Double-color temperature-sensitive nanogel as well as preparation method and application thereof

Abstract

The invention relates to a double-color temperature-sensitive nanogel as well as a preparation method and application of the double-color temperature-sensitive nanogel. The double-color temperature-sensitive nanogel disclosed by the invention not only has a structural color, but also has fluorescence. The nanogel not only can enhance the fluorescence intensity, but also can be used for detecting the temperature change. The structural color can amplify a fluorescence signal and can be used for accurately adjusting the fluorescence intensity of different fluorophores, so that an optical device and a photoluminescence-based sensor have remarkable progress in the aspects of sensitivity, simplicity, convenience and stability.

Description

Technical Field

[0001] The invention belongs to the field of gel materials, and particularly relates to a dual-color temperature-sensitive nano gel and a preparation method and application thereof. Background Art

[0002] Colloidal photonic crystals (CPCs), characterized by their self-assembled periodic arrangements of monodisperse colloidal particles, have attracted considerable attention due to their unique optical properties. Notably, monodisperse colloidal thermosensitive poly(N-isopropylacrylamide) (PNIPAM) nanogels undergo reversible volume changes near the lower critical solution temperature (LCST, 32 °C) in aqueous media, enabling the polymer chains to respond to temperature fluctuations. This promising candidate for CPC development has sparked tremendous interest due to its optical properties such as bright, durable, and non-fading colors, representing a key advancement for a wide range of applications in various fields, including optical devices, colorimetric sensors, and displays.

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

[0004] In view of the defects of the prior art, the technical problem to be solved by the present invention is to provide a dual-color temperature-sensitive nanogel and a preparation method and application thereof.

[0005] The invention provides a dual-color temperature-sensitive nanogel. The nanogel is obtained by polymerization using 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; the fluorescent material has the 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 deionized water of the system is (0.01wt%-0.10wt%); the mass ratio of the initiator to the deionized water of the system is (0.01wt%-0.05wt%); the mass ratio of the fluorescent material to the deionized water of the system is (0.001wt%-0.006wt%).

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

[0011] Furthermore, the amount of SDS added to the mass ratio of the deionized water in the system (0.01wt%-0.10wt%). In particular, when other conditions remain unchanged and only the content of SDS is changed, which is 0.027wt%, 0.045wt% and 0.073wt%, respectively, the nanogels have different structural colors, namely purple, blue and blue-green.

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

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

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

[0015] (3) The fluorescent intermediate NI2, triethylamine Et3N and CH2Cl2 are mixed, cooled to 0°C, acryloyl chloride is added dropwise, stirred at room temperature overnight, and purified to obtain the fluorescent material NI3.

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

[0017] The purification in step (1) is as follows: after the reaction is completed, the mixture is cooled to room temperature, and then the product is recovered by filtration and recrystallization with anhydrous ethanol, cooled to room temperature, recovered by filtration, recrystallized with anhydrous ethanol, and the desired product is dried to obtain an off-white solid NI1.

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

[0019] Purification in the step (2): 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, in step (3), the ratio of the fluorescent intermediate NI2, triethylamine Et3N, CH2Cl2 and acryloyl chloride is 1.2-1.6mmol:2-2.5mmol:10-20mL:1-2mmol.

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

[0022] The preparation of N-acryloyl-L-phenylalanine Aphe comprises: dissolving l-phenylalanine in a NaOH solution, maintaining the solution at 0°C for 5-15 minutes, then dripping acryloyl chloride, stirring at room temperature for 1-2 hours, and purifying to obtain Aphe; wherein the ratio of l-phenylalanine, NaOH, and acryloyl chloride is 5-7 g:2-4 g:2-5 mL; the dripping is performed by using a dropper to maintain constant pressure and slowly dripping acryloyl chloride; the purification comprises: after the reaction is completed, adding concentrated hydrochloric acid to make the pH value reach 2, obtaining a white precipitate and filtering it out, and washing the white powder with water and drying it.

[0023] The present invention provides a method for preparing any of the above-mentioned dual-color temperature-sensitive nanogels, comprising:

[0024] N-isopropylacrylamide NIPAm, N,N'-methylenebisacrylamide BIS, N-acryloyl-L-phenylalanine Aphe, an emulsifier and water are mixed and stirred, and an initiator is added. After 5-15 minutes, a fluorescent material is added, and a polymerization reaction is performed, dialyzed and concentrated to obtain a 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 carried out at 60-70°C for 10-60 min; the polymerization reaction is carried out at 50-80°C for 3-6 h; 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.

