A bicolour thermosensitive nanogel and a preparation method and application thereof

Abstract

The present application relates to a kind of bicolored temperature-sensitive nanogel and its preparation method and application, the present application nanogel has structural color, and also has the bicolored temperature-sensitive nanogel of fluorescence.The nanogel can not only enhance fluorescence intensity, but also be used to realize detection to the change of temperature.Structural color can amplify fluorescence signal, can be used to accurately adjust the fluorescence intensity of different fluorophores, so that optical device and photoluminescence-based sensor have significant progress in sensitivity, simplicity and stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of gel materials, and particularly relates to a bicolored temperature-sensitive nanogel and a preparation method and application thereof. BACKGROUND

[0002] Colloidal photonic crystals (CPCs) are characterized by the periodic arrangement of self-assembled monodisperse colloidal particles, and have attracted extensive attention due to their unique optical properties. Notably, monodisperse colloidal thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) nanogels undergo reversible volume changes near the lower critical solution temperature (LCST, 32℃) in aqueous media, enabling the polymer chains to respond to temperature fluctuations. This promising CPC development candidate has triggered great interest due to its bright, durable and non-fading color optical properties, representing a key advancement widely applied in various fields, including optical devices, colorimetric sensors and displays.

[0003] Traditional organic fluorescent groups exhibit weak emission or no emission in solid state and aqueous solution due to the aggregation-induced quenching (ACQ) effect. SUMMARY

[0004] In view of the defects of the prior art, the present application aims to provide a bicolored temperature-sensitive nanogel and a preparation method and application thereof.

[0005] The present application provides a bicolored temperature-sensitive nanogel, which is obtained by polymerization of raw materials containing N-isopropylacrylamide NIPAm, N-acryloyl-L-phenylalanine Aphe, N,N'-methylenebisacrylamide BIS, an emulsifier, an initiator and a fluorescent material.

[0006] Preferably, the emulsifier is sodium dodecyl sulfate SDS, the initiator is ammonium persulfate APS, and the fluorescent material has the following structural formula:

[0007]

[0008] The reaction raw materials contain water.

[0009] Preferably, the molar ratio of NIPAm, Aphe and BIS is 85-90% mol: 2-10% mol: 1-5% mol, the mass ratio of the emulsifier to the system deionized water is (0.01wt%-0.10wt%), the mass ratio of the initiator to the system deionized water is (0.01wt%-0.05wt%), and the mass ratio of the fluorescent material to the system deionized water is (0.001wt%-0.006wt%).

[0010] The ratio of the monomers (total amount of NIPAm, Aphe and BIS) to the emulsifier is 10 mol:(0.03-0.08) g.

[0011] Further, the amount of SDS added accounts for 0.01wt%-0.10wt% of the deionized water in the system. In particular, when other conditions remain unchanged, only the content of SDS is changed, which is 0.027wt%, 0.045wt% and 0.073wt% respectively, and the nanogel has different structural colors, which are purple, blue and blue-green respectively.

[0012] Preferably, the preparation of the fluorescent material comprises:

[0013] (1) mixing 4-bromo-1,8-naphthalic anhydride, ethanolamine, solvent, refluxing, purifying to obtain fluorescent intermediate NI1;

[0014] (2) mixing fluorescent intermediate NI1, phenylboronic acid, catalyst, solvent, stirring under nitrogen, then adding Na2CO3 aqueous solution by syringe, reacting, purifying to obtain fluorescent intermediate NI2;

[0015] (3) mixing fluorescent intermediate NI2, triethylamine Et3N, CH2Cl2, cooling to 0℃, dropping acryloyl chloride, stirring at room temperature overnight, purifying to obtain fluorescent material NI3.

[0016] Preferably, in step (1), the ratio of 4-bromo-1,8-naphthalic anhydride, ethanolamine, solvent is 9-12 mmol:9-12 mmol:1-20 mL; the solvent is anhydrous ethanol; the refluxing reaction: the stirring temperature is 70-80℃ under refluxing conditions, and the stirring time is 1-2h.

[0017] In step (1), after the reaction is completed, the mixture is cooled to room temperature, then filtered and recrystallized with anhydrous ethanol to recover the product, cooled to room temperature, recovered by filtration, recrystallized with anhydrous ethanol, and the desired product is dried to obtain off-white solid NI1.

