Application of a Near-Infrared Fluorescent Probe for Rapid Identification of Organic Amines and Its Prepared Sensing Tags in the Detection of Fish Freshness

Abstract

Application of a near-infrared fluorescent probe for rapid identification of organic amines and its prepared sensing label in the detection of fish freshness. The structural formula of the fluorescent probe is as follows: The fluorescent probe has the advantages of a simple synthesis route, near-infrared emission, fast response speed, and dual-channel response of colorimetry and fluorescence. Using this probe to prepare a standard colorimetric card for fish freshness, which is divided into a fresh colorimetric area under sunlight and ultraviolet light, a qualified colorimetric area under sunlight and ultraviolet light, and a spoiled colorimetric area under sunlight and ultraviolet light. The sensing label loaded with this probe combined with the standard colorimetric card can realize real-time monitoring of fish freshness through dual channels of colorimetry and fluorescence, without destroying the sample and complex pretreatment, and the evaluation results are accurate and reliable.

Description

Technical Field

[0001] The present invention relates to an application of a near-infrared fluorescence probe for rapid identification of organic amines and a sensing label prepared therefrom in the detection of fish freshness. Background Art

[0002] Fish products are deeply loved by consumers. However, freshness is a key factor in evaluating the quality of fish. How to effectively evaluate fish freshness is related to the food safety of consumers. Therefore, it is extremely important to study methods for evaluating fish freshness. As early as 2007, methods for real-time detection of fish freshness have been widely emphasized. So far, many effective instruments have been developed, including electronic noses, electronic tongues, etc., which can accurately evaluate fish freshness. However, these instruments are generally expensive, the sample pretreatment is relatively complicated, and the product outer packaging needs to be damaged, etc. The test results are often delayed and cannot monitor the freshness of fish in real time. Therefore, it is particularly important to develop a new non-destructive real-time evaluation method for fish freshness.

[0003] In recent years, the use of colorimetry to detect fish freshness has received extensive attention from researchers. For example, a pH-sensitive dye is applied to the packaging. During the spoilage process of fish, amine vapor is released, which is alkaline. After contacting the dye, the pH of the dye is changed, thereby realizing a color change. This type of method shows the grade of fish freshness through real-time color changes and has great advantages. However, some dyes have insufficient sensitivity, resulting in insignificant color development in the later stage of fish freshness, unable to effectively distinguish between qualified and spoiled changes, or the changes are not significant, causing discrimination errors (such as Anal. Methods, 2020, 12, 1744–1751, Food Research International, 2019, 126, 108604, etc.). Therefore, it is urgent to develop a new sensing method that does not damage ordinary packaging materials and can accurately display fish freshness in real time.

[0004] In recent years, fluorescence analysis has attracted extensive attention due to its advantages such as high sensitivity, rapid response, good selectivity, no need for complex instruments, and real-time detection. In view of the need for food safety detection, it is urgent to develop a near-infrared fluorescence probe for detecting fish freshness. Since the near-infrared fluorescence probe with an emission wavelength in the range of 600 nm to 800 nm is less interfered by background fluorescence and the fluorescence change is more significant, which is more conducive to consumers observing the fluorescence change. Therefore, it is more conducive to developing a probe sensitive to fish freshness, and has broad application prospects. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an application of a near-infrared fluorescence probe for rapid identification of organic amines and a sensing label prepared therefrom in the detection of fish freshness. The probe can perform colorimetric and fluorescence dual responses to various organic amine compounds in a pure water system, with high sensitivity, rapid response time, and near-infrared emission. When the probe is prepared into a sensing label, it can achieve qualitative analysis of fish freshness in the packaging box, without destroying the sample and complex pretreatment, and the results are accurate and reliable, which can be used for non-destructive, rapid and real-time detection of fish freshness.

