A membrane-based assay device for detecting the presence or quantity of an analyte residing in a test sample is provided. The device utilizes a chromatographic zone on which is disposed a plurality of microporous particles. The chromatographic zone can effectively reduce the "hook effect" in a simple, efficient, and relatively inexpensive manner. In particular, the plurality of microporous particles allows larger-sized analyte/probe complexes to reach the detection zone before the uncomplexed analyte. Because the uncomplexed analyte is substantially inhibited from competing with the complexes for the binding sites at the detection zone, the incidence of "false negatives" may be limited, even at relatively high analyte concentrations.
