Programming fluid transport in paper-based microfluidic devices using razor-crafted open channels.

Manipulating fluid transport in microfluidic, paper-based analytical devices (μPADs) is an essential prerequisite to enable multiple timed analytical steps on the same device. Current methods to control fluid distribution mainly rely on controlling how slowly the fluid moves within a device or by activating an on/off switch to flow. In this Article, we present an easy approach for programming fluid transport within paper-based devices that enables both acceleration as well as delay of fluid transport without active pumping. Both operations are programmed by carving open channels either longitudinally or perpendicularly to the flow path using a craft-cutting tool equipped with a knife blade. Channels are crafted after μPADs fabrication enabling the end user to generate patterns of open-channels on demand by carving the porous material of the paper without cutting or removing the paper substrate altogether. Parameters to control the acceleration or delay of flow include the orientation, length, and number of open channels. Using this method, accelerated as well as reduced fluid transport rates were achieved on the same device. This methodology was applied to μPADs for multiple and time-programmable assays for metal ion determination.