Researchers of University of California, Berkeley have used silver nanowires as key elements in a sensitive explosives detector.

The researchers made about a trillion silver nanowires, essentially nanocopic needles and packed them tightly together in a thin layer with all needles pointing in the same direction. The layer of ordered nanowires made an ideal site for chemicals to bind for detection by a very sensitive technique called surface-enhanced Raman spectroscopy, because Raman spectroscopy is an extremely sensitive and specific technique that basically gives a chemical signature, a fingerprint.

A monolayer of silver nanowires can act as a very sensitive substrate to detect molecules like DNT (dinitrotoluene, a cousin to TNT), which is used in making essentially all explosives, including land mines. These explosives have DNT vapor coming out, allowing us to do airborne detection. The surface of packed silver nanowires is more ordered and gives a more clearly defined signal, making interpretation of the Raman vibrational spectrum easier. The packed silver nanowires are uniform, reproducible and suitable for use in air or in liquid.

The researchers hope to miniaturize the laser and other components required by Raman spectroscopy to create a microscopic sensor on a chip, allowing very sensitive and specific detection of chemicals like explosives.

This nanowire-based sensing scheme could have significant implications in chemical and biological warfare detection, national and global security, as well as medical detection applications. The nanowire layers have other potential uses, too. The researchers claim that the monolayers can be transferred to any surface, including silicon, glass or flexible plastic polymers, to provide a large area. The nanowire layers can be fabricated in large areas providing a flexible monolayer that would be a key component in a number of flexible electronic devices, such as flexible solar cells and light emitting diodes.