[0006] The technical solution of the present invention is as follows:

[0007] An application of a near-infrared fluorescence probe for rapid identification of organic amines and a sensing label prepared therefrom in the detection of fish freshness. The structural formula of the fluorescence probe is as follows:

[0008]

[0009] Further, the specific synthesis steps of the fluorescence probe are as follows:

[0010] Using tetrahydrofuran as a solvent, benzopyran derivative DCA-Ap and acetic anhydride are fed in a molar ratio of 1:(1-1.5). The structure of the benzopyran derivative DCA-Ap is Stir at room temperature under nitrogen protection for 3 to 5 hours. After spinning out the solvent, wash with water 3 times, collect the solid, and purify by column chromatography to obtain the fluorescence probe DCA-Apa

[0011] A dual-channel standard colorimetric card for fish freshness prepared from the above fluorescence probe, which is characterized in that: the standard colorimetric card is divided into a natural light colorimetric area and an ultraviolet light colorimetric area. In the upper half area of the colorimetric card, there are a fresh natural light colorimetric area, a qualified natural light colorimetric area, and a spoiled natural light colorimetric area respectively. In the lower half area of the colorimetric card, there are a fresh ultraviolet light colorimetric area, a qualified ultraviolet light colorimetric area, and a spoiled ultraviolet light colorimetric area respectively.

[0012] The specific preparation process of the sensing label is as follows:

[0013] Dissolve 10 mg of the fluorescence probe in 2 mL of absolute ethanol, add 8 mL of deionized water and stir continuously to obtain a probe solution. Then soak the cut circular filter paper in the probe solution, take it out and dry it after overnight to obtain a sensing label for monitoring fish freshness.

[0014] Furthermore, the hue corresponding to the natural light colorimetric area of the fresh product is blue-green, and the hue corresponding to the ultraviolet light colorimetric area of the fresh product is pink fluorescence; the hue corresponding to the natural light colorimetric area of the qualified product is yellow-green, and the hue corresponding to the ultraviolet light colorimetric area of the qualified product is pink-orange fluorescence; the hue corresponding to the natural light colorimetric area of the unqualified product is light yellow-green, and the hue corresponding to the ultraviolet light colorimetric area of the unqualified product is orange fluorescence.

[0015] Application of a dual-channel standard colorimetric card for fish freshness determination in determining fish freshness.

[0016] Application of a dual-channel standard colorimetric card for fish freshness determination in determining fish freshness. The sensing label is pasted inside the package for use, and the sensing label does not come into direct contact with the food. By comparing the color change of the sensing label with the standard colorimetric card, the freshness of the fish is monitored in real time to evaluate the freshness level of the fish.

[0017] Under visible light, a blue-green color of the sensing label indicates freshness, a yellow-green color indicates qualified, and a light yellow-green color indicates unqualified.

[0018] Under ultraviolet light irradiation at 365 nm, when the color of the sensing label is pink fluorescence, it indicates freshness; when the color of the sensing label is pink-orange fluorescence, it indicates qualified; when the color of the sensing label is orange fluorescence, it indicates unqualified.

[0019] Advantages of the present invention:

[0020] (1) The designed and synthesized fluorescent probe has near-infrared emission, is less affected by scattering and fluorescence background interference, has a high quantum efficiency, stable fluorescence signal and obvious change; it can not only respond to a variety of organic amine compounds ultra-fast in a pure water system, with an obvious change in the solution color, and a blue shift in the maximum absorption intensity and a significant quenching of the fluorescence intensity.

[0021] (2) The sensing label prepared from the fluorescent probe can perform colorimetric and fluorescence dual-channel detection. The sensing label, combined with the standard colorimetric card, can monitor the freshness of fish in real time.

[0022] In summary, the designed and synthesized fluorescent probe of the present invention has near-infrared emission, can detect a variety of organic amine compounds ultra-fast, and the sensing label prepared from the probe can perform colorimetric and fluorescence dual-channel detection of fish freshness, with more accurate and reliable qualitative analysis. The sensing label can non-contact and non-destructively monitor the freshness of fish in real time, and can provide effective freshness information for producers, retailers and consumers in a timely manner, having good practical application value. Description of the drawings

[0023] Figure 1 is of the fluorescent probe DCA-Apa of the present invention 11H NMR spectrum;

[0024] Figure 2 is the 13 13C NMR spectrum of the fluorescent probe DCA-Apa of the present invention;

[0025] Figure 3 is the high-resolution mass spectrum of the fluorescent probe DCA-Apa of the present invention;

[0026] Figure 4 is the graph of the change in fluorescence intensity of the fluorescent probe DCA-Apa of the present invention over time after adding diethylamine;

[0027] Figure 5 is the fluorescence emission spectrum of the fluorescent probe DCA-Apa of the present invention before and after the action of organic amines;