[0018] Preferably, in step (2), the ratio of fluorescent intermediate NI1, phenylboronic acid, catalyst, solvent, Na2CO3 aqueous solution is 1.2-1.6 mmol:2-2.5 mmol:10-20 mg:1-20 mL:0.1-1 mL; the reaction is under N2 atmosphere, the reaction temperature is 50-60℃, and the time is 24-72h; the catalyst is Pd(PPh3)4;

[0019] The purification in step (2) is as follows: after cooling to room temperature, the solvent is removed from the mixture, the product is extracted with dichloromethane, and then the organic phase is dried with anhydrous MgSO4, the solvent is removed by rotary evaporation, and the crude product is purified by column chromatography (CH2Cl2 / PE = 20:1 (v / v)) to obtain NI2 as a yellow solid.

[0020] Preferably, the ratio of the fluorescent intermediate NI2, triethylamine Et3N, CH2Cl2, acryloyl chloride in step (3) is 1.2-1.6 mmol: 2-2.5 mmol: 10-20 mL: 1-2 mmol.

[0021] The purification in step (3) is as follows: the solvent is removed under reduced pressure, and the residue is purified by silica gel (PE / DCM = 20 / 1 (v / v)) chromatography to obtain the desired NI3.

[0022] The preparation of the N-acryloyl-L-phenylalanine Aphe includes: dissolving l-phenylalanine in a NaOH solution, keeping at 0℃ for 5-15 min, then adding acryloyl chloride dropwise, stirring at room temperature for 1-2 h, purification to obtain Aphe; wherein the ratio of l-phenylalanine, NaOH, acryloyl chloride is 5-7 g: 2-4 g: 2-5 mL; the dropwise addition is a constant pressure dropwise addition of acryloyl chloride using a dropper; the purification is as follows: after the reaction is completed, concentrated hydrochloric acid is added to make the pH value reach 2, a white precipitate is obtained and filtered off, and the white powder is washed with water and dried.

[0023] The present application provides a preparation method of any one of the dual-color temperature-sensitive nanogels, comprising:

[0024] N-isopropyl acrylamide NIPAm, N,N'-methylene bisacrylamide BIS, N-acryloyl-L-phenylalanine Aphe, an emulsifier, and water are mixed, stirred, and then the fluorescent material is added after 5-15 min of adding an initiator, polymerization, dialysis, and concentration to obtain the dual-color temperature-sensitive nanogel P(NIPAM-Aphe-NI3).

[0025] The fluorescent material is first dissolved in a solvent and then added.

[0026] Preferably, the stirring is stirring at 60-70℃ for 10-60 min; the polymerization is reaction at 50-80℃ for 3-6 h; and the dialysis is soaking with ultrapure water for 3-7 days, changing the water 2-3 times a day, and the molecular weight cut-off of the dialysis bag used for dialysis is 8000-14000.

[0027] Preferably, the mass concentration after concentration is 3%-7%.

[0028] The concentration is evaporation concentration, and the temperature is 70℃.

[0029] The application provides application of the bicolored temperature-sensitive nanogel in a photoluminescence sensor.

[0030] The P(NIPAM-Aphe-NI3) nanogel obtained by the application is a bicolored structural color and fluorescent nanogel, which not only enhances the fluorescence intensity, but also has a response to temperature.

[0031] The nanogel is studied by Bragg diffraction, and the effectiveness of the slow photon effect on enhancing the fluorescence intensity of different structural color nanogels is proved. The sol-gel transition of the nanogel makes the structural color remain unchanged, and the fluorescence intensity is enhanced with the decrease of the diameter of the nanogel. The principle of realizing the sol-gel transition after heating is that the carboxyl and benzene ring in the Aphe interact with each other, and the aggregation of the polymer chain significantly enhances the fluorescence effect.

[0032] The application provides a bicolored temperature-sensitive nanogel and a preparation method thereof. The bicolored temperature-sensitive nanogel has both structural color and fluorescence, and the emitted fluorescence color is blue-green, and the structural colors are purple, blue and blue-green.

