A novel microfluidic concept for bioanalysis using freely moving beads trapped in recirculating flows.

There are only a few examples in which beads are employed for heterogeneous assays on microfluidic devices, because of the difficulties associated with packing and handling these in etched microstructures. This contribution describes a microfluidic device that allows the capture, preconcentration, and controlled manipulation of small beads (<6 microm) in etched microchannels using fluid flows only. The chips feature planar diverging and converging channel elements connected by a narrow microchannel. Creation of bi-directional liquid movement by opposing electro-osmotic and pressure-driven flows can lead to the generation of controlled recirculating flow at these elements. Small polymer beads can actually be captured in the controlled rotating flow patterns. The clusters of freely moving beads that result can be perfused sequentially with different solutions. A preliminary binding curve was determined for the reaction of streptavidin-coated beads and fluorescein-labelled biotin, demonstrating the potential of this bead-handling approach for bioanalysis.