Atomic Force Microscopy: Interaction Forces Measured in Phospholipid Monolayers, Bilayers and Cell Membranes

Abstract

Atomic force microscopy (AFM) is a powerful technique which is commonly used to image surfaces at the nanoscale and single-molecule level, as well as to investigate physical properties of the sample surface using a technique known as force spectroscopy. In this chapter, we review our recent research where we used AFM to investigate physical properties of phospholipid monolayers, bilayers, and cell membranes. We describe the experimental procedures for AFM imaging, force measurements, and theoretical models to analyze force spectroscopy data. The data obtained allowed correlations between AFM topography and local adhesion and mechanoelastic properties of supported lipid bilayers in water, supported pulmonary surfactant films in air, and the plasma membrane of epithelial type II cells. Finally, AFM was applied to help elucidate the effect of anesthetics and cholesterol present in the lipid films.

Nanomechanical Properties of Phospholipid Microbubbles

“…Strictly speaking, the Reissner approximation is only valid where the loading of the MB is point-like, however Elsner et al [52] showed by AFM force spectroscopy measurements of polymeric shells in conjunction with finite element analysis the theory can be applied to systems having non-point like loads and over large contact areas. The Reissner solution has been used in studies on polymer microbubbles, [48,53] microcapsules [48,53,54] and phospholipid vesicles, [55,56] when a linear relation was observed at the initial stage of the F-Δ curves.…”

Conductance modulation of charged lipid bilayer using electrolyte-gated graphene-field effect transistor

“…Some smaller molecules, such as carbon dioxide and oxygen, can pass through without difficulty on their own, but larger molecules such as water, sodium, or magnesium cannot pass easily [ 13 ]. The interior of the membrane is also liquid, and this lets proteins, cholesterol, sphingolipids, or sterols converge in it.…”

“…The interior of the membrane is also liquid, and this lets proteins, cholesterol, sphingolipids, or sterols converge in it. The role of sphingolipids is to protect the outside of the cell, and the role of the sterols and cholesterols is to stabilize the phospholipid bilayer in plant and animal cells, respectively [ 13 ]. Although this is critical for cells to have enough constancy, a large amount of cholesterol can make them inflexible, which is hazardous especially if they are part of a vein that must be flexible to allow blood flow [ 10 ].…”

Analytical investigation of bilayer lipid biosensor based on graphene

“…14,15 Normally there is water both outside and inside the cells, hence the molecules form themselves between two sheets, with the hydrophobic ends of both layers in inward direction and the hydrophilic ends of them pointing outwards. 16–18…”

“…14,15 Normally there is water both outside and inside the cells, hence the molecules form themselves between two sheets, with the hydrophobic ends of both layers in inward direction and the hydrophilic ends of them pointing outwards. [16][17][18] A key role of phospholipid bilayer is to prepare the structure to a cell. This is achieved when the hydrophobic and hydrophilic ends of phospholipids are naturally arranged, and when stable, cholesterol and sterols contribute to this too.…”