[0033] Advantageous effects

[0034] The application combines the unique NI light-emitting molecule into a cross-linked nanogel polymer network that can self-assemble to generate structural color, and prepares a bicolored temperature-sensitive nanogel that has both structural color and fluorescence. The nanogel not only enhances the fluorescence intensity, but also can be used for detecting the change of temperature. The structural color can amplify the fluorescence signal, and can be used for accurately adjusting the fluorescence intensity of different fluorescent groups, so that the optical devices and the photoluminescence-based sensors have significant progress in sensitivity, simplicity and stability.

[0035] The application obtains the P(NIPA-Aphe-NI3) nanogel by copolymerization of NIPAM, Aphe and NI3, and the nanogel is not only a bicolored material with fluorescence and structural color. In the response to temperature, the sol-gel transition can keep the structural color unchanged, and for the introduced fluorescent material, not only is the fluorescent material changed from a hydrophobic material to a hydrophilic material, but also the fluorescence intensity is enhanced by two times after heating. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The particle size distribution graph and scanning electron microscope morphology (a~c) and the reflection spectrum (d) of the bicolored temperature-sensitive nanogel prepared in Examples 1-3 and Comparative Example 1 are shown in the figure; when other preparation conditions are unchanged, only the content of SDS is changed, and the figure legend respectively represents no SDS (Comparative Example 1), 0.03g SDS (Example 1), 0.05g SDS (Example 2) and 0.08g SDS (Example 3). Figure 2The relative fluorescence intensity (left) and fluorescence enhancement factor (right) of the different blocking band P(NIPA-Aphe-NI3) nanogels of Example 1-3 and Comparative Example 1. When preparing other conditions remain unchanged, only the content of SDS is changed, respectively, no SDS (Comparative Example 1), 0.03 g SDS (Example 1), 0.05 g SDS (Example 2) and 0.08 g SDS (Example 3) are shown in the legend. Figure 3 The relative fluorescence intensity (left) and thermal reversibility (right) of the bicolour thermosensitive nanogel of Example 2 at different temperatures (25-49℃). DETAILED DESCRIPTION

[0037] The application is further described in conjunction with the specific examples. It should be understood that these examples are used to explain the application and are not intended to limit the scope of the application. Furthermore, it should be understood that various modifications and changes can be made to the application by those skilled in the art which are within the scope of the application as taught by the present disclosure. Accordingly, the application is not limited to the examples described herein.

[0038] In step (5) of Example 1-3 and Comparative Example 1, the molar ratio of NIPAM, Aphe and BIS in step (1) is 92%:6%:2%, and the total molar amount is 10 mol; the content of SDS is 0.03 g (Example 1), 0.05 g (Example 2), 0.08 g (Example 3) and no SDS (Comparative Example 1) respectively; the content of APS is 0.05 g.

[0039] Example 1

[0040] (1) Synthesis of monomer Aphe: In a 100 mL round bottom flask, l-phenylalanine (6.2 g) was dissolved in 20 mL NaOH solution (3.2 g) at 0 °C for 15 min. Acryloyl chloride (3.6 mL) was added slowly using a dropping constant pressure. After the addition was complete, it was stirred at room temperature for 2 h, and after the reaction was complete, concentrated hydrochloric acid was added to make the pH value 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried, and the solid phase yield was about 5.3 g, with a yield of 85%.1H NMR (400 MHz, DMSO-d6, d): 12.78 (br. s., 1H), 8.43 (d, J = 8.25 Hz, 1H), 7.26-7.29 (m, 2H), 7.19-7.24 (m, 3H), 6.27 (dd, J = 17.06, 9.90 Hz, 1H), 6.05 (dd, J = 17.33, 1.93 Hz, 1H), 5.58 (dd, J = 10.45, 2.20 Hz, 1H), 4.49-4.54 (m, 1H), 3.10 (dd, J = 13.75, 4.95 Hz, 1H), 2.90 (dd, J = 13.76, 9.90 Hz, 1H).

[0041] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round bottom flask, 4-bromo-1,8-naphthalic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirring at 80 °C under reflux conditions for 2 h. After the reaction was complete, the mixture was cooled to room temperature. Then the product was recovered by filtration and recrystallization with anhydrous ethanol. After cooling to room temperature, it was recovered by filtration and recrystallized with anhydrous ethanol. The desired product was dried to obtain a gray-white solid NI1.1H NMR (400 MHz, DMSO-d6, d): 8.57 (d, J = 7.15 Hz, 1H), 8.54 (d, J = 8.80 Hz, 1H), 8.33 (d, J = 7.70 Hz, 1H), 8.22 (d, J = 7.70 Hz, 1H), 8.00 (t, J = 7.98 Hz, 1H), 4.82 (t, J = 6.05 Hz, 1H), 4.14 (t, J = 6.60 Hz, 2H), 3.63 (q, J = 6.60 Hz, 2H).

