A planar micro-device capable of rapidly separating large volumes of dilute suspensions was designed and modelled using a commercial CFD package. The device consists of a single planar Archimedean spiral micro channel with a bifurcation at the exit. The device exploits small inertial and hydrodynamic differences between particles of dissimilar size, which arise as the sample is rapidly pumped through the device. The channel length and location of the bifurcation were found to affect the separation achievable by the devices. Devices of varying geometries were fabricated using conventional silicon micro fabrication processes and were tested by flowing dilute aqueous suspensions of polystyrene particles (diameters of 1μm, 8μm and 10μm) through the devices at various flow rates. A 3.5 fold concentration enhancement of 10μm particles was achieved in the longer devices at flow rates of 2 ml/min, whereas the 1μm particles showed negligible concentration increases at similar flow rates. The device may be used as a sample preparation stage in a complex μTAS, where rapid, continuous concentration of dilute suspensions is often required.

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