Study On The Self-assembly Of Surfactant And Carbon Quantum Dots/DCFH-DA And Its Applications

Self-assembly is an important means to construct functional nanostructures like chemical synthesis.Self-assembly is the process in which the construction blocks self-aggregated driven by the non-covalent weak interactions to form ordered aggravates,such as micelles,vesicles,coacervation,and so on.The nano-aggregates formed by self-assembly have potential applications in carrier,antibacterial,and nanoreactors,which have received enormous attention.The novel building block carbon quantum dots contain rich polar groups,which is beneficial to the self-assembly of carbon quantum dots and other building units through weak interaction,and can give self-assembly new properties such as fluorescence properties.Therefore,this thesis mainly focuses on the self-assembly behavior of fluorescent material carbon quantum dots/2’,7’-dichlorofluorescein diacetate（DCFH-DA）,and surfactant system in aqueous solution,determining the phase behavior,microstructures,and rheological properties of the system,and explored their potential applications.The main contents are as follows:（1）The self-assembly of negatively charged selenium-doped carbon quantum dots（Se-CQDs）and surfactant N,N-dimethyl oleoaminde-propylamine（DOAPA）was investigated.At p H=6.5,the system exhibited rich phase behavior,which went through the process of transparent phase-turbid phase-transparent phase,which can be defined as isotropic phase（I₁）,turbid phase（T）,precipitated phase（P）,and second isotropic phase（I₂）.We focus on investigating the morphologies of the samples.Spherical aggregates can be observed by cryogenic transmission electron microscopy in each phase sequence solution.Spindle-like aggregates and unique"nanocapsules-like"aggregates can also be observed in the I₂ phase.The"nanocapsules-like"aggregates are formed by the self-assembly of supramolecular polymer"branched polymer",which is formed by the self-assembly of DOAPA and Se-CQDs.The self-assembly aggregates in the P phase have p H responsiveness.When the p H of the solution is adjusted from6.5 to 5.0,the self-assembly in the solution changes from spherical aggregates to vesicles.The research shows that surfactant and carbon quantum dots can construct different aggregates through self-assembly,which expands the potential application of carbon quantum dots in self-assembly.（2）Sulfur and nitrogen-doped fluorescent carbon quantum dots（S,N-CQDs）can be self-assembled with DOAPA to form coacervation nanodroplets.The nanodroplets were observed by fluorescence microscope,laser confocal microscope,and frozen transmission electron microscope,which have good fluorescence properties and rich internal texture.The nanodroplets have CO₂/N₂ responsiveness,which can be dissociated quickly after bubbling CO₂ and can be self-assembled again after bubbling N₂.Nanodroplets have a good loading capacity for a variety of different guest molecules,such as amphiphilic molecule Rhodamine B,hydrophobic molecule Nile red,biological macromolecule DNA,and glucose oxidase（Gox）.Nanodroplets have good antibacterial properties,and the MIC（minimum inhibitory concentration）against E.coli and S.aureus were 21.34μg/m L and 32.86μg/m L respectively.The antibacterial mechanism of nanodroplets against E.coli is mainly related to inducing bacteria to produce ROS（reactive oxygen species）,reducing mitochondrial membrane potential,and destroying cell membrane.Nanodroplets can effectively destroy the biofilm formed by S.aureus.When its concentration is 100μg/m L,it can destroy 82.67%biofilm formed S.aureus.（3）Photocatalytic nanoreactor was constructed by self-assembly of DCFH-DA（2’,7’-dichlorofluorescein diacetate）and cationic surfactant STAB（octadecyl trimethyl ammonium bromide）.In the nanoreactor,DCFH-DA was hydrolyzed and oxidized to DCF（2’,7’-dichlorofluorescein）by photocatalysis,which enhanced the fluorescence intensity of the solution.The fluorescence intensity of the nanoreactor increased with the increase of irradiation time and p H of the solution.When C_STAB=0.2 mmol/L,the wavelength of irradiation light is 420 nm,and the photocatalysis effect is highest.With the 420 nm irradiation,the vesicles constructed by self-assembly of STAB and DCFH-DA can catalyze the formation of DCF and enrich DCF to amplify the fluorescence signal.The fluorescence intensity of the nanoreactor after irradiation has a linear relationship with the concentration of H₂O₂,which has potential application in detecting H₂O₂ in vitro.