This article presents a simple and highly reliable method for preparing PDMS microfluidic double emulsion devices that employs a single-step oxidative plasma treatment to both pattern the wettability of the microchannels and to bond the chips. As a key component of our strategy we use epoxy glue to define the required hydrophobic zones and then remove this after plasma treatment, but prior to bonding. This novel approach achieves surface modification and device sealing in a single process, which reduces chip preparation times to minutes and eliminates the need for unreliable coating processes. The second key element of our procedure is the maintenance of the patterned surfaces, where we demonstrate that immediate filling of the prepared device with water or the use of solvent-extracted PDMS vastly extends the operational lifetimes of the chips. The reliability of this technique is confirmed by generating water-in-oil-in-water (W/O/W) double emulsion droplets with controlled core/shell structures and volumes, and diameters as small as 55 μm. Its versatility is shown by simply using a different placement of the epoxy glue on the same chip design to create oil-in-water-in-oil (O/W/O) double emulsion droplets. Both W/O/W and O/W/O double emulsion droplets can therefore be created from the same soft-lithography mould. This simple method overcomes one of the key problems limiting the wider use of double emulsions - lack of reliability - while its speed and simplicity will facilitate the high-throughput production of monodisperse double emulsions. It could also be readily extended to produce microfluidic chips with more complex hydrophilic and hydrophobic patterns.
Li, Shunbo, Xiuqing Gong, Ciara S. Mc Nally, Muling Zeng, Thembaninkosi Gaule, Clara Anduix-Canto, Alexander N. Kulak, Lukmaan A. Bawazer, Michael J. McPherson, Fiona C. Meldrum