Can a machine mimic the human—or better yet, the canine—sense of smell? To do so, it would have to not only determine whether a chemical vapor is present in small amounts but also figure out, at least partially, what chemical it is.
Carbon nanotubes and other nanomaterials do a good job on the first front. Their small size means that the presence of just a few gas molecules is enough to measurably change their electrical properties. But to discriminate among many different molecules, an “electronic nose” must contain an array of sensors, each with different response characteristics.
In 2005 A. T. Charlie Johnson (University of Pennsylvania), Alan Gelperin (Monell Chemical Senses Center in Philadelphia), and their colleagues began to investigate whether a nanotube sensor decorated with single-stranded DNA, as shown in figure 1, might provide the needed specificity to serve as an array element.1 They found that sensors...
