Microfluidic devices offer a wide range of improvements over legacy applications as well as entirely new uses. The purpose of this work is to address a diagnostic need regarding wound infections, which are predominantly caused by only a few bacterial strains, by demonstrating a combination of methods capable of extracting, washing and detecting these pathogens. Considering the electrophoretic mobility of bacteria [PVH+12], the primary extraction mechanism was thus chosen to be DC electrophoresis, with electro-osmotic flow (EOF) serving to provide a counter flow, separating live cells from any debris and residue contained in the sample. Collection of target cells will take place in any location where fluid velocity exceeds the target cell migration speed in the local electric field, which can be achieved in a gradual constriction within the channel, resembling a funnel. Ideally, the electric properties of this structure should be indistinguishable from those of the working fluid, leaving the electric field profile unaltered, which initially suggests the use of a hydrogel as a building material. However, issues arising from geometric precision, materials compatibility and a parallel current path bypassing the constriction strongly indicate the use of a narrow slab of substrate instead. The described setup depends on the electrolyte ion concentration, which must be tuned to a band where cell movement occurs within the channel, but not through the nozzle.
