Bomb-Sniffing Plants

Plants That Earn Their Keep

Could airport security gardens be the wave of the future? (“Please have photo ID and boarding pass ready and walk past the rhododenrons.”) How about a defensive line of bomb-sniffing tulips in Central Park in New York, or at the local shopping mall’s indoor waterfall, or lining the streets of Baghdad?

Researchers at Colorado State University have created the platform for just such a plant-kingdom early warning system: plants that subtly change color when exposed to minute amounts of TNT in the air.

They are redesigned to drain off chlorophyll — the stuff that makes them green — from leaves, blanching to white when bomb materials are detected.

“It had to be simple, something your mom could recognize,” said June Medford, a professor of biology at Colorado State, referring to the idea of linking a plant’s chemical response to its color, visible to the naked eye.

The research, published in the peer-reviewed online science journal PLoS One, and financed mostly by the Departments of Defense and Homeland Security, said that plants are uniquely suited by evolution to chemical analysis of their environment, in detecting pests, for example.

Plants in the lab, when modified to sense TNT, the most commonly used explosive, reacted to levels one one-hundredth of anything a bomb-sniffing dog could muster, the paper said.

The trick, still in refinement, is how to make sure the plant’s signal is clear enough and fast enough to be of use.

“Right now, response time is in the order of hours,” said Linda Chrisey, a program manager at the Office of Naval Research, which hopes to use the technology to help protect troops from improvised explosive devices.

Practical application, she said, requires a signal within minutes, and a natural reset system back to healthy green in fairly short order.

Professor Medford said she thought both goals were attainable, perhaps within three years — the goal that military backers are pushing for, she said — but more likely in five to seven years.

One scientist who read the scientific paper on Wednesday and was not involved in the project said he was concerned that the difference between all-clear green and TNT-detected white might be too subtle or subject to false inputs.

“What you want is something that is extreme on-and-off and reliable, and I don’t think they’re there yet,” said Sean R. Cutler, an associate professor of plant cell biology at the University of California, Riverside. “It’s a very interesting work-in-progress.”