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

Abstract

Disclosed are a nano colorimetric sensor based on natural pigment signal enhancement and a preparation method thereof, the nano colorimetric sensor being a nano colorimetric sensor array formed by nano colorimetric materials, the nano colorimetric materials comprising POEs materials and natural pigments. After 6 POEs materials and 4 natural pigments are respectively self-assembled under magnetic stirring, the nano colorimetric materials with sensitization effect are screened through RGB response values and Euclidean distances, the precursor substance mass ratio is optimized, and finally the sensitization effect is verified. The nano colorimetric sensor has high sensitivity, the colorimetric material is green and environmentally friendly, and can effectively realize rapid quantitative detection of the freshness of aquatic products, and has important practical significance in meeting the needs of consumers for food quality and safety and maintaining market order.

Description

TECHNICAL FIELD

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

[0002] Oysters are recognized as high-yield shellfish around the world and are deeply loved by the majority of people. However, due to the characteristics of high moisture, high protein and high unsaturated fatty acids of oyster meat, it is extremely easy to be affected by bacteria and enzymes during storage or sales, leading to protein decomposition and fatty acid oxidation, producing ammonia and amine alkaline nitrogen substances, and causing food safety problems. With the gradual increase of oyster production and consumer population, the edible safety of oyster meat has attracted more and more attention, and total volatile basic 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 and the like. These methods generally have the disadvantages of strong sample destruction, low detection efficiency and long time consumption, and are not suitable for on-site detection of modern meat processing industry. As a new type of electronic nose, the colorimetric sensor has been widely used in the field of food in recent years. The commonly used colorimetric sensor is mostly composed of porphyrin and its derivatives, which has certain limitations in practical application. First, this kind of colorimetric sensor belongs to organic reagent, and there is still a safety hazard in food detection. Secondly, when the concentration of volatile organic compounds is too low, there is an inevitable cross-response problem when the volatile organic compounds interact with the color-sensitive material, resulting in unobvious color reaction of the color-sensitive material and low sensitivity of the sensor. Therefore, it is of great significance to construct a nano colorimetric sensor with high sensitivity and high safety to detect volatile organic compounds. SUMMARY

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

[0005] According to an aspect of the present application, a nano colorimetric sensor based on natural pigment signal enhancement is provided, which is a nano colorimetric sensor array formed by nano colorimetric material, the nano colorimetric material including POFs material and natural pigment, the POFs material including ZIF-8, MIL-53(Al), NH2-UIO-66, COF-10, TPB-DMTP-COF and COF-V, and the six POFs materials are self-assembled with the natural pigment to form the nano colorimetric material. The POFs material used in the present application includes metal organic framework (MOF) and covalent organic framework (COF), the MOF including ZIF-8, MIL-53(Al) and NH2-UIO-66, and the COF including COF-10, TPB-DMTP-COF and COF-V, and the above POFs have the characteristics of regular pore, large specific surface area and adjustable framework structure, and are suitable scaffolds for storing and releasing gas, and the target volatile organic compounds can diffuse on the surface and in the pores of the POFs material, thereby generating enrichment effect. The colorimetric material used is natural pigment, which has the characteristics of green environmental protection and high safety, and the natural pigment added in the POFs can form a stable structure, improve the stability of the colorimetric material, enhance the color development of the colorimetric sensor array, and further improve the sensitivity of the sensor.

[0006] Further, the natural pigment includes anthocyanin, alizarin, curcumin and cochineal red pigment. The selected natural pigment is relatively easy to obtain, and has bright color, which can meet the requirements of the nano colorimetric material on transparency and brightness.

[0007] According to a second aspect of the present application, a preparation method of a nano colorimetric sensor based on natural pigment signal enhancement is provided, which specifically includes the following steps:

[0008] S1, synthesizing six POFs materials;

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

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

[0011] S4, performing constant temperature stirring on the mixed solution, cooling to room temperature after reaction, and obtaining nano colorimetric material, which can be stored in a refrigerator at 4℃ under light protection for standby use;

[0012] S5, uniformly distributing the nano colorimetric material on a silica gel plate by using a capillary tube (0.5mm*100mm) to form a nano colorimetric sensor array under a fume hood.

[0013] Further, in the 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 can fully self-assemble.

[0014] Further, the nanosized colorimetric material in the S4 is screened to screen the nanosized colorimetric material with a sensitization effect. Through screening, a nanosized colorimetric material with high sensitivity, high selectivity, and good stability to a target object can be obtained, so as to ensure that the sensor can provide accurate and reliable data.

