Experimental setup C: Implementation of a DNA-mediated vesicle-vesicle self-assembly.

<p>(A) Schematic representation of the result of experimental setup C (cp. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009886#pone-0009886-g001" target="_blank">Figure 1</a>, setup C, panels e.i and e.ii). (B–E) Confocal laser scanning fluorescence (left) and differential interference contrast (right) micrographs in two columns of merged vesicle populations (VPs) C1 to C4 (VP C1 & VP C2, VP C3 & VP C4). For a detailed description of the experimental procedure see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009886#pone-0009886-g001" target="_blank">Figure 1</a> (setup C). The biotinylated membranes (receptor surface density: 1.0 mol % biotin labeled PEG phospholipids) of all VPs were loaded with biotinylated single stranded DNA (biotin-ssDNA) using streptavidin as a cross-linking agent. VPs differed in streptavidin labeling (VPs C1/3: Alexa Fluor® 488, pseudocolored green in fluorescence micrographs, VPs C2/4: unlabeled) and biotin-ssDNA sequence (VP C1/3: α, VP C2: α', VP C4: β') – only sequences α and α' were complementary. Row headings indicate sodium iodide concentrations in the vesicle lumen and the surrounding medium. Fluorescence labeling of the membranes, silhouette blurring indicating vesicle lysis (cp. B.1, B.2), and accumulation of fluorescence signal positively correlate with sodium iodide concentration (microscope settings were identical for all pictures) causing a tradeoff between membrane loading, DNA hybridization, and vesicle stability. Adhesion plaques indicate stable vesicle-vesicle-linkage (visible adhesion plaques are highlighted in the differential interference contrast micrograph of D.1 by an image overlay with the confocal laser scanning fluorescence (processed) micrograph). The adhesion plaques of one vesicle (D.1) and DNA-independent vesicle-vesicle linkages (C.2) are highlighted by arrows. See text for a discussion of the loss of specificity of the DNA-mediated adhesion process observed in panels C.1 and C.2. Panel D.1 is reproduced with kind permission of Springer Science+Business Media (for original publication see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009886#pone.0009886-Hadorn2" target="_blank">[21]</a>). Scale bars represent 10 µm.