Abstract

Droplet-in-Oil Microfluidics for the Lab-on-a-Disc Platform

Ho Pui Ho, Professor, The Chinese University of Hong Kong

We report the use of droplet-in-oil strategy in a lab-on-a-disc (LOAD) device platform. In common lab-on-a-disc devices, movement of the aqueous sample inside the microchannel is predominantly affected by surface tension coming from the channel surface. Typically one would make the surface hydrophobic to ensure smooth sample movement. In centrifugal microfluidic (i.e. lab-on-a-disc) devices, the control of surface tension becomes critically important, as the operation of microfluidic components such as the capillary burst valve and siphon valve rely solely on surface tension effects. However, in practice, surface tension is fabrication and temperature dependent, thus leading to large variations in device parameters. In addition, it is also difficult to control the sample loading volume in the presence of surface tension. The droplet-in-oil approach is an effective approach to address problems associated with surface tension. By suspending the sample droplet in a carrier oil medium, one can remove surface tension completely. Furthermore, by incorporating the droplet-inoil approach in the lab-on-a-disc device platform, actuation force in the absence of surface tension becomes much easier to control as it depends primarily on the spinning speed and density difference. Centrifugal force acting on the droplets is also present everywhere within the disc surface, thereby completely removing the need of external pumping. Most importantly, movement of the droplets is completed driven by inertial forces and therefore does not require any motion of the carrier fluid. The mineral oil medium remains stationary throughout the course of the bioassay. In this presentation, we report several microfluidic components we have developed for droplet generation, performing stop-go actuation and merging droplets in order to carry out typical sample processing steps as required by common bioassays. We also demonstrate the use of our device for performing nucleic acid am