The invention is directed to an apparatus useful in conducting detection of compounds on blotting membranes. The device is comprised of several layers including a porous support layer below the blotting membrane(s), a flow distributor above the blotting membrane(s) and optionally a well on the flow distributor to contain the liquid to the desired area and to allow for lower starting volumes of such liquid. Preferably, the flow distributor is a non-binding or low binding hydrophilic porous membrane such as a 0.22 micron membrane and the support layer is a grid or sintered porous material. The distributor and support are held together to form an envelope around the membrane(s). The use of a hinge, clips and other such devices is preferred in doing so.