Rapid, easy-to-use, and portable devices that can provide a read-out without the need for expensive equipment represent the future of sensing technology, with applications in areas like environmental, food, chemical, and biological safety. Enzymes immobilized on a surface function as micropumps in the presence of species (e.g., substrate, cofactor, or biomarker) that trigger the enzymatic reaction. The flow speed in these devices increases with increasing reaction rate. This allows the detection of substances that inhibit the enzymatic reaction. Using this principle, sensors for toxic substances, like mercury, cadmium, cyanide, and azide, were designed using urease and catalase-powered pumps, respectively, with limits of detection well below the concentrations permitted by the Environmental Protection Agency. The study was also extended to other inhibitors for these enzymes. The sensing range of fluid flow-based inhibitor assays depends on the type of inhibition, the enzyme concentration on the sensing platform, and, for competitive inhibition, the concentration of substrate used.