Microfluidics refers to the manipulation of fluids in sub-millimeter length scale channels. Traditionally, microfluidic devices have been used extensively to miniaturize bioassays. However, bulky pumps are still needed for pushing fluids through traditional microfluidic devices. Paper-based microfluidic devices, on the other hand, can be used to transport fluids without pumps using the capillary action (wicking) of porous paper. This phenomenon is used in many low-cost medical diagnostic devices, e.g. pregnancy strips. The ultimate solution to the challenge of point-of-care diagnostics is to conduct complex multi-step and highly sensitive chemical assays on low-cost and power-free paper microfluidic devices. To accomplish this, our lab has expanded and continues to expand the capabilities of paper microfluidic devices by designing new architectures, valving and control systems, and by developing new flow-based design tools for paper microfluidic devices. We have developed a versatile valving toolkit for paper microfluidics that uses compressed sponges as actuating elements. The timing of valve actuation is controlled by controlling the length of actuation channels (timing wicks). We have demonstrated the utility of such a valving system in conducting a completely power-free and automatic signal enhanced immunoassay at the point-of-care.
The movie below shows a few fluid control tricks that can be accomplished using porous materials alone, without using batteries or electricity:
Shown below are time lapse images of a handheld paper microfluidic device that automatically delivers four different fluids to a test zone in a well-timed manner.
Research publication: Toley BJ, Wang JA, Gupta M, Buser JR, Lafleur LK, Lutz BR, Fu E, Yager P. “A versatile valving toolkit for automating fluidic operations in paper microfluidic devices”, Lab on a Chip, 2015, 15, 1432-1444.
Research group website: https://toleylab.weebly.com