[0042] (3) Synthesis of fluorescent intermediate NI2: In a 100 mL round bottom flask, NI1 (500 mg, 1.56 mmol) from step (2), phenylboronic acid (285.65 mg, 2.34 mmol) and Pd(PPh3)4(20 mg) were added to a DMF solution (10 mL) and stirred under N2atmosphere. Then Na2CO3aqueous solution (0.5 mL) was added by syringe. The reaction mixture was heated at 60 °C under N2atmosphere for 72 h. After cooling to room temperature, the solvent was removed from the mixture. The product was extracted with dichloromethane and the organic phase was dried over anhydrous MgSO4. The solvent was removed by rotary evaporation and the crude product was purified by column chromatography (CH2Cl2 / PE = 20:1 (v / v)) to give NI2 as a yellow solid.1H NMR (400 MHz, DMSO-d6, d): 8.55 (d, J = 7.53 Hz, 2H), 8.25 (d, J = 8.41 Hz, 1H), 7.83-7.88 (m, 1H), 7.81 (d, J = 7.53 Hz, 1H), 7.54-7.63 (m, 5H), 4.85 (t, J = 6.02 Hz, 1H), 4.19 (t, J = 6.46 Hz, 2H), 3.65 (q, J = 6.44 Hz, 2H).

[0043] (4) Synthesis of fluorescent material NI3: NI2 (500 mg, 1.58 mmol) from step (2) and Et3N (239.16 mg, 2.36 mmol) were mixed in dry CH2Cl2(20 mL) and cooled to 0 °C in an ice-water bath, then acryloyl chloride (171.12 mg, 1.89 mmol) was added dropwise. The resulting mixture was stirred at room temperature overnight, then the solvent was removed under reduced pressure. The residue was purified by silica gel (PE / DCM = 20 / 1 (v / v)) chromatography to give the desired NI3 in 30% yield.1H NMR (400 MHz, DMSO-d6, d): 8.55-8.58 (m, 2H), 8.25-8.28 (m, 1H), 7.87 (dd, J = 8.25, 7.15 Hz, 1H), 7.82 (d, J = 7.15 Hz, 1H), 7.61-7.64 (m, 2H), 7.57-7.60 (m, 3H), 6.23-6.27 (m, 1H), 6.06-6.12 (m, 1H), 5.89-5.92 (m, 1H), 4.44-4.48 (m, 2H), 4.39-4.43 (m, 2H).

[0044] Structure of fluorescent material NI3:

[0045] (5) Synthesis of the thermosensitive nanogel P(NIPA-Aphe-NI3) with two colors: Under nitrogen atmosphere, the total molar amount was 10 mol, NIPAM was 92% mol, BIS 2% mol, Aphe (6% mol) synthesized in step (1) and SDS (0.03 g) were dissolved in 100 mL deionized water according to the percentage of the total molar mass of the three monomers NIPAM, BIS, and Aphe, and stirred at 70 °C for 30 min in a 250 mL round-bottom flask. Then, an aqueous solution of APS (APS was taken 0.05 g dissolved in 10 mL water) was injected into the flask to initiate polymerization. After 10 min, NI3 (dissolved in DMF (1 mL)) 6 mg in step (4) was added. The polymerization reaction was carried out at 70 °C for 4 h, and then cooled to room temperature. The obtained nanogel was dialyzed against deionized water for 5 days with a dialysis bag (MWCO was 8000-14000 Da) to obtain the thermosensitive nanogel P(NIPA-Aphe-NI3) with two colors. The obtained nanogel was concentrated by heating, and the concentration was 3 wt%.

[0046] Example 2

[0047] (1) Synthesis of monomer Aphe: In a 100 mL round-bottom flask, l-phenylalanine (6.2 g) was dissolved in 20 mL NaOH solution (3.2 g) and kept at 0 °C for 15 min. Acryloyl chloride (3.6 mL) was slowly added using a constant pressure dropper. After the addition was completed, it was stirred at room temperature for 2 h, and after the reaction was completed, concentrated hydrochloric acid was added to make the pH value reach 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried, and the solid-phase yield was about 5.3 g, with a yield of 85%.

