Flipping: A Control Strategy for Centrifugal Microfluidic Systems

Over the last decades, centrifugal microfluidics has been employed as a promising technique for handling fluids in a spinning microfluidic disk, with minimal instrumentation. Fluid control can be elegantly achieved thanks to passive capillary and siphon valves that are simply operated by varying the angular speed of the disk. However, in many microfluidic disks, the integration of complex networks to execute sequential microfluidic functions is limited by the robustness of these valves. In this study, we introduce a strategy to implement such sequences without any valving system. The microfluidic features are placed on a chip that is embedded in the disk (chip-on-a-disk). Once the liquid is centrifuged in a given chamber, the chip can be removed and flipped to allow the centrifugal force to redirect the liquid towards another chamber. In this work, we designed chips that each contain a metering chamber (to select a given volume of liquid from a sample) and a chamber downstream . We centrifuged the microfluidic chips in two different setups, a Lab-on-a-disk bench and an Eppendorf 5430R centrifuge. In each experiment, we first rotated the microfluidic chip to select a given volume of liquid inside the metering chamber. We then stopped the rotation to flip the chip and restarted the centrifugation to move the selected volume into the further chamber. We measured the threshold of centrifugal acceleration at which the liquid is removed from a given chamber after flipping. We report the variations of this threshold with the dimensions of the chamber, and relate them to the Rayleigh-Taylor instability. The project is funded by the Wallonia Public Service (grant 2010126 Win2Wal ChipOmics).