Spinach plants with embedded nanosensors fluorescently detect explosives
IR light emitted by the nanosensors is measured with a small IR camera and Raspberry Pi computer.
By embedding the leaves of spinach plants with carbon nanotubes, researchers at the Massachusetts Institute of Technology (MIT; Cambridge, MA) have turned the plants into sensors that emit fluorescence measured by an IR camera to detect explosives,1 an approach the researchers call "plant nanobionics."
"The goal of plant nanobionics is to introduce nanoