Any technique for ferreting out explosives needs to meet a few requirements. It must be sensitive, ideally capable of detecting trace amounts in air. It must also exhibit the utmost accuracy, to distinguish a dangerous molecule from a related but innocuous one. With those principles in mind, Fernando Patolsky of Israel’s Tel Aviv University and colleagues have developed a nanoscale device array that can fingerprint two classes of explosives, some down to the parts-per-quadrillion concentration range (Nat. Commun. 2014, DOI: 10.1038/ncomms5195). Patolsky’s multi-institution team combined a few established concepts to build the chip. It contains silicon nanowires, which change their electrical properties in response to tiny amounts of chemicals adsorbing on their surface. In addition, various regions of the chip have different chemical modifications. These lead to better discrimination between explosives and related molecules. For instance, the array can tell TNT from a closely related compound called musk ketone, Patolsky points out. The device also detects other nitro-group-containing explosives, and peroxide-based explosives such as triacetone triperoxide (TATP), in air samples. The team now hopes to conduct field tests to learn more about the nanosensors’ performance.