Using the atomic force microscope to study the interaction between two solid supported lipid bilayers and the...

Area of Science:

• Biophysics
• Materials Science
• Surface Chemistry

Background:

• Understanding lipid bilayer interactions is crucial for cell membrane dynamics and biomaterial design.
• Atomic force microscopy (AFM) provides high-resolution force measurements at the nanoscale.

Purpose of the Study:

• To quantify the interaction forces between lipid bilayers using AFM.
• To investigate the influence of lipid composition and salt concentration on bilayer interactions.
• To explore the effect of the protein synapsin I on lipid bilayer stability.

Main Methods:

• Formation of solid-supported lipid bilayers on a planar surface via spontaneous vesicle fusion.
• Coating AFM tips with gold and a mercapto undecanol monolayer for bilayer adsorption.
• Measurement of interaction forces between different lipid bilayers (DOPC, DOPS, DOTAP) using AFM.
• Analysis of electrostatic double-layer forces and shorter-range repulsions.

Main Results:

• Lipid bilayer interactions are characterized by electrostatic double-layer forces and short-range exponential repulsion.
• Decay lengths of repulsion varied for different lipids: 0.7 nm (DOPC), 1.2 nm (DOPS), 0.8 nm (DOTAP).
• Salt concentration significantly altered the interaction forces between DOTAP bilayers.
• Synapsin I increased membrane stability, inhibiting AFM tip penetration.

Conclusions:

• AFM is a suitable technique for measuring lipid bilayer interactions, sensitive to lipid type and environmental conditions.
• The presence of synapsin I significantly enhances lipid bilayer stability, impacting membrane fusion and integrity.
• Long-chain alkyl thiols on AFM tips promote spontaneous vesicle fusion due to increased van der Waals attraction.