Enzymes play critical roles in health and disease. In cancer, enzymes called proteases help tumor cells escape and invade by degrading the surrounding tissue matrix. In order to understand how proteases aid in cancer progression, it’s important to be able to visualize where these enzymes are active. The Bhatia Lab has developed chemical probes that can measure and localize protease activity within tissue sections. To validate our approach, we first applied our probes to the colon, in which proteases play important roles under normal, healthy conditions.  Here, we found that our protease-activity probe (red) selectively labeled certain types of cells in the colon called “epithelial cells”, which are dyed in green. These probes could lead to new insights into how proteases produced by epithelial cells contribute to intestinal health and disease, and may also be applied more broadly in other diseases, like cancer, in which protease activity is important.