A lateral flow assay device for detecting the presence or quantity of an enzyme or enzyme inhibitor is provided. The lateral flow assay device utilizes a molecular substrate to facilitate the detection of an enzyme or enzyme inhibitor via detection of the substrate and/or a product formed in an enzyme-catalyzed reaction of the substrate. In one embodiment, for example, upon contacting a molecular substrate, an enzyme catalyzes a reaction with the molecular substrate and forms a product. The lateral flow assay device also includes a detectable substance that may generate a detectable signal for determining the presence or amount of enzyme in a test sample. For example, the detectable substance may be directly or indirectly attached to a specific binding member that has affinity for the product. Following the enzyme catalyzed reaction, the product may bind the detectable substance which may, in turn, generate the detectable signal. The signal exhibited by the substance may then be used to indicate the presence or quantity of an enzyme or enzyme inhibitor within the test sample.