Mechanical Properties of Pore-Spanning Lipid Bilayers Probed by Atomic Force Microscopy

Abstract

We measure the elastic response of a free-standing lipid membrane to a local indentation by using an atomic force microscope. Starting point is a planar gold-coated alumina substrate with a chemisorbed 3-mercaptopropionic acid monolayer displaying circular pores of very well defined and tunable size, over which bilayers composed of N,N,-dimethyl-N,N,-dioctadecylammonium bromide or 1,2-dioleoyl-3-trimethylammonium-propane chloride were spread. Centrally indenting these "nanodrums" with an atomic force microscope tip yields force-indentation curves, which we quantitatively analyze by solving the corresponding shape equations of continuum curvature elasticity. Since the measured response depends in a known way on the system geometry (pore size, tip radius) and on material parameters (bending modulus, lateral tension), this opens the possibility to monitor local elastic properties of lipid membranes in a well-controlled setting.

Unraveling lipid/protein interaction in model lipid bilayers by Atomic Force Microscopy

“…New approaches such as SLBs on nano-holes (Gonçalves et al, 2006;Steltenkamp et al, 2006) will allow a better understanding of the bilayer/substrate interaction and will permit to expose the membrane to different water phases at the two sides. For examples, the possibility to fill the holes with a gel material similar to the cell cytoplasm could reproduce a situation very similar to the biological cell case.…”

Nanoscale mechanical probing of supported lipid bilayers with atomic force microscopy

“…An AFM tip can bend a freely suspended membrane, and compress a supported membrane. In recent work, Steltenkamp et al [11] showed how to extract the bending modulus of lipid bilayers from AFM force-distance curves for bilayers deposited over well defined sized holes (indentation of 'nanodrums'), in which they could safely ignore area compression due to the lack of a supported surface. Another issue neglected in previous AFM studies is the double leaflet form of lipid bilayers, which is known to influence the dynamics of fluctuations [12].…”

Nanomechanical properties of few-layer graphene membranes

“…The AFM tip is modeled as a point force, as it's radius of curvature ͑of the order of 10 nm͒ is much smaller than the radius of the hole R. This differs from studies on lipid bilayer membranes, where the hole diameter is of the same order as the radius of the tip. 16 The force applied at ͑r 0 , 0 ͒ is opposed by the bending rigidity D and the tension T, which we assume to be isotropic, 17 i.e., the flake is equally stretched in both horizontal directions. The equation for deflections that are small compared to the thickness h is 11,18 ͑Dٌ 4 − Tٌ 2 ͒u͑r, ;r 0 , 0 ͒ = F tip r ␦͑r − r 0 , − 0 ͒, ͑1͒ which is solved analytically for a flake that is clamped at the edge of a circular hole ͑i.e., u͑R͒ = 0 and du / dr͑R͒ =0͒.…”