A paper-based sensor based on coumarin-based ionic liquid, its preparation method and application

Abstract

The present invention discloses a paper-based sensor based on coumarin-based ionic liquid, a preparation method thereof and an application. The coumarin-based ionic liquid [P 66614 [7-HDC] is added to ethanol and stirred evenly at room temperature to obtain a mixed solution; a piece of filter paper is laid flat and placed in the mixed solution until it is completely immersed, and then taken out and air-dried to obtain the paper-based sensor; the portable and reusable paper-based sensor prepared by the present invention can be used for specific detection of NH 3 and volatile biogenic amines. By using its high specificity and selectivity, instant and non-destructive visual detection of the freshness of aquatic products is realized.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation and analysis and detection, and specifically relates to a paper-based sensor based on coumarin-based ionic liquid and a preparation method thereof, and is applied to the non-destructive and rapid visual monitoring of the freshness of aquatic products in actual samples. Background Technique

[0002] With the steady development of China's economy, consumers' demand for seafood consumption has been increasing continuously. However, aquatic products are prone to deterioration and spoilage during transportation due to improper storage conditions. Therefore, rapid and effective monitoring of the freshness of aquatic products is an urgent problem to be solved in the aquatic product consumption market. Protein-rich foods, such as seafood and meat, are invaded by microorganisms during food processing and manufacturing, and free amino acids are decomposed, and then converted into biogenic amines through decarboxylase. Biogenic amines are one of the markers of food spoilage. Therefore, the monitoring of biogenic amines is crucial for freshness evaluation.

[0003] There are four methods for evaluating the freshness of aquatic products in national standards, namely sensory evaluation method, microbial index method, K value and total volatile basic nitrogen (TVB-N). However, most of these traditional freshness determination methods are destructive determinations, with complex operations and time-consuming detections, which are contrary to the consumption nature and instant nature of food. In addition, traditional optical instruments judge the spoilage process of aquatic products by detecting changes in fluorescence intensity, but this process is affected by external environmental factors such as temperature, solvent and pH. With the rapid development of characterization instruments, more and more instrumental methods have been used for the monitoring of volatile amines in food, such as liquid chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry and electrophoresis techniques. However, the detection processes of these instruments are time-consuming and have complex pre-treatments, so it is difficult to be widely used in actual detection processes. The edibility and consumability of seafood make it very urgent to design an instant, rapid and non-destructive monitoring method for the freshness of aquatic products.

[0004] As a new type of green solvent, ionic liquid has the advantages of low vapor pressure, high conductivity and good designability, and has been gradually widely used in the fields of organic synthesis, electrochemistry, extraction and separation. In recent years, many researchers have carried out related research on ammonia capture using ionic liquids (ILs). However, there are few reports on the design of fluorescence ionic liquid FIL based on the tunability of ILs to monitor volatile biogenic amines.

[0005] In order to solve the problems of complex pre-treatment, cumbersome operation and long determination time for the detection of the freshness of aquatic products in actual samples, the present invention designs a pH-sensitive fluorescence ionic liquid [P 66614 [7-HDC] for visual monitoring of food freshness. Through the alkaline environment provided by the biogenic amine gas volatilized from food spoilage, [P66614 [7-HDC] exhibits a fluorescence "turn-on" response. In addition, [P 66614 [7-HDC] is prepared into a paper-based substrate by impregnation. For NH 3 , it has good sensitivity, selectivity, anti-interference ability and reversibility in response, providing a new method for instant, non-destructive and visual monitoring of food freshness. Summary of the Invention

[0006] The present invention provides a paper-based sensor based on coumarin-type ionic liquid, a preparation method thereof and an application.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a paper-based sensor based on coumarin-type ionic liquid, and the preparation method is:

[0009] Add coumarin-type ionic liquid into ethanol, stir evenly at room temperature (preferably the stirring time is 1 min) to obtain a mixed solution; take a filter paper and lay it flat in the mixed solution until it is completely immersed (preferably the immersion time is 1 - 5 min), then take it out and air dry (preferably the air drying time is 1 - 2 min) to obtain the paper-based sensor;

[0010] The obtained paper-based sensor has blue fluorescence under ultraviolet light;

[0011] The dosage ratio of the coumarin-type ionic liquid to ethanol is 0.2 - 0.5 (g) : 3 - 15 (mL);

[0012] The chemical formula of the coumarin-type fluorescent ionic liquid is [P 66614 [7-HDC], and the structural formula is as follows:

[0013]

[0014] The paper-based sensor based on coumarin-type ionic liquid prepared by the present invention is placed in NH with different concentrations 3 environment, and the fluorescence of the paper-based sensor will have a fluorescence "turn-on" response and show different degrees of fluorescence enhancement. The higher the environmental concentration of NH 3 , the shorter the time required for the paper-based sensor to have "fluorescence" turn-on. The paper-based sensor of the present invention has reversibility in the detection of NH 3 . When it is placed in an NH 3 environment, the paper-based substrate will show a fluorescence enhancement phenomenon. After being placed in a ventilated environment for 1 - 5 min, the fluorescence of the paper-based sensor will go out again.

