Researchers at Tel Aviv University, Israel have developed a prototype for a nanosensor array on a chip that can rapidly and accurately detect explosives in air at ultralow concentrations irrespective of their chemical composition. A description of the sensing device was published June 24, 2014, in Nature Communications. See also: Environmental sensors; Integrated nanosensors; Microsensor; Nanotechnology
Most explosive detectors in use today for transportation security were built to identify nitrogen-containing molecules such as trinitrotoluene (TNT) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) but not peroxide-based explosives, such as triacetone triperoxide (TATP), which can be made using household chemicals. In addition, most nitrogen-based explosives are low in volatility, which means that their concentrations in ambient air samples are typically very low. See also: Analytical chemistry; Aviation security; Explosive; Explosives detection; Nitroaromatic compound; Peroxide
To overcome those limitations, the researchers developed a sensor that consists of an array of nanowire transistors chemically treated to bind with molecules of explosives. This binding interaction changes the conductance of the nanowires, creating an electrical signal. Because different explosives show unique binding interactions, their resulting signals can be characterized like fingerprints to catalog a variety of explosives. The sensor is therefore insensitive to the explosive type but highly sensitive to the presence of explosives, and its accuracy does not vary with the type of explosive because it does not depend on concentration. See also: Semiconductor; Signal processing; Transistor
In tests of the nanosensor array, TATP and TNT were detected within 4–5 meters of their sources in 5 seconds at parts-per-quadrillion (1 x 10−15) concentration, a nearly incomprehensible number equal to a few molecules in 1000 trillion.
Chip-scale sensor arrays have other potential advantages. Their compact size lends itself to use in handheld detectors. They can also be mass produced at low cost using microelectronic manufacturing techniques. See also: Microlithography
