Kinetics Of Substrate-induced Phospholipid Vesicle Fusion

As an ideal system for studying the structural characteristics and physiological functions of biomembrane,model membranes have been perfected day by day.The structure of the supported lipid bilayer?SLB?formed by the self-assembly of phospholipids is similar to the structure of biomembrane,which is a promising model for studying the interaction between interface and biomolecule and related physiological functions.This thesis is based on the vesicle and supported lipid bilayer system,using the method of vesicle fusion to prepare SLB.We characterized the spatiotemporal kinetics of vesicle fusion on functional substrates such as SiO₂,Au and TiO₂ using quartz crystal microbalance with dissipation monitoring?QCM-D?,Total internal reflection fluorescence microscopy?TIRFM?and fluorescence spectrometry.The process of vesicle to supported lipid bilayer is complicated and affected by many factors.In ideal condition,the vesicles spontaneously fuse on the surface of the hydrophilic substrate to form SLB.However,it is difficult for zwitterionic vesicles to form SLB on substrates such as Au and TiO₂ using the method of vesicle fusion.In the third chapter,QCM-D was used to study the mechanism of membrane on surface-modified gold substrate.Changing the chargeability of vesicles and substrate revealed that there are four types of deposition pathways:?A?vesicles do not adsorbed;?B?vesicles adsorb and form SVL;?C?vesicle adsorb and rupture at high vesicular coverage and SLB is formed;?D?vesicles adsorb and rupture instantaneously to form SLB.The difference in deposition pathway is attributed to the direction and strength of the electrostatic double layer between the vesicle and substrate of the anion or cation.This novel process to form bilayers on gold shifts the focus to modify the excellent substrate and away from surface dependent constraints.Our study provides reference for creating biosensors on others biocompatible functional substrate such as TiO₂ and ITO.The formation of SLB involves multiple paths.A large number of studies have empirically studied the process of SLB formation can be regulated by changing a single factor,but the internal physical mechanism is not yet clear.In the fourth chapter,we studied the effect and internal mechanism of the SLB formation process,which is influenced by salt concentration and bivalent cation for the first time.It is found that the rise in salt concentration and introduction of Ca²⁺could promote SLB formation separately,imposing them simultaneously did not result in a favorable effect.This reveals that the combined effects of salt concentration and Ca²⁺are not a simple superposition from individual factors.Furthermore,we performed single vesicle characterization,it was found that the extent of the spontaneous and edge-catalyzed vesicle ruptures is different in efficient SLB formation.The analysis of continuity theory and DLVO theory shows that the spontaneous rupture of vesicles depends on the affinity between the membrane and the substrate,and the electrostatic double layer plays a major role between the vesicles and the substrate.In all,the deep understanding of the microscopic mechanism of vesicle rupture and supply and strengthened the controllability of the process in this study.The above research deepened the understanding and control of the SLB formation process,and further studied the interaction between the detergents and the biomembrane using supported lipid bilayer.In the fifth chapter,we studied the interaction between three detergents and biomembranes,using QCM-D and TIRFM.We found that:below the micelle concentration?CMC?,the most obvious three-dimensional morphology change of membrane was found in the biomembrane interaction with the Triton X-100,damaging the membrane structure.It is inferred that the non-ionic Triton X-100 does not have intermolecular electrostatic repulsion,so it can be easy to insert into the biomembrane in large quantities.The result is inducing the membrane to form a highly dissipation microbubble budding structure.The cationic CTAB or SDS can be inhibit into the biomembranes,because of the electrostatic repulsion between their molecules.The result is not damaging the integrity and morphology of membrane.Our research deep the understanding of the mechanism and regulations between detergents and biomembranes.At last,we summarize the thesis,and present outlooks for the future work.