Visualization And Probing Of Polymer-small Molecule Interaction Based On Gold Nanocluster-encapsulated Polyethyleneimine

The polymer-small molecule interactions are widely used in bio-manufacturing,cosmetics,and industrial production,making the relavent research very significant.Among those polymers,hyperbranched polyethyleneimine(h PEI)has been widely used in surface adsorption,gene delivery,nanomaterials synthesis due to the three-dimensional molecular network,high reactivity,high positive charge density and strong adsorption.However,such interaction is primarily investigaed based on Zeta potential,p H,hydrodynamic diameter,and viscosity,and its direct and quick visulization is difficult.As a result,the development a rapid visualization method is critial to the deep understanding of interaction process and mechanism.In this thesis,taking h PEI-dopamine/surfactant interaction as the research object,two kinds of h PEI-protected gold nanoclusters(Au NCs)were designed and synthesized for constructing efficient and ratiometric fluorescence and visulizing the interaction between h PEI and small molecules.The main research contents are listed as follows:(1)Using h PEI as the template,red emissive Au NCs(h PEI-Au NCs)were prepared at room temperature by introducing mercaptoundecanoic acid,and a highly selective and ratiometric dopamine fluorescence probe was developed based on h PEI-Au NCs.The detection mechanism is based on the formation of azamonardine via selective DA-catechin chemical reaction and subsequent enhanced fluorescence emission.The dopamine sensing principle includes two aspects: a.h PEI-triggers the self-polymerization of dopamine,which forms polymeric dopamine nanoparticles with green fluorescence;b.The changed molecular conformation of h PEI regulates the charge transfer pathway of h PEI-Au NCs,which diminshes the red fluorescence and results in ratiometric fluorescence variation.Through optimization,highly sensitive dopamine fluorescence probe was explored for dopamine analysis in aqueous solution and urine samples.(2)Dual-emissive gold nanocluster complexes(h PEI-DE-Au NCs)with blue and red fluorescence were prepared by simly adjusting the concentration of h PEI,and has been proposed for visulizing the h PEI-sodium dodecyl sulfonate(SDS,anionic surfactant)interaction.The h PEI-SDS interaction changes the conformation of h PEI,which causes decreased red fluorescence and negligible variation of blue fluorescence.This is mainly because that the red fluorescence originates from the ligand to the metal-metal charge transfer(S→Au(I)…Au(I),LMMCT),which is sensitive to the spatial configuration of surface thiol molecules.In constrast,the blue fluorescence originates from the d-sp electronic transition,which is insensitive toward surface molecular environment.Further studies demonstrate that the conformation of h PEI could also be changed by increasing the temperature,leading to the decrease of red fluorescence and unchanged blue fluorescence.Therefore,the cationic polymer-anionic surfactant interaction process can be visualized with h PEI-DE-Au NCs as probes.Meanwhile,this method also provides a new characterization technique and stratgey for understanding the interaction between polymers and small molecules.