[0048] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round-bottom flask, 4-bromo-1,8-naphthalic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirring at 80 °C under reflux conditions for 2 h. After the reaction was completed, the mixture was cooled to room temperature. Then the product was recovered by filtration and recrystallization with anhydrous ethanol. After cooling to room temperature, it was recovered by filtration and recrystallized with anhydrous ethanol. The desired product was dried to obtain a gray-white solid NI1.

[0049] (3) Synthesis of fluorescent intermediate NI2: In a 100 mL round bottom flask, NI1 (500 mg, 1.56 mmol) from step (2), phenylboronic acid (285.65 mg, 2.34 mmol) and Pd(PPh3)4(20 mg) were added to a DMF solution (10 mL) and stirred under N2atmosphere. Then Na2CO3aqueous solution (0.5 mL) was added by syringe. The reaction mixture was heated at 60 °C under N2atmosphere for 72 h. After cooling to room temperature, the solvent was removed from the mixture. The product was extracted with dichloromethane and the organic phase was dried over anhydrous MgSO4. The solvent was removed by rotary evaporation and the crude product was purified by column chromatography (CH2Cl2 / PE = 20:1 (v / v)) to give NI2 as a yellow solid.

[0050] (4) Synthesis of fluorescent material NI3: NI2 (500 mg, 1.58 mmol) from step (2) and Et3N (239.16 mg, 2.36 mmol) were mixed in dry CH2Cl2(20 mL) and cooled to 0 °C in an ice-water bath, then acryloyl chloride (171.12 mg, 1.89 mmol) was added dropwise. The resulting mixture was stirred at room temperature overnight, then the solvent was removed under reduced pressure. The residue was purified by silica gel (PE / DCM = 20 / 1 (v / v)) chromatography to give the desired NI3 in 30% yield.

[0051] (5) Synthesis of bichromatic thermoresponsive nanogel P(NIPA-Aphe-NI3): Under nitrogen atmosphere, NIPAM (92% mol), BIS (2% mol), Aphe (6% mol) synthesized in step (1) and SDS (0.05 g) were dissolved in 100 mL deionized water in a 250 mL round bottom flask with a total molar mass of 10 mol according to the percentage of the total molar mass of the three monomers, NIPAM, BIS, Aphe, and stirred at 70 °C for 30 min. Subsequently, an aqueous solution of APS (APS was taken 0.05 g dissolved in 10 mL water) was injected into the flask to initiate polymerization. After 10 min, NI3 (dissolved in DMF (1 mL)) 6 mg from step (4) was added. The polymerization reaction was carried out at 70 °C for 4 h, then cooled to room temperature. The bichromatic thermoresponsive nanogel P(NIPA-Aphe-NI3) was obtained by dialysis against deionized water in dialysis bags (MWCO 8000-14000 Da) for 5 days. The obtained nanogel was concentrated by heating and the concentration was 3 wt%.

[0052] Example 3

[0053] (1) Synthesis of monomer Aphe: In a 100 mL round bottom flask, l-phenylalanine (6.2 g) was dissolved in 20 mL NaOH solution (3.2 g) and kept at 0 °C for 15 min. Acryloyl chloride (3.6 mL) was added dropwise using a dropping pipette at constant pressure. After the addition was complete, it was stirred at room temperature for 2 h and after the reaction was complete, concentrated HCl was added to bring the pH to 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried, and the solid yield was about 5.3 g with a yield of 85%.

[0054] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round bottom flask, 4-bromo-1,8-naphthalene anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). It was stirred at 80 °C under reflux conditions for 2 h. After the reaction was complete, the mixture was cooled to room temperature. Then the product was recovered by filtration and recrystallization with anhydrous ethanol. It was recovered by filtration after cooling to room temperature and recrystallized with anhydrous ethanol. The desired product was dried to obtain a grayish white solid NI1.