[0028] Figure 6 is the ultraviolet absorption spectrum of the fluorescent probe DCA-Apa of the present invention before and after the action of organic amines;

[0029] Figure 7 is the fluorescence emission spectrum of the fluorescent probe DCA-Apa of the present invention after the action with different concentrations of diethylamine;

[0030] Figure 8 is the ultraviolet absorption spectrum of the fluorescent probe DCA-Apa of the present invention before and after the action with different concentrations of diethylamine;

[0031] Figure 9 is the linear relationship between the fluorescence intensity of the fluorescent probe DCA-Apa of the present invention and the concentration of diethylamine;

[0032] Figure 10 is the linear relationship between the absorption intensity of the fluorescent probe DCA-Apa of the present invention and the concentration of diethylamine;

[0033] Figure 11 is the change in fluorescence intensity of the fluorescent probe DCA-Apa of the present invention at different pH values after adding diethylamine;

[0034] Figure 12 is the high-resolution mass spectrum of the fluorescent probe DCA-Apa of the present invention after adding diethylamine, calculated [M-H] -

[0035] = 359.1765, the measured value is 359.1749;

[0036] Figure 13 is the photo of the change in daylight color (top) and fluorescence color (bottom) of the sensing tag prepared by the present invention before and after identifying different organic amines in a simulated amine vapor environment;

[0037] Figure 14It is the TVB-N content of salmon fish meat at 4°C and the color of the corresponding sensing label under natural light and ultraviolet light as the storage time extends.

[0038] Figure 15 It is a standard color comparison card made according to the corresponding relationship between the TVB-N value of fish meat and the color of the sensing label; from left to right on the upper layer of the standard color comparison card are the fresh natural light color comparison area, the qualified natural light color comparison area, and the spoiled natural light color comparison area, and from left to right on the lower layer of the standard color comparison card are the fresh ultraviolet light color comparison area, the qualified ultraviolet light color comparison area, and the spoiled ultraviolet light color comparison area.

[0039] Figure 16 It is the freshness of salmon fish meat determined by the color change of the daylight and ultraviolet light of the sensing label prepared by the present invention during storage with salmon samples at 4°C in combination with the standard color comparison card; the fish meat on the 0th day of storage at 4°C belongs to fresh products, when stored for 4 days, the fish meat belongs to qualified products at this time, and when stored for 8 days, the fish meat belongs to unqualified products. Detailed implementation manners

[0040] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments.

[0041] Example 1

[0042] The specific synthesis steps of the fluorescent probe DCA-Apa are as follows:

[0043]

[0044] Dissolve solid DCA-Ap (359 mg, 1 mmol) in 5 mL of tetrahydrofuran, add acetic anhydride (102 mg, 1 mmol), react at room temperature for 3 hours under nitrogen protection, spin out the solvent and wash with water, and obtain the fluorescent probe DCA-Apa by column chromatography purification (yield 76%); 1 1H NMR spectrum, 13 13C NMR spectrum and mass spectrum are as Figures 1-3 shown.

[0045] 1 1H NMR (400 MHz, CDCl 3 ) δ 8.55 (s, 1H), 7.19 (d, J = 8.6 Hz, 2H), 7.05 (d, J = 8.6 Hz, 2H), 6.89 (d, J = 9.2 Hz, 1H), 6.38–6.28 (m, 3H), 3.35 (q, J = 7.0 Hz, 4H), 2.89–2.83 (m, 2H), 2.75–2.70 (m, 2H), 2.29 (s, 3H), 1.18 (t, J = 7.0 Hz, 6H).

[0046] 13 13C NMR (101 MHz, DMSO-d 6 ) δ 169.79, 159.65, 153.63, 152.29, 150.91, 148.77, 148.04, 134.44, 127.86, 122.76, 122.03, 115.39, 114.23, 110.79, 107.89, 98.21, 56.46, 25.60, 21.31, 19.01, 12.91.

[0047] HRMS (ESI + ) for C 25 H 26 N 2 O 3 [2M + Na] + calcd: 827.3779, found: 827.3720。

[0048] Example 2

[0049] Dissolve solid DCA-Ap (3.59 g, 10 mmol) in 50 mL of tetrahydrofuran, add acetic anhydride (1.23 g, 12 mmol), react at room temperature for 4 hours under nitrogen protection, spin out the solvent, wash with water, and purify by column chromatography to obtain the fluorescent probe DCA-Apa (yield 57%); 1 1H NMR spectrum, 13 13C NMR spectrum and mass spectrum are as Figures 1-3 shown.

