Figure 2.

Fluorescence microscopy images of membrane patches illustrating docking, hemi-fusion and full fusion with LUVs. (A) Fluorescence image (red and blue channel overlay) showing two membrane patches (ROI 1 and 2) after applying lateral stress together with a white box at which the intensities of dye A390 and A594 are averaged and plotted in (B). (B) The area scan shows the mean intensity of both dyes taken from the white box shown in (A) using the corresponding color for each dye. Both intensities were normalized by the mean A390 emission of the SLB patches as a reference. The lipid dye A594, initially only present in the LUVs, emits less light from ROI 2 with a tension of (1.1 ± 0.8) mN m⁻¹ compared to ROI 1 that reached a membrane tension of (4.4 ± 0.8) mN m⁻¹. A threshold for the mean intensity I _patch was chosen (black line) to measure the fusion efficiency F _eff (Eq. 3) by lipid mixing so that higher intensities from docked LUVs were excluded. Scale bar: 10 µm.