Nano colorimetric sensor based on natural pigment signal enhancement and preparation method thereof

Abstract

The invention discloses a nano colorimetric sensor based on natural pigment signal enhancement and a preparation method thereof, the nano colorimetric sensor is a nano colorimetric sensor array formed by a nano color-sensitive material, and the nano color-sensitive material comprises a POFs material and a natural pigment. After the six POFs materials and the four natural pigments are self-assembled under magnetic stirring, the nanocrystallization color-sensitive material with the sensitization effect is screened through an RGB response value and an Euclidean distance, the mass ratio of precursor substances is optimized, and finally the sensitization effect of the nanocrystallization color-sensitive material is verified. The nanometer colorimetric sensor is high in sensitivity, the color-sensitive material is environmentally friendly, rapid quantitative detection of the freshness of aquatic products can be effectively achieved, and the nanometer colorimetric sensor has important practical significance in meeting the requirements of consumers for food quality and safety and maintaining the market order.

Description

Technical Field

[0001] The present application relates to the technical field of food quality detection, and mainly to a nano colorimetric sensor based on natural pigment signal enhancement and a preparation method thereof. Background Art

[0002] Oysters are recognized as a high-yield shellfish worldwide and are deeply loved by the general public. However, due to the characteristics of high moisture, high protein, and high unsaturated fatty acids, oyster meat is easily affected by bacteria and enzymes during storage or sales, leading to protein decomposition and fatty acid oxidation, producing alkaline nitrogen-containing substances such as ammonia and amines, causing food safety issues. With the gradual increase in oyster production and consumer population, the edible safety of oyster meat has attracted more and more attention. Total volatile alkaline nitrogen (TVB-N) is an important indicator for evaluating the quality of aquatic products.

[0003] At present, the freshness detection of aquatic products mainly includes sensory detection, physical and chemical detection, microbial detection, etc. These methods generally have the disadvantages of strong destructiveness to samples, low detection efficiency and long time consumption, and are not suitable for on-site detection in the modern meat processing industry. As a new type of electronic nose, colorimetric sensors have been widely used in the food field in recent years. Currently, most commonly used colorimetric sensors are composed of porphyrin and its derivatives, which have certain limitations in practical applications: first, this type of colorimetric sensor belongs to organic reagents, and there are still safety hazards in food detection; second, when the concentration of volatile organic compounds is too low, there is inevitably a cross-response problem when interacting with color-sensitive materials, resulting in unclear color development of color-sensitive materials and low sensor sensitivity. Therefore, it is of great significance to construct a highly sensitive and safe nanocolorimetric sensor to detect volatile organic compounds. Summary of the invention

[0004] In view of the problems existing in the prior art, the present application proposes a nanocolorimetric sensor based on natural pigment signal enhancement and a preparation method thereof.

[0005] According to one aspect of the present application, a nanocolorimetric sensor based on natural pigment signal enhancement is proposed, wherein the nanocolorimetric sensor is a nanocolorimetric sensor array formed by nanoscale color-sensitive materials, wherein the nanoscale color-sensitive materials include POFs materials and natural pigments, wherein the POFs materials include ZIF-8, MIL-53(Al), NH2-UIO-66, COF-10, TPB-DMTP-COF and COF-V, and the six POFs materials are respectively self-assembled with the natural pigments to form the nanoscale color-sensitive materials. The POFs materials used in this application include metal organic frameworks (MOFs) and covalent organic frameworks (COFs). MOFs include ZIF-8, MIL-53 (Al) and NH2-UIO-66, and COFs include COF-10, TPB-DMTP-COF and COF-V. The above POFs have the characteristics of regular pores, large specific surface area, and adjustable framework structure. They are suitable supports for storing and releasing gases. The target volatile organic compounds can diffuse on the surface and pores of POFs materials, thereby producing an enrichment effect. The color-sensitive material used is a natural pigment, which has the characteristics of green environmental protection and high safety. Adding natural pigments inside POFs can form a stable structure, improve the stability of the color-sensitive material, enhance the color rendering of the colorimetric sensing array, and thus improve the sensitivity of the sensor.

[0006] Furthermore, the natural pigments include anthocyanin, alizarin, curcumin and cochineal red pigment. The selected natural pigments are relatively easy to obtain and have bright colors, which can meet the requirements of nano-color-sensitive materials for transparency and brightness.