[0050] Example 3

[0051] Dissolve solid DCA-Ap (1.80 g, 5 mmol) in 30 mL of tetrahydrofuran, add acetic anhydride (765 mg, 7.5 mmol), react at room temperature for 5 hours under nitrogen protection, spin out the solvent, wash with water, and purify by column chromatography to obtain the fluorescent probe DCA-Apa (yield 62%); 1 1H NMR spectrum, 13 13C NMR spectrum and mass spectrum are as Figures 1-3 shown.

[0052] Example 4

[0053] Dissolve 10 mg of the fluorescent probe in 2 mL of absolute ethanol, add 8 mL of deionized water and stir continuously to obtain a probe solution. Then soak the cut round filter paper in the probe solution, take it out and dry it overnight to obtain a sensing label for monitoring the freshness of fish.

[0054] I. Response Time of Fluorescent Probe DCA-Apa to Organic Amine Compounds

[0055] After adding the amine solution to the solution containing the fluorescent probe, the test solution was immediately shaken manually. About 7 seconds later, the color of the test solution changed significantly (see Figure 4 ), achieving the effect of ultra-fast recognition, laying a foundation for the subsequent preparation of fish freshness sensing labels and realizing rapid real-time detection.

[0056] II. Selectivity of Fluorescent Probe DCA-Apa for Organic Amine Compounds

[0057] A 10 μmol / L solution was prepared by adding the fluorescent probe DCA-Apa solution to 2 mL of pure water for use. Then, 20 μmol / L cyclohexanediamine, diethylamine, n-propylamine, isopropylamine, triethylamine, ethylamine, spermine, cadaverine, putrescine, 2-phenylethylamine, tyramine, tryptamine, and aniline solutions were added respectively, and the changes in their fluorescence intensities were observed. As Figure 5 shown, the fluorescent probe DCA-Apa emits fluorescence at 655 nm. After adding various organic amines, except for aniline, the maximum emission wavelengths of the other 12 organic amine compound solutions all blue-shifted to 610 nm, and under the irradiation of a 365 nm ultraviolet lamp, the fluorescence changed from weak fluorescence to pink or orange fluorescence. The measured UV-visible spectra are as Figure 6 shown. The probe DCA-Apa has a strong absorption at 600 nm. After adding various organic amine compounds, except for aniline, the maximum absorption wavelengths of the other 12 organic amine compounds significantly blue-shifted to 470 nm, and the color change was obvious. The above results indicate that the fluorescent probe DCA-Apa can achieve colorimetric and fluorescence dual-channel recognition of various organic amine compounds in pure aqueous solution, with excellent selectivity.

[0058] III. Titration Test of Fluorescent Probe DCA-Apa for Representative Organic Amine Diethylamine

[0059] Taking diethylamine as an example, the relationships between the fluorescence intensity and UV absorption intensity of 10 μmol / L fluorescent probe DCA-Apa in pure water and the concentration of diethylamine solution were respectively tested. As Figure 7 shown, when the concentration of the added diethylamine solution (0 - 35 times) gradually increased, the maximum emission wavelength of the fluorescent probe DCA-Apa showed a gradient blue shift. When 350 μmol / L of diethylamine solution was added, the fluorescence intensity no longer changed, indicating that it reached a saturated state. As Figure 8 shown, when the concentration of added diethylamine (0 - 35 times) gradually increased, the UV absorption intensity of the probe DCA-Apa gradually decreased, and the maximum absorption wavelength was accompanied by a blue shift. When 350 μmol / L of diethylamine solution was added, the UV absorption intensity no longer changed, indicating that it reached a saturated state. Except for aniline, other organic amines have a similar effect on the UV and fluorescence of the probe DCA-Apa.

