Extended Data Fig. 8: AFM-based force spectroscopy to study the interfacial dynamics of cholesterol SCLs in a polar liquid.
From: Entropic repulsion of cholesterol-containing layers counteracts bioadhesion
(a) The interaction forces of a nonpolar AFM tip (see Extended Data Fig. 7b) with cholesterol SCLs and thiocholesterol SAMs were repeatedly quantified at a singular location on the sample surface. To minimize the influence of the AFM tip on the dynamics of the interfacial cholesterol molecules, the measurement parameters were chosen in such a way that a pause of 20 s was maintained between two consecutive measurements. Sixteen consecutive force-distance measurements were obtained per position with high spatial repeatability to ensure that an identical set of surface molecules contributed to the interaction with the AFM tip. At least six different locations per condition were analyzed on three independent sample surfaces. (b) Plot of the absolute interaction forces for all measurement series. The consecutive number of force-displacement curves measured at a single point and the elapsed time are plotted on the lower and upper x-axes, respectively. The individual measurement series were normalized to the mean value of each series. The resulting values are plotted in (c). (d) The distribution of the relative standard deviations determined from the individual curves in (c). The mean + standard deviation are shown. (e) Average slopes of linear regressions fitted to the individual measurement series presented in (c). There is only marginal evidence of a systematic change in interaction forces over the course of an individual measurement series (i.e., the recording of 16 force-distance curves at one position on the sample), whereby any influence of the measurement process due to wear or contamination of the modified AFM tip or the sample surface can be excluded. The mean ± standard deviation are shown. The number of observations (n) is indicated. P values were determined using unpaired t-tests.
