As reported by [wired]:
Like the subtle complexities of sound and sight, the sense of smell is equally complex with a power all its own. Rats have been trained to detect the faint molecules found in explosives to find landmines, and dogs have been trained to detect specific diseases, both with high levels of accuracy. So it should come as no surprise that a team of scientists have been working on creating an artificial nose to replicate this sensory ability. To do so, they created artificial noses by lathering receptors onto a series of circuits, and then pipe scents onto them recording the resulting electrical output and comparing them to a list of known patterns, with amazing results. The initial device, dubbed the Nano-Nose, was tested and trained on smells from their custom "StinkJet" printer, and later submitted to Darpa where it passed testing. Current models are much more compact, with many possible applications, such as attached to bioreactors to detect their contents, healthcare, explosives detection, and more.
Its a rather facinating read on the perceptions and qualities of the sense of smell, including peoples ability to pick out specific smells in things, much like how we pick out sounds in a crowded room.