Anti-biofouling hydrophobic liquid surface for plasmid extraction on a digital microfluidics chip

Digital microfluidics (DMF) shows a great application prospect in droplet manipulation. However, the fouling of the hydrophobic surfaces caused by biomolecules limits its development. In this study, we report a new strategy to enhance the functionality and anti-biofouling performance of the DMF chip by using a hydrophobic liquid surface (HLS) rather than a regular hydrophobic solid surface (HSS). The DMF chip with such a configuration can efficiently drive various liquids with full-function operations. Moreover, our DMF chips can directly manipulate biomolecular droplets without restrictive conditions like adding surfactants or filling with silicon oil. The liquid-liquid contact between the droplet and the hydrophobic surface ensures that the non-specifically adsorbed biomolecules move along with the droplet. Thus, no residue is left behind to ruin the hydrophobicity of the hydrophobic surface. Meanwhile, the long-term reversibility of contact angle change and stability of droplet movement demonstrate the excellent ability against biofouling. In addition, high- and low-temperature tests also show the temperature stability of the HLS. Finally, a biochemical application, plasmid extraction of Escherichia coli (E.coli) cells, is successfully carried out on the DMF chip with HLS as a proof of its usability. This HLS is expected to offer versatile functionalities and anti-biofouling performance for DMF chips in handling biomolecular droplets.