Paper-Based Surfaces with Extreme Wettabilities for Novel, Open-Channel Microfluidic Devices

In this work, a facile methodology is discussed, involving fluoro-silanization followed by oxygen plasma etching, for the fabrication of surfaces with extreme wettabilities, i.e., surfaces that display all four possible combinations of wettabilities with water and different oils: hydrophobic–oleophilic, hydrophilic–oleophobic, omniphobic, and omniphilic. Open-channel, paper-based microfluidic devices fabricated using these surfaces with extreme wettabilities allow for the localization, manipulation, and transport of virtually all high- and low-surface tension liquids. This in turn expands the utility of paper-based microfluidic devices to a range of applications never before considered. These include, as demonstrated here, continuous oil–water separation, liquid–liquid extraction, open-channel microfluidic emulsification, microparticle fabrication, and precise measurement of mixtures' composition. Finally, the biocompatibility of the developed microfluidic devices and their utility for cell patterning are demonstrated.