Atomic force microscopy study of elastic properties of vapor-phase-deposited lipid membranes
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2018
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Abstract
In this work we present a study of phase transitions and their relation with the elastic properties of three phospholipid membranes, namely 1,2-dimyristoyl-snglycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). Samples were generated individually by physical-vapor-deposition of the lipid molecules mentioned over acid-cleaned polished silicon chips. The thickness of the samples were measured with Very High Resolution Ellipsometry. Average thickness are 60˚Athickness on average. The molecular consistency of the lipids were characterized using Raman spectroscopy. The Young’s modulus of the lipid membranes was obtained applying the Hertz model to data acquired with Atomic Force Microscopy in Quantitative Imaging feedback mode. Finally, the individual dependence of these lipids respect to temperature changes was used to detect the main gel-to fluid phase transition.The results in the present work show an expected softening of the lipid membranes just after the main phase transition, although the values of the elastic modulus found do not match the ones reported in the literature. However, the general trends correlate well with the ones found in other works. Nevertheless,systematic investigations using similar conditions as ours are still scarce.The acquisition of information related to the elastic properties and stability of the membranes is relevant for future works on protein insertion, and to understand the lipid membranes dependance on several other environmental conditions like changes in temperature, pH-dependence or ionic strength concentration.
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Tesis (Master in Physics)--Pontificia Universidad Católica de Chile, 2018