that, The porous network structure is a single-layer interlaced structure with a porosity of 50%-85% and a pore size of 50-500 μm.

5. A method for preparing a reversible responsive MOF-confined colorimetric sensor patch according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of UiO-66 / methyl red composite nanoparticles: Zirconium source, terephthalic acid and methyl red were dissolved in N,N-dimethylformamide / glacial acetic acid mixed solvent and hydrothermally reacted at 100-140℃ for 8-24 hours. After centrifugation and washing, UiO-66 / methyl red composite nanoparticles were obtained. (2) Preparation of UiO-66 / methyl red / polyethylene glycol mixture: Disperse the UiO-66 / methyl red composite nanoparticles obtained in step (1) in an aqueous solution, add polyethylene glycol, and stir at 40-70℃ for 0.5-2 hours to obtain mixture A; (3) Preparation of agarose composite gel precursor: Add agarose to the mixture A obtained in step (2), heat and stir at 80-100℃ until completely dissolved to obtain mixture B; (4) Freeze-drying molding: Inject the mixture B into the mold and freeze-dry for 12-48 hours to obtain the colorimetric sensor patch.

6. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of methyl red to the total mass of zirconium source and terephthalic acid is 1:5 to 1:12, the reaction temperature is 120°C, and the reaction time is 12 hours.

7. The preparation method according to claim 6, characterized in that, The mass ratio of methyl red to the total mass of zirconium source and terephthalic acid in step (1) is 1:5 to 1:

10.

8. The preparation method according to claim 5, characterized in that, The amount of polyethylene glycol added in step (2) is 0.1-1 times the mass of UiO-66 / methyl red, and the molecular weight of the polyethylene glycol is 200-20000 Da.

9. The preparation method according to claim 5, characterized in that, The amount of agarose added in step (3) is 1%-3% of the total mass of mixture B.

10. The use of the reversible responsive MOF-confined colorimetric sensor patch according to any one of claims 1-4 in the preparation of products for pH detection.

Images