[0055] (3) Synthesis of fluorescent intermediate NI2: In a 100 mL round bottom flask, NI1 (500 mg, 1.56 mmol) from step (2), phenylboronic acid (285.65 mg, 2.34 mmol) and Pd(PPh3)4(20 mg) were added to a DMF solution (10 mL) and stirred under N2atmosphere. Then Na2CO3aqueous solution (0.5 mL) was added by syringe. The reaction mixture was heated at 60 °C under N2atmosphere for 72 h. After cooling to room temperature, the solvent was removed from the mixture. The product was extracted with dichloromethane and then the organic phase was dried with anhydrous MgSO4. The solvent was removed by rotary evaporation and the crude product was purified by column chromatography (CH2Cl2 / PE = 20:1 (v / v)) to obtain NI2 as a yellow solid.

[0056] (4) Synthesis of fluorescent material NI3: Step (2) NI2 (500 mg, 1.58 mmol) and Et3N (239.16 mg, 2.36 mmol) were mixed in dry CH2Cl2(20 mL) and cooled to 0 °C in an ice water bath, then acryloyl chloride (171.12 mg, 1.89 mmol) was added dropwise. The resulting mixture was stirred at room temperature overnight, then the solvent was removed under reduced pressure. The residue was purified by silica gel (PE / DCM = 20 / 1 (v / v)) chromatography to obtain the desired NI3 with a yield of 30%.

[0057] (5) Synthesis of the thermosensitive nanogel P(NIPAM-Aphe-NI3) with two colors: Under nitrogen atmosphere, NIPAM (92% mol), BIS (2% mol), Aphe (6% mol) synthesized in step (1) and SDS (0.08 g) were dissolved in 100 mL deionized water in a 250 mL round-bottom flask with the total molar mass of 10 mol, and stirred at 70 °C for 30 min. Then, an aqueous solution of APS (APS was taken 0.05 g dissolved in 10 mL water) was injected into the flask to initiate polymerization. After 10 min, NI3 (dissolved in DMF (1 mL)) 6 mg in step (4) was added. The polymerization reaction was carried out at 70 °C for 4 h, and then cooled to room temperature. The resulting nanogel was dialyzed against deionized water in a dialysis bag (MWCO 8000-14000 Da) for 5 days to obtain the thermosensitive nanogel P(NIPAM-Aphe-NI3) with two colors. The obtained nanogel was concentrated by heating, and the concentration was 3 wt%.

[0058] Comparative Example 1

[0059] (1) Synthesis of monomer Aphe: In a 100 mL round-bottom flask, l-phenylalanine (6.2 g) was dissolved in 20 mL NaOH solution (3.2 g) and kept at 0 °C for 15 min. Acryloyl chloride (3.6 mL) was slowly added dropwise using a constant pressure dropper. After the addition was completed, it was stirred at room temperature for 2 h, and after the reaction was completed, concentrated hydrochloric acid was added to make the pH value reach 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried, and the solid-phase yield was about 5.3 g, with a yield of 85%.

[0060] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round-bottom flask, 4-bromo-1,8-naphthalic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirring at 80 °C under reflux conditions for 2 h. After the reaction was completed, the mixture was cooled to room temperature. Then the product was recovered by filtration and recrystallization with anhydrous ethanol. After cooling to room temperature, it was recovered by filtration and recrystallized with anhydrous ethanol. The desired product was dried to obtain a gray-white solid NI1.

[0061] (3) Synthesis of fluorescent intermediate NI2: In a 100 mL round bottom flask, NI1 (500 mg, 1.56 mmol) from step (2), phenylboronic acid (285.65 mg, 2.34 mmol) and Pd(PPh3)4(20 mg) were added to a DMF solution (10 mL) and stirred under N2atmosphere. Then Na2CO3aqueous solution (0.5 mL) was added by syringe. The reaction mixture was heated at 60 °C under N2atmosphere for 72 h. After cooling to room temperature, the solvent was removed from the mixture. The product was extracted with dichloromethane and the organic phase was dried over anhydrous MgSO4. The solvent was removed by rotary evaporation and the crude product was purified by column chromatography (CH2Cl2 / PE = 20:1 (v / v)) to give NI2 as a yellow solid.

[0062] (4) Synthesis of fluorescent material NI3: NI2 (500 mg, 1.58 mmol) from step (2) and Et3N (239.16 mg, 2.36 mmol) were mixed in dry CH2Cl2(20 mL) and cooled to 0 °C in an ice-water bath, then acryloyl chloride (171.12 mg, 1.89 mmol) was added dropwise. The resulting mixture was stirred at room temperature overnight, then the solvent was removed under reduced pressure. The residue was purified by silica gel (PE / DCM = 20 / 1 (v / v)) chromatography to give the desired NI3 in 30% yield.

