A gelatin-based deep eutectic gel sensor and its preparation and application

Abstract

This invention relates to the field of gel sensor technology, and in particular to a gelatin-based deep eutectic gel sensor and its preparation and application. The invention first involves mixing and reacting a gelatin solution with an activator, a stabilizer, and 4-carboxyphenylboronic acid, followed by post-treatment to obtain 4-carboxyphenylboronic acid-grafted gelatin. Choline chloride and glycerol are mixed to obtain a deep eutectic solvent, serving as the first mixture. Then, the 4-carboxyphenylboronic acid-grafted gelatin is dissolved and mixed with lithium chloride to obtain a second mixture. Finally, the first and second mixtures are mixed and subjected to low-temperature treatment to obtain a colorless, transparent, tough, freeze-resistant, and conductive gelatin-based deep eutectic gel sensor. The gelatin-based deep eutectic gel sensor prepared by this invention through chemical modification and physical cross-linking exhibits good sensitivity, anti-interference, and accuracy in detecting sweet substances, and the preparation process is simple, environmentally friendly, and produces stable gel properties.

Description

Technical Field

[0001] This invention relates to the field of gel sensor technology, and in particular to a gelatin-based deep eutectic gel sensor and its preparation and application. Background Technology

[0002] Sweetness, as one of the five basic tastes, is a core indicator for evaluating food flavor quality, consumer acceptance, and nutritional grade. In the food industry, the accurate determination of sweetness intensity and sweetness profiles is not only related to formula optimization and sugar substitution strategies, but also directly affects the health management of people with hypoglycemia, obese patients, and those with special dietary needs. Traditional sweetness evaluation relies on human sensory evaluation, which has inherent drawbacks such as strong subjectivity, susceptibility to fatigue, and poor reproducibility. While laboratory methods such as high-performance liquid chromatography and electronic tongues offer high precision, they face bottlenecks such as cumbersome pretreatment, expensive equipment, and difficulty in online monitoring. Therefore, developing sweetness sensors that can be implanted in production lines, have rapid response, and are compatible with food systems has become a key technological requirement for achieving real-time quantification and intelligent control of sweetness.

[0003] In recent years, taste sensors have been able to effectively identify tastes such as sour, salty, and umami by loading taste receptors, molecularly imprinted polymers, or specific response units onto conductive substrates. However, due to the electrically neutral nature of most sweet compounds, it is difficult to directly generate electrochemical signals. Furthermore, the taste-sensitive layers of these sensors often use hydrophobic polymers or rigid glassy carbon substrates, resulting in poor interfacial wettability with the complex food matrix, leading to response drift and short lifespan. Therefore, progress in the selective detection of sweet molecules remains slow. Thus, there is an urgent need to develop a sensing material that combines sweetness response performance, excellent mechanical flexibility, and good environmental stability to achieve high sensitivity, wide measurement range, and long-term stable monitoring of sweetness intensity.

[0004] Hydrogels, due to their three-dimensional cross-linked network, elastic modulus matching the soft tissue of the tongue, and tunable ion conduction channels, are considered the soft, moist materials most similar to artificial tongues. However, existing hydrogel sensors still suffer from drawbacks such as low selectivity, poor stability, and short lifespan. Recent studies have shown that gelatin-based deep eutectic hydrogels, through the synergistic effect of gelatin physical cross-linking and deep eutectic solvent hydrogen bonding, can maintain high ionic conductivity from -20 ℃ to 80 ℃. However, no gel material has yet been able to mimic the pleasure derived from the perception of sweet substances by an electronic tongue, and mimicking the human tongue's perception of sweetness remains a significant challenge.

[0005] Therefore, it is crucial to provide a technical solution that can solve the above-mentioned technical problems. Summary of the Invention

[0006] To overcome the drawbacks of traditional biochemical analyzers, chromatographs, and spectrometers, such as cumbersome operation, long processing time, and high equipment cost, and to meet the real-time online detection and monitoring needs of sweet components in practical applications, this invention provides a gelatin-based deep eutectic gel sensor, its preparation, and its application. The gelatin-based deep eutectic gel sensor provided by this invention has advantages such as simple preparation process, fast response speed, high sensitivity, and good biocompatibility, and can adapt to complex sample systems and achieve long-term stable operation.

