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Paper microfluidics has recently emerged as simple and lowcost paradigm for fluid manipulation and diagnostic testing.[1–3] Compared to traditional “lab-on-a-chip” technologies, it has several distinct advantages that make it especially suitable for point-of-care testing in low-resource settings. The most obvious benefits are the low cost of paper and the highly developed infrastructure of the printing industry, making production of paper-based devices both economical and scalable.[3] Other important benefits include the ease of disposal, stability of dried reagents,[4] and the reduced dependence on expensive external instrumentation.[5, 6] While the paper microfluidics concept has transformative potential, this class of devices is not without drawbacks. Many assays have limited sensitivity in the paper format because of reduced sample volumes and limitations of colorimetric readouts.[6] These devices also exhibit large dead volumes as the entire channel must be filled to drive capillary flow. But perhaps the most significant challenge for paper-based microfluidic devices is their passive nature, which makes it difficult to perform complex multiplexing and multistep assays (eg, sandwich enzyme-linked immunosorbent assay (ELISA)). There has been progress in expanding device complexity through the development of three-dimensional channel networks [7, 8] and adapting channel length, width and matrix properties can provide control of reagent sequencing and time of arrival at specific points on the device.[9] Active “valve” analogues have also been demonstrated using cut-out fluidic switches,[10] and manual folding;[11] however, these techniques …