A microfluidic assay device for determining the presence or absence of an analyte within a fluid test sample is provided. The present invention provides a technique for achieving continuous flow in a microfluidic device by using at least one input channel, an analysis zone, and a plurality of wicking channels disposed about the perimeter of the analysis zone. In one embodiment, for example, the wicking channels extend radially from the analysis zone. As a result of the particular configuration of the microfluidic device, an assay may performed in a "single step" without the need for active forces, such as a pressure source, electrokinetic force, etc., to induce flow of the fluid test sample through the device. Likewise, flow rate is controlled so that the dwell time of the fluid test sample within the analysis zone is long enough to allow for the desired reactions and/or detection.