Researchers have developed nanoscale agents that allow the diagnosis of noncommunicable diseases—such as colorectal cancer—through a simple urine paper-test. The method is based on the principle of detecting disease-specific biomarkers with engineered exogenous molecules. The authors injected synthetic protease-sensitive nanoparticles into the blood stream of mice; once the nano-agent passively reached the disease site, it was cleaved by MMP9, a matrix metalloproteinase that is specifically deregulated in colorectal cancer, releasing a reporter that was eliminated in the urine. As more than 500 proteases can be deregulated in cancer, this approach could be tailored for many other types of tumours.