Hierarchical micro and nano structured, hydrophilic, superhydrophobic and superoleophobic surfaces incorporated in microfluidics, microarrays and lab on chip microsystems

Control of wetting properties at the extremes of wetting states (superhydrophilic and superhydrophobic) is important for many applications, such as self-cleaning, anti-fogging, anti-icing, and antibacterial action. While significant effort has been devoted to develop and characterize such open surfaces for various applications, their incorporation in sensors, microfluidics, and labs on chip, offers new functional devices and systems, and poses different requirements compared to open-area surfaces. In this paper, dedicated to the 30 year anniversary of Microelectronic Engineering, we aim to review the extreme wetting states of surfaces, their fabrication processes focusing on plasma processing technology, and their incorporation into devices and systems. We start with an introduction and terminology for superhydrophilic, superhydrophobic, and superoleophobic surfaces, and continue with a review of the fabrication of such surfaces by plasma processing. We then review how such surfaces are incorporated in microdevices and microsystems, and their applications. We address (a) Hydrophilic capillary pumps and superhydrophobic valves, (b) Drag reduction in superhydrophobic microchannels and slip length increase, (c) Superhydrophobic surfaces for droplet manipulation, applied to chemical and biological analysis, (d) Biomolecule adsorption control on nanostructured surfaces, and (e) Cell adhesion on such surfaces. Finally, we conclude with perspectives and challenges.