[0007] According to the second aspect of the present application, a method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement is proposed, which specifically comprises the following steps:

[0008] S1, synthesis of 6 POFs materials;

[0009] S2, dissolving the synthesized POFs material and the natural pigment in DMF (N,N-dimethylformamide) solution and anhydrous ethanol, respectively, to obtain solution A and solution B;

[0010] S3, mixing the solution A and the solution B to obtain a mixed solution, wherein the concentration of the natural pigment in the mixed solution is 2 mg / mL;

[0011] S4, stirring the mixed solution at a constant temperature, cooling it to room temperature after the reaction, and obtaining a nano-color-sensitive material, which can be stored in a refrigerator at 4° C. away from light for later use;

[0012] S5. Use a capillary (0.5 mm*100 mm) to evenly distribute the nano-color-sensitive material on a silica gel plate to form a nano-colorimetric sensor array under a fume hood.

[0013] Furthermore, in S4, the stirring temperature is 40° C., the stirring rate is 350 rpm, and the stirring time is 2 h. The selected stirring conditions can ensure that the POFs material and the natural pigment are fully self-assembled.

[0014] Furthermore, the nano-color-sensitive materials in S4 are screened to select the nano-color-sensitive materials with sensitization effect. Through the screening, nano-color-sensitive materials with high sensitivity, high selectivity and good stability to the target can be obtained, ensuring that the sensor can provide accurate and reliable data.

[0015] Furthermore, the mass ratio of precursor materials is optimized for the nano-color-sensitive material in S4. The different mass ratios between natural pigments and POFs materials during the self-assembly process determine the transparency and brightness of the nano-color-sensitive material, which in turn affects the gray value difference before and after the reaction with gas molecules. Therefore, optimizing the mass ratio of precursor materials can ensure the accuracy of the detection effect.

[0016] Specifically, the precursor material includes the natural pigment and the POFs material, and the mass ratio of the natural pigment to the POFs material includes 1:0, 1:0.5, 1:1, 1:2, 1:4, 1:8, 1:12, 1:16 and 1:20. In order to ensure that the nano-color-sensitive material after self-assembly of the POFs material and the natural pigment can be evenly distributed on the silica gel plate, as the mass of the added POFs material increases, its concentration also increases, but the solubility is limited and the capillary diameter is only 0.5mm (0.5mm*100mm), therefore, the maximum ratio selected is 1:20. It should be noted that the solubility of different POFs materials and different natural pigments in the self-assembly process is different, so the selected ratio is also different.

[0017] Specifically, the specific steps of the screening and the optimization of the mass ratio of the precursor materials are as follows: the nano-colorimetric material is evenly distributed on a substrate, a nano-colorimetric sensor array is constructed, and ammonia is used as a simulated gas to perform a gas collection reaction with the constructed nano-colorimetric sensor. Ammonia is one of the main sources of total volatile alkaline nitrogen, and therefore is most suitable as a simulated gas to test the performance of the nano-colorimetric material.

[0018] Specifically, an ammonia solution was used to verify the sensitivity enhancement effect of the nanocolorimetric sensor array with the best detection performance in S5, and the sensitivity enhancement effect was verified by statistically analyzing the difference in RGB response and Euclidean distance before and after nano-scaling. The two analytical statistical methods can intuitively and effectively verify the sensitivity enhancement effect.

[0019] Furthermore, the concentration of the ammonia solution includes 500ppb, 1ppm, 5ppm, 10ppm, 50ppm, 100ppm and 500ppm. The threshold of the concentration of volatile gases produced by the corruption of aquatic products is very low, and most of the detection concentrations rarely reach the ppb level. The Chinese national standard stipulates that the TVB-N value of shellfish products oysters shall not exceed 15mg / 100g, where 1mg / 100g is converted to ppm as 10ppm. Therefore, the selected ammonia solution concentration corresponds to the threshold of the TVB-N value in the national standard and expands the division interval.

[0020] Compared with the prior art, this application has the following beneficial effects:

[0021] (1) This application synthesized 6 POFs materials, which have the characteristics of large pores, large specific surface area, and adjustable framework structure, and can be used to encapsulate natural pigments with poor stability to improve detection sensitivity and stability;

[0022] (2) This application uses natural pigments, namely anthocyanins, alizarin, curcumin and cochineal red pigment, to self-assemble with POFs materials, namely metal organic frameworks (MOFs) and covalent organic frameworks (COFs) to construct an environmentally friendly, highly safe and highly sensitive nanocolorimetric sensor;

[0023] (3) The nanocolorimetric sensor array synthesized in this application can change color after reacting with the total volatile alkaline nitrogen produced by corrupt oysters, providing an important theoretical basis for the detection of freshness of aquatic products;

[0024] (4) Compared with traditional detection methods, this application does not require sample pretreatment and the nano-color-sensitive materials used are highly safe and sensitive, which has important practical significance in meeting consumers' demand for food quality and safety and maintaining market order. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated into and constitute a part of this specification. The accompanying drawings illustrate the embodiments and are used together with the description to explain the principles of the present invention. It will be easy to recognize other embodiments and many expected advantages of the embodiments because they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale with each other. The same reference numerals refer to corresponding similar parts.

