This new sensor technology may be able to detect a single molecule of the nerve gas sarin, the most toxic of biological warfare agents. Existing sarin sensors are significantly less sensitive and less stable to boot.

The researchers, led by Dr. Li Shi, use a nanometer-thin crystal of tin oxide sandwiched between two electrodes. When a built-in microheater heated the superthin device, the tin oxide reacted with exquisite sensitivity to gases. The sensor element responded to as few as about 50 molecules of DMMP, a compound widely used to mimic sarin, in a billion air molecules.

Both the nanosizing of the metal oxide and the unique microheater element of the sensor give the detector its high sensitivity, stability, and low power consumption. The thinner a metal-oxide sensor becomes, the more sensitive it is to molecules that react with it. In addition to improved sensitivity, the group found their single-crystal metal-oxide nanomaterials let the detector quickly dispose of previously detected toxins and accurately warn if there are new toxins present. By contrast, previous polycrystalline metaloxide thin-film sensors could not recover automatically after being exposed to toxic or flammable gases. This effect is known as sensor poisoning.

This group is the first to successfully grow the ribbonlike, single crystals of tin oxide for sensing DMMP. Other sensors of this type consist of crystals with many imperfections, and recover slowly because molecules previously detected can become trapped in these imperfections.

Shi's group aims to eventually package multiple sensor elements together on the road toward a commercial sensing device.