[0063] (5) Synthesis of bichromatic thermoresponsive nanogel P(NIPA-Aphe-NI3): NIPAM (92% mol), BIS (2% mol), Aphe (6% mol) synthesized in step (1) and SDS (not added) were dissolved in 100 mL deionized water in a 250 mL round bottom flask under nitrogen atmosphere with the percentage of the total molar mass of the three monomers being 10 mol, 70 °C stirring for 30 min. Subsequently, an aqueous solution of APS (APS was taken 0.05 g dissolved in 10 mL water) was injected into the flask to initiate polymerization. After 10 min, NI3 (dissolved in DMF (1 mL)) 6 mg in step (4) was added. The polymerization reaction was carried out at 70 °C for 4 h, then cooled to room temperature. The thermoresponsive nanogel P(NIPA-Aphe-NI3) was obtained by dialysis in a dialysis bag (MWCO 8000-14000 Da) against deionized water for 5 days. The obtained nanogel was concentrated at elevated temperature with a concentration of 3 wt%, but no structural color.

[0064] As Figure 1The structural colors of Examples 1-3 and Comparative Example 1 are shown. The hydrodynamic diameters of the nanogels of Examples 1, 2, and 3, measured in aqueous solution, were 353.7 nm, 304.5 nm, and 289.8 nm, respectively, with polydispersity indices (PDI) of 0.089, 0.095, and 0.094, indicating good monodispersity. SEM analysis showed that the nanogels of Examples 1-3 maintained a uniform spherical shape. Depending on the particle size, the structural colors of the nanogels of Examples 1-3 were purple, blue, and blue-green (e.g., cyan, blue, and green). Figure 1 (As shown in d). The characteristic reflection peaks of the nanogels in Examples 1-3 are located at 410 nm, 520 nm, and 580 nm, respectively. With the increase of SDS content, the particle size of the nanogels tends to decrease, and the wavelength of the reflection spectrum tends to blue shift. The Bragg diffraction law can be calculated using the Bragg equation. When no SDS is added, such as the nanogel of Comparative Example 1, there is no structural color and no characteristic reflection peak signal.

[0065] like Figure 2 The fluorescence characteristics of Examples 1-3 and Comparative Example 1 are shown in the figure. Figure 2 The left-middle section shows the fluorescence enhancement of the four nanogels at different stopbands. The fluorescence intensity of the structured colored nanogels in Examples 1-3 is higher than that of the unstructured colored nanogel in Comparative Example 1. At the maximum emission wavelength in Examples 2 and 3, the fluorescence enhancement is 4-fold and 3-fold, respectively, compared to Comparative Example 1. This phenomenon generates a slow photon effect that can be effectively localized within the photonic crystal (PC) structure. The position of the light wave in the structure depends on the photon energy; materials with lower refractive indices exhibit a more pronounced interaction with light at the edge of the blue band in the stopband. The results indicate that incorporating a colloidal photonic crystal structure into fluorescent nanogels is an effective method to improve fluorescence intensity.

[0066] like Figure 3 As shown, the fluorescence intensity of Example 2 and Comparative Example 1 is related to temperature. When the temperature increases from 25°C to 49°C, the emission intensity at 490 nm (eL = 380 nm) increases. Notably, the fluorescence intensity does not change significantly between 25°C and 37°C. However, within the response temperature range of 37°C to 43°C, the fluorescence intensity of the nanogel shows a significant increase, reaching a maximum at 43°C. With further increases in temperature to 49°C, the fluorescence intensity shows a gradually slowing upward trend. Importantly, the fluorescence intensity reaches its maximum value at 49°C, approximately 2.3 times higher than the original intensity at room temperature. Furthermore, the fluorescence intensity of the nanogel in Example 2 shows a linear relationship with temperature in the range of 37°C to 43°C. Figure 3 (Left). Meanwhile, the reversibility of the fluorescence behavior was verified through five temperature change cycles ranging from 25℃ to 49℃. Figure 3Example 2 (right) has good thermal cycle performance. It is worth noting that the comparative example 1 without structural color has no fluorescence response to fluorescence after heating Figure 3 Example 2 (left) indirectly shows that structural color has potential influence on temperature rise, and the fluorescence intensity of Example 2 is more than 6 times higher than that of comparative example 1 after heating. Therefore, the nanogel of Example 2 shows good temperature reversible fluorescence behavior after heat treatment, and has great potential application in thermal fluorescence materials and biological systems.