[0015] Further, the precursor substance mass ratio of the nanosized colorimetric material in the S4 is optimized. Different mass ratios between the natural pigment and the POFs material in the self-assembly process determine the transparency and brightness of the nanosized colorimetric material, and then affect the gray value difference before and after the reaction with the gas molecules, so that the optimization of the precursor substance mass ratio can ensure the accuracy of the detection effect.

[0016] Specifically, the precursor substance 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 nanosized colorimetric material after the self-assembly of the POFs material and the natural pigment can be uniformly distributed on the silica gel plate, as the added mass of the POFs material increases, its concentration also increases, however, the solubility is limited and the capillary diameter is only 0.5 mm (0.5 mm*100 mm), 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, therefore, the selected ratio is also different.

[0017] Specifically, the specific steps of the screening and the precursor substance mass ratio optimization are as follows: the nanosized colorimetric material is uniformly distributed on the substrate to construct a nanometer colorimetric sensor array, and ammonia gas is used as a simulation gas to react with the constructed nanometer colorimetric sensor. Ammonia gas is one of the main sources of total volatile basic nitrogen, and therefore is most suitable as a simulation gas to test the performance of the nanosized colorimetric material.

[0018] Specifically, the nanometer colorimetric sensor array with the optimal detection performance in the S5 is verified for the sensitization effect using an ammonia solution, and the sensitization effect is verified by statistically analyzing the difference in the RGB response difference and the Euclidean distance before and after the nanosizing. Through the two analysis and statistical methods, the sensitization effect can be intuitively and effectively verified.

[0019] Further, the concentration of the ammonia solution includes 500 ppb, 1 ppm, 5 ppm, 10 ppm, 50 ppm, 100 ppm and 500 ppm. The threshold of the volatile gas concentration generated by the spoilage of aquatic products is low, and most of the detected concentrations can only reach the ppb level. The national standard of China stipulates that the TVB-N value of shellfish products such as oysters should not exceed 15 mg / 100g, wherein 1 mg / 100g is converted to ppm as 10 ppm. Therefore, the concentration of the ammonia solution selected corresponds to the threshold of the TVB-N value in the national standard, and the interval is expanded.

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

[0021] (1) Six POFs materials are synthesized in the present application. These materials have the characteristics of large pore size, large specific surface area and adjustable framework structure, and can be used to encapsulate natural pigments with poor stability, thereby improving the detection sensitivity and stability.

[0022] (2) In the present application, natural pigments, i.e. anthocyanins, alizarin, curcumin and cochineal red pigment, are self-assembled with POFs materials, i.e. metal organic frameworks (MOFs) and covalent organic frameworks (COFs), to construct an environmentally friendly, highly safe and highly sensitive nanometer colorimetric sensor.

[0023] (3) The nanometer colorimetric sensor array synthesized in the present application can change color after reacting with total volatile basic nitrogen generated by spoiled oysters, thereby providing an important theoretical basis for realizing the freshness detection of aquatic products.

[0024] (4) Compared with traditional detection methods, the present application does not require sample pretreatment, and the nanometer color-sensitive material used is highly safe and highly sensitive, which has important practical significance in meeting the needs of consumers for food quality and safety and maintaining market order. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments and together with the description serve to explain the principles of the application. Other embodiments and many of the intended advantages of the present application will be readily appreciated as the same becomes better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

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

[0027] Figure 2 The XRD graph of six POFs materials of one specific embodiment of the present application is shown.

[0028] Figure 3 A schematic diagram of the self-assembly of the POFs material and natural pigments of one specific embodiment of the present application is shown.

[0029] Figure 4 A screening result diagram of the natural pigment-based nanosized color-sensitive material with a sensitization effect of one specific embodiment of the present application is shown.

[0030] Figure 5 A precursor substance mass ratio optimization result diagram of the natural pigment-based nanosized color-sensitive material with a sensitization effect of one specific embodiment of the present application is shown.

[0031] Figure 6 A result diagram of the reaction of the natural pigment-based nanosized color-sensitive material with NH3 of one specific embodiment of the present application is shown.

[0032] In the formula, ATCN is anthocyanin, CCM is curcumin, ARS is alizarin, and CCNL is cochineal. DETAILED DESCRIPTION

[0033] The present application will be further described in detail below with reference to the accompanying drawings and examples. It can be understood that the specific embodiments described herein are only used to explain the related application, and are not a limitation on the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0034] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. 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 preparation and sensitization effect verification schematic diagram of the natural pigment signal enhancement-based nanometer colorimetric sensor according to one embodiment of the present application is shown.

[0036] Example 1

[0037] Synthesis of nanosized color-sensitive material

[0038] S101, synthesis of POFs material.