[0015] Therefore, the present invention also relates to a paper-based sensor based on coumarin-type ionic liquid in NH 3And its application in the detection of volatile biogenic amines. The paper-based sensor of the present invention shows excellent selectivity for the detection of NH 3 . Moreover, when placed in these volatile biogenic amines such as TMA, diethylamine, putrescine, benzylamine, histamine, ethylamine, pyrrolidine, triethylamine, and morpholine, the paper-based sensor emits bright blue fluorescence, showing an obvious visual detection effect.

[0016] To evaluate the sensing performance of [P 66614 [7-HDC] for NH 3 , titration was carried out on NH 3 at an excitation wavelength of 365 nm, and excitation and emission slit widths of 1 - 20 nm and 1 - 10 nm respectively. As the concentration of NH 3 increases, the fluorescence intensity of [P 66614 [7-HDC] gradually increases. Fluorescence spectral data before and after the reaction were collected. With the concentration of NH 3 as the abscissa and the difference in fluorescence intensity of the [P 66614 [7-HDC] solution before and after the reaction as the ordinate, a standard fitting curve was plotted.

[0017] There is a good linear relationship between the fluorescence intensity and the concentration of NH 3 in the range of 85 to 380 mg / L. The equation can be described as y = 12.77x - 340.25, R 2 = 0.9967; the detection limit of NH 3 is 0.3 mg / L. As the concentration of NH 3 increases, the fluorescence enhancement of [P 66614 [7-HDC] within the same time becomes more and more significant, gradually changing from dim blue fluorescence to dazzling bright blue fluorescence.

[0018] By placing the [P 66614 [7-HDC] solution before the reaction in the actual environment to be measured, after standing for 3 - 60 s for reaction, collecting the fluorescence spectral data after the reaction, and substituting it into the standard fitting curve, the concentration information of NH 3 in the actual environment to be measured can be obtained.

[0019] The excitation wavelength of the coumarin-based fluorescent ionic liquid [P 66614 [7-HDC] of the present invention is 365 nm, and the emission wavelength is 378 - 550 nm.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention designs and uses a paper-based sensor based on an ionic liquid-based fluorescent probe. Utilizing its high specificity and selectivity, it realizes the instant and non-destructive visual detection of the freshness of aquatic products. The paper-based sensor shows excellent selectivity for the detection of NH3 The response is rapid, reversible, and has good anti-interference ability. This ionic liquid can be loaded on filter paper by impregnation. After contacting NH 3 , it shows a fluorescence "turn-on" response from dark blue to bright blue, achieving the purpose of portable and real-time detection of biogenic amines. The paper-based sensor based on hydroxycoumarin ionic liquid has good selectivity, sensitivity, and reusability, providing a new method for visual monitoring of the freshness of aquatic products.

[0022] In the present invention, the fluorescent ionic liquid [P 66614 [7-HDC] is used as a fluorescent / colorimetric probe, and low-concentration NH 3 is used as the analyte. Through the specific binding of NH 3 with [P 66614 [7-HDC], the fluorescence of the probe is enhanced. Quantitative analysis is carried out according to the linear curve fitted with the difference in fluorescence intensity before and after the reaction as the ordinate and the NH 3 concentration as the abscissa, realizing the accurate recognition and quantitative detection of NH 3 in the actual environment. At the same time, [P 66614 [7-HDC] is prepared into the paper matrix to obtain a portable and reusable paper-based intelligent label for specific detection of NH 3 and volatile biogenic amines. Description of the Drawings

[0023] Figure 1 Figure is the visualization photo of [P 3 [7-HDC] after reaction at different NH 66614 concentrations (0 ppm, 64 ppm, 100 ppm, 141 ppm, 230 ppm, 355 ppm, 470 ppm) in Example 1 taken under ultraviolet light.

[0024] Figure 2 Figure is the fluorescence emission spectrum of [P 3 [7-HDC] after reaction at different NH 66614 concentrations (9 ppm, 19 ppm, 28 ppm, 34 ppm, 41 ppm, 60 ppm, 90 ppm, 135 ppm) in Example 1.

