Liquid recirculation in microfluidic channels by the interplay of capillary and centrifugal forces
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We demonstrate a technique to recirculate liquids in a microfluidic channel by alternating predominance of centrifugal and capillary forces to rapidly bring the entire volume of a liquid sample to within one diffusion length, δ, of the surface, even for sample volumes hundreds of times the product of δ and the geometric device area. This is accomplished by repetitive, random sampling of an on-disc sample reservoir to form a thin fluid layer of thickness δ in a microchannel, maintaining contact for the diffusion time, then rapidly exchanging the fluid layer for a fresh aliquot by disc rotation and stoppage. With this technique, liquid volumes of microlitres to millilitres can be handled in many sizes of microfluidic channels, provided the channel wall with greatest surface area is hydrophilic. We present a theoretical model describing the balance of centrifugal and capillary forces in the device and validate the model experimentally.
KeywordsBio-sensors Recirculation Capillary forces Centrifugal microfluidics Surface tension Diffusion
This study was supported by Science Foundation Ireland under Grant No. 05/CE3/B754. We thank Kevin Newman for helping with the camera and motor control, and Profs. Luke P. Lee of U.C. Berkeley and Z. Hugh Fan of University of Florida for helpful discussions.
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