Lithography-Free Technology for the Preparation of Digital Microfluidic (DMF) Lab-Chips with Droplet Actuation by Optoelectrowetting (OEW).

Electrically conducting liquid droplets can be activated and moved by electrowetting-on-dielectric (EWOD) and optoelectrowetting (OEW). An important application is droplet manipulation in digital microfluidics (DMF, lab-on-a-chip 2.0) as a chip-sized chemical laboratory. For spectroscopic analyses of chemical reactions, it is often necessary to prepare or examine the reagent droplets before, during, and after the reaction. With OEW, single droplets with volumes of 50-250 nl can be moved, analyzed, and merged in one pipetting step. To ensure analysis sensitivity in many applications, lab-chips should only be used once due to contamination of the surface and chemical modification of the layers by the droplets. Single-use chip preparation without a lithographic step, e.g., for the definition of the spacer layer, reduces efforts and costs. Here, exemplarily, we demonstrate the OEW-driven movement and mixing of chemical reagents in a simple color change reaction analyzed by absorption spectroscopy. Stripes made from the insulating tape serve as spacers between sub and superstrate, and any lithographic step can be avoided.