[0007] The objective of this invention can be achieved through the following technical solutions: The first objective of this invention is to provide a gelatin-based deep eutectic gel sensor, which is obtained by mixing a first mixture of 4-carboxyphenylboronic acid-grafted gelatin and a lithium chloride solution, and then processing the deep eutectic solvent at low temperature. The mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 5~7:1; The mass ratio of the first mixture to the deep eutectic solvent is 1:1~1.5.

[0008] In one embodiment of the present invention, the deep eutectic solvent comprises choline chloride and glycerol in a molar ratio of 1:1.3~1.5; The mass percentage of lithium chloride in the lithium chloride solution is 5-10%.

[0009] In one embodiment of the present invention, the 4-carboxyphenylboronic acid-grafted gelatin is prepared by the following method: Gelatin solution was mixed with activator, stabilizer and 4-carboxyphenylboronic acid and reacted, and then post-treated to obtain 4-carboxyphenylboronic acid-grafted gelatin.

[0010] In one embodiment of the present invention, the activator is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; The stabilizer is N-hydroxysuccinimide; The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4~5:1; The molar ratio of stabilizer, activator and 4-carboxyphenylboronic acid is 1:1~1.5:1.5~2.

[0011] In one embodiment of the present invention, the reaction process is carried out at a temperature of 20-30 °C for 2-3 h. The post-treatment involves sequentially dialysis (7-10 days) and freeze-drying (at -50 ℃ for 3-5 days) of the reacted solution.

[0012] The second objective of this invention is to provide a method for preparing a gelatin-based deep eutectic gel sensor, comprising the following steps: (S1) Mix choline chloride with glycerol to obtain a deep eutectic solvent, which is used as the first mixture; (S2) The gelatin grafted with 4-carboxyphenylboronic acid was dissolved and mixed with lithium chloride to obtain a second mixture; (S3) Mix the first mixture prepared in step (S1) with the second mixture prepared in step (S2) to obtain the gelatin-based deep eutectic hydrogel precursor solution; (S4) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S3) is subjected to low temperature treatment to obtain a gelatin-based deep eutectic hydrogel sensor.

[0013] In one embodiment of the present invention, in step (S1), the temperature is 60~90 ℃ and the time is 1~2 h during the mixing process; In step (S2), the mixing process is carried out at a temperature of 60-70 ℃ for 1-2 h.

[0014] In one embodiment of the present invention, in step (S4), the mass ratio of the first mixture to the second mixture is 1:1 to 1.5; During the mixing process, the temperature is 60~70 ℃ and the time is 1~2 h.

[0015] In one embodiment of the present invention, in step (S5), the temperature during the low-temperature treatment is 0~4 ℃ and the time is 1~2 h.

[0016] The third objective of this invention is to provide an application of a gelatin-based deep eutectic gel sensor in the online detection and monitoring of sweet components.

[0017] The gelatin-based deep eutectic gel sensor prepared by the present invention through chemical modification and physical crosslinking has good sensitivity, anti-interference and accuracy in detecting sweet substances, and the preparation process is simple, environmentally friendly and the prepared gelatin-based deep eutectic gel sensor has stable performance.

[0018] In this invention, the gelatin-based deep eutectic gel sensor allows the detection of the gel current change rate via the IT chronoamperometry (three-electrode method) in an electrochemical workstation to detect the concentration of glucose solution; Specifically, the method for detecting glucose solutions of different concentrations using this gelatin-based deep eutectic gel sensor is as follows: The electrochemical workstation chronoamperometry method is employed, with the IT operating parameters set (DC voltage of 2 V, sampling interval of 0.1 s, and settling time of 2 s). Glucose solutions of different concentrations are dropped onto the gelatin-based deep eutectic gel sensor. The current values ​​of the gel before and after the addition of the glucose solution are recorded at a fixed voltage, and the relative rate of change of current is calculated.

[0019] In the gelatin-based deep eutectic gel sensor provided by this invention, 4-carboxyphenylboronic acid grafted in the gelatin molecule is the main responding group, natural macromolecular gelatin is a porous gel network, lithium chloride is used as a conductive medium, and the deep eutectic solvent composed of choline chloride and glycerol is used as a gel network stabilizer.

