Classic microfluidic devices that exploit transverse diffusionacross adjacent flow streams are Y (or T) structures combining multiple inlet streams into a common channel. These geometries have been used to study interdiffusion of one or multiple species, to evaluate transport processes, and to sense analytes ranging from pH to immunoassay targets. In conventional microfluidic devices, this requires a very stable diffusion interface, which requires at least two extremely stable pumps. The paper Y device shown here demonstrates a pumpless alternative to the conventional microfluidic Y device.
As two flow streams run parallel to one another, molecules from each stream diffuse across the fluid interface. The extent of the spreading depends on a variety of factors, allowing molecules of interest to be identified by the concentration profile of visible solution components across the flow streams.
Once the interface is established, its position is stable as long as there is sufficient source fluid in the source pad. Molecules diffuse across this interface to create a diffuse region that expands in a predictable manner down the channel length. The observed concentration profile of visible solution components can thus be used to determine the presence, absence, or concentration of analytes in an unknown sample.
For more information see:
“Microfluidics without pumps: reinventing the T-sensor and H-filter in paper networks,” Lab on a Chip (2011).
Jennifer L. Osborn, Barry Lutz, Elain Fu, Peter Kauffman, Dean Y. Stevens, and Paul Yager.
Department of Bioengineering, University of Washington, Seattle, WA, USA
Original microfluidic T-sensor:
“A rapid diffusion immunoassay in a T-Sensor,” Hatch, Kamholz, Hawkins, Munson, Schilling, Weigl, and Yager. Nature Biotechnology, 19 (5), 461- 465 (2001).
“Microfluidic diffusion-based separation and detection,” Weigl and Yager. Science, 283 (5400), 346-347 (1999).
“Optical measurement of transverse molecular diffusion in a microchannel,” Kamholz, Schilling, and Yager. Biophysical Journal, 80 (4), 1967-1972 (2001).