'Bionic' spinach plants can detect explosives!

Spinach is no longer just our favourite cartoon character Popeye's superfood - thanks to MIT scientists who have transformed the leafy plants into sensors that can detect explosives within minutes.
By embedding leaves with carbon nanotubes, the plants were designed to detect chemical compounds known as nitroaromatics, which are often used in landmines and other explosives.
When one of these chemicals is present in the groundwater sampled naturally by the plant, carbon nanotubes embedded in the plant leaves emit a fluorescent signal that can be read with an infrared camera.
The camera can be attached to a small computer similar to a smartphone, which then sends an email to the user.

"This is a novel demonstration of how we have overcome the plant/human communication barrier," said Michael Strano, professor at Massachusetts Institute of Technology (MIT).
Plants are ideally suited for monitoring the environment because they already take in a lot of information from their surroundings, Strano said.

"Plants 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," he said.
Strano's lab has previously developed carbon nanotubes that can be used as sensors to detect a wide range of molecules, including hydrogen peroxide, the explosive TNT, and the nerve gas sarin

When the target molecule binds to a polymer wrapped around the nanotube, it alters the tube's fluorescence.
In the new study, researchers embedded sensors for nitroaromatic compounds into the leaves of spinach plants.
Using a technique called vascular infusion, which involves applying a solution of nanoparticles to the underside of the leaf, they placed the sensors into a leaf layer known as the mesophyll, which is where most photosynthesis takes place.
They also embedded carbon nanotubes that emit a constant fluorescent signal that serves as a reference.
This allows the researchers to compare the two fluorescent signals, making it easier to determine if the explosive sensor has detected anything.

If there are any explosive molecules in the groundwater, it takes about 10 minutes for the plant to draw them up into the leaves, where they encounter the detector.
To read the signal, the researchers shine a laser onto the leaf, prompting the nanotubes in the leaf to emit near-infrared fluorescent light.
This can be detected with a small infrared camera connected to a credit-card-sized computer similar to the computer inside a smartphone.
The study was published in the journal Nature Materials.