The strength of spinach isn't only in its nutrients, but also in its ability to be hacked to function as a sensor, according to researchers at the Massachusetts Institute of Technology. An MIT team used wonder-material carbon nanotubes to give the greens the ability to detect explosives and wirelessly transmit information to a mobile device.
MIT engineers applied a solution of nanoparticles to the underside of the leaves, allowing them to be taken up into the mesophyll layer where photosynthesis takes place. The embedded nanotubes then acted as sensors able to detect nitroaromatic compounds – which are often used in explosives like land mines – in the groundwater taken up by the plants' roots.
If the chemicals are present in the water the plant is feeding from, the carbon nanotubes in the leaves emit a fluorescent signal that can be picked up with an infrared camera when a laser is shined on the leaves. The researchers hooked up such a camera to an inexpensive Raspberry Pi system and set it to email the user when the compounds were detected.
"This setup could be replaced by a cell phone and the right kind of camera," says Michael Strano, the leader of the research team. "It's just the infrared filter that would stop you from using your cell phone."
The process of explosive molecules making their way from the plant's roots to the leaves can take about ten minutes, the researchers say.
We've also seen MIT researchers do similar bomb-sniffing work with carbon nanotubes and bee venom, but plants have advantages all their own.
"Plants are very good analytical chemists," Strano says. "They have an extensive root network in the soil, are constantly sampling groundwater, and have a way to self-power the transport of that water up into the leaves."
Right now the system allows the researchers to read the signal from the plants from a distance of about one meter, but they're working on making it work from further away. It may also be possible to engineer techniques that allow bionic plants to receive radio signals or change color.
The researchers are also interested in using the technology as a means of starting a conversation of sorts with plants about their inner workings. They see the potential to improve the yields of compounds synthesized by plants that can be used to treat cancer. Plants may also know more about the current environment than we do.
"Plants are very environmentally responsive," Strano says. "They know that there is going to be a drought long before we do. They can detect small changes in the properties of soil and water potential. If we tap into those chemical signaling pathways, there is a wealth of information to access."
Strano is the senior author of a paper describing the nanobionic plants in the journal Nature Materials.
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