Preparation method and use of nh2-bdc-fe cu mof hydrogel sensor based on peroxidase-like activity

Abstract

The application discloses a preparation method and application of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity. Through the superposition of bimetallic MOF and TMB discoloration, in combination with the color of the hydrogel material itself, the color superposition of oxidized TMB and the good enrichment effect of the hydrogel, a wider linear range than that in a solution system is realized. In the concentration range of 4-4000 muM VC aqueous solution, the B / (R+G+B) value as the color parameter has a good linear relationship with the logarithm of the VC water concentration, and the detection limit is as low as 1.33 muM. Compared with traditional detection methods, the colorimetric detection method of VC mentioned in the application has the advantages of simple operation, simple equipment, low detection cost, portability and wearability, and can meet the detection requirements of fruits with different VC content.

Description

Technical Field

[0001] This invention belongs to the field of colorimetric detection, specifically relating to the preparation method of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity and its application in the colorimetric detection of vitamin C. Background Technology

[0002] Vitamin C (VC) is a vitamin similar to glucose polyols and is one of the safest and most effective nutrients in the human diet. VC is widely found in fruits, and its content is considered an important indicator of fruit freshness and nutritional quality. As an important antioxidant and enzymatic factor, it participates in many important biological reactions and physiological and biochemical processes in the human body. Furthermore, VC has the function of scavenging reactive oxygen species and some free radicals in the body, protecting cells from oxidative damage and enhancing immunity. Imbalances or deficiencies in VC levels have also been found to be associated with many diseases, such as sepsis, cardiovascular disease, iron absorption, osteoporosis and fractures, and various cancers. Therefore, rapid and accurate detection of VC in the production process and product testing is of great significance for ensuring food safety and physiological health levels.

[0003] With the development of nanotechnology and bioengineering, methods for detecting vitamin C are constantly being updated and iterated. Based on different detection principles, current methods for detecting vitamin C can be categorized into titration analysis, ultraviolet spectrophotometry, fluorescence analysis, and chromatography. Titration analysis is simple, reliable, and low-cost, but it has poor specificity, and the resulting colored compounds are unstable. Ultraviolet spectrophotometry can perform quantitative detection, but its application is limited by laboratory conditions. Fluorescence and chromatography offer high sensitivity, good linearity, and good reproducibility, but their operation is relatively cumbersome, restricting their further application.

[0004] In summary, existing methods for detecting vitamin C are mainly concentrated in the laboratory. For example, high-precision chromatographic and fluorescence methods require instruments in a laboratory environment. These methods also require in vitro sampling of the analytes and have specific requirements for sample pretreatment. This limits the effectiveness of these methods. Therefore, wearable devices have emerged. Wearable devices are those that can be worn directly on the body or attached to a surface to detect relevant parameters. For instance, they can be used to comprehensively assess quality of life by detecting the content of certain nutrients in human sweat; they can also be applied to the detection of nutrients in food production processes, providing a reference for daily nutrient intake.

[0005] Colorimetric biosensing has gained increasing attention due to its practicality, simplicity, and low cost. Traditional colorimetric sensing methods are a rapid analytical strategy that uses the naked eye to compare the intensity of color in a colored solution to qualitatively or semi-quantitatively identify substances; hence, it is also known as visual colorimetry. Because color changes can be read by the naked eye, colorimetric biosensing does not require complex and expensive instruments and can be used for point-of-care diagnosis and on-site analysis. In the presence of H₂O₂, the substrate 3,3',5,5'-tetramethylbenzidine (TMB) is catalyzed and oxidized to a deep blue color by a peroxidase-like enzyme. Adding a certain amount of vitamin C (VC) will cause the blue color in the system to fade to some extent; this color change can be used to quantitatively analyze the VC content. However, the peroxidases used are mostly nanomaterials, and their catalytic performance is easily affected by the aggregation and polydispersity of the nanomaterials, which can affect the detection performance to some extent. Detecting VC in a solution system requires ultrasonication to completely disperse the nanomaterials, which is not conducive to the development of portable colorimetric sensors.

[0006] Hydrogels are a class of hydrophilic materials with a three-dimensional network structure, made from natural or synthetic materials. They are porous and contain a large amount of water, making them generally soft. Furthermore, because hydrogels typically use non-biotoxic polymers as components of their internal network, they exhibit high biocompatibility and can directly adhere to human skin or plant surfaces. These advantages make hydrogels a promising candidate for wearable device applications. Summary of the Invention

[0007] Based on this, we invented a hydrogel sensor made of NH2-BDC-FeCu MOF with peroxidase-like activity. By combining the color change of the bimetallic MOF and TMB with the good enrichment effect of the hydrogel itself, it can meet the detection requirements of fruits with different VC contents and achieve a wider detection range and a lower detection limit than in general solution systems.