[0025] Figure 3 Figure shows the fluorescence change trend with the difference in fluorescence intensity (ΔF) of [P 3 [7-HDC] before and after reaction with NH 66614 as the ordinate and the NH 3 concentration (0 - 500 ppm) as the abscissa. The inset shows the linear relationship between ΔF and the NH 3 concentration (85 - 380 ppm).

[0026] Figure 4 In which, a is the fluorescence reaction of [P 66614 [7-HDC] to ammonia and other organic amines in water (10 -3 M); excitation wavelength, 440 nm; b is the fluorescence image of [P 66614 [7-HDC] in EtOH / H 2 O solution and other organic amines (trimethylamine, diethylamine, putrescine, benzylamine, histamine, ethylamine, pyrrolidine, triethylamine and morpholine).

[0027] Figure 5 is the fluorescence image of [P 66614 [7-HDC] in Example 1 when using EtOH / H 2 O as the solvent, and the paper-based image in the presence of other coexisting substances. 1. Blank; 2. Ammonium hydroxide; 3. n-Hexane; 4. Toluene; 5. Tetrahydrofuran; 6. Acetonitrile; 7. N,N-Dimethylformamide; 8. Ethylene glycol; 9. Methanol; 10. Ethyl acetate; 11. Toluene.

[0028] Figure 6 In which, a is the preparation process of the portable [P 66614 [7-HDC] paper-based sensor in Example 1; b is the image of the [P 66614 [7-HDC] paper-based sensor before and after being exposed to NH 3 under visible light and ultraviolet light.

[0029] Figure 7 is the fluorescence "turn-on" response time of the [P 66614 [7-HDC] paper-based sensor in different concentrations of ammonia gas in Example 1.

[0030] Figure 8 In which, a is the image record of the [P 66614 [7-HDC] paper-based sensor in Example 1 for monitoring the freshness of shrimp samples stored under different conditions; b is the response time of the [P 66614 [7-HDC] paper-based sensor to spoiled shrimp at -16 °C; c is the graph showing the change of the TVBN value of shrimp samples under different storage conditions over time. Detailed implementation manners

[0031] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments only, and the following content should not be understood as a limitation to the scope of protection of the claims of the present invention.

[0032] The chemical reagents and solvents used in the examples are all analytically pure. The fluorescence spectrum measurement conditions are that the excitation wavelength is 365 nm, the emission wavelength is 378-550 nm, and the excitation and emission slit widths are 5 nm and 5 nm respectively.

[0033] Example 1: Ionic liquids as colorimetric / fluorescent probes for low-concentration NH 3 The specific steps of detection include:

[0034] (1) Fluorescent / colorimetric probes for NH 3 Gas detection:

[0035] Dissolve 0.0322 g of ionic liquid in 50 mL of ethanol to prepare a 1 mM stock solution. 3 atmosphere, let it stand for 20 seconds, and take a visual image under UV light, such as Figure 1 When the excitation wavelength is 365nm, the excitation and emission slit widths are 5nm and 5nm respectively, the ionic liquid after the reaction is diluted 10 times with deionized water, and then the fluorescence spectrum data is collected. The results are as follows Figure 2 shown.

[0036] from Figure 1 You can see [P 66614 ][7-HDC] appears dark blue under 365nm UV light. 3 As the concentration increases, the blue fluorescence gradually increases. Figure 2 It can be seen that the fluorescence spectrum also shows the same changes, [P 66614 The fluorescence of ][7-HDC] increases with the NH 3 Increases with the increase of concentration.

[0037] (2) Drawing of standard curve

[0038] Before and after reaction [P 66614 The difference in fluorescence intensity of ][7-HDC] is the vertical axis, and NH 3 The results of quantitative analysis are shown in Figure 2. Figure 3 As shown. 3 When the concentration is 85-380 ppm, the equation obtained by linear fitting is y=12.77x-340.25, (R 2 =0.9967).

[0039] (3)[P 66614 Response of ][7-HDC] to biogenic amines

[0040] Take a series of 100uL 10 -4 M biogenic amine solution, 10 -4M ammonia aqueous solution and blank solution were respectively added to 900 μL of 3×10 -6 M [P 66614 [7-HDC] ethanol solution. After [P 66614 [7-HDC] ionic liquid contacted with TMA, diethylamine, putrescine, benzylamine, histamine, ethylamine, pyrrolidine, ammonia water, triethylamine and morpholine, [P 66614 [7-HDC] fluorescence intensity increased significantly, as Figure 4 shown.

