Revisiting the Interaction Force Measurement between Lipid Bilayers Using a Surface Forces Apparatus (SFA).

In this review, previous researches that measured intermembrane forces using the Surface Forces Apparatus are recapitulated. Different types of interaction forces are reported between two lipid bilayers including non-specific interactions (e.g., van der Waals, electrostatic, steric hydration, thermal undulation, and hydrophobic) and specific interactions (e.g., ligand-receptor). By measuring absolute distance and interaction forces at the sub-angstrom level and at a few nano-Newtons resolution, respectively, magnitudes, working ranges, and decay lengths of interaction between lipid bilayers are investigated. Utilizing recently developed fluorescence microscopy attachments, simultaneous fluorescence imaging of membrane proteins and lipid phases can be performed during approach/separation cycles of two lipid bilayer deposited surfaces, which can reveal cooperative effects between lipid phases and various types of membrane proteins.