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

[0028] The concentration is evaporation concentration at a temperature of 70°C.

[0029] The invention provides an application of the dual-color temperature-sensitive nanogel in a photoluminescence sensor.

[0030] The P(NIPAM-Aphe-NI3) nanogel obtained by the present invention contains dual-color structural color and fluorescent nanogel, which not only enhances the fluorescence intensity but also responds to temperature.

[0031] Nanogels were studied by Bragg diffraction, and the effectiveness of the slow photon effect in enhancing the fluorescence intensity of nanogels with different structural colors was demonstrated. The sol-gel transition of the nanogel keeps its structural color unchanged, while the fluorescence intensity increases as the diameter of the nanogel decreases. The principle of achieving sol-gel conversion after heating is through the interaction between the carboxyl group and the benzene ring in Aphe, and the aggregation of the polymer chains leads to a significant fluorescence enhancement effect.

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

[0033] Beneficial Effects

[0034] The present invention combines this unique NI luminescent molecule into a cross-linked nanogel polymer network that can self-assemble to produce structural colors, and prepares a dual-color temperature-sensitive nanogel that has both structural colors and fluorescence. This nanogel can not only enhance the fluorescence intensity, but also be used to detect temperature changes. The structural color can amplify the fluorescence signal and can be used to accurately adjust the fluorescence intensity of different fluorophores, so that optical devices and sensors based on photoluminescence have significant improvements in sensitivity, simplicity and stability.

[0035] The present invention obtains P(NIPA-Aphe-NI3) nanogel by copolymerization of NIPAM, Aphe and NI3, which not only has fluorescence and structural color dual-color materials. In response to temperature, the sol-gel conversion can keep the structural color unchanged. For the introduced fluorescent material, it not only changes the fluorescent material from a hydrophobic material to a hydrophilic material, but also increases its fluorescence intensity by two times after heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Particle size distribution diagrams and scanning electron microscope morphologies (a-c) and reflectance spectra of structural colors (d) of dual-color thermosensitive nanogels prepared in Examples 1-3 and Comparative Example 1; when other preparation conditions remain unchanged and only the SDS content is changed, the figures indicate no SDS (Comparative Example 1), 0.03 g SDS (Example 1), 0.05 g SDS (Example 2) and 0.08 g SDS (Example 3). Figure 2The relative fluorescence intensity (left figure) and fluorescence enhancement factor (right figure) of different stop band P (NIPA-Aphe-NI3) nanogels of Examples 1-3 and Comparative Example 1. When other preparation conditions remain unchanged, only the content of SDS is changed, and the legends represent no SDS (Comparative Example 1), 0.03g SDS (Example 1), 0.05g SDS (Example 2) and 0.08g SDS (Example 3). Figure 3 The relative fluorescence intensity (left figure) and thermal reversibility (right figure) of the two-color thermosensitive nanogel prepared in Example 2 at different temperatures (25-49°C). DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0038] In Examples 1-3 and step (5) described in Comparative Example 1, the molar ratios of NIPAM, Aphe in step (1) and BIS are 92%:6%:2%, respectively, and the total molar amount is 10 mol; the contents of SDS are 0.03 g (Example 1), 0.05 g (Example 2), 0.08 g (Example 3) and no SDS (Comparative Example 1), respectively; and 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) and kept at 0°C for 15 min. Using a dropper to maintain constant pressure, acryloyl chloride (3.6 mL) was slowly added dropwise. After the addition was completed, the mixture was stirred at room temperature for 2 h. After the reaction was completed, concentrated hydrochloric acid was added to adjust the pH value to 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried. The solid phase yield was about 5.3 g, and the yield was 85%. 1H NMR(400MHz, DMSO-d6,d):12.78(br.s.,1H),8.43(d,J=8.25Hz,1H),7.26-7.29(m,2H),7.19-7.24(m,3H),6.27(dd,J=17.06,9.90Hz,1H),6.0 5(dd,J=17.33,1.93Hz,1H), 5.58(dd,J=10.45,2.20Hz,1H), 4.49-4.54(m,1H), 3.10(dd,J=13.75,4.95Hz,1H), 2.90(dd,J=13.76,9.90Hz,1H).

