The war on terror is shrinking

Using cell phones to detect ‘dirty bombs’
A separate project spearheaded by researchers at Purdue University aims to harness the ubiquity of electronic devices already known for their portability, including cell phones. The eventual goal: a national consumer-based network of sensors capable of detecting and tracking radiation from “dirty bombs” or nuclear weapons. Most cell phones already contain global positioning systems, suggesting a way for small and cheap radiation sensors to be included and provide precise tracking for even light residues of radioactive material.

In November, researchers led by Purdue’s Ephraim Fischbach and Jere Jenkins demonstrated the system’s ability to detect a weak radiation source by equipping volunteers with the sensors and directing them to randomly walk around the West Lafayette, Ind., campus. Every time a sensor passed the hidden radiation and relayed on its finding, the sensor's GPS coordinates helped researchers narrow down the source's location. Ultimately, the scientists tracked the radiation to a spot about 15 feet from the passersby (the source was sealed and far weaker than anything that would be associated with a “dirty bomb,” scientists noted).

Hypothetically, if a car transporting radioactive material for a bomb passes bystanders, their sensor-equipped cell phones could detect the source and relay the signal to a command center, allowing authorities to discretely track the radiation. The system could be tweaked to ignore known hospital radiation and other everyday sources, like the low-level radioactive potassium isotope found in bananas.

Barry Partridge, director of the Indiana Department of Transportation’s Division of Research and Development, said his department was initially interested in testing out radiation sensors at weigh stations. The transportation department, which helped fund the Purdue study, ultimately decided the weigh stations would be too easy for trucks to bypass. Officials also considered attaching sensors to the department’s fleet of vehicles, but worried about whether the strategy would offer enough coverage.

But with the ubiquity of cell phones and laptops and the low cost of commercially available sensors, Partridge noted, a radiation detection network based on electronic devices could offer ample coverage. “Here, you would just add another radiological sensor to do the detecting — the cell phone user or laptop user would not even know that it is happening.”

An effective network would require widespread public support, of course, and Partridge stressed that privacy concerns would need to be addressed. He noted, however, that volunteers have been involved in origination-destination studies in which GPS-equipped cell phones reveal the location of the user’s vehicle at different time points. “As long as you can mask who is actually driving the vehicle, they don’t seem to care,” he said.

Indiana’s Department of Homeland Security has expressed interest in following up with the project, though Partridge conceded that other challenges remain, such as finding a corporate sponsor to manufacture the sensors and figuring out how to handle all the incoming data.

An ‘avalanche’ of tiny detectors
In the meantime, other bulky detectors are going the way of the dinosaur. Douglas Yoder, an associate professor of electrical and computer engineering at Georgia Institute of Technology in Atlanta, said a new device known as an avalanche photodiode could replace the U.S. military’s bulky, power-hungry and expensive equipment designed to warn of anthrax spores and other bioterrorism agents.

The photodiode contains a material known as gallium nitride that only absorbs photons in the short-wavelength spectrum of ultraviolet light. Many biological spores, including those of the anthrax-causing Bacillus anthracis bacteria, absorb and then re-emit light at specific ultraviolet wavelengths.  “Anthrax spores and yeast spores — and mold spores for that matter — all have a fluorescent fingerprint that we can exploit to distinguish among them and identify them,” Yoder said.

The “avalanche” moniker refers to the new device’s ability to multiply tiny electrical currents by up to one million times, increasing its sensitivity so much that it can detect a tiny amount of anthrax spores. The technique, published earlier this year in the journal Electronics Letters, requires detection units no bigger than 40 microns apiece, or less than the diameter of most human hair. “It’s very, very small, which is good because we can pack a lot of them into very small areas,” Yoder said. “Certainly this sort of thing could fit in your hand. There no reason it couldn’t.”

Elsewhere, engineers at Massachusetts Institute of Technology in Cambridge are developing a mini-sensor to quickly detect trace quantities of hazardous gases, whether toxic industrial chemicals or chemical warfare agents. Following the trend of repurposing or scaling down off-the-shelf technology, the researchers have taken the common identification methods of gas chromatography and mass spectrometry and shrunk them from the size of a grocery bag to that of a computer mouse. The smaller device, expected to be ready within two years, requires 2,500-fold less energy than current versions and yields results in four seconds instead of 15 minutes. Eventually, MIT engineer Akintunde Ibitayo Akinwande hopes to further reduce the size to that of a matchbox.

If ultra-small is the new detection paragon, researchers at Tufts University School of Medicine might soon claim an ever bigger feat. Preliminary research published January in the online journal PLoS Biology suggests an unexpected property for single stranded DNA. When tagged with a fluorescent dye and dried onto a solid surface, the DNA can selectively sniff out airborne chemicals, suggesting a whole new benchmark in the ever-shrinking war on terror.

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