[0060] IV. Detection Limit of Fluorescent Probe DCA-Apa for Representative Organic Amine Diethylamine

[0061] Prepare a 10 μmol / L PAL solution of the fluorescent probe with pure water, test the fluorescence intensities of no less than 11 parallel samples, and according to the formula: ∑(X i -X) 2 =(X 1 -X) 2 +(X 2 -X) 2 +……+(X n -X) 2 Find the sum of the squared differences (X i is the fluorescence intensity value of the receptor itself for each measurement, X is the average fluorescence intensity, n is the number of tests, n≥11), and then according to the formula: S = [∑(X i -X) 2 / (n - 1)] 0.5 Find the sensitivity S, and then according to the detection limit formula: Detection limit = 3S / K, where K is the slope of the selected linear part (Note: The straight line is plotted based on the titration, with the ion concentration on the abscissa and the fluorescence intensity on the ordinate), and the detection limit is found to be 9.036×10 - 6 mol / L (see Figure 9 ).

[0062] Based on the test results of the UV titration, plot the points of the straight line to obtain Y = AX + B (A is the slope of the selected linear part, B is the intercept), and according to the formula Detection limit = 10 -A / B , with the log of the diethylamine concentration on the abscissa and the ratio of (maximum absorption intensity - absorption intensity) to (maximum absorption intensity - absorption intensity value) on the ordinate. When Y = 0, the obtained value is the detection limit. After calculation, the UV detection limit is 2.162×10 -5 mol / L (see Figure 10 ), which indicates that this probe can detect diethylamine at a relatively low concentration in aqueous solution, has high sensitivity, and has good potential for practical applications.

[0063] V. pH Range for Detecting Organic Amine Compounds by Fluorescent Probe DCA-Apa

[0064] The influence of pH on the detection of organic amine compounds was explored. Taking diethylamine as an example, the fluorescence intensities of DCA-Apa under different pH conditions are as Figure 11As shown (Note: The ordinate is the ratio of the fluorescence intensities at 610 and 655 nm), the probe DCA-Apa has a low ratio in the pH range of 2 - 8, indicating that the fluorescence change of the probe is not significant in weakly acidic, neutral, and weakly basic conditions, and it has good stability. After adding diethylamine solution to the probe, the ratio increases, indicating that the fluorescence intensity at 610 nm is gradually increasing. Combining the significant degree of fluorescence change before and after recognition, we can conclude that in the pH range of 4 - 8, the fluorescence probe DCA-Apa has a significant recognition effect on diethylamine, indicating that the probe has a wide pH applicable range.

[0065] VI. Mechanism of Fluorescent Probe DCA-Apa for Detecting Organic Amines

[0066] We speculate that the mechanism of the fluorescent probe DCA-Apa for recognizing organic amines is as follows:

[0067]

[0068] Different organic amines underwent aminolysis reactions of the ester group with the probe DCA-Apa. The lone pair electrons on the N in the organic amine attacked the carbonyl group, causing the ester group to break and restoring the structure of the precursor compound DCA-Ap. This result was confirmed by testing the high-resolution mass spectrometry of the reaction solution (see Figure 12 ), and a mass spectrometry peak with m / z of 359.1749 was obtained in the high-resolution mass spectrometry, corresponding to the molecular weight of the precursor compound DCA-Ap ([M-H] - The calculated value is 359.1765), indicating that the aminolysis reaction of the ester group did occur. After the acetyl group in the probe DCA-Apa was cut off, the original electron-donating-π-electron-withdrawing structure of the probe DCA-Apa was destroyed, resulting in a significant reduction in the intramolecular charge transfer effect, thereby causing a blue shift in the emission wavelength and a decrease in the absorption intensity.

[0069] VII. Recognition Effect of the Sensing Tag on Organic Amines in a Simulated Environment (a cylindrical glass bottle with a height of 65 mm and a diameter of 18 mm)

[0070] During the spoilage process of fish, some small-molecule volatile organic amines such as triethylamine, n-propylamine, and diethylamine are produced. Detecting small-molecule volatile organic amines can monitor the freshness of fish. To verify whether the fabricated sensing tag has selectivity for volatile organic amines, we placed the sensing tag in the headspace of a 0.5% aqueous solution of volatile organic amines to simulate the environment of fish spoilage and check whether the sensing tag responds to volatile organic amines.

