Dissolvable Film-Controlled Buoyancy Pumping and Aliquoting on a Lab-On-A-Disc

Lab-on-a-Disc (LoaD) has great potential for applications in decentralised bioanalytical testing where speed and robustness are critical. Here, a disc-shaped microfluidic chip is rotated to pump liquid radially outwards; thus, all microfluidic structures must be fitted into the available radial length. To overcome this limitation, several centripetal pumping technologies have been developed. In this work, we combine buoyancy pumping, enabled by displacing aqueous samples and reagents centripetally inwards by a dense liquid (fluorocarbon FC-40), with dissolvable film (DF) to automate a multi-step assay. The DF dissolves in the presence of water but is not in contact with the FC-40. Therefore, the FC-40 can be stored behind the DF membranes and is autonomously released by contact with the arriving aqueous sample. Using this technology, tasks such as blood centrifugation can be located on the disc periphery where 'disc real estate' is less valuable and centrifugal forces are higher. To demonstrate this, we use the combination of the buoyancy-driven centripetal pumping with DF barriers to implement a fully automated multi-parameter diagnostic assay on the LoaD platform. The implemented steps include plasma extraction from a structure, automatically triggered metering/aliquoting, and the management of five onboard stored liquid reagents. Critically, we also demonstrate highly accurate aliquoting of reagents using centripetal pumping. We also provide a mathematical model to describe the pumping mechanism and apply lumped-element modelling and Monte Carlo simulation to estimate errors in the aliquoting volumes caused by manufacturing deviations.