Supported phospholipid membranes as biometric labs-on-a-chip: analytical devices that mimic cell membrane architectures and provide insight into the mechanism of biopreservation

Abstract

This dissertation focuses on the applications of solid supported phospholipid membranes as mimics of the cellular membrane using lab-on-a-chip devices in order to study biochemical events such as ligand-receptor binding and the chemical mechanism for the preservation of the biomembrane. Supported lipid bilayers (SLBs) mimic the native membrane by presenting the important property of two-dimensional lateral fluidity of the individual lipid molecules within the membrane. This is the same property that allows for the reorganization of native membrane components and facilitates multivalent ligand-receptor interactions akin to immune response, cell signaling, pathogen attack and other biochemical processes. The study is divided into two main facets. The first deals with developing a novel lipopolymer supported membrane biochip consisting of Poly(ethylene glycol) (PEG)-lipopolymer incorporated membranes. The formation and characterization of the lipopolymer membranes was investigated in terms of the polymer size, concentration and molecular conformation. The lateral diffusion of the PEG-bilayers was similar to the control bilayers. The air-stability conferred to SLBs was determined to be more effective when the PEG polymer was at, or above, the onset of the mushroom-to-brush transition. The system is able to function even after dehydration for 24 hours. Ligandreceptor binding was analyzed as a function of PEG density. The PEG-lipopolymer acts as a size exclusion barrier for protein analytes in which the binding of streptavidin was unaffected whereas the binding of the much larger IgG and IgM were either partially or completely inhibited in the presence of PEG. The second area of this study presents a molecular mechanism for in vivo biopreservation by employing solid supported membranes as a model system. The molecular mechanism of how a variety of organisms are preserved during stresses such as anhydrobiosis or cryogenic conditions was investigated. We investigated the interaction of two disaccharides, trehalose and maltose with the SLBs. Trehalose was found to be the most effective in preserving the membrane, whereas maltose exhibited limited protection. Trehalose lowers the lipid phase transition temperature and spectroscopic evidence shows the intercalation of trehalose within the membrane provides the chemical and morphological stability under a stress environment.