(168a) A Membraneless Continuous-Flow Microfluidic Filter

We describe a new microfluidic-based filtration method capable of performing simultaneous size-based particle separation and enrichment. Instead of forcing the particle-laden suspension through a microporous membrane, microchannels are constructed with embedded weir-like barriers oriented parallel to the flow direction. When this geometry is incorporated into a curved flow path the resulting centrifugal forces act to push the suspended components across the barrier from the inner wall to the outer wall, with only those smaller than the barrier gap able to pass across. Excessive pressure drops are not imposed because the barrier is oriented parallel to the flow direction rather than perpendicular to it, and the process is ideally suited for high-throughput analysis of large sample volumes because filtration occurs most efficiently at high flow rates where the magnitude of the curvature-induced transverse flow is inherently maximized. We also describe a new laminar flow-based microfabrication approach we have developed to construct these barrier structures that enables complex microchannel topologies to be precisely etched without the multiple lithography steps that would otherwise be needed. Filtration capability is evaluated by injecting mixtures containing fluorescent beads of different sizes, after which separated samples are collected and analyzed by flow cytometry. In addition to demonstrating extremely high selectivity, clogging effects are minimized because the primary flow acts to sweep aggregates downstream.