Transistor off-Valve Based Feedback, Metering and Logic Operations in Capillary Microfluidics

Capillary microfluidic devices enable portable, pre-programmed assays without the need for external equipment. Automation of liquid handling and reactions in capillaric circuits can be achieved by passive elements alone, making such devices ideally suited for point-of-care applications. However, conventional circuit elements are limited to linear, tree-like operations. In this paper we describe how a new category of elements based on passive ‘transistor’ off-valves can be used to introduce feedback from downstream to upstream in a capillaric circuit. Using micro-milled devices, we demonstrate the use of these valves for autonomous sample intake metering and liquid logic NOR and NAND operations with scalable fan-in.