[0041] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round-bottom flask, 4-bromo-1,8-naphthoic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirred at 80 °C for 2 h under reflux conditions. After the reaction was completed, the mixture was cooled to room temperature. The product was then recovered by filtration and recrystallization with anhydrous ethanol. Cooled to room temperature, recovered by filtration, and recrystallized with anhydrous ethanol. The desired product was dried to give NI1 as an off-white solid. 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 a N2 atmosphere. Then, an aqueous Na2CO3 solution (0.5 mL) was added via a syringe. The reaction mixture was heated at 60°C under a N2 atmosphere 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 then 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 obtain NI2 as a yellow solid. 1HNMR (400MHz, DMSO-d6,d):8.55(d,J=7.53Hz,2H),8.25(d,J=8.41Hz,1H),7.83-7.88(m,1H),7.81(d,J =7.53Hz,1H),7.54-7.63(m,5H),4.85(t,J=6.02Hz,1H),4.19(t,J=6.46Hz,2H),3.65(q,J=6.44Hz,2H).

[0043] (4) Synthesis of fluorescent material NI3: NI2 (500 mg, 1.58 mmol) and Et3N (239.16 mg, 2.36 mmol) from step (2) were mixed in dry CH2Cl2 (20 mL), cooled to 0°C in an ice-water bath, and then acryloyl chloride (171.12 mg, 1.89 mmol) was added dropwise. The resulting mixture was stirred at room temperature overnight, and then the solvent was removed under reduced pressure. The residue was purified by chromatography on silica gel (PE / DCM=20 / 1 (v / v)) to obtain the desired NI3 with a yield of 30%. 1HNMR (400MHz, DMSO-d6,d):8.55-8.58(m,2H),8.25-8.28(m,1H),7.87(dd,J=8.25,7.15Hz,1H),7.82(d,J=7.15Hz,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] Fluorescent material NI3 structural formula:

[0045] (5) Synthesis of dual-color thermosensitive nanogel P (NIPA-Aphe-NI3): Under nitrogen atmosphere, NIPAM, BIS, and Aphe were added according to the percentage of the total molar mass of the three monomers, with a total molar amount of 10 mol, 92% mol of NIPAM, 2% mol of BIS, 6% mol of Aphe synthesized in step (1), and SDS (0.03 g) were dissolved in 100 mL of deionized water and stirred at 70°C for 30 min in a 250 mL round-bottom flask. Subsequently, an APS aqueous solution (0.05 g of APS was dissolved in 10 mL of water) was injected into the flask to initiate polymerization. After 10 min, 6 mg of NI3 (dissolved in DMF (1 mL)) in step (4) was added. The polymerization reaction was carried out at 70°C for 4 h and then cooled to room temperature. Deionized water was dialyzed for 5 days using a dialysis bag (MWCO of 8000-14000 Da) to obtain dual-color thermosensitive nanogel P (NIPAM-Aphe-NI3). The obtained nanogel was concentrated by heating to a concentration of 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. Using a dropper to maintain constant pressure, acryloyl chloride (3.6 mL) was slowly added dropwise. After the addition was completed, the mixture was stirred at room temperature for 2 h. After the reaction was completed, concentrated hydrochloric acid was added to adjust the pH value to 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried. The solid phase yield was about 5.3 g, and the yield was 85%.

[0048] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round-bottom flask, 4-bromo-1,8-naphthoic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirred at 80 °C for 2 h under reflux conditions. After the reaction was completed, the mixture was cooled to room temperature. The product was then recovered by filtration and recrystallization with anhydrous ethanol. Cooled to room temperature, recovered by filtration, and recrystallized with anhydrous ethanol. The desired product was dried to obtain an off-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 a N2 atmosphere. Then, an aqueous Na2CO3 solution (0.5 mL) was added via a syringe. The reaction mixture was heated at 60°C under a N2 atmosphere 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 then 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 obtain NI2 as a yellow solid.