[0026] Figure 1 A schematic diagram showing the preparation of a nanocolorimetric sensor based on natural pigment signal enhancement and verification of the sensitization effect according to an embodiment of the present application is shown;

[0027] Figure 2 The XRD diagrams of six POFs materials of a specific embodiment of the present application are shown;

[0028] Figure 3 A schematic diagram showing the self-assembly of a POFs material and a natural pigment according to a specific embodiment of the present application is shown;

[0029] Figure 4 A diagram showing the screening results of natural pigment-based nano-color-sensitive materials with a sensitization effect according to a specific embodiment of the present application is shown;

[0030] Figure 5 A graph showing the optimization result of the mass ratio of precursor substances of a natural pigment-based nano-color-sensitive material with a sensitization effect according to a specific embodiment of the present application is shown;

[0031] Figure 6 A result diagram showing the reaction between a natural pigment-based nano-color-sensitive material with a sensitizing effect and NH3 in a specific embodiment of the present application is shown;

[0032] Among them, ATCN is anthocyanin, CCM is curcumin, ARS is alizarin, and CCNL is cochineal red. DETAILED DESCRIPTION

[0033] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should also be noted that, for ease of description, only the parts related to the relevant invention are shown in the accompanying drawings.

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] Figure 1 A schematic diagram of the preparation of a nanocolorimetric sensor based on natural pigment signal enhancement and verification of the sensitization effect according to an embodiment of the present application is shown.

[0036] Example 1

[0037] Synthesis of nano-color sensitive materials

[0038] S101. Synthesize POFs material.

[0039] (1) NH2-UiO-66 was synthesized by solvothermal method. First, 0.08g zirconium chloride and 0.06g 2-aminoterephthalic acid were weighed into a beaker, and then 35mL DMF solution and 7.63mL acetic acid were added in sequence; after the mixture was ultrasonicated for 30min, it was poured into a 100mL polytetrafluoroethylene reactor liner and placed in a 120℃ oven for reaction for 16h; after the reaction was completed, it was cooled to room temperature, and the obtained liquid was centrifuged and washed three times with anhydrous ethanol to remove unreacted chemical reagents; finally, the obtained material was placed in an oven at 60℃ and dried for 6h to obtain a white powder.

[0040] (2) Synthesis of COF-10. First, 2.05 mmol of 4,4'-biphenyl diboronic acid (BPDA) and 1.37 mmol of 2,3,6,7,10,11-hexahydroxytriphenyl (HHTP) were weighed into a 100 mL beaker, and then 50 mL of mesitylene and 1,4-dioxane with a V:V ratio of 1:1 were added; in order to fully dissolve the mixture, it was ultrasonicated for 30 min and heated in an oven at 80 °C for 3 days; after the reaction, the powder was filtered and washed with acetone, and then activated for 2 days to remove the unreacted chemical reagents; finally, the obtained material was dried at 80 °C for 12 h to obtain a gray powder.

[0041] (3) Synthesis of TPB-DMTP-COF. First, 0.32 mmol of 1,3,5-tris(4-aminophenyl)benzene (TAPB), 0.48 mmol of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTA), 3.0 mL of 1,4-dioxane, 3.0 mL of mesitylene and 1 mL of 3 M acetic acid were added to a 50 mL beaker in sequence; the mixture was ultrasonically dissolved and stirred at room temperature for 3 days to obtain a yellow precipitate; after the reaction was completed, the mixture was centrifuged and washed three times with methanol, and finally the obtained material was dried at 80 °C overnight.

[0042] (4) Spherical COF-V was generated by imine condensation reaction. First, 0.04 mmol of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 0.06 mmol of 1,4-dialdehyde-2,5-divinylbenzene (DVA) were weighed in different beakers, and 5 mL of acetonitrile solution was added respectively; after ultrasonication until they were completely dissolved, 0.4 mL of 12 M acetic acid was added respectively; after thorough shaking, the two were mixed and finally allowed to stand at room temperature for 3 days to obtain a yellow precipitate; after the reaction was completed, the mixture was washed three times by centrifugation with tetrahydrofuran and ethanol, and dried at 80 °C overnight.

