The powdery promise of ‘Smart Dust’

While it might sound like something out of a sci-fi flick, intelligent motes that gather and transmit data in real time are already here. A research group at the University of California, San Diego (UCSD), has developed dust-sized ? chips of silicon that can detect a variety of agents, including substances that a terrorist might dissolve in drinking water or spray into the atmosphere.
“The idea is that you can have something that’s as small as a piece of dust with some intelligence built into it so that it could be inconspicuously stuck to paint on a wall or to the side of a truck or dispersed into a cloud of gas to detect toxic chemicals or biological materials,” said MichaelSailor, a professor of chemistry and biochemistry at UCSD who heads the research team.
Inconspicuous and capable of detecting thousands of possible agents at once, the silicon dust can sense hazardous compounds, remotely allowing it to be employed as an advance warning system in the event of a biological or chemical attack.
“When the dust recognizes whatkinds of chemicals or biological agents are present, that information can be read like a series of bar codes by a laser that’s similar to a grocery store scanner to tell us if the cloud that’s coming toward us is filled with anthrax bacteria, or if the tank of drinking water into which we’ve sprinkled the smart dust is toxic,” said Sailor.
Created by blasting apart encoded silicon wafers using ultrasound, each particle is about 1/10,000 of an inch wide and capable of reflecting specific wavelengths of light when illuminated by a laser beam. In the presence of a chemical or biological agent, the dust reacts by effectively changing color; the change in the wavelength of the returned light identifies the contaminant.
Right now, the laser can detect the color changes in the smart dust outdoors in bright sunlight, from 80 feet away, and the team hopes to extend the range to one kilometer.
An even more astonishing enterprise that the group is currently engaged in involves making smart dust that’s capable of assembling itself, sensing, orienting and reporting on the local environment. This type of smart dust can at present locate an oil drop in water, but the same methodology could one day locate harmful agents, pollutants or even cells.
Each particle of this variety of smart dust contains two highly reflective colored mirrors, which have been chemically modified to stick to a pre-determined type of surface. Once the dust finds—in this case, an oil-water interface—the individual mirrored particles begin to line up, or “tile” themselves appropriately on the surface of the target and change color slightly to indicate that they’ve found their target.
“This is a key development in what we hope will one day make possible the development of robots the size of a grain of sand,” said Sailor. “The vision is to build miniature devices that can move with ease through a tiny environment, such as a vein or an artery, to specific targets, then locate and detect chemical or biological compounds and report this information to the outside world. Such devices could be used to monitor the purity of drinking or sea water, or even to locate and destroy tumor cells in the body.”
While they aren’t as sophisticated as transformers, the particles have the ability to assemble into a larger, more complex structure. Sailor said the purpose of the structure is to allow the assembled particles to signal to the outside world that it has found the surface more easily than would an individual particle.
“This can be thought of as operating like a choir,” said Sailor. “Just as an individual voice cannot be heard as easily as all the voices in a choir singing together, an individual particle has a very weak ‘voice’; it is not easily seen because it is so small. When many particles assemble on the interface, all of the reflectivity properties combine into one big signal that is easily seen by eye or with a spectrometer.”
A sensing revolution
When “smart dust” matures as a technology, it could revolutionize the way sensing mechanisms are deployed.
“How could it be used? Use your imagination,” said Robert Turner, a professor at the University of Virginia School of Law and an associate director at the Center for National Security Law. “ Reporting terrorist volunteers slipping across the Syrian or Iranian border into Iraq, guarding the vast borders in the American southwest, monitoring compliance with arms-control agreements, detecting movement around sensitive infrastructure targets … etc., and the sensors are so tiny they would escape detection in many settings.”
This is a detail that could prove extremely vital. In 1967, the United States began a program called Operation Igloo White that involved dropping battery-powered remote sensors along the Ho Chi Minh Trail in Laos and Cambodia to detect and report vibrations caused by North Vietnamese trucks carrying troops and supplies to South Vietnam. Designed to detect various forms of human activity,such as body heat, truck engines, motion and scent, the sensors were disguised as twigs, plants, and animal droppings. In response, the Vietnamese simply learned to confuse the sensors using decoys, provoking countless tons of bombs released onto empty jungle, which they could then cross safely because the bombings would destroy the sensors until they were replaced. The whole system cost around a $1 billion a year to operate, and despite the huge cost, was deployed for five years.
“In a sense, ‘smart dust’ is a successor technology with far greater potential,” said Turner. “It could ultimately allow us to distribute tiny—say, 1mm—cubed sensors that can detect anything from the movement of a tank or a man to residue from nuclear, chemical or biological weapons tests and report it to a remote location. Each tiny sensor could ultimately cost as little as $1. The relatively low price tag would permit the deployment of far more sensors providing much more reliable coverage.

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