The plasma membrane plays an important role in cellular processes. Not only does the membrane act as a barrier to the outside world, compartmentalizing cell functions by providing a two-dimensional solvent, but directly, by changing protein conformation and function, and indirectly, by changes in diffusional properties of the membrane through changes in chemical composition. The utility of model membrane systems in chemical sensing is predicated upon housing transmembrane proteins in their active conformation(s). Therefore, an understanding of the role the supporting surface has on mimicking the physical properties of plasma membranes is necessary in the creation of biomimetic films that maintain the functional properties of the imbedded proteins.Measuring diffusional motions via time-resolved picosecond laser spectroscopies and fluorescence microscopies, the fluidity and interfacial adhesion strength at an organic/inorganic interface of both monolayer thin films and supported lipid bilayers has been examined. Films have been prepared using both Langmuir-Blodgett deposition and small unilamellar vesicle (SUV) deposition. Both physical and chemical interactions were found to play an important role in mediating the dynamical properties exhibited by these films. First, the addition of an aqueous adlayer to lipid films produced using SUV deposition was found to significantly disrupt the organizational order within the alkyl chain region. Second, by combining rotational and translational diffusion measurements from a tethered fluorescent probe molecule, compositional variations within alkylphosphonic acid Langmuir films induced varying degrees of adhesion and fluidity. Lastly, the extent to which the fluidity of a supported lipid film is mediated by the ionic interactions between head-group and supporting surface vs. that of the lipid-lipid tail-group interactions was examined and shown to be system dependent.This research has led to an adaptable methodology based on the use of rotational and translational diffusional data to quantitate the strength of supported films over a range of length scales (sub-diffraction limit – to – hundreds of microns). A novel family of interfaces that can be physically bound to a surface and at the same time have controlled fluidity depending upon a range of chemical conditions of the underlying inorganic support has been developed. These developments move closer to providing an understanding of the impact a supporting surface plays in mediating model membrane dynamical properties and function.
Read
