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Scientists know some of the hazards contaminating the New Orleans floodwaters, but not all of them. As this ScienCentral News video explains, researchers are developing something called "smart dust" to reveal what lurks in such environments.
Tiny Toxin Tracker
The destruction that hurricane Katrina left in her wake along the Gulf Coast is glaringly obvious. But cleaning up after big hurricanes means more than picking up debris and replacing roofs. Invisible damage lurks too, as when floodwaters breed bacteria and viruses, and harmful chemicals mix in a toxic stew.
"[They're] little devices that'll move through the environment, find something harmful… and then signal to the outside world that they can find it, that they found it," explains nanotechnology researcher Mike Sailor from the University of California, San Diego. "A first responder could wear them on their clothing… [indicating] very quickly to them what kind of agent they've been exposed to."
Smart Dust image: Michael Sailor and Jamie Link, UCSD.
The glittering smart dust is made up of tiny silicon pieces, smaller than the width of a hair, drilled with even tinier holes, or pores. "If one of our holes were the size of a quarter, a human hair would be about a football field wide… half a mile wide actually. These are very, very small holes," Sailor says.
Sailor and his colleagues etched tiny holes in a silicon wafer, cut the wafer into thin layers, and then blasted them with ultrasound to create particles about 1/10,000 of an inch wide. The resulting structures have an almost sponge-like composition to them so they can sop up chemicals. "If we do the right chemistry inside those pores, we can get them to add, or attach, or grab onto, specific molecules," he explains.
By layering the minute silicon pieces and creating a pattern of these tiny holes — known as photonic crystals — the smart dust gains an almost iridescent color, somewhat like a soap bubble film. "It's what makes beetle shells the color they are; it gives butterfly wings their color," says Sailor. "In a beetle shell, a series of layers of organic material produce iridescence. We mimic these layers in silicon."
Sailor says when the smart dust soaks up pollutants, the silicon signals a warning by changing color that is visible to the naked eye. The colors change depending on which chemical or biological agents are present. For instance, a particle of smart dust may have one green side and one red; when the particle detects a drop of a toxin, the green side attaches to the drop and the red side flashes a warning.
Sailor calls this a "nano disco ball": it's smart dust that has turned red because it has detected and glommed onto a drop of oil. image: Jamie R. Link, UCSD
"You can look at these things and see the color change with your eye," he explains. "It's very dramatic, and you know when you've seen a pollutant with that change."
The research team can program the smart dust to detect lots of things. "We know we can do viruses, proteins, biological agents, pollutants… we haven't seen any limitations with them yet." Sailor says, adding, "We're just scratching the surface of what we could do with these particles."
He says that because smart dust is so cheap to make, it would be easy to spread hundreds of thousands of particles into suspect areas to help detect pollution. "If ten of them are lighting up, and then twenty of them light up, and then fifty, then you know that something's happening."
Sailor hopes these tiny particles will eventually be a front line of defense against unknown hazards when disaster strikes.