[0020] The main interactions in gelatin-based deep eutectic gels are hydrogen bonds and van der Waals forces between gelatin molecules, boronic acid ester bonds formed by phenylboronic acid groups, and hydrogen bonds and van der Waals forces between the deep eutectic system and the gel network. When glucose solution is added, the boronic acid ester bonds originally formed by the phenylboronic acid groups grafted onto the gelatin molecules and other groups are disrupted by the ortho-dihydroxy structures on glucose and other sugar molecules, forming new boronic acid ester bonds. This increases the pore size of the microstructured gel network, expanding the electrolyte transfer channels and promoting the flow of conductive ions in the gelatin-based deep eutectic gel, thus causing a current-enhancing phenomenon.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The gelatin-based deep eutectic gel sensor provided by the present invention can detect glucose solutions of 0.0001 wt% to 1 wt% and has a fast response time (~180 s). (2) The addition of choline chloride / glycerol natural deep eutectic solvent to the gelatin-based deep eutectic gel sensor provided by the present invention helps to increase the hydrogen bond density in the hydrogel and increase the hydrogen bond interaction sites, so that the gelatin-based deep eutectic gel sensor remains flexible and conductive at -24 ℃ and maintains good detection performance when stored at room temperature.

[0022] (3) The preparation method of the gelatin-based deep eutectic gel sensor provided by the present invention has the advantages of simple preparation process and low raw material cost. Attached Figure Description

[0023] Figure 1 These are SEM images of the 4-carboxyphenylboronic acid-grafted gelatin from Example 1 and the gelatin-based deep eutectic gel sensor after adding glucose solution. Figure 2 This demonstrates the specific response of the gelatin-based deep eutectic gel sensor prepared in Example 1 to different flavors. Figure 3 The graph shows the current response of the hydrogel after adding different glucose solutions to the gelatin-based deep eutectic gel sensor prepared in Example 1. Figure 4 The graph shows the change in current change rate Δ (ΔI / I0) as a function of glucose concentration and the fitted curve in the gelatin-based deep eutectic gel sensor prepared in Example 1. Figure 5The image shows the detection results of different sweet compounds by the gelatin-based deep eutectic gel sensor prepared in Example 1. Figure 6 The image shows the sweetness detection results of fresh-cut watermelon by the gelatin-based deep eutectic gel sensor prepared in Example 1. Figure 7 The image shows the sweetness detection results of various real samples by the gelatin-based deep eutectic gel sensor prepared in Example 1. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0025] Unless otherwise specified, all reagents used in the following embodiments are commercially available reagents, and all detection methods and techniques used are conventional detection methods and techniques in the art.

[0026] Example 1 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) A gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days, and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid-grafted gelatin (its SEM image is shown below). Figure 1 As shown, it exhibits a distinct porous structure; this is due to the formation of a complex gel network system by intramolecular / intermolecular hydrogen bonds, van der Waals forces, and chain entanglement during the low-temperature treatment of gelatin chains. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0027] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic gel sensor (which still maintains flexibility and conductivity at -24 °C).

[0028] In use, a gelatin-based deep eutectic gel sensor with a thickness of 1 mm is attached to the gold interdigital electrode.

[0029] Performance testing: ① A 1 wt% glucose solution was added dropwise to the gelatin-based deep eutectic hydrogel sensor. SEM images of the gelatin-based deep eutectic hydrogel before and after the addition of the glucose solution are shown below. Figure 1 As shown; pass Figure 1 It can be observed that the pore size of the hydrogel increases after contact with glucose solution, indicating that the electrolyte transport channels expand and the current change value increases.

[0030] ② The gelatin-based deep eutectic gel sensor prepared in this embodiment was used to detect the responsiveness of each raw material using the IT method of an electrochemical workstation, as detailed below: (A1) Prepare solutions of 1 wt% glucose (sweet), 1 wt% citric acid (sour), 1 wt% sodium chloride (salty), 1 wt% quinine sulfate (bitter), and 1 wt% monosodium glutamate (umami) respectively. (A2) Add 100 μL of the solution obtained in step (A1) to the gelatin-based deep eutectic gel sensor for testing, and calculate the relative rate of change of current (results are shown in Figure 1). Figure 2 (as shown) Test parameters: initial voltage is 2 V, sample test interval is 0.1 s, resting time before test is 2 s, single sample test time is 300 s, test sensitivity is 0.01 V / A; pass Figure 2 It can be observed that among the five basic tastes (sour, sweet, bitter, salty, and umami), this gelatin-based deep eutectic gel sensor exhibits a unique positive current feedback effect for sweetness, enabling specific detection of sweetness.

