Active Janus Droplet as a Micro‐Reactor for Automatic DNA/RNA Precipitation and Extraction

We explore the possibility to precipitate and to extract DNA, or RNA using an active water/ethanol Janus droplet. The active Janus droplet is initially formed by a single droplet made of a water/ethanol mixture in an oil/surfactant solution. This active droplet self‐propels and absorbs surfactant molecules, by advection, while moving in the oily phase. The surfactant absorption leads to a phase separation of the water/ethanol mixture and the formation of an active Janus droplet. This active Janus droplet is made of a water‐rich leading droplet and an ethanol‐rich trailing droplet. We employ this phase separation method to precipitate and to extract DNA, RNA, or DNA/RNA mixtures independently, in an automatic manner. This automatic precipitation and extraction of DNA, or RNA, is achieved by tuning their water solubility with the addition of salt and then it is demonstrated by fluorescence. We employ active janus droplet, made of a mixture of water/ethanol, to automatically precipitate and extract sDNA and RNA into an oil mixture. The active droplet is similar a micro‐reactor that does not need any additional centrifuging step, the precipitation and extraction is performed in minutes (compare to hours in lab), and we manipulate liquid volume below the nanoliter.