A new chemical sensor chip made with ultra-thin carbon nanotubes promises to enable rapid, low-cost detection of noxious agents in rivers and reservoirs.
The Stanford University researchers who devised the chip say that, even though many types of chemical sensors have been developed, their sensor offers a rare combination of low cost, low power, instant response and flexible performance, all the result of the properties of nanotubes.
“We have shown that nanomaterials, when carefully assembled and organized, demonstrate excellent detection and sensor characteristics,” said Melburne LeMieux, a scientist in lead researcher Zhenan Bao’s laboratory.
Nanomaterials exhibit extraordinary strength and unique electrical properties, yielding immense potential in this application. The trick is to harness this potential through controlled assembly.
LeMieux told Homeland1 that Stanford had “found a nice way to do that with carbon nanotubes.”
Nanotubes are rolled sheets of carbon atoms only one atom thick, meaning that every atom is on the surface.
“This makes single-walled nanotubes very sensitive to any noxious molecule that drifts past,” LeMieux said.
The Stanford sensor technology could mean that the low-cost, low-power units could be distributed uniformly in sensitive areas to, in effect, lie in wait. The devices, which are about one nanometer in thickness, would be virtually undetectable and can even be dispersed in bodies of water, like municipal reservoirs.
“They could be placed in specified zones and remain like drones unnoticed for long periods of time, providing real-time information to a network,” LeMieux said. If anything were detected, that information would be transmitted electronically to attached networks.
Other water-borne nanotube-type sensors exist, but their conducting nanotubes are assembled in a jumbled and erratic fashion, reducing their sensitivity, according to the Stanford researchers. Nanotubes in the Stanford sensors, on the other hand, are built in a precise, aligned manner, ensuring that they are almost purely semiconducting.
Semiconducting nanotubes, those that switch electrical current on and off rather than always conducting it like a wire, can detect a wider range of molecular reactions with greater sensitivity.
In lab tests, the sensors instantly reported unmistakable changes in electrical current when exposed to water with just 2 ppb of TNT or dimethyl methylphosphonate, a cousin of the nerve gas sarin.
The researchers acknowledge that the chips will have to be packaged in a field-worthy device, with a power supply and wireless transmitter. The sensors will also require more sophisticated nanotube circuitry in order to distinguish benign from toxic chemicals likely present in real-world water supplies. Both issues are currently being addressed.