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

[0051] (5) Synthesis of dual-color thermosensitive nanogel P (NIPA-Aphe-NI3): Under nitrogen atmosphere, NIPAM, BIS, and Aphe were added according to the percentage of the total molar mass of the three monomers, with a total molar amount of 10 mol. NIPAM (92% mol), BIS (2% mol), Aphe synthesized in step (1) (6% mol), and SDS (0.05 g) were dissolved in 100 mL of deionized water and stirred at 70°C for 30 min in a 250 mL round-bottom flask. Subsequently, an APS aqueous solution (0.05 g of APS was dissolved in 10 mL of water) was injected into the flask to initiate polymerization. After 10 min, 6 mg of NI3 (dissolved in DMF (1 mL)) from step (4) was added. The polymerization reaction was carried out at 70°C for 4 h and then cooled to room temperature. Deionized water was dialyzed for 5 days using a dialysis bag (MWCO of 8000-14000 Da) to obtain dual-color thermosensitive nanogel P (NIPAM-Aphe-NI3). The obtained nanogel was concentrated by heating to a concentration of 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. Using a dropper to maintain constant pressure, acryloyl chloride (3.6 mL) was slowly added dropwise. After the addition was completed, the mixture was stirred at room temperature for 2 h. After the reaction was completed, concentrated hydrochloric acid was added to adjust the pH value to 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried. The solid phase yield was about 5.3 g, and the yield was 85%.

[0054] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round-bottom flask, 4-bromo-1,8-naphthoic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirred at 80 °C for 2 h under reflux conditions. After the reaction was completed, the mixture was cooled to room temperature. The product was then recovered by filtration and recrystallization with anhydrous ethanol. Cooled to room temperature, recovered by filtration, and recrystallized with anhydrous ethanol. The desired product was dried to obtain an off-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 a N2 atmosphere. Then, an aqueous Na2CO3 solution (0.5 mL) was added via a syringe. The reaction mixture was heated at 60°C under a N2 atmosphere 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 then 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 obtain NI2 as a yellow solid.

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

[0057] (5) Synthesis of dual-color thermosensitive nanogel P (NIPA-Aphe-NI3): 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 of deionized water according to the percentage of the total molar mass of the three monomers NIPAM, BIS and Aphe, with a total molar amount of 10 mol. In a 250 mL round-bottom flask, the mixture was stirred at 70°C for 30 min. Subsequently, an APS aqueous solution (0.05 g of APS was dissolved in 10 mL of water) was injected into the flask to initiate polymerization. After 10 min, 6 mg of NI3 (dissolved in DMF (1 mL)) from step (4) was added. The polymerization reaction was carried out at 70°C for 4 h and then cooled to room temperature. Deionized water was dialyzed for 5 days using a dialysis bag (MWCO of 8000-14000 Da) to obtain dual-color thermosensitive nanogel P (NIPAM-Aphe-NI3). The obtained nanogel was concentrated by heating to a concentration of 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. Using a dropper to maintain constant pressure, acryloyl chloride (3.6 mL) was slowly added dropwise. After the addition was completed, the mixture was stirred at room temperature for 2 h. After the reaction was completed, concentrated hydrochloric acid was added to adjust the pH value to 2. A white precipitate was obtained and filtered off. The white powder was washed with water and dried. The solid phase yield was about 5.3 g, and the yield was 85%.

[0060] (2) Synthesis of fluorescent intermediate NI1: In a 100 mL round-bottom flask, 4-bromo-1,8-naphthoic anhydride (3.0374 g, 10.83 mmol) and ethanolamine (693.2 mg, 10.83 mmol) were mixed with anhydrous ethanol (10 mL). Stirred at 80 °C for 2 h under reflux conditions. After the reaction was completed, the mixture was cooled to room temperature. The product was then recovered by filtration and recrystallization with anhydrous ethanol. Cooled to room temperature, recovered by filtration, and recrystallized with anhydrous ethanol. The desired product was dried to obtain an off-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 a N2 atmosphere. Then, an aqueous Na2CO3 solution (0.5 mL) was added via a syringe. The reaction mixture was heated at 60°C under a N2 atmosphere 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 then 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 obtain NI2 as a yellow solid.

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

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

[0064] like Figure 1As shown in the figure, the structural colors of Examples 1-3 and Comparative Example 1. The hydrodynamic diameters of the nanogels of Example 1, Example 2 and Example 3 measured in aqueous solution were 353.7nm, 304.5nm and 289.8nm, respectively, and the polydispersity indexes (PDI) were 0.089, 0.095 and 0.094, respectively, 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 (eg Figure 1 d). The characteristic reflection peaks corresponding to the nanogels of Examples 1-3 are located at 410nm, 520nm and 580nm respectively. As the SDS content increases, the particle size of the nanogel decreases and the wavelength of the reflection spectrum shifts blue. The Bragg diffraction law can be calculated by the Bragg equation. When no SDS is added, the nanogel of Comparative Example 1 has no structural color and no characteristic reflection peak signal.

