A thin-film chemical sensor coated onto an electrode offers a simple, practical way to detect minute traces of toxic gas. Sensors that use metal-organic frameworks (MOFs) can be highly selective for a particular gas because of the porous nature of these crystalline materials and their nanoscale cavities. Recently, Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) researchers developed a MOF-based sensor that can selectively sense hydrogen sulfide at concentrations of just a few parts per billion (ppb). Their method of altering the structure of the MOF electrode coating allows them to detect a range of gases.