C2lc21089d 1238..1241

Fig. 1 Schematic top view on the channel separator, showing a full separation cycle. A periodically inverting external force Fext drags two diffusive particles featuring different drift velocities in the y-direction, starting from the small saw teeth. Possible diffusion paths are schematically depicted. Channel width d, large sawtooth length L, and profile amplitudes h and h/2 are indicated. The integration of microparticle separators into lab-on-a-chip devices is a crucial issue for the ongoing development in the field of microfluidics. Preferably, such a separator would exhibit a channel structure to easily integrate with other microfluidic components. In order to achieve lab-on-a-chip devices with small overall dimensions and to enable versatile designs of microfluidic circuits, the construction of compact separators is essential. Previously, various separation mechanisms have been demonstrated, such as hydrodynamic filtration, electrophoresis, magnetophoresis, acoustophoresis and separation through optical forces. Further, Brownian ratchets have been identified as a concept to transport microparticles, and have been suggested and implemented as separators before. However, none of the before-mentioned techniques features the desired compactness. This article presents a new class of extremely compact microsieves. By performing the separation in a single channel, our device features dimensions which are about one order of magnitude smaller than the smallest separator fabricated by other methods to date. We schematically illustrate our separation method in Fig. 1. The device consists of a single channel made of two opposing sawtoothshaped walls. A periodically inverting external force Fext is applied to the particles perpendicular to the channel (y-direction). We consider two particles with distinct drift velocities, i.e., a slow particle (blue)