A Clean Sense

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Science  20 Apr 2012:
Vol. 336, Issue 6079, pp. 277
DOI: 10.1126/science.336.6079.277-c

A primary goal in designing better sensors is to find ways to enhance sensitivity without sacrificing selectivity. Nanoscale materials such as carbon nanotubes should offer an easy route to better sensitivity because of their exceptionally high surface area–to–volume ratio and because their electronic properties are strongly affected by changes in their local environment. Thus, it should be possible to measure exposure to gases that bind to the nanotube surface through changes in electrical conductivity. However, the nanotube surface can easily be altered by low levels of contaminants or by incomplete recovery after an initial sensing cycle, thus changing the electronic properties in an undesired way. Chen et al. show that continuous illumination of single-walled carbon nanotubes by ultraviolet (UV) light leads to a cleaning of the nanotube surface. Detection of dry gases such as NO in an air stream was enhanced, but active sensor material degraded because of the formation of ozone. Detection of NO2 and NH3 in a nitrogen stream reached limits of a few parts per trillion (ppt), and for NO a sub-ppt amount was observed—an improvement of two to three orders of magnitude over other nanoscale devices. The UV light is also responsible for removing the detected gases from the nanotube surface, which enhances the rate at which the sensors can be cycled, but at the risk of increasing the detection limits.

Sci. Rep. 2, 10.1038/srep00343 (2012).

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