Process, test device, and test kit for a rapid assay having a visible readout

A device for use in an assay for detecting the presence of an analyte using a tracer having a particulate label comprising:

• a porous support having upper and lower surfaces and a test area on its upper surface;
• a binder attached to the test area;
• an absorptive layer in fluid communication with the porous support;
• and
• a porous flow control layer positioned between the lower surface of the porous support and the absorptive layer;
• wherein:
• the porous support has pore sizes sufficient to allow passage of liquid and any analyte and tracer not bound to the test area,
• the support area does not specifically bind the tracer,
• the test area has a surface area sufficiently large to support binder in a concentration whereby tracer specifically bound to the test area under assay conditions is visible,
• the porous flow control layer has unidirectional channels with their pore sizes smaller than those of the porous support and large enough to allow passage at controlled rates of liquid and any analyte and tracer not bound at the test area, and
• the porous support, the porous flow control layer and the absorptive layer cooperate to control flow of reagents through the porous support and to receive liquids and any analyte and tracer not specifically bound at the test area in absorptive layer.