Bottom Effect in Atomic Force Microscopy Nanomechanics

Abstract

In this work, the influence of the rigid substrate on the determination of the sample Young's modulus, the so‐called bottom‐effect artifact, is demonstrated by an atomic force microscopy force‐spectroscopy experiment. The nanomechanical properties of a one‐component supported lipid membrane (SLM) exhibiting areas of two different thicknesses are studied: While a standard contact mechanics model (Sneddon) provides two different elastic moduli for these two morphologies, it is shown that Garcia's bottom‐effect artifact correction yields a unique value, as expected for an intrinsic material property. Remarkably, it is demonstrated that the ratio between the contact radius (and not only the indentation) and the sample thickness is the key parameter addressing the relevance of the bottom‐effect artifact. The experimental results are validated by finite element method simulations providing a solid support to Garcia's theory. The amphiphilic nature of the investigated material is representative of several kinds of lipids, suggesting that the results have far reaching implications for determining the correct Young's modulus of SLMs. The generality of Garcia's bottom‐effect artifact correction allows its application to every kind of supported soft film.

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“…S2 † (for more detail see Young's Modulus in the ESI †). This value (2 GPa) is about 1 order of magnitude higher than reported so organic thin lms such as synthetic glycosphingolipid 35 or octanethiol 36 based molecular layers, and comparable with other reported polyconjugation SAMs for example quarterthiophene. 37 Due to the high rigidity of SAMs 1 and 2, the bottom effect from the gold substrate was not considered a signicant effect in this work (Scheme 1).…”

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“…This feature provides a convenient experimental model for testing the validity of the theory. Chiodini et al used lipid bilayers to apply bottom-effect corrections to FDCs . Lipid bilayers are of relevance in cell biology and biotechnology. − …”

“…Chiodini et al used lipid bilayers to apply bottom-effect corrections to FDCs. 34 Lipid bilayers are of relevance in cell biology and biotechnology. 68−70 Figure 3 shows the topography (Figure 3a) and Young's modulus maps (Figure 3b,c) of a region that includes singlelipid bilayer and double-lipid bilayers domains.…”

“…Dimitriadis, Chadwick, and coworkers showed that the elastic modulus of the rigid support influences the AFM measurement on cells. This finding led to the so-called bottom-effect artifact, which, in turn, has stimulated different correction models to address the determination of elastic and viscoelastic properties measured by force volume (AFM-based FDCs). − Bottom-effect corrections were also proposed for multilayer materials. ,− Several of the corrections were numerical solutions that were difficult to implement to process AFM experiments.…”

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“…Nanoarchitectonics represents today a promising and powerful strategy in which the LB method yields a perfectly molecular organization within a 2D plane [295,296]. Therefore, because of the wide generality of the nanoarchitectonics concept, LB films can also be applied to a wide range of research fields with practical importance, such as materials production [297][298][299], sensing [300,301], catalysis [302,303], device [304,305], energy [306][307][308][309][310], or biological/biomedical applications [311][312][313][314], or even in the fabrication of smart textile-based sensors (TEX sensors) [311]. These studies underscore the almost limitless possibilities of the LB technique to fabricate well-ordered 2D films of a wide range of materials.…”