[0039] (1) NH2-UiO-66 was synthesized by solvothermal method. First, 0.08 g of zirconium chloride and 0.06 g of 2-amino terephthalic acid were weighed into a beaker, then 35 mL of DMF solution and 7.63 mL of acetic acid were added in turn; after the mixture was ultrasonicated for 30 min, it was poured into a 100 mL polytetrafluoroethylene reaction kettle liner and placed in a 120 °C oven for 16 h; after the reaction was completed, it was cooled to room temperature, the resulting liquid was washed with anhydrous ethanol by centrifugation three times to remove unreacted chemicals; finally, the resulting material was placed in an oven at 60 °C for 6 h to dry, obtaining a white powder.

[0040] (2) Synthesis of COF-10. First, 2.05 mmol of 4,4'-biphenyldiboronic acid (BPDA) and 1.37 mmol of 2,3,6,7,10,11-hexahydroxytriphenyl (HHTP) were weighed into a 100 mL beaker, then 50 mL of V:V = 1:1 mesitylene and 1,4-dioxane were added; in order to fully dissolve the mixture, it was ultrasonicated for 30 min and heated in an 80 °C oven for 3 days; after the reaction was completed, the powder was filtered and washed with acetone, then activated for 2 days to remove unreacted chemicals; finally, the resulting 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-diformaldehyde (DMTA), 3.0 mL of 1,4-dioxane, 3.0 mL of mesitylene, and 1 mL of 3M acetic acid were added in turn into a 50 mL beaker; after the mixture was ultrasonicated to dissolve, it was stirred at room temperature for 3 days to obtain a yellow precipitate; after the reaction was completed, it was washed with methanol by centrifugation three times, and finally the resulting material was dried at 80 °C overnight.

[0042] (4) Synthesis of spherical COF-V 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 into different beakers, and 5 mL of acetonitrile solution was added to each; after ultrasonication to fully dissolve, 0.4 mL of 12M acetic acid was added to each; after shaking well, the two were mixed, and finally a yellow precipitate was obtained after standing at room temperature for 3 days; after the reaction was completed, it was washed with tetrahydrofuran and ethanol by centrifugation three times, and dried at 80 °C overnight.

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

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

[0045] S102, synthesis of nanosized color-sensitive material

[0046] A certain amount of POFs material and natural pigment were weighed and dissolved in an appropriate amount of DMF and anhydrous ethanol, respectively, and ultrasonic treatment was performed for 30 min to ensure complete dissolution. Then the two were mixed to ensure that the final concentration of 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 350 rpm for 2 h to obtain a nanosized color-sensitive material. After the reaction was completed, it was cooled to room temperature and stored in a refrigerator at 4°C in the dark for standby. At the same time, a solution with a final concentration of 2 mg / mL of natural pigment was prepared without adding POFs material, which was used as a non-nanosized color-sensitive material.

[0047] Figure 3 The above is a schematic diagram of the self-assembly process of natural pigments and POFs materials. The less stable natural pigments are encapsulated inside the POFs materials to prepare a nanosized color-sensitive material with high stability and high sensitivity.

[0048] Example 2

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

[0050] S201, the color-sensitive materials before and after nanosizing in Example 1 were evenly distributed on a silica gel plate using a capillary (0.5 mm*100 mm) to form a 4*4 colorimetric sensing array;

[0051] S202, ammonia gas volatilized by 10 mM ammonia was used as a simulated gas, and the array was reacted with the ammonia gas in a sealed space for 15 min. The image information of the array before and after the reaction was recorded using a scanner, and finally the RGB values in the image were extracted using Matlab 2022a.

[0052] S203, according to the size of the RGB response difference and the Euclidean distance, the nanosized color-sensitive material with enhanced sensitivity to ammonia was preliminarily screened.

[0053] Figure 4 The screening results of natural pigment-based nanosized color-sensitive materials with sensitization effect are shown in the figure. From the figure, it can be seen that the natural pigment-based nanosized color-sensitive materials with sensitization effect are Figure 4It can be seen that the response signal of the nano-sized color-sensitive material ATCN@MIL-53, CCNL@MIL-53, CCM@COF-10 and ATCN@TPB-DMTP-COF to ammonia is enhanced compared with the non-nano-sized color-sensitive material, and there is a significant difference. While the nano-sized color-sensitive material ARS@TPB-DMTP-COF has an enhancement effect, the error line is high, indicating that the stability of the pigment before and after nanoization is poor.