[0008] This invention aims to provide an NH2-BDC-FeCu MOF hydrogel sensor that combines high accuracy, high sensitivity, and a wide measurement range. The hydrogel sensor has a simple fabrication process, low cost, and achieves rapid quantitative detection of vitamin C.

[0009] This invention is achieved through the following specific technical solutions:

[0010] The preparation method of the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity includes the following steps:

[0011] Step 1: Preparation of NH2-BDC-FeCu MOF material:

[0012] FeCl3·6H2O and CuCl2·2H2O were dissolved in N,N-dimethylformamide DMF, and this solution was denoted as solution A.

[0013] Dissolve 2-aminoterephthalic acid in DMF, and denote the solution as solution B;

[0014] Solution B was added to solution A, along with ethanol. The mixture was stirred until completely dissolved and sonicated. The solution was then added to a reaction vessel for solvothermal reaction. The resulting product was washed with DMF, deionized water, and ethanol, and then dried under vacuum to obtain NH2-BDC-FeCu MOF material.

[0015] Step 2: Fabrication of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity:

[0016] First, the NH2-BDC-FeCu MOF material was ultrasonically dispersed in HAc-NaAc buffer solution. After it was completely dispersed, agarose was added. The mixture was magnetically stirred and heated until the agarose was completely dissolved. Then, the solution was taken out while it was hot and evenly dropped onto the pre-made mold using a pipette. After it cooled to room temperature, a circular hydrogel film was obtained.

[0017] After thoroughly mixing TMB dimethyl sulfoxide solution, H2O2 aqueous solution and HAc-NaAc buffer solution, the mixture was dropped into the hydrogel film. After the film completely changed color, it was removed and the solvent on the surface was wiped off to obtain the discolored hydrogel film, which is the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity.

[0018] In step 1, the ratio of FeCl3·6H2O, CuCl2·2H2O and 2-aminoterephthalic acid is 1-2 mmol: 1-2 mmol: 1 mmol; the solvothermal reaction temperature is 150℃ and the time is 24 h.

[0019] In step 2, the ratio of NH2-BDC-FeCu MOF material, HAc-NaAc buffer solution, and agarose is 3-11 mg: 10 mL: 0.25 g; the heating temperature is 140℃; the material of the pre-made mold is polytetrafluoroethylene; the circular hydrogel film has a diameter of d = 2 cm.

[0020] In step 2, the volume ratio of TMB dimethyl sulfoxide solution, H2O2 aqueous solution, and HAc-NaAc buffer solution is 200 μL: 100 μL: 700 μL; wherein, the concentration of TMB dimethyl sulfoxide solution is 10 mM; the concentration of H2O2 aqueous solution is 10 mM; the concentration of HAc-NaAc buffer solution is 0.1 M, and the pH is 3.

[0021] The application of the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity prepared in this invention for colorimetric detection of vitamin C involves the following steps:

[0022] (1) The NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity prepared above was completely immersed in VC aqueous solutions of different concentrations and allowed to stand until the color completely faded. In order to realize portable biosensing, the RGB values ​​of the color were analyzed using Adobe Photoshop 2021 software; in addition, the photography process was carried out under LED lights to ensure the stability of the ambient light conditions; the hydrogel sensor was photographed under illumination, and the B / (R+G+B) value in the image was read to obtain the linear relationship between B / (R+G+B) as a color parameter and the concentration of VC aqueous solution;

[0023] (2) The NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity is completely immersed in an aqueous solution of VC with unknown concentration. The color parameters of the aqueous solution of VC with unknown concentration are obtained through the same operation. The concentration value of the aqueous solution of unknown VC is obtained by using the linear relationship obtained in step (1).

[0024] In step (1), the concentration range of the VC aqueous solution is 4-4000 μM, and the standing time is 10-15 min.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) The NH2-BDC-FeCu MOF material prepared by the solvothermal method in this invention has superior peroxidase-like activity compared with its monomer.

[0027] (2) The NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity prepared in this invention can achieve sensitive colorimetric detection of VC. Due to the color superposition of the hydrogel material itself and the color of TMB oxide, as well as the good enrichment effect of the hydrogel, a wider linear range is achieved than that in the solution system. In the concentration range of 4 to 4000 μM, the B / (R+G+B) value as a color parameter has a good linear relationship with the logarithm of VC concentration, while the detection limit is as low as 1.33 μM.