[0041] (4) [P 66614 [7-HDC] response to common organic solvents

[0042] A series of 100 μL organic solvents, 10 -4 M ammonia aqueous solution and blank solution were respectively added to 900 μL of 3×10 -6 M [P 66614 [7-HDC] ethanol solution. After [P 66614 [7-HDC] ionic liquid contacted with n-hexane, toluene, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, ethylene glycol, methanol, ethyl acetate and dichloromethane, almost no "turn-on" response was observed, as Figure 5 shown.

[0043] (5) [P 66614 [7-HDC] was prepared into a paper-based sensor

[0044] Take a 25 cm 3 petri dish, add 0.3 g of [P 66614 [7-HDC] ionic liquid to 10 mL of ethanol, and stir for 1 min at room temperature. Take a 20 cm×30 cm Beimu qualitative filter paper and lay it flat in the petri dish until the solution is completely immersed. The immersion time is 2 min, then take it out and air dry for 2 min to obtain a paper-based sensor containing [P 66614 [7-HDC], as Figure 6 shown in (a). Under visible light, the color of the [P 66614 [7-HDC] paper-based sensor did not change significantly before and after contacting NH 3 ; under an ultraviolet lamp (λ ex = 365 nm), the [P 66614 [7-HDC] paper-based sensor showed a fluorescence "turn-on" response 1 - 36 s after contacting NH 3 and returned to its original state within 1 - 5 min in a ventilated environment, as Figure 6 shown in (b).

[0045] (6) [P 66614[7-HDC] Paper-based Sensor's Response Time to NH 3 and Record the response time of the sensor to NH

[0046] by visual observation under ultraviolet light. The paper-based sensor responds rapidly to NH 3 . The time required to monitor 39 mg / L NH 3 is less than 36 s. When the concentration of NH 3 reaches 442 mg / L, the response time is less than 1 s, as shown in 3 Figure 7 .

[0047] (7) [P 66614 [7-HDC] Paper-based Sensor's Monitoring of Shrimp Freshness

[0048] According to the national standard method, the TVBN content of fresh white shrimp is 5.3 mg / 100 g. After 6 h at 25 °C, it increases to 14.2 mg / 100 g. The corresponding color of [P 66614 [7-HDC] is positive blue. At this time, the shrimp has slight spoilage but is still within the edible range. After storing for 10 h, TVBN reaches 30.8 mg / 100 g, and spoilage has occurred, making it inedible. After storing for 1 day, the TVBN content increases to 102.1 mg / 100 g, and the color of [P 66614 [7-HDC] is sky blue. At this time, the white shrimp emits a foul smell of spoilage and has completely deteriorated and is inedible. After storing at 4 °C for 6 h, the TVBN content of the white shrimp is 7.2 mg / 100 g, which is relatively fresh, and the corresponding fluorescence color of the paper-based sensor is darker. After 1 day, the TVBN content increases to 15.2 mg / 100 g, and the white shrimp is in a slightly rotten state, while the corresponding color of the [P 66614 [7-HDC] paper-based sensor is positive blue. After storing at 4 °C for 2 days, the TVBN content is 28.4 mg / 100 g, and the white shrimp has spoiled. The fluorescence color of the [P 66614 [7-HDC] paper-based sensor is light blue, and it is no longer edible. The TVBN content after storing at -16 °C for 5 days is 14.2 mg / 100 g, and the color of [P 66614 [7-HDC] is positive blue, indicating that the white shrimp has slight spoilage but is still edible, as shown in Figure 8 .​

Claims

1. Application of a paper-based sensor based on coumarin-type fluorescent ionic liquid in the detection of NH 3 and volatile biogenic amines; The preparation method of the paper-based sensor based on coumarin-type fluorescent ionic liquid is as follows: Add the coumarin-type fluorescent ionic liquid into ethanol, stir evenly at room temperature to obtain a mixed solution; take a piece of filter paper and lay it flat in the mixed solution until it is completely immersed, and then take it out and air-dry to obtain the paper-based sensor; The chemical formula of the coumarin-based fluorescent ionic liquid is [P 66614 [7-HDC], and the structural formula is shown as follows:

2. The application according to claim 1, characterized in that, in the preparation method of the paper-based sensor based on coumarin-type fluorescent ionic liquid, the dosage ratio of the coumarin-type fluorescent ionic liquid to ethanol is (0.2 - 0.5 g):(3 - 15 mL).

3. The application according to claim 1, characterized in that, in the preparation method of the paper-based sensor based on coumarin-type fluorescent ionic liquid, the immersion time of the filter paper in the mixed solution is 1 - 5 min.

4. The application according to claim 1, characterized in that, the volatile biogenic amines are TMA, diethylamine, putrescine, benzylamine, histamine, ethylamine, pyrrolidine, triethylamine, morpholine.

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