When the Department of Homeland Security (DHS) put out its request in 2007, NASA Ames Research Center scientist Jing Li already had a sensor that reacted to various gases and compounds—she’d been working on it for space applications, like evaluating atmospheres on other planets.
But to answer the DHS specs, she needed a way for the device to “sniff” the air for samples and a system that would allow it to interface with a smartphone.
http://techxplore.com/news/2016-06-smartphone-kind-sensor.html