AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Monday Sessions
       Session NS1-MoA

Paper NS1-MoA7
Effect of Temperature on the Nanomechanics of Lipid Bilayers Studied by Force Spectroscopy

Monday, October 31, 2005, 4:00 pm, Room 204

Session: Nanotribology
Presenter: G. Oncins, University of Barcelona, Spain
Authors: S. Garcia-Manyes, University of Barcelona, Spain
G. Oncins, University of Barcelona, Spain
F. Sanz, University of Barcelona, Spain
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The effect of temperature on the nanomechanical response of supported lipid bilayers has been studied topographically and by Force Spectroscopy with Atomic Force Microscopy. An AFM equiped with a high temperature stage heater has been used. It has been experimentally proved that the force needed to puncture a phosphatidylcholine lipid bilayer (yield threshold force, Fy)deposited on mica and tested in liquid environment is extremely temperature-dependent. The quantitative measurement of the evolution of Fy with temperature has been related to the structural changes ( phase transitions)that the bilayer undergoes as observed through AFM images. These studies have been carried out with three different phosphatidylcholine bilayers that exhibit different main phase transition temperatures (TM), namely, 1,2-Dimyristoyl-sn-glycero-3-phosphocholine(DMPC), 1,2-Dipalmitoyl-sn-glycero-3-Phosphocholine (DPPC) and 2-Dilauroyl-sn-glycero-3-Phosphocholine (DLPC). The solid-like phase shows a much higher Fy than the liquid-like phase, which also has been proved to exhibit a jump (breakthrough) in the force-curve. Within the solid-like phase Fy decreases as temperature is increased, and suddenly drops as it approaches TM. Interestingly, a well in the Fy vs. temperature plot occurs around TM, thus proving an anomalous mechanical softening around TM. Such mechanical softening has been predicted by experimental techniques and also by MD simulations and interpreted in terms of water ordering around the phospholipid headgroups. A further temperature increase when the phospholipid bilayer is in the liquid phase does not change Fy significantly. Furthermore, ion-binding has been demonstrated to increase Fy@footnote 1@ and its influence on both solid and liquid phases has also been discussed. @FootnoteText@ @footnote 1@Garcia-Manyes,S.; Oncins,G.; Sanz,F.;(Submitted to Biophysical Journal).