Regulation And Application Of The Aggregation Behavior Of Amphiphilic Alginate-based Fluorescent Polymers

The natural macromolecule sodium alginate has the advantages of good biocompatibility,non-toxicity and low cost,and has been widely used in the fields of cosmetics,medicine and food.Modification with abundant hydroxyl and carboxyl groups in the main chain of the molecule can give it more functions and meet different application requirements.In this paper,amphiphilic alginate-based fluorescent polymer（Alg-TPVA）was synthesized by grafting functional group molecules with aggregation-induced emission（AIE）onto the molecular framework of sodium alginate by Ugi four-component condensation reaction.Moreover,the aggregation behavior of Alg-TPVA in aqueous solution and oil-water interface and the application of Alg-TPVA in cell imaging,plant leaf imaging,drug encapsulation and controlled release were explored.First,an amphiphilic fluorescent polymer with AIE properties was prepared by Ugi reaction,and the aggregation behavior of the polymer in aqueous solution was investigated.The results of ¹H nuclear magnetic resonance spectroscopy（¹H NMR）,fourier transform infrared spectroscopy（FTIR）and UV-Visible spectrophotometer（UV-Vis）indicate that Alg-TPVA was successfully synthesized.The optical properties and morphology of the synthesized Alg-TPVA were characterized by fluorescence spectroscopy（FM）,transmission electron microscopy（TEM）and dynamic light scattering（DLS）.The direct visualization of Ca²⁺regulated amphiphilic Alg-TPVA micelles was studied by laser confocal microscopy（CLSM）.The results show that Alg-TPVA has classical agglomeration-induced luminescence in both solid and liquid state.The critical aggregation concentration is 0.125 mg·m L^-1,and the micelles can self-assemble into spherical micelles of 125±20 nm in aqueous solution.Ca²⁺is cross-linked with–COO^-in Alg-TPVA molecules to form a gel network structure,which enables amphiphilic Alg-TPVA micelles to aggregate together.This process can be directly visualized by CLSM.Secondly,the aggregation behavior of Alg-TPVA micelles regulated by Ca²⁺at the oil-water interface was investigated.Based on the experimental results in Chapter 2,we further studied the effects of Ca²⁺addition on the self-assembly of Alg-TPVA by DLS.The results showed that theζpotential of Alg-TPVA micelles was significantly reduced by 0.02M Ca²⁺.With the increase of Ca²⁺,the intermolecular cross-linking of Alg-TPVA micelles and Ca²⁺aggregated,resulting in the increase of particle size due to the decrease of electrostatic repulsion.The effects of Ca²⁺addition on the properties of Pickering emulsion prepared by Alg-TPVA were investigated by optical microscopy（OM）,DHR rotary rheometer,scanning electron microscopy（SEM）and CLSM.The results show that 0.04 M Ca²⁺can significantly improve the stability of the emulsion;0.1 M Ca²⁺causes emulsion droplets to coalesce,resulting in water-phase release,and the emulsion becomes unstable.Moreover,the oil-water interface film can be directly visualized by CLSM,and it is found that the thickness of the interface-film with the strongest stability is 2.92μm,which provides an important reference for understanding the stability mechanism of Pickering emulsion.Finally,based on the good AIE fluorescence properties of Alg-TPVA,the potential applications of Alg-TPVA were further explored,including the applications in cell imaging,plant leaf imaging,drug encapsulation and controlled release.The results show that the introduction of AIE active material gives the fluorescence characteristics of Alg-TPVA,which can emit a variety of colors from blue to red at different excitation wavelengths.The Alg-TPVA also showed excellent polychromatic imaging ability on cells and stomata of plant leaves,and excellent biocompatibility.Moreover,Alg-TPVA has stable micellar properties and can be used for drug encapsulation and delivery in microenvironment.This will lay a foundation for the later application of Alg-TPVA in drug targeted delivery and tracer experiments in vivo and leaf target diagnosis and treatment experiments.