Abstract: A filtration unit for separating at least one analyte from a fluid sample. The filtration unit includes: an inlet configured to receive the fluid sample and an outlet configured to receive the at least one analyte; a fluid pathway providing fluid communication between the inlet and the outlet, where the fluid pathway has a longitudinal axis along which the fluid sample flows, in use; a filter located in the fluid pathway, where the filter includes at least one surface configured to allow the passage of the at least one analyte and the at least one surface is substantially transverse to the longitudinal axis of the fluid pathway; and an impeller located adjacent to the filter, where the impeller is configured to generate tangential fluid flow in the vicinity of the filter and wherein the impeller includes a rotatable shaft coupled to at least one blade having a rounded leading edge.