Capillary flow control in lateral flow assays via delaminating timers.

Lateral flow assays (LFAs) use capillary flow of liquids for simple detection of analytes. While useful for spontaneously wicking samples, the capillary flow inherently limits performing complex reactions that require timely application of multiple solutions. Here, we introduce a technique to control capillary flow on paper by imprinting roadblocks on the flow path with water-insoluble ink and using the gradual formation of a void between a wetted paper and a sheath polymer tape to create timers. Timers are drawn at strategic nodes to hold the capillary flow for a desired period and thereby enable multiple liquids to be introduced into multistep chemical reactions following a programmed sequence. Using our technique, we developed (i) an LFA with built-in signal amplification to detect human chorionic gonadotropin with an order of magnitude higher sensitivity than the conventional assay and (ii) a device to extract DNA from bodily fluids without relying on laboratory instruments.