[0043] (5) ZIF-8 and MIL-53 were purchased from MacLean Biochemical Co., Ltd. (Shanghai, China).

[0044] Figure 2XRD spectra of six POFs materials are shown. According to relevant references, all six POFs materials have corresponding characteristic diffraction peaks, which indicates that the POFs material with expected performance is successfully prepared or obtained in this embodiment.

[0045] S102, Synthesis of Nano-Color-Sensitive Materials

[0046] A certain amount of POFs material and natural pigment were weighed and dissolved in appropriate amounts of DMF and anhydrous ethanol respectively, and ultrasonic treatment was performed for 30 minutes to fully dissolve them; then the two were mixed to ensure that the final concentration of the natural pigment in the mixed solution was 2 mg / mL; the mixed solution was reacted in a magnetic stirring water bath at 40°C and 350rpm for 2 hours to obtain a nano-sized color-sensitive material; after the reaction was completed, it was cooled to room temperature and stored in a refrigerator at 4°C away from light for later use; at the same time, without adding POFs material, a solution with a final concentration of natural pigment of 2 mg / mL was prepared as a non-nano-sized color-sensitive material.

[0047] Figure 3 This is a schematic diagram of the self-assembly process of natural pigments and POFs materials. The relatively unstable natural pigments are encapsulated inside the POFs material to prepare nano-color-sensitive materials with strong stability and high sensitivity.

[0048] Example 2

[0049] Screening of nano-color-sensitive materials with sensitization effect

[0050] S201, using a capillary (0.5 mm*100 mm) to evenly distribute the color-sensitive material before and after nano-sizing in Example 1 on a silica gel plate to form a 4*4 colorimetric sensor array;

[0051] S202, using ammonia gas volatilized from 10 mM ammonia water as a simulated gas, reacting the array with ammonia gas in a closed space for 15 minutes, using a scanner to record image information of the array before and after the reaction, and finally using Matlab2022a to extract RGB values ​​in the image;

[0052] S203. Preliminarily screen out nano-color-sensitive materials with enhanced sensitivity to ammonia based on the RGB response difference and the Euclidean distance.

[0053] Figure 4 The figure shows the screening results of natural pigment-based nano-color-sensitive materials with sensitization effect. Figure 4It can be seen that the response signals of the nano-scale color-sensitive materials ATCN@MIL-53, CCNL@MIL-53, CCM@COF-10 and ATCN@TPB-DMTP-COF to ammonia are enhanced and significantly different from those of the non-nano-scale color-sensitive materials. Although the nano-scale color-sensitive material ARS@TPB-DMTP-COF has an enhanced effect, the error line is high, indicating that the stability of the pigment before and after nano-scale is poor.

[0054] Example 3

[0055] Optimizing the mass ratio of precursor materials of nano-color-sensitive materials

[0056] S301, according to the diffusibility of the nano-color-sensitive material on the silica gel plate, prepare different combination materials with a mass ratio of natural pigment to POFs material of 1:0, 1:0.5, 1:1, 1:2, 1:4, 1:8, 1:12, 1:16 and 1:20 respectively;

[0057] S302, dissolving the POFs material and the natural pigment in appropriate amounts of DMF and anhydrous ethanol respectively, and ultrasonically treating them for 30 minutes to fully dissolve them; then mixing the two to ensure that the final concentration of the natural pigment in the mixed solution is 2 mg / mL; reacting the mixed solution in a magnetic stirring water bath at 40°C and 350rpm for 2 hours to obtain a nano-color-sensitive material;

[0058] S303, using a capillary (0.5 mm*100 mm) to evenly distribute the nanometer color-sensitive material on the silica gel plate to form a 4*4 nanometer colorimetric sensor array;

[0059] S304, using ammonia gas volatilized from 10 mM ammonia water as a simulated gas, reacting the array with ammonia gas in a closed space for 15 minutes, and obtaining the optimization result of the precursor material mass ratio by statistically analyzing the Euclidean distance before and after nano-sizing.

[0060] Figure 5 The figure shows the optimization results of the mass ratio of precursor substances of natural pigment-based nano-color-sensitive materials with sensitization effect. The one-way analysis of variance shows that P<0.05. Therefore, ATCN and MIL-53 with a mass ratio of 1:2, CCM and COF-10 with a mass ratio of 1:2, CCNL and MIL-53 with a mass ratio of 1:1, and ATCN and TPB-DMTP-COF with a mass ratio of 1:0.5 were finally selected to prepare nano-color-sensitive materials for array design for subsequent analysis.