[0031] ③ The gelatin-based deep eutectic gel sensor prepared in this embodiment was used to detect the responsiveness to sweetness using the IT method of an electrochemical workstation, as detailed below: (A1) Prepare glucose standard solutions with concentrations of 0.0001 wt%, 0.001 wt%, 0.01 wt%, 0.1 wt%, and 1 wt%, respectively; (A2) 100 μL of the glucose standard solution obtained in step (A1) and deionized water (DI) were respectively added to the gelatin-based deep eutectic gel sensor for detection, and the relative rate of change of current was calculated (results are shown in Figure 1). Figure 3 (as shown) Test parameters: initial voltage is 2 V, sample test interval is 0.1 s, rest time before test is 2 s, single sample test time is 0, 50, 100, 150, 200, 250, 300 s respectively, test sensitivity is 0.01 V / A; pass Figure 3 It can be observed that the gelatin-based deep eutectic gel sensor prepared in this embodiment can quantitatively detect sweetness at different concentrations; the minimum threshold for sweetness detection is 0.0001 wt%. Furthermore, the greater the relative rate of change of current, the more pronounced the positive feedback effect of the current.

[0032] ③ The gelatin-based deep eutectic gel sensor prepared in this embodiment was used to detect the responsiveness to sweetness using the IT method of an electrochemical workstation, as detailed below: (A1) Prepare glucose standard solutions with concentrations of 0.0001 wt%, 0.001 wt%, 0.01 wt%, 0.1 wt%, and 1 wt%, respectively; (A2) Add 100 μL of the glucose standard solution obtained in step (A1) to the gelatin-based deep eutectic gel sensor for detection, and calculate the relative rate of change of current (results are shown in Figure 1). Figure 4 (as shown) Test parameters: initial voltage is 2 V, sample test interval is 0.1 s, rest time before test is 2 s, single sample test time is 180, 240, and 300 s respectively, and test sensitivity is 0.01 V / A; pass Figure 4 It can be observed that, explained by the adsorption-dominated process, this process follows the empirical power-law curve of the adsorption isotherm, Δ(Current changes (ΔI / I0)) = aC Glu n C Glu denoted as glucose (Glu), and a and n as adsorption capacity and strength, respectively. The exponents “n” obtained at 180, 240, and 300 s are 0.147, 0.154, and 0.150, respectively, indicating that all exponents are less than 0.5, suggesting that the adsorption of glucose molecules in the deep eutectic gel is favorable: the adsorption isotherm changes rapidly at low concentrations, and saturation ΔI / I0 is reached at 180 s due to the limited number of adsorption sites.

[0033] ④ The gelatin-based deep eutectic gel sensor prepared in this embodiment was used to detect the sweetness responsiveness of different sweet samples using the IT method of an electrochemical workstation, as detailed below: (A1) Prepare 1 wt% glucose solution, 1 wt% sucrose solution, 1 wt% trehalose solution and 1 wt% sodium saccharin solution respectively; (A2) Add 100 μL of the solution obtained in step (A1) to the gelatin-based deep eutectic gel sensor for detection, and calculate the relative rate of change of current (results are shown in Figure 1). Figure 5 (as shown) Test parameters: initial voltage is 2 V, sample test interval is 0.1 s, resting time before test is 2 s, single sample test time is 300 s, test sensitivity is 0.01 V / A; pass Figure 5 It can be observed that this gelatin-based deep eutectic gel sensor can respond to different natural sweeteners.

[0034] ⑤ The gelatin-based deep eutectic gel sensor prepared in this embodiment was used to detect the responsiveness of sweetness in different parts of a fresh-cut watermelon using the IT method on an electrochemical workstation, as detailed below: (A1) Select three test points on fresh-cut watermelon and take 100 μL of watermelon juice at each point; (A2) 100 μL of the watermelon juice obtained in step (A1) was added to the gelatin-based deep eutectic gel sensor for detection, and the relative rate of change of current was calculated (results are shown in Figure 1). Figure 6 (as shown) Test parameters: initial voltage is 2 V, sample test interval is 0.1 s, resting time before test is 2 s, single sample test time is 300 s, test sensitivity is 0.01 V / A; pass Figure 6 It can be observed that the gelatin-based deep eutectic gel sensor reflects its actual response capability to real samples with different sweetness levels by detecting the sweetness of extracts from different parts of fresh-cut watermelon.

