Nanowires darken in the face of danger

17 Jun 2002

US scientists have developed photoluminescent nanowires that detect trace residues of explosives.

TNT handprint

Chemists at the US-based University of California, San Diego have devised a method to combat potential terrorist attacks and locate unexploded mines and bombs, either on land or under water. By chemically synthesizing nanowires of polysiloles - a silicon polymer that glows under ultraviolet light - Michael Sailor and his colleagues were able to detect trace amounts of TNT and picric acid in air and seawater.

"The [polysiloles] consist of strands of silicon atoms that have organic molecules wrapped round them," explained Sailor. "These wires are electronically active, which means that they can be made to glow under certain conditions."

The team put their polysilole nanowires to the test by depositing thin films on substrates, including filter paper, glass cover slips and silicon chips and wafers. As expected, the substrates glowed when viewed under either ulltraviolet or blue light, but on exposure to either explosive-spiked flowing air or seawater, they faded.

"This mechanism of quenching is attributable to electron transfer from the excited polysilole to the [electron deficient] analyte," said Sailor. Exciting the polysilole with ultraviolet light means that TNT and picric acid, which are electron-deficient molecules, can "grab" the polymer's excited electrons, and stop the polysilole from glowing.

"There are millions of unexploded land mines from past wars all over the world that people want to get rid of for humanitarian reasons," said Sailor. "You could use these silicon nanowire detectors to look for TNT leaking out of land mines and also in bays and inlets."

The team is also developing its detectors to pick up trace carcinogenic chromium contaminants in groundwater.