Claims

1. A dual-color thermosensitive nanogel, characterized in that, The nanogel is obtained by polymerization using raw materials containing N-isopropylacrylamide NIPAm, N-acryloyl-L-phenylalanine Aphe, N,N'-methylenebisacrylamide BIS, emulsifier, and fluorescent material. The emulsifier is sodium dodecyl sulfate (SDS). The structural formula of the fluorescent material is The molar ratio of NIPAm, Aphe, and BIS is 85-90% mol: 2-10% mol: 1-5% mol; the emulsifier accounts for 0.01 wt%-0.10 wt% of the deionized water in the system; and the fluorescent material accounts for 0.001 wt%-0.006 wt% of the deionized water in the system.

2. The dual-color thermosensitive nanogel according to claim 1, characterized in that, The raw material contains an initiator; the initiator is ammonium persulfate (APS).

3. The dual-color thermosensitive nanogel according to claim 2, characterized in that, The initiator accounts for 0.01wt%-0.05wt% of the deionized water in the system.

4. The dual-color thermosensitive nanogel according to claim 1, characterized in that, The preparation of the fluorescent material includes: Step (1) Mix 4-bromo-1,8-naphthoic anhydride, ethanolamine and solvent, reflux reaction, purify to obtain fluorescent intermediate NI1; Step (2) Mix fluorescent intermediate NI1, phenylboronic acid, catalyst and solvent, stir under nitrogen, then add Na2CO3 aqueous solution, react, purify to obtain fluorescent intermediate NI2; Step (3) Mix the fluorescent intermediate NI2, triethylamine Et3N and CH2Cl2, cool to 0°C, add acryloyl chloride dropwise, stir overnight at room temperature, and purify to obtain the fluorescent material NI3.

5. The dual-color thermosensitive nanogel according to claim 4, characterized in that, In step (1), the ratio of 4-bromo-1,8-naphthoic anhydride, ethanolamine, and solvent is 9-12 mmol: 9-12 mmol: 1-20 mL; the solvent is anhydrous ethanol; the reflux reaction is carried out under reflux conditions at a stirring temperature of 70-80°C for 1-2 hours.

6. The dual-color thermosensitive nanogel according to claim 4, characterized in that, In step (2), the ratio of fluorescent intermediate NI1, phenylboronic acid, catalyst, solvent, and Na2CO3 aqueous solution is 1.2-1.6 mmol: 2-2.5 mmol: 10-20 mg: 1-20 mL: 0.1-1 mL; the reaction is carried out under N2 atmosphere at a temperature of 50-60℃ for 24-72 h; the catalyst is Pd(PPh3)4. In step (3), the ratio of fluorescent intermediate NI2, triethylamine Et3N, CH2Cl2, and acryloyl chloride is 1.2-1.6 mmol: 2-2.5 mmol: 10-20 mL: 1-2 mmol.

7. A method for preparing the dual-color thermosensitive nanogel according to any one of claims 1-6, comprising: N-isopropylacrylamide (NIPAm), N,N'-methylenebisacrylamide (BIS), N-acryloyl-L-phenylalanine (Aphe), emulsifier, and water were mixed and stirred. After adding an initiator for 5-15 minutes, fluorescent material was added, and polymerization was carried out. The mixture was then dialyzed and concentrated to obtain a dual-color thermosensitive nanogel.

8. The preparation method according to claim 7, characterized in that, The stirring is carried out at 60-70℃ for 10-60 minutes; the polymerization reaction is carried out at 50-80℃ for 3-6 hours; the dialysis is carried out by soaking in ultrapure water for 3-7 days, changing the water 2-3 times a day, and the molecular weight cutoff of the dialysis bag used for dialysis is 8000-14000.

9. The preparation method according to claim 7, characterized in that, The concentrated mass concentration is 3% to 7%.

10. The application of the dual-color temperature-sensitive nanogel of claim 1 in a photoluminescence sensor.

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