Fig. 1. Programmable liquid circuits implemented in capillary-driven microfluidics.

Concept on controlling, monitoring, sequential delivery, and merging of multiple liquids flowing in microfluidic chips using an array of electrically actuated microfluidic gates (e-gates) and a protocol applied from a smartphone. Liquids pipetted to a capillary-driven microfluidic chip autonomously flow inside microfluidic channels by capillary action until the flow is stopped by pinning the liquid meniscus at a trench-patterned orthogonal to the flow path. The flow is resumed by applying a potential difference (<5 V) between the liquid (positive) and an electrode patterned over the trench (ground). The location of the meniscus is monitored using capacitance measurements as a feedback. Using capillary valves with air vents and self-vented channels and e-gates, pipetted liquids can sequentially flow through the same channel in any order and combination, and liquids flowing in opposite directions can be merged without creating air bubbles.