[0071] First, take 2 mL of volatile organic amine with a concentration of 50 mmol / L and add it to 3 mL of distilled water to prepare a 20 mmol / L volatile organic amine solution. Twelve kinds of volatile organic amines such as ethylamine, diethylamine, triethylamine, and n-propylamine were selected as the experimental groups, and pure water was used as the blank control group. The sensing labels of the 12 experimental groups and the blank control group were green under natural light and had no fluorescence under ultraviolet light. After being fumigated with volatile organic amines for 1 hour, under natural light, the colors of the sensing labels of the 12 experimental groups all changed to different colors, and under ultraviolet light, they all showed a decrease in pink fluorescence or changed to orange (see Figure 13 ), and there was no change in the blank control group. This indicates that the sensing label has good colorimetric and fluorescence dual responses to these 12 kinds of volatile organic amines such as ethylamine, diethylamine, triethylamine, and n-propylamine, indicating that the sensing label has the potential to detect the freshness of fish.

[0072] VIII. Preparation of the Standard Colorimetric Card for the Sensing Label

[0073] To prepare the standard colorimetric card, we need to monitor the changes in the natural light color and the color under fluorescent lamp irradiation of the sensing label during the process of fish meat from fresh to spoiled. We selected salmon fish meat as the experimental object, peeled the salmon fish meat, divided the fish meat into small pieces of 5 - 6 g each, placed them in disposable round transparent plastic petri dishes respectively, put the sensing label at the headspace of the petri dish lid, tightened the lid, and stored it in a 4°C refrigerator. The TVB-N content of the salmon fish meat was detected once every 24 hours, and natural light photos and fluorescence photos of the sensing label were collected. The data obtained are as Figure 14 shown. The TVB-N content of fresh salmon fish meat showed an overall upward trend starting from the initial 6.06 ± 2.13 mg / 100 g. The TVB-N content reached 16.93 ± 2.13 mg / 100 g on the 4th day, and then began to increase rapidly, reaching 30.13 ± 1.40 mg / 100 g on the 8th day, while the acceptable limit of TVB-N is 30 mg / 100 g. Therefore, the 8th day of storage of salmon fish meat at 4°C can be regarded as the threshold of storage spoilage.

[0074] According to the regulations in the national standard of the People's Republic of China GB / T 18108-2019 (General Rules for Fresh Seawater Fish), the maximum limit of TVB-N content in seawater fish is 30 mg / 100 g. When the TVB-N value ≤ 15 mg / 100 g, the sample is considered a superior grade product; when 15 mg / 100 g < TVB-N value ≤ 30 mg / 100 g, the sample is considered a qualified product; when the TVB-N value > 30 mg / 100 g, the sample is considered a spoiled product at this time. Based on the measured TVB-N values and the corresponding natural light color and ultraviolet light color photos of the sensing labels, we selected the sensing labels corresponding to TVB-N values of 6.06 ± 2.13 mg / 100 g and 14.66 mg / 100 g, which respectively showed blue-green in natural light and pink fluorescence under ultraviolet light irradiation, as the reference standards for the fresh part in the standard color comparison card. When the sensing label shows one of the above color states, it can be judged that this sample is a fresh product (see Figure 15 in the fresh area). We selected the sensing labels corresponding to TVB-N values of 16.93 ± 2.13 mg / 100 g and 28.86 mg / 100 g, which respectively showed yellow-green in natural light and medium-strength pink-orange fluorescence under ultraviolet light irradiation, as the reference standards for the qualified part in the standard color comparison card. When the sensing label shows one of the above color states, it can be judged that this sample is a qualified product (see Figure 15 in the qualified area). We selected the sensing labels corresponding to TVB-N values of 30.13 mg / 100 g and 33.40 mg / 100 g, which respectively showed light yellow-green in natural light and orange fluorescence under ultraviolet light irradiation, as the reference standards for the spoiled part in the standard color comparison card. When the sensing label shows one of the above color states, it can be judged that this sample is a spoiled product (see Figure 15 in the spoiled area).

