Rate dependent rupture of solid-supported phospholipid bilayers.

Abstract

An experimental study on solid-supported phospholipid bilayers was performed in order to investigate rate-dependent behavior of force and probability of bilayer rupture. 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) solid-supported lipid bilayers were created on mica using vesicle fusion technique and then ruptured normal to the surface using a silicon nitride cantilever tip (radius#80nm). High resolution force spectroscopy was performed using the Molecular Force Probe (1D) to obtain force versus distance curves between the tip and substrate, varying the rate of penetration between a range of 250 nm/sec to 8.0 pm/sec. Statistical analysis was used to find distributions for average yield distance and yield force at different rates to find correlations in our data. Lastly, experimental data was compared to proposed theoretical models that describe rupture probability as a function of activation energy. A two yield force profile on approach was achieved with consistency at all rates. The yield forces occurred at statistical significant distances of around 4 nm and 9 nm, which are consistent with bond calculations of the phospholipid. However, no relationship was found between force and tip velocity within the range of experimentation.

(cont.) Because rupture occurred even at the lowest penetration rates, activation energy for bilayer rupture appears to be quite low. Moreover, this also suggests that standard atomic force microscopy imaging stimulates perturbation of the surface, leading to imprecise characterization. Further investigation into a larger range of tip velocities, as well as the role of tip radius on rupture probability are recommended for a greater quantitative understanding of solid-supported bilayers.