Multivortex micromixing

The ability to mix liquids in microchannel networks is fundamentally important in the design of nearly every miniaturized chemical and biochemical analysis system. Here, we show that enhanced micromixing can be achieved in topologically simple and easily fabricated planar 2D microchannels by simply introducing curvature and changes in width in a prescribed manner. This goal is accomplished by harnessing a synergistic combination of (i) Dean vortices that arise in the vertical plane of curved channels as a consequence of an interplay between inertial, centrifugal, and viscous effects, and (ii) expansion vortices that arise in the horizontal plane due to an abrupt increase in a conduit's cross-sectional area. We characterize these effects by using confocal microscopy of aqueous fluorescent dye streams and by observing binding interactions between an intercalating dye and double-stranded DNA. These mixing approaches are versatile and scalable and can be straightforwardly integrated as generic components in a variety of lab-on-a-chip systems

Droplet-Based Pyrosequencing Using Digital Microfluidics

The feasibility of implementing pyrosequencing chemistry within droplets using electrowetting-based digital microfluidics is reported. An array of electrodes patterned on a printed-circuit board was used to control the formation, transportation, merging, mixing, and splitting of submicroliter-sized droplets contained within an oil-filled chamber. A three-enzyme pyrosequencing protocol was implemented in which individual droplets contained enzymes, deoxyribonucleotide triphosphates (dNTPs), and DNA templates. The DNA templates were anchored to magnetic beads which enabled them to be thoroughly washed between nucleotide additions. Reagents and protocols were optimized to maximize signal over background, linearity of response, cycle efficiency, and wash efficiency. As an initial demonstration of feasibility, a portion of a 229 bp Candida parapsilosis template was sequenced using both a de novo protocol and a resequencing protocol. The resequencing protocol generated over 60 bp of sequence with 100% sequence accuracy based on raw pyrogram levels. Excellent linearity was observed for all of the homopolymers (two, three, or four nucleotides) contained in the C. parapsilosis sequence. With improvements in microfluidic design it is expected that longer reads, higher throughput, and improved process integration (i.e., “sample-to-sequence” capability) could eventually be achieved using this low-cost platform