Figure 4 : SCD of the three lipids calculated from QSCM measurements.

From: Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

Figure 4

(a) Histograms of the Δh images (Fig. 2g–i) of the three lipids with Gaussian distributions fitted to the lipid and mica peaks. The histograms were shifted to centre mica at 0 nm. The lipid peak position times mσ=5.79 (mC m−2) nm−1 give the difference in SCD between mica and lipid. (b) The absolute SCD of lipids and mica is determined by fitting triangles with sides of Δd (height measured at −100 mV subtracted the physical height) and Δσ to the scanning height at −100 mV. The values of mica from the three measurements match within errors. (c) Measured SCD versus theoretical SCD for the three lipids. For all the three lipids, experimental and theoretical values match within errors (s.d.). The black line is 1:1 to guide the eye. (d) Overlay of DPPE topography and charge map. Topography is taken from Fig. 2e, while the charge is calculated as Δh times mσ=5.79 (mC m−2) nm−1. Charge and topography co-localize extremely well.