[0075] IX. Practical Application of Sensing Labels

[0076] The sensing label was used for the actual monitoring application of the freshness of salmon. Figure 16The figure shows the color change of the sensor tag of salmon at room temperature as the storage time increases. The sensor tag in the newly purchased salmon is blue-green under natural light and pink fluorescence under ultraviolet light, which corresponds to the fresh part in the standard colorimetric card. After testing, the TVB-N value is 7.82mg / 100g, which proves that the fish meat is indeed fresh at this time. After being placed at room temperature for 16 hours, the color of the sensor tag in natural light is yellow-green, and it is a medium-intensity pink-orange fluorescence under ultraviolet light. The color of the sensor tag corresponds to the color of the qualified area in the colorimetric card. At this time, the TVB-N value of the test is 15.7mg / 100g, which proves that the fish meat is indeed within the qualified range. Further increase the storage time. At 30h, the color of the sensor tag in natural light is light yellow-green, and it is orange fluorescence under ultraviolet light. The color of the sensor tag corresponds to the corrupt part in the colorimetric card. At this time, the TVB-N value of the test is 30.6mg / 100g, indicating that the salmon meat at this time does exceed the national standards and cannot be eaten.

[0077] In summary, the sensor tag of the present invention has a simple preparation process, can realize colorimetric and fluorescence dual-channel detection of fish freshness, and the qualitative analysis is more accurate and reliable, whether in the simulated environment or in the application of real fish. In addition, the probe emits near-infrared light and has a fast response speed to organic amines, which is suitable for the development of real-time non-destructive sensor tags, thereby realizing non-contact and non-destructive rapid real-time monitoring of fish freshness, and has good practical application value.

Claims

1. Application of a near-infrared fluorescent probe for rapid identification of organic amines and a sensing label prepared therefrom in detecting the freshness of fish Characterized in that: The structural formula of the fluorescent probe is as follows:

2. Application of a near-infrared fluorescent probe for rapid identification of organic amines and a sensing label prepared therefrom in detecting the freshness of fish according to claim 1 Characterized in that: The specific synthesis steps are as follows: Using tetrahydrofuran as a solvent, the benzopyran derivative DCA-Ap and acetic anhydride are fed in a molar ratio of 1:(1 - 1.5). The structure of the benzopyran derivative DCA-Ap is Stir under nitrogen protection at room temperature for 3 to 5 hours. After spinning out the solvent, wash with water three times, collect the solid, and purify by column chromatography to obtain the fluorescent probe DCA-Apa 3. Application of a near-infrared fluorescent probe for rapid identification of organic amines and a sensing label prepared therefrom in detecting the freshness of fish according to claim 1. The specific preparation process of the sensing label is as follows: Dissolve 10 mg of the fluorescent probe in 2 mL of absolute ethanol, add 8 mL of deionized water and stir continuously to obtain a probe solution. Then immerse the cut circular filter paper in the probe solution, take it out and dry it overnight to obtain a sensing label for monitoring the freshness of seawater fish.

4. Application of a near-infrared fluorescent probe for rapid identification of organic amines and a sensing label prepared therefrom in detecting the freshness of fish according to claim 1. The application includes comparing the color change of the sensing label with a standard colorimetric card Characterized in that: The natural light sensing label of fresh products is blue-green, and the corresponding hue of the ultraviolet light sensing label of fresh products is pink fluorescence; the natural light sensing label of qualified products is yellow-green, and the corresponding hue of the ultraviolet light sensing label of qualified products is pink-orange fluorescence; the natural light sensing label of unqualified products is light yellow-green, and the corresponding hue of the ultraviolet light sensing label of unqualified products is orange fluorescence.

5. Application of a near-infrared fluorescent probe for rapid identification of organic amines and a sensing label prepared therefrom in evaluating the freshness of fish as described in claim 3 6. Application of a near-infrared fluorescent probe for rapid identification of organic amines and a sensing label prepared therefrom in evaluating the freshness of fish according to claim 5 Characterized in that: The sensing label is pasted and used inside the package, and the sensing label does not come into direct contact with food. The freshness of the fish is monitored in real time by comparing the color change of the sensing label with a standard colorimetric card to determine the grade of the fish. Under visible light, a blue-green color of the sensing label indicates that the fish is in a fresh grade, a yellow-green color of the sensing label indicates that the fish is in a qualified grade, and a light yellow-green color of the sensing label indicates that the fish is in a spoiled grade. Under ultraviolet light of 365 nm, when the color of the sensing label is pink fluorescence, it indicates that the fish is in a fresh grade, when the color of the sensing label is medium-strength pink-orange fluorescence, it indicates that the fish is in a qualified grade, and when the color of the sensing label is orange fluorescence, it indicates that the fish is in a spoiled grade.

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