Reduced Graphene Oxide Directed Self-assembly Of Phospholipid Monolayers In Liquid And Gel Phases

Cell membranes play an important role in intercellular substance transport and signal and power transmission. The response of cell membranes to the local physical environment significantly determines these biological processes and the practical applications of biomaterials. A better understanding of the dynamic assembly and environmental response of lipid membranes can help understand these processes and design novel nanomaterials for biomedical applications. In this work, we take advantage of AFM technique to investigate the directed self-assembly of phospholipid molecules, in both liquid and gel phases, in response to the surface features of monolayered reduced graphene oxide(r GO) sheets that are supported on a mica surface. Results show that subtle structural details in r GO substrate are amplified into dramatic differences in morphology and lateral fluidity in supported lipid monolayers. This work provides a new framework for understanding the cell membrane responses to r GO and help design novel r GO/lipid nanocomposite biomaterials.This thesis includes:(1) monolayered graphene oxide and reduced graphene oxide sheets were fabricated on mica surface;(2) phospholipid molecules, in both liquid and gel phases, were assembled on the r GO surface by the Langmuir-Blodgett(LB) method. The surficial property of them was characterized with atomic force microscope(AFM).(3) Through reducing the surface pressure of the phospholipid membrane, the assembly mechanism of the lipid molecules was investigated;(4) we further increased the temperature to above the phase transition point of the lipid to learn about the influence from the lipid-r GO interaction on the lateral fluidities of the lipid membrane. The results indicate that the hydrophobic aromatic plane and the defect holes due to reduction of GO sheets, along with the phase state and planar surface pressure of lipids, corporately determine the morphology and lateral structure of the assembled lipid monolayers. The DOPC molecules, in liquid phase, probably spread over the r GO surface with their tails associating closely with the hydrophobic aromatic plane, and accumulate to form circles of high area surrounding the defect holes on r GO sheets. However, the DPPC molecules, in gel phase, prefer to form a layer of continuous membrane covering the whole r GO sheet including defect holes. The strong association between r GO sheets and lipid tails further influences the melting behavior of lipids. This work reveals a dramatic effect of the local structure and surface property of r GO sheets on the substrate-directed assembly and subsequent phase behavior of the supported lipid membranes.