Carbon Nanotube-Based Sensor Detects Toxins With a Mobile Phone

Carbon nanotubes wrapped in a polymer offer a powerful sensing platform for many chemicals

2 min read
Carbon nanotubes wrapped in a polymer offer a powerful sensing platform for many chemicals.
Illustration: iStockphoto

A little over four years ago, researchers at the University of California, Riverside, developed a sensor made from carbon nantoubes for detecting toxic chemicals. So enthusiastic were the researchers with the prospects of their technology that they launched a company, Nano Engineered Applications, that intends to add this sensor to people’s mobile phones.

While the commercial prospects of a smartphone toxin detector are still uncertain, another team of researchers has recently demonstrated a sensing device that also relies on carbon nanotubes (CNTs) to detect different chemicals. Researchers from Japan’s International Center for Materials Nanoarchitectonics and the National Institute for Materials Science, working with collaborators from MIT, combined CNTs with a polymer and discovered that this resulting material offers a powerful sensing platform for toxic chemicals. Their results look to be the first viable demonstration of the power of sensors known as chemresistors.

To demonstrate the effectiveness of their CNT-based material, the researchers integrated it into the electronic circuit of a near-field communication (NFC) tag. Using a smartphone or other device capable of reading the tag, the sensor could be used to detect toxins in seconds and at concentrations as low as 10 parts per million. 

The researchers were able to achieve this high speed and sensitivity by wrapping the carbon nanotubes in supramolecular polymers. A supramolecule is actually a number of different molecules that are fused together to act as a single molecule and carry out a particular programmed function. The sensor itself would be considered disposable since only 1 gram of the material is capable of making four million sensors.

The researchers found that when they wrapped the supramolecular polymers around the carbon nanotubes, the polymer acted as an insulator. When the polymer wrapping comes in contact with a toxic gas, it begins to disassemble, which leads to a big spike in the conductivity of the nanotubes.

In research described in the Journal of the American Chemical Society, the researchers found that when they wrapped the supramolecular polymers around the CNTs, the polymer acted as an insulator that limited the natural high conductivity of the CNTs. When the polymer wrapping comes in contact with a toxic gas, it begins to disassemble, which leads to a big spike in the conductivity of the CNTs—as much as a 3000 times increase in electrical conductivity.

“Think of the wrappers as insulation around CNT wires,” explained Timothy M. Swager, a professor at MIT who worked on the project, in an e-mail interview with IEEE Spectrum. “Reactions with toxic chemicals cause the disassembly and the wires touch and make a circuit. Increased conduction gives detection.”

Sensors like this are known as chemiresistors and have long been thought to be a very powerful tool for detecting small amounts of chemicals, and, according to Swager, this is the first viable demonstration. “You don’t have to move many electrons to measure this and we can inductively power and read the sensor with near-field communication devices, such as a smartphone,” he said.

In future work, the research team is looking to make modifications to the supramolecular polymer to detect different types of toxins more quickly and more sensitively. “We are likely to work with live chemical agents in the future,” Swager added. “I am also using this concept to create sensors with selectivity to different types of toxins.”

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Two Startups Are Bringing Fiber to the Processor

Avicena’s blue microLEDs are the dark horse in a race with Ayar Labs’ laser-based system

5 min read
Diffuse blue light shines from a patterned surface through a ring. A blue cable leads away from it.

Avicena’s microLED chiplets could one day link all the CPUs in a computer cluster together.

Avicena

If a CPU in Seoul sends a byte of data to a processor in Prague, the information covers most of the distance as light, zipping along with no resistance. But put both those processors on the same motherboard, and they’ll need to communicate over energy-sapping copper, which slow the communication speeds possible within computers. Two Silicon Valley startups, Avicena and Ayar Labs, are doing something about that longstanding limit. If they succeed in their attempts to finally bring optical fiber all the way to the processor, it might not just accelerate computing—it might also remake it.

Both companies are developing fiber-connected chiplets, small chips meant to share a high-bandwidth connection with CPUs and other data-hungry silicon in a shared package. They are each ramping up production in 2023, though it may be a couple of years before we see a computer on the market with either product.

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