Spontaneous formation in air of DPPC Supported Lipid Bilayers (SLBs) evaporated in a solvent free process on silicon substrates

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Artificial membranes are models for biological systems and are important to gain deeper insight into biological membranes and for various applications. We introduce a dry two-step self-assembly method consisting of the high-vacuum evaporation of phospholipid molecules over silicon, followed by a subsequent annealing step in air. We evaporate dipalmitoylphosphatidylcholine (DPPC) molecules over bare silicon without the use of polymer cushions or solvents. High-resolution ellipsometry and AFM temperature-dependent measurements are performed in air to detect the characteristic phase transitions of DPPC bilayers. Complementary AFM force-spectroscopy breakthrough events are induced to detect single- and multi-bilayer formations. These combined experimental methods confirm the formation of stable non-hydrated lipid bilayers with phase transitions between gel to ripple phases at 311.5 ± 0.9 K, ripple to liquid crystalline phases at 323.8 ± 2.5 K and liquid crystalline to fluid disordered phases at 330.4 ± 0.9 K, which was consistent with such structures reported in wet environments. We find that the AFM tip induces a restructuring or intercalation of the bilayer that is strongly related to the applied tip-force. These dry supported lipid bilayers show long-term stability. These findings are relevant for the development of functional biointerfaces, specifically for fabrication of biosensors and membrane protein platforms. The observed stability is relevant in the context of lifetimes of such systems protected by bilayers in dry environments, such as e.g. SARS-CoV-2 virus.
Tesis (Doctor en Física)--Pontificia Universidad Católica de Chile, 2021