Nanoscale mechanical probing of supported lipid bilayers with atomic force microscopy

Abstract

We present theory and experiments for the force-distance curve $F\left(z_0\right)$ of an atomic force microscope (AFM) tip (radius $R$) indenting a supported fluid bilayer (thickness $2d$). For realistic conditions the force is dominated by the area compressibility modulus ${\kappa }_A$ of the bilayer and, to an excellent approximation, given by $F=\pi {\kappa }_{A}R{z}_0^2/{\left(2d-z_0\right)}^2$. The experimental AFM force curves from coexisting liquid ordered and liquid disordered domains in three-component lipid bilayers are well described by our model, which provides ${\kappa }_A$ in agreement with literature values. The liquid ordered phase has a yieldlike response that we model as due to the breaking of hydrogen bonds. DOI: http://dx.doi.org/10.1103/PhysRevE.82.041920 © 2010 The American Physical Society