The recent bombings in Boston have highlighted how vulnerable people are to terrorism. Police even swept the area beforehand to check for anything unusual, using the time-honored tools of sharp eyes, ears and a bomb-sniffing dog.
But new high-tech ways of detecting the residues and vapors left by explosive chemicals are on the horizon that could one day complement — or even replace — their human and animal counterparts.
The problem is that finding that type of residue is no easy task. In airports, passengers are let through a checkpoint one at a time and their luggage can be swabbed and a sample taken that way. That's less practical at public events where people literally walk up off the street.
"It's a hard problem," said Jimmie Oxley, professor of chemistry at the University of Rhode Island and co-director of the Department of Homeland Security's Center for Excellence.
The issue, Oxley noted, is that substances have to get into the surrounding air in order to be detected from any distance, and many explosive chemicals don't give off much chemical vapor. ( Gunpowder, of the kind in fireworks, is actually a big exception to this, as it has an odor people can pick up.)
In order to find a bomb, one would have to detect the tiny amount of vapor in the air or identify a telltale bomb-making substance based on a small amount of residue. Currently, there is no commercially available technology that scans for vapor signatures in a sweep of a public street — at least not yet, said Rich Stoddard, director of Trace Platforms at Newark, Calif.-based Morpho Detection, Inc., which makes airport explosives detection systems as well as handheld devices to detect explosives.
The current generation of handheld devices work in a similar way to the devices in airports —an object must be swabbed before an explosive can be detected. "For [long-distance] detection, there's nothing I am aware of," he said. That is, there isn't some device like a Star Trek tricorder one can wave around and see traces of something dangerous several feet away.
Morpho's systems work via ion mobility spectroscopy, or IMS, which Stoddard says is the only method that that has been certified by U.S. government agencies such as the Transportation Security Administration.
IMS works by drawing vapor from a substance (along with the air) into a chamber where it gets converted into electrically charged particles. An electric field moves the ions to a detector. The speed at which the ions move can tell the operator what trace chemicals are in the air.
Implant Sciences Corporation of Wilmington, Mass., has a device called the Quantum Sniffer, used in airports to check bags that are getting loaded onto cargo holds in planes. Their device resembles a small cordless vacuum and uses IMS technology to suck up, charge and funnel vapor particles to a detector.
Glenn Bolduc, CEO of Implant, said he believes if there were a something like a ticket gate for the area where the bombs went off during the Boston Marathon, allowing only one or two people in at a time, the Quantum Sniffer, or any similar device, could have picked up the residue of an explosive on a backpack or on the surface of the bomb. However, the Quantum Sniffer would have to be held pretty close to the backpack or bomb to work, Bolduc said.
Implant Sciences is also working on a mass spectrometer the size of a D-cell battery that can pick up traces of explosives from farther away. A mass spectrometer is a device that analyzes substances by measuring the weight of individual ions. But even that device works best when there is a particular physical area of interest in mind.
Large sweeps not possible yet
There are also technologies that are used by the military in war zones that can do something akin to [long distance] detection, but those are designed to scan specific areas, said John Goodpaster, a professor and director of the Forensic Sciences Program at Indiana University-Purdue University Indianapolis.
"That's where you're going from point A to point B and need to look at something right in front of you," he said. That's not the same thing as sweeping a large open area, he added.
For now, at least, almost every available technology that detects trace amounts of explosives works best in controlled environments — such as airports or stadiums – where people enter in neat lines. In a situation where the access is open, it's much more difficult to pick up threats no matter what method is used.
Even explosive-sniffing dogs have limitations. "A dog needs a pretty big plume [of vapor]," Oxley said. Dogs are quite sensitive, but there's a lower limit to the concentration of explosive chemicals they can detect, and the vapor has to reach the dog in the first place. On top of that, it isn't always clear when the dog is working because like people, they get tired or bored.
On the other hand, Stoddard said, dogs are intelligent and can cover large areas quickly, because a big part of what they do is narrow down a search area. In that sense, they can complement a handheld device like the ones Morpho makes.
This doesn't mean there's no other way to detect explosives. Xplosafe, of Stillwater, Okla., makes nanoparticles that are sprayed onto a surface, or used inside a small tube to test liquids. When the particles change color, it's a sign that a suspect chemical — peroxides and chlorates — is there.
Shoaib Shaikh, CEO of Xplosafe, said a team sweeping an area could spray suspect objects with the particles. He added that Xplosafe is going through the process with the Department of Homeland Security to be approved for use at checkpoints.
That doesn't mean there never will be any kind of "sniffer" technology. Over the last several years, several institutions have attempted to build something that works as well or better than a bomb-sniffing dog. Some technologies use nanometer-thick wires and some with carbon nanotubes and even genetically engineered mice.
"Everyone is working on ways to do this," Oxley said, noting that there are least a dozen companies in Massachusetts alone that are developing explosive detection technologies. "It all depends on funding."