AVS 50th International Symposium
    Nanometer Structures Wednesday Sessions
       Session NS-WeM

Paper NS-WeM8
Effect of the Ionic Strength on a Natural Lipid Bilayer Assembling and Stability: A Force Spectroscopy(nanomechanical) Study

Wednesday, November 5, 2003, 10:40 am, Room 308

Session: Nanomechanics
Presenter: S. Garcia-Manyes, University of Barcelona, Spain
Authors: S. Garcia-Manyes, University of Barcelona, Spain
M.J. Kogan, University of Barcelona, Spain
F. Sanz, University of Barcelona, Spain
D. Ludevid, CSIC, Spain
E. Giralt, University of Barcelona, Spain
Correspondent: Click to Email
Lipid bilayers have been widely studied on account of their biological interest regarding cell characterization, membrane protein transport, etc. In the last recent years many studies have been focused on the study of such membranes using Atomic Force Microscopy, since it gives chemical and topographic information in the nanometer scale. Some of these studies dealt with lipid deposition on flat substrates such as mica, silica or graphite either in the form of Langmuir-Blodget films or after bilayer self-assembling. Some of these lipid surfaces have been used to support proteins in order to study lipid-protein interaction or to test new drugs. Most of these studies used synthetized bilayers for the a priori sake of reproducibility and simplicity in their chemical composition. In these work we present novel results concerning the study of a natural plant bilayer membrane formation under physiological conditions. By using force spectroscopy we demonstrate that solution ionic strength is crucial in the self-assembling process and that small variations in ionic strength give rise to huge variations in bilayer compactness. There is a threshold ionic strength under which bilayers are not self-assembled, connected with the charge repulsion between the hydrophilic charged heads of the molecule. As the ionic strength is increased the charge repulsion seems screened out and the assembling process achieved, and this is reflected in a discrete jump in the force plot. The force at which this break takes place (the so-called yield point) is highly influenced by the own magnitude of the ionic strength, and ranges from ~ 1.5 nN at 10 mM to ~ 9 nN at 1 M. A nanomechanical study concerning the elasticity of the bilayer, as well as an evaluation of the forces that take place (double layer, hydration forces, Van der Waals, etc.) is also included.