[0028] (3) Compared with traditional detection methods, the colorimetric detection method for VC mentioned in this invention has the advantages of simple operation, simple equipment, low detection cost, portability and wearability, and can meet the detection needs of fruits with different VC contents. Attached Figure Description

[0029] Figure 1(A) is a scanning electron microscope image of the NH2-BDC-FeCu MOF material in Example 1; (B) is an X-ray diffraction pattern of the NH2-BDC-FeCu MOF material.

[0030] Figure 2 The image shows the X-ray photoelectron spectrum of the NH2-BDC-FeCu MOF material in Example 1.

[0031] Figure 3 This is a comparison of the peroxidase-like activities of Fe-MOF, Cu-MOF, and NH2-BDC-FeCu MOF materials.

[0032] Figure 4 A schematic diagram of the construction of a hydrogel sensor.

[0033] Figure 5 The linear curve for the detection of VC aqueous solution in the concentration range of 4–4000 μM is shown. Detailed Implementation

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these embodiments.

[0035] Example 1:

[0036] (1) Preparation of NH2-BDC-FeCu MOF material:

[0037] 1 mmol CuCl2·2H2O (170.5 mg) and 1 mmol FeCl3·6H2O (270.3 mg) were dissolved in N,N-dimethylformamide solvent (7 ml); in another flask, 1 mmol (181.15 mg) of 2-aminoterephthalic acid was dissolved in 7 ml DMF, and the resulting solution was added to the above metal solution, followed by 1 ml of ethanol. The mixture was stirred at room temperature for 30 min, sonicated for 20 min, and then transferred to a reaction vessel for solvothermal reaction. The mixture was heated at 150 °C for 24 h. The resulting product was washed with DMF, deionized water, and ethanol, respectively. The resulting solid product was placed in a vacuum drying oven and dried at 80 °C for 12 h to obtain NH2-BDC-FeCu MOF material.

[0038] like Figure 1 A is a scanning electron microscope image of NH2-BDC-FeCu MOF material. The image shows that the main morphology of NH2-BDC-FeCu MOF material is a typical rod-shaped octahedral structure with pointed ends and small MOF particles attached to the surface. Figure 1The image B is the XRD pattern of the NH2-BDC-FeCu MOF material. The test results show that the (002), (101), (102), (103), (200), (202), (204), and (302) phases exhibit significant reflections at 2θ = 9.2° and 10.2°, and weak reflections at 2θ = 16.5°, 18.7°, 19.3°, 20.5°, 25.7°, and 28.1°, which are in good agreement with the standard reference peaks of simulated NH2-MIL-88B(Fe). The absence of Cu-related peaks is due to their low content.

[0039] Figure 2 The XPS spectra of the NH2-BDC-FeCu MOF material in Figure A show that there are five main elements in the MOF, including Fe, Cu, C, N and O. The XPS spectrum of C 1s, as shown in Figure B, has four peaks at 284.8 eV (C=C), 285.32 eV (CN), 286.2 eV (CO), and 288.98 eV (C=O), originating from the organic ligands present in the NH2-BDC-FeCu MOF. In Figure C, N 1s has two peaks at 399.40 eV and 400.22 eV, corresponding to the CN bond and the -NH2 group, respectively. The XPS spectrum of O 1s, as shown in Figure D, has peaks at 531.13 eV, 532.06 eV, and 533.05 eV, corresponding to the Fe-O, CO, and OC=O bonds, respectively. The XPS spectrum of Fe, as shown in Figure E, has peaks at 715.82 eV and 728.62 eV, respectively, corresponding to the Fe-O, CO, and OC=O bonds, respectively. 3+ 2p 3 / 2 and Fe 3+ 2p 1 / 2 Related to Fe, 712.17 eV and 725.60 eV are respectively related to Fe 2+ 2p 3 / 2 and Fe 2+ 2p 1 / 2 The XPS spectrum of Cu, as shown in Figure F, indicates that 932.98 eV and 949.17 eV belong to Cu. 0 934.04 eV and 953.39 eV belong to Cu 2+ This indicates the successful synthesis of the material.

[0040] from Figure 3 It can be seen that the addition of Cu enhances the peroxidase-like activity of Fe-MOF.

[0041] (2) Fabrication of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity:

[0042] 7 mg of NH₂-BDC-FeCu MOF material was ultrasonically dispersed in 10 mL of HAc-NaAc buffer solution (0.1 M, pH 3). After complete dispersion, the solution was transferred to a round-bottom flask, and 0.25 g of agarose was added. The mixture was heated at 140 °C and magnetically stirred until completely dissolved. Then, while still hot, 600 μL of the solution was added to a mold, and air bubbles were removed. The mold was allowed to cool naturally in air to obtain a circular hydrogel film (d = 2 cm).