[0054] Example 3

[0055] Optimization of mass ratio of precursor of nano-sized color-sensitive material

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

[0057] S302, dissolve the POFs material and the natural pigment in appropriate amount of DMF and anhydrous ethanol respectively, and ultrasonic treat for 30 min to make them fully dissolved; then mix them, ensure the final concentration of natural pigment in the mixed solution is 2 mg / mL; react the mixed solution in a magnetic stirring water bath at 40℃, 350 rpm for 2h, get the nano-sized color-sensitive material;

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

[0059] S304, use the ammonia gas volatilized by 10mM ammonia water as a simulation gas, react the array with the ammonia gas in a closed space for 15 min, get the precursor mass ratio optimization result by statistical analysis of Euclidean distance before and after nanoization.

[0060] Figure 5 The precursor mass ratio optimization result of natural pigment-based nano-sized color-sensitive material with sensitization effect is shown, single factor variance analysis shows P<0.05, therefore finally select ATCN and MIL-53 with mass ratio of 1:2, CCM and COF-10 with mass ratio of 1:2, CCNL and MIL-53 with mass ratio of 1:1, and ATCN and TPB-DMTP-COF with mass ratio of 1:0.5 to prepare nano-sized color-sensitive material, which is used for the design of array for subsequent analysis.

[0061] Example 4

[0062] Verification of signal enhancement of nano colorimetric sensor detection

[0063] S401, respectively using nanometer color-sensitive material ATCN@MIL-53, CCNL@MIL-53, CCM@COF-10 and ATCN@TPB-DMTP-COF, 2*4 nanometer colorimetric sensor array NCS is prepared;

[0064] S402, respectively, 500 ppb, 1 ppm, 5 ppm, 10 ppm, 50 ppm, 100 ppm and 500 ppm concentration of ammonia solution is prepared;

[0065] S403, the nanometer colorimetric sensor array is placed in a closed space with 7 different concentrations of ammonia solution for reaction, and each concentration gradient is repeated 7 times.

[0066] Figure 6 The results of the reaction of natural pigment-based nanometer color-sensitive materials with sensitizing effect and NH3 are shown, and from the Euclidean distance statistical results in the figure, compared with un-nanometer color-sensitive materials ATCN, CCM and CCNL, the loudness signals of nanometer color-sensitive materials ATCN@MIL-53, CCM@COF-10 and CCNL@MIL-53 after reaction with ammonia are obviously increased, while the signal intensity of ATCN@TPB-DMTP-COF is weaker than that of un-nanometer ATCN when the ammonia concentration is 50 ppm.

[0067] The specific embodiments of the present application are described above, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0068] In the description of the present application, it is understood that the wording 'comprising' does not exclude the presence of elements or steps not listed in the claims. The simple fact that certain measures are recorded in mutually different dependent claims does not mean that the combination of these measures cannot be used for improvement. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A method for fabricating a nanocolorimetric sensor based on signal enhancement of natural pigments, characterized in that, Specifically, the following steps are included: S1. Synthesize 6 types of POFs materials; S2. Dissolve the POFs material and the natural pigment in N,N-dimethylformamide solution and anhydrous ethanol, respectively, to obtain solution A and solution B. S3. Mix the solution A and the solution B to obtain a mixture, wherein the concentration of the natural pigment in the mixture is 2 mg / mL; S4. The mixture is stirred at a constant temperature, and then cooled to room temperature after the reaction to obtain nano-sized color-sensitive material; S5. The nano-sized color-sensitive material is uniformly distributed on a silicone plate to construct a nano-colorimetric sensor array; The nano-sized color-sensitive materials in S4 are screened to identify those with sensitizing effects. The precursor mass ratio of the nano-sized color-sensitive material in S4 is optimized. The nanocolorimetric sensor is a nanocolorimetric sensor array formed by nanoscale colorimetric materials. The nanoscale colorimetric materials include POFs materials and natural pigments. 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 respectively self-assembled with the natural pigments to form the nanoscale colorimetric materials. The natural pigments include anthocyanins, alizarin, curcumin, and cochineal red pigment.

2. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 1, characterized in that, In step S4, the stirring temperature is 40 ℃, the stirring speed is 350 rpm, and the stirring time is 2 h.

3. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 1, 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.

4. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 1, characterized in that, The specific steps of the screening and the optimization of the precursor material mass ratio are as follows: the nano-sized color-sensitive material is uniformly distributed on the substrate to construct a nano-colorimetric sensor array, and ammonia is used as a simulated gas to perform a gas collection reaction with the constructed nano-colorimetric sensor.

5. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 1, characterized in that, The enhancement effect of the nanoscale colorimetric sensor array with optimal detection performance in S5 was verified by using ammonia solution. The enhancement effect was verified by statistically analyzing the difference in RGB response and Euclidean distance before and after nano-sizing.

6. The method for preparing a nanocolorimetric sensor based on natural pigment signal enhancement according to claim 5, 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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