Path-Driven Washing and Drying Co-Optimization in Continuous-Flow Lab-on-Chips

Rapid advances in microfluidics technologies have facilitated the emergence of highly integrated lab-on-a-chip (LoC) biochip systems. With such a coin-sized biochip, complicated bioassay procedures can be executed efficiently without any human intervention. To ensure the correctness of assay outcomes, however, cross-contamination among different fluid samples and reagents needs to be dealt with separately during assay execution. As a consequence, washing operations have to be introduced and a washing path network needs to be established on the chip to remove the residues left behind in flow channels/devices. Also, chip drying after washing operations is crucial for maintaining some properties (e.g., pH values) of the subsequent reagents, so that precision degradation caused by residual buffer fluids can be avoided for those concentration-sensitive assays. To realize optimized assay procedures, we consider both washing operations and chip drying for the first time and propose an integer linear programming (ILP)-based path-driven washing and drying cooptimization method called PathDriver-WD for continuous-flow LoC biochip systems. The proposed method includes the following four key techniques: 1) The necessity of contamination removals and channel drying is analyzed systemically to avoid unnecessary washing and drying operations, 2) washing and drying operations are integrated with the regular removal of excess fluids, so that extra channel occupation can be minimized, 3) practical computation models are adopted to evaluate the durations of different washing and drying operations, and 4) optimized washing/drying paths and time windows are computed and assigned so that the completion time of assays can be minimized. Simulation results on multiple benchmarks demonstrate that the proposed method leads to highly efficient washing and drying procedures as well as minimized assay completion time.