[0065] like Figure 2 As shown, the fluorescence conditions of Examples 1-3 and Comparative Example 1. Figure 2 The middle left shows the fluorescence enhancement of four nanogels under different stopbands. The fluorescence intensity of the nanogels with structural colors in Examples 1-3 is higher than that of the nanogel without structural color in Comparative Example 1. At the maximum emission wavelength of Examples 2 and 3, the fluorescence enhancement is 4 times and 3 times respectively compared with Comparative Example 1. This phenomenon produces a slow photon effect that can be effectively positioned in a photonic crystal (PC) structure. The position of the light wave in the structure depends on the photon energy, and the material with a lower refractive index shows a more obvious interaction with the light at the blue band edge of the stopband. The results show that adding a colloidal photonic crystal structure to fluorescent nanogels is an effective way to increase the fluorescence intensity.

[0066] like Figure 3 As shown, the relationship between the fluorescence intensity and temperature of Example 2 and Comparative Example 1. When the temperature increases from 25°C to 49°C, the emission intensity at 490nm (lex=380nm) increases. It is worth noting that 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. As the temperature further increases to 49°C, the fluorescence intensity tends to increase gradually and slowly. Importantly, at a temperature of 49°C, the fluorescence intensity reaches a maximum value, which is about 2.3 times higher than the original intensity at room temperature. In addition, the fluorescence intensity of the nanogel in Example 2 is linearly related to the temperature in the range of 37°C to 43°C ( Figure 3 Left). At the same time, the reversibility of the fluorescence behavior was verified by five temperature change cycles from 25°C to 49°C ( Figure 3Right), with good thermal cycling performance. It is worth noting that the comparative example 1 without structural color has no fluorescence response after heating ( Figure 3 Left), which indirectly indicates that structural color has a potential effect on temperature increase, and the fluorescence intensity of Example 2 increases by more than 6 times compared with that of Comparative Example 1 after heating. Therefore, the nanogel of Example 2 exhibits good temperature-reversible fluorescence behavior after heat treatment, and has great application potential in thermofluorescent materials and biological systems.

Claims

1. A two-color temperature-sensitive 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, an emulsifier and a fluorescent material.

2. The dual-color temperature-sensitive nanogel according to claim 1, characterized in that: The emulsifier is sodium dodecyl sulfate SDS; the raw material contains an initiator; the initiator is ammonium persulfate APS; the fluorescent material structural formula is:

3. The dual-color temperature-sensitive nanogel according to claim 1, characterized in that: 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 deionized water of the system is 0.01wt%-0.10wt%; the mass ratio of the initiator to the deionized water of the system is 0.01wt%-0.05wt%; the mass ratio of the fluorescent material to the deionized water of the system is 0.001wt%-0.006wt%.

4. The dual-color temperature-sensitive nanogel according to claim 1, characterized in that: The preparation of the fluorescent material comprises: (1) mixing 4-bromo-1,8-naphthoic anhydride, ethanolamine and a solvent, refluxing and purifying to obtain a fluorescent intermediate NI1; (2) mixing the fluorescent intermediate NI1, phenylboric acid, a catalyst and a solvent, stirring under nitrogen, then adding a Na2CO3 aqueous solution, reacting, and purifying to obtain a fluorescent intermediate NI2; (3) The fluorescent intermediate NI2, triethylamine Et3N and CH2Cl2 are mixed, cooled to 0°C, acryloyl chloride is added dropwise, stirred at room temperature overnight, and purified to obtain the fluorescent material NI3.

5. The preparation method according to claim 4, characterized in that: In the 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: under reflux conditions, the stirring temperature is 70-80° C. and the stirring time is 1-2 h.

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

7. A method for preparing the dual-color temperature-sensitive nanogel according to any one of claims 1 to 6, comprising: N-isopropylacrylamide NIPAm, N,N'-methylenebisacrylamide BIS, N-acryloyl-L-phenylalanine Aphe, an emulsifier and water are mixed and stirred, and an initiator is added and then a fluorescent material is added after 5-15 minutes of polymerization reaction, dialyzed and concentrated to obtain a dual-color temperature-sensitive nanogel.

8. The preparation method according to claim 7, characterized in that: The stirring is carried out at 60-70° C. for 10-60 min. The polymerization reaction is carried out at 50-80° C. for 3-6 h. 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 mass concentration after concentration is 3% to 7%.

10. Use of the dual-color temperature-sensitive nanogel according to claim 1 in a photoluminescent sensor.

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