[0061] Example 4

[0062] Signal enhancement validation for nanocolorimetric sensor detection

[0063] S401, using nano-color-sensitive materials ATCN@MIL-53, CCNL@MIL-53, CCM@COF-10 and ATCN@TPB-DMTP-COF to prepare 2*4 nano-colorimetric sensor array NCS;

[0064] S402, preparing ammonia solutions with concentrations of 500 ppb, 1 ppm, 5 ppm, 10 ppm, 50 ppm, 100 ppm and 500 ppm respectively;

[0065] S403, placing the nanocolorimetric sensor array in a closed space to react with 7 ammonia solutions of different concentrations, and repeating each concentration gradient 7 times.

[0066] Figure 6 The result graph of the reaction between natural pigment-based nano-color-sensitive materials with sensitization effect and NH3 is shown. From the Euclidean distance statistics in the figure, compared with the non-nano-color-sensitive materials ATCN, CCM and CCNL, the loudness signals of the nano-color-sensitive materials ATCN@MIL-53, CCM@COF-10 and CCNL@MIL-53 all increased significantly after reacting with ammonia, while the signal intensity of ATCN@TPB-DMTP-COF after the ammonia concentration reached 50ppm was weaker than that of the non-nano-color-sensitive ATCN.

[0067] The above describes the specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0068] In the description of the present application, it is to be understood that the word 'comprising' does not exclude the presence of elements or steps not listed in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A nanocolorimetric sensor based on natural pigment signal enhancement, characterized in that: The nanocolorimetric sensor is a nanocolorimetric sensor array formed by nano-color-sensitive materials, wherein the nano-color-sensitive materials include POFs materials and natural pigments, and the POFs materials include ZIF-8, MIL-53(Al), NH2-UIO-66, COF-10, TPB-DMTP-COF and COF-V. The six POFs materials are self-assembled with the natural pigments to form the nano-color-sensitive materials.

2. The nanocolorimetric sensor based on natural pigment signal enhancement according to claim 1, characterized in that: The natural pigments include anthocyanin, alizarin, curcumin and cochineal red pigment.

3. A method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement as described in any one of claims 1 to 2, characterized in that: The specific steps include: S1, synthesis of 6 POFs materials; S2, dissolving the POFs material and the natural pigment in DMF solution and anhydrous ethanol, respectively, to obtain solution A and solution B; S3, mixing the solution A and the solution B to obtain a mixed solution, wherein the concentration of the natural pigment in the mixed solution is 2 mg / mL; S4, stirring the mixed solution at a constant temperature, and cooling it to room temperature after the reaction to obtain a nano-color-sensitive material; S5. Evenly distribute the nano-color-sensitive material on a silica gel plate to construct a nano-colorimetric sensor array.

4. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 3, characterized in that: In the S4, the stirring temperature is 40° C., the stirring rate is 350 rpm, and the stirring time is 2 h.

5. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 3, characterized in that: The nanometer color-sensitive materials in S4 are screened to select the nanometer color-sensitive materials with a sensitization effect.

6. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 3, characterized in that: The precursor mass ratio of the nano-sized color-sensitive material in S4 is optimized.

7. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 6, characterized in that: The precursor material includes the natural pigment and the POFs material, and the mass ratio of the natural pigment to the POFs material includes 1:0, 1:0.5, 1:1, 1:2, 1:4, 1:8, 1:12, 1:16 and 1:

20.

8. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 5 or 6, characterized in that: The specific steps of the screening and the optimization of the mass ratio of the precursor materials are as follows: the nanometer color-sensitive material is evenly distributed on a substrate, a nanometer colorimetric sensor array is constructed, and ammonia is used as a simulated gas to perform a gas collection reaction with the constructed nanometer colorimetric sensor.

9. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 3, 5 or 6, characterized in that: The sensitivity enhancement effect of the nanocolorimetric sensor array with the best detection performance in the S5 was verified using an ammonia solution, and the sensitivity enhancement effect was verified by statistically analyzing the difference in RGB response and Euclidean distance before and after nano-scaling.

10. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 9, characterized in that: The concentrations of the ammonia solution include 500 ppb, 1 ppm, 5 ppm, 10 ppm, 50 ppm, 100 ppm and 500 ppm.

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