Abstract: The subject invention relates to a rapid, field-portable, modular, versatile and highly reliable assay device for substances, particularly drugs of abuse, which provides a positive signal in the presence of a specific substance for which the device has been specifically adapted to test. The subject invention also concerns methods for making and using the assay device. The device is easily and reliably manufactured by laminating a series of manufactured layers to each other to form an upper card assembly and a lower card assembly. The upper card assembly is bonded to the upper side of a layer which has an immobilized reagent specific for a test substance bound thereto, and the lower card assembly is bonded to the lower side of the layer having the immobilized reagent. The device can be manufactured and distributed in a unitary, ready-to-use form.