[0035] ⑥ The gelatin-based deep eutectic gel sensor prepared in this embodiment was used to detect the responsiveness of beverages and fruits to sweetness using the IT method of an electrochemical workstation, as detailed below: (A1) The following products were selected as samples: Coca-Cola, Coca-Cola Sprite, Anmuxi Original Yogurt, Mengniu Pure Milk, Oriental Leaf Jasmine Tea, Oriental Leaf Black Tea, Nestlé Latte, Nestlé Americano, Strawberry Juice, Pear Juice, Grape Juice, Apple Juice, Sugarcane Juice, Orange Juice, Lemon Juice, and Lemon Slices. If the sample contains pulp or suspended particles, take the clear liquid after centrifugation or filtration; if it is a clear liquid, take the sample directly. (A2) 100 μL of the following products obtained in step (A1) were respectively added to a gelatin-based deep eutectic gel sensor: Coca-Cola, Coca-Cola Sprite, Ambrosial Original Yogurt, Mengniu Pure Milk, Oriental Leaf Jasmine Tea, Oriental Leaf Black Tea, Nestlé Latte, Nestlé Americano, strawberry juice, pear juice, grape juice, apple juice, sugarcane juice, orange juice, and lemon juice. The relative rate of change of current was calculated (results are shown in Figure 1). Figure 7 (as shown) A 3 mm thick lemon slice was flatly attached to a gelatin-based deep eutectic gel sensor for detection, and the relative rate of change of current was calculated (results are shown below). Figure 7 (as shown) Test parameters: initial voltage is 2 V, sample test interval is 0.1 s, resting time before test is 2 s, single sample test time is 300 s, test sensitivity is 0.01 V / A; Sweetness is defined by the formula, and the current response value is converted into sweetness SD (Sweet Degree) = SD = 10^(△I / I0 - 2.897). Figure 7 It can be seen that the gelatin-based deep eutectic gel sensor provided in this embodiment can be well used to evaluate the sweetness of various fruits and beverages, representing the potential of this sweetness sensor as an artificial tongue in sensing real samples.

[0036] Example 2 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0037] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.3) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0038] Example 3 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0039] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.5) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0040] Example 4 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0041] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.1) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0042] Example 5 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0043] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.5) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0044] Example 6 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) A gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 20 °C for 3 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain gelatin grafted with 4-carboxyphenylboronic acid. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.5:2.

[0045] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0046] Example 7 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) A gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 30 °C for 2 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid-grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1:1.5.

[0047] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0048] Example 8 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0049] (S2) Choline chloride and glycerol (molar ratio of choline chloride to glycerol is 1:1.3) were stirred at 60 °C for 2 h and mixed to obtain a deep eutectic solvent, which was used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0050] Example 9 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0051] (S2) Choline chloride and glycerol (molar ratio of choline chloride to glycerol is 1:1.5) were stirred at 90 °C for 1 h and mixed to obtain a deep eutectic solvent, which was used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0052] Example 10 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0053] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 5:1) are placed at 60 °C and stirred for 2 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0054] Example 11 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0055] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 7:1) are placed at 70 °C and stirred for 1 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.3) are placed at 65 °C and stirred for 1.5 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 1.5 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0056] Example 12 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0057] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1) are placed at 60 °C and stirred for 2 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (0 °C, 2 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0058] Example 13 This embodiment provides a method for preparing a gelatin-based deep eutectic gel sensor, including the following steps: (S1) Gelatin solution was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide and 4-carboxyphenylboronic acid at 25 °C for 2.5 h. The resulting solution was dialyzed in deionized water for 7 days and then freeze-dried at -50 °C for 3 days to obtain 4-carboxyphenylboronic acid grafted gelatin. The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4.5:1. The molar ratio of N-hydroxysuccinimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-carboxyphenylboronic acid is 1:1.3:1.7.

