Fig. 4
From: Spatiotemporal control of cargo delivery performed by programmable self-propelled Janus droplets
DNA precipitation and controlled cargo delivery. a Sketch; the intensity of the blue and yellow colors indicate increasing concentration of water, respectively of ethanol. b Fluorescent microscopy time series showing the precipitation of fluorescent DNA into the ethanol-rich droplet, which finally pinches off. The initial droplet phase contained 50 vol% ethanol, 0.2 mg/ml DNA, 0.25 mg/ml Hoechst 33342, and 25 mg/ml sodium acetate. c–e Overlapped time series of droplets being hydrodynamically attracted to circular PDMS pillars in stage 1 and delivering cargo in stage 3 (c); attracted to square Teflon-coated pillars in stage 1, but not delivering cargo (d); and repelled from circular pillars in stage 3 (e). The shown traces denote 140 s (c), 180 s (d), and 50 s (e) from blue to red. The scale bars in b denote 100 μm, while the pillars in c–e are 800 μm across. f Sketch of possible delivery scenarios depending on target geometry and wettability. Green color (and left hashed) indicates attractive hydrodynamic interactions, while situations of repulsive hydrodynamic interactions are shown in red color (and right hashed). The top/bottom half sketches the situation for square and circular pillars, respectively, while the left/right half presents the situation for PDMS and Teflon surfaces
