Extended Data Fig. 8: Optical imaging of probes in different droplets in oil.
From: Water structure and electric fields at the interface of oil droplets
a, Oil droplets prepared with different solvents. Stable oil emulsions only form in water, but not in methanol (MeOH), acetonitrile (MeCN) and DMSO, indicating negligible zeta potential in the latter three systems. b, Chemical structure of positively charged Rhodamine 800 fluorescent probe used in c. c, Top, confocal fluorescence imaging on Rhodamine 800 doped microdroplets in oil. From left to right, the droplet is prepared using a 10 μM Rhodamine 800 solution in water, methanol (MeOH), acetonitrile (MeCN) or DMSO surrounded by hexadecane, respectively. Bottom, fluorescence intensity distributions along the white dashed lines in images. In water microdroplets, the ring-like distribution indicates the probe is enriched at the interface; the signal is strongest at the vertical direction (the same as the laser polarization) and weakest at the horizontal direction, indicating the probe orientation is aligned perpendicular to the interface. Both effects can be readily explained by an interfacial electric field. In contrast, both effects are absent in the other three microdroplets. Scale bars, 5 μm.