[0059] (S2) Choline chloride and glycerol (the molar ratio of choline chloride to glycerol is 1:1.4) are stirred at 70 °C for 1.5 h and mixed to obtain a deep eutectic solvent, which is used as the first mixture. (S3) The 4-carboxyphenylboronic acid-grafted gelatin prepared in step (S1) and 7 wt% lithium chloride solution (the mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 6:1) are placed at 65 °C and stirred for 1.5 h to obtain a second mixture. (S4) The first mixture prepared in step (S2) and the second mixture prepared in step (S3) (the mass ratio of the first mixture to the second mixture is 1:1.5) are placed at 70 °C and stirred for 1 h to obtain gelatin-based deep eutectic hydrogel precursor liquid. (S5) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S4) is subjected to low temperature treatment (4 °C, 1 h) to obtain a gelatin-based deep eutectic hydrogel sensor.

[0060] The gelatin-based deep eutectic gel sensors prepared in Examples 2 to 13 are all capable of online detection and monitoring of sweet components.

[0061] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the interpretation of the present invention, without departing from the scope of the invention, should be within the protection scope of the present invention.

Claims

1. A gelatin-based deep eutectic gel sensor, characterized in that, The mixture was prepared by mixing 4-carboxyphenylboronic acid-grafted gelatin with lithium chloride solution and then processing it with a deep eutectic solvent at low temperature. The mass ratio of 4-carboxyphenylboronic acid-grafted gelatin to lithium chloride is 5~7:1; The mass ratio of the first mixture to the deep eutectic solvent is 1:1~1.

5.

2. The gelatin-based deep eutectic gel sensor according to claim 1, characterized in that, The deep eutectic solvent comprises choline chloride and glycerol in a molar ratio of 1:1.3~1.5; The mass percentage of lithium chloride in the lithium chloride solution is 5-10%.

3. The gelatin-based deep eutectic gel sensor according to claim 1, characterized in that, The 4-carboxyphenylboronic acid-grafted gelatin was prepared by the following method: Gelatin solution was mixed with activator, stabilizer and 4-carboxyphenylboronic acid and reacted, and then post-treated to obtain 4-carboxyphenylboronic acid-grafted gelatin.

4. A gelatin-based deep eutectic gel sensor according to claim 3, characterized in that, The activator is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; The stabilizer is N-hydroxysuccinimide; The mass ratio of gelatin to 4-carboxyphenylboronic acid is 4~5:1; The molar ratio of stabilizer, activator and 4-carboxyphenylboronic acid is 1:1~1.5:1.5~2.

5. A gelatin-based deep eutectic gel sensor according to claim 3, characterized in that, During the reaction, the temperature was 20~30 ℃ and the time was 2~3 h; The post-processing involves sequentially dialysis and freeze-drying the reacted solution.

6. A method for preparing a gelatin-based deep eutectic gel sensor as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (S1) Mix choline chloride with glycerol to obtain a deep eutectic solvent, which is used as the first mixture; (S2) The gelatin grafted with 4-carboxyphenylboronic acid was dissolved and mixed with lithium chloride to obtain a second mixture; (S3) Mix the first mixture prepared in step (S1) with the second mixture prepared in step (S2) to obtain a gelatin-based deep eutectic hydrogel precursor solution; (S4) The gelatin-based deep eutectic hydrogel precursor liquid prepared in step (S3) is subjected to low temperature treatment to obtain a gelatin-based deep eutectic hydrogel sensor.

7. The method for preparing a gelatin-based deep eutectic gel sensor according to claim 6, characterized in that, In step (S1), the mixing process is carried out at a temperature of 60~90 ℃ for 1~2 h. In step (S2), the mixing process is carried out at a temperature of 60-70 ℃ for 1-2 h.

8. The method for preparing a gelatin-based deep eutectic gel sensor according to claim 6, characterized in that, In step (S4), the mixing process is carried out at a temperature of 60-70 ℃ for 1-2 h.

9. The method for preparing a gelatin-based deep eutectic gel sensor according to claim 6, characterized in that, In step (S5), the temperature during the low-temperature treatment is 0~4 ℃ and the time is 1~2 h.

10. The application of a gelatin-based deep eutectic gel sensor as described in any one of claims 1 to 5 in the online detection and monitoring of sweet components.

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