Investigation of temperature induced mechanical changes in supported bilayers by variants of tapping mode atomic force microscopy

Abstract

Tapping mode atomic force microscopy (AFM) is an invaluable technique for examining topographical features of biological materials in solution, and there has been a growing interest in developing techniques to provide further compositional contrast and information concerning surface mechanical properties. Phase shifts, cantilever response at higher harmonic frequencies of the drive, and time-resolved tip/sample force reconstruction have all been shown to provide additional compositional contrast of surfaces, as compared to basic tapping mode AFM imaging. This study aimed to demonstrate the relative ability of these different imaging techniques to detect temperature induced changes in the elastic modulus of supported total brain lipid extract (TBLE) bilayer patches on mica. To aid in direct comparison between the different imaging techniques, all required data was obtained simultaneously while capturing traditional tapping mode AFM topography images. While all of the techniques were able to provide compositional contrast consistent with known temperature-induced changes in the bilayer patch, interpretation of the resulting contrast was not always straightforward. Phase imaging suffered from contrast inversion. Individual harmonics responded in a variety of ways to the temperature-induced changes in elastic modulus of the bilayer. The maximum tapping force (or peak force) associated with imaging the bilayer correctly reflected the changes in elastic modulus of the lipid bilayer. Importantly, as the required data can be obtained simultaneously, combining these different imaging techniques can lead to a more complete understanding of a sample's mechanical features.

Periplasmic flagella in Borrelia burgdoferi function to maintain cellular integrity upon external stress

“…Under such conditions, the applied force to the sample can be maintained and systematically varied by changing the set point ratio ( s = A tapping /A o , where A tapping is the tapping amplitude), with lower ratios resulting in a larger total force applied to the surface during each tapping event [ 36 , 37 ]. The ability to maintain a constant F total was verified from experiment to experiment by measuring the force associated with imaging the mica substrate, which can be used as an internal reference standard [ 37 , 38 ].…”

Characterization Techniques for Studying the Properties of Nanocarriers for Systemic Delivery

“…The tapping mode is appropriate for samples weakly bound to the surface or soft samples, such as polymers, lipid bilayers, DNA, or proteins. [38], [39], [40].…”

Seeing is believing: atomic force microscopy imaging for nanomaterial research

“…The tapping mode is usually used to image weakly bound-to-support samples or so samples (polymers, DNAs, proteins, and lipid bilayers). [101][102][103][104] Height imaging can be used to analyze the morphology of characterized nanomaterials, such as nanoparticles, 105 nanotubes, 106 and nanosheets, 107,108 wherein it is important to measure the 3D sizes of the nanomaterials and to analyze the effect parameters on the nanomaterials (Fig. 2).…”