[0043] TMB was dissolved in dimethyl sulfoxide to prepare a TMB dimethyl sulfoxide solution with a concentration of 10 mM.

[0044] Hydrogen peroxide (H2O2) was diluted in deionized water to prepare an aqueous solution of H2O2 with a concentration of 10 mM.

[0045] A mixture of 200 μL TMB dimethyl sulfoxide solution, 100 μL H2O2 aqueous solution, and 700 μL HAc-NaAc buffer solution (0.1 M, pH 3) was thoroughly mixed and then dropped into the hydrogel film. After the film underwent complete color change, it was removed, and the solvent on the surface was wiped dry, resulting in the colored hydrogel film, which is the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity. The specific operation is as follows... Figure 4 As shown.

[0046] Detection: VC detection and color recognition

[0047] The purchased vitamin C was continuously diluted in distilled water to prepare aqueous solutions of vitamin C at different concentrations, ranging from 4 to 4000 μM. This included the following steps:

[0048] (1) The above-mentioned NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity was completely immersed in aqueous solutions of VC of different concentrations. After reacting thoroughly for 10 minutes, the solution on the surface was wiped off, and a picture was taken using a smart device. To achieve portable biosensing, the RGB values ​​of the colors were analyzed using Adobe Photoshop 2021 software. In addition, the picture taking process was carried out under LED lights to ensure the stability of the ambient light conditions. The hydrogel sensor after reaction was photographed under light, and the RGB values ​​in the image were read.

[0049] (2) Subsequently, the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity was completely immersed in an aqueous solution of VC with unknown concentration. The color parameters of the aqueous solution of VC with unknown concentration were obtained through the same operation. The concentration value of the unknown aqueous solution of VC was obtained by using the linear relationship between the known color parameters and the concentration of the aqueous solution of VC.

[0050] like Figure 5As shown, using the normalization method, B / (R+G+B) was taken as the color parameter. The color parameter B / (R+G+B) showed a good linear relationship with the concentration of the VC aqueous solution. The entire linearity was divided into two segments: 4-1000 μM and 1000-4000 μM. The linear equations for the two segments were Y = -1.8373 × 10⁻⁶ and -1.8373 × 10⁻⁶, respectively. -4 X+0.4185(R 2 =0.994) and Y = -3.07×10 -5 X+0.2638(R 2 =0.988), and the detection limit is 1.33 μM.

[0051] Example 2:

[0052] Step (1) is the same as step (1) in Example 1.

[0053] (2) Fabrication of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity:

[0054] 5 mg of NH₂-BDC-FeCu MOF material was ultrasonically dispersed in 10 mL of HAc-NaAc buffer solution (0.1 M, pH 3). After complete dispersion, the solution was transferred to a round-bottom flask, and 0.25 g of agarose was added. The mixture was heated at 140 °C and magnetically stirred until completely dissolved. Then, while still hot, 600 μL of the solution was poured into a mold, and air bubbles were removed. The mold was allowed to cool naturally in air to obtain a circular hydrogel film (d = 2 cm).

[0055] TMB was dissolved in dimethyl sulfoxide to prepare a TMB dimethyl sulfoxide solution with a concentration of 10 mM.

[0056] Hydrogen peroxide (H2O2) was diluted in deionized water to prepare an aqueous solution of H2O2 with a concentration of 10 mM.

[0057] A mixture of 200 μL TMB solution, 100 μL H2O2 aqueous solution, and 700 μL HAc-NaAc buffer solution (0.1 M, pH 3) was thoroughly mixed and then dropped into the hydrogel film. After the film underwent complete color change, it was removed, and the solvent on the surface was wiped dry, yielding the color-changing hydrogel film. This is the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity. The specific operation is as follows... Figure 4 As shown.

[0058] Example 3:

[0059] Step (1) is the same as step (1) in Example 1.

[0060] (2) Fabrication of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity:

[0061] 9 mg of NH₂-BDC-FeCu MOF material was ultrasonically dispersed in 10 mL of HAc-NaAc buffer solution (0.1 M, pH 3). After complete dispersion, the solution was transferred to a round-bottom flask, and 0.25 g of agarose was added. The mixture was heated at 140 °C and magnetically stirred until completely dissolved. Then, while still hot, 600 μL of the solution was poured into a mold, and air bubbles were removed. The mold was allowed to cool naturally in air to obtain a circular hydrogel film (d = 2 cm).

[0062] TMB was dissolved in dimethyl sulfoxide to prepare a TMB dimethyl sulfoxide solution with a concentration of 10 mM.

[0063] Hydrogen peroxide (H2O2) was diluted in deionized water to prepare an aqueous solution of H2O2 with a concentration of 10 mM.

[0064] A mixture of 200 μL TMB solution, 100 μL H2O2 aqueous solution, and 700 μL HAc-NaAc buffer solution (0.1 M, pH 3) was thoroughly mixed and then dropped into the hydrogel film. After the film underwent complete color change, it was removed, and the solvent on the surface was wiped dry, yielding the color-changing hydrogel film. This is the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity. The specific operation is as follows... Figure 4 As shown.

Claims

1. A method for preparing an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity, characterized in that, Includes the following steps: (1) Preparation of NH2-BDC-FeCu MOF material: FeCl3·6H2O and CuCl2·2H2O were dissolved in N,N-dimethylformamide DMF, and this solution was denoted as solution A. Dissolve 2-aminoterephthalic acid in DMF, and denote the solution as solution B; Solution B was added to solution A, along with ethanol. The mixture was stirred until completely dissolved and sonicated. The solution was then added to a reaction vessel for solvothermal reaction. The resulting product was washed with DMF, deionized water, and ethanol, and then dried under vacuum to obtain NH2-BDC-FeCu MOF material. (2) Fabrication of an NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity: The NH2-BDC-FeCu MOF material was ultrasonically dispersed in HAc-NaAc buffer solution. After it was completely dispersed, agarose was added. The mixture was magnetically stirred and heated until the agarose was completely dissolved. The solution was then taken out while hot and evenly dropped onto a pre-made mold using a pipette. After it cooled to room temperature, a circular hydrogel film was obtained. After thoroughly mixing TMB dimethyl sulfoxide solution, H2O2 aqueous solution and HAc-NaAc buffer solution, the mixture was dropped into the hydrogel film. After the film changed color completely, it was removed and the solvent on the surface was wiped off to obtain the discolored hydrogel film, which is the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity.

2. The preparation method according to claim 1, characterized in that, In step (1), the ratio of FeCl3·6H2O, CuCl2·2H2O and 2-aminoterephthalic acid is 1-2 mmol: 1-2 mmol: 1 mmol; the temperature of the solvothermal reaction is 150℃ and the time is 24 h.

3. The preparation method according to claim 1, characterized in that, In step (2), the ratio of NH2-BDC-FeCu MOF material, HAc-NaAc buffer solution and agarose is 3-11 mg: 10 mL: 0.25 g; the heating temperature is 140 °C.

4. The preparation method according to claim 1, characterized in that, In step (2), the material of the prefabricated mold is polytetrafluoroethylene; the circular hydrogel film d = 2cm.

5. The preparation method according to claim 1, characterized in that, In step (2), the ratio of TMB dimethyl sulfoxide solution, H2O2 aqueous solution, and HAc-NaAc buffer solution is 200 μL: 100 μL: 700 μL, wherein the concentration of TMB dimethyl sulfoxide solution is 10 mM; the concentration of H2O2 aqueous solution is 10 mM; the concentration of HAc-NaAc buffer solution is 0.1 M, and the pH is 3.

6. The preparation method according to any one of claims 1 to 5 yields an NH2-BDC-FeCuMOF hydrogel sensor based on peroxidase-like activity.

7. The use of the NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity as described in claim 6 for colorimetric detection of vitamin C.

8. The use as described in claim 7, characterized in that, Includes the following steps: (1) The NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity was completely immersed in vitamin C aqueous solutions of different concentrations and allowed to stand until the color faded completely. The RGB values ​​of the color were analyzed using Adobe Photoshop 2021 software. The photography process was carried out under LED lights. The hydrogel sensor was photographed under light and the B / (R+G+B) value in the image was read. The linear relationship between B / (R+G+B) as a color parameter and the concentration of vitamin C aqueous solution was obtained. (2) The NH2-BDC-FeCu MOF hydrogel sensor based on peroxidase-like activity is completely immersed in an aqueous solution of vitamin C of unknown concentration. The color parameters of the aqueous solution of vitamin C of unknown concentration are obtained through the same operation. The concentration value of the aqueous solution of unknown vitamin C is obtained by using the linear relationship obtained in step (1).

9. The use as described in claim 8, characterized in that, In step (1), the concentration of vitamin C aqueous solution ranges from 4 to 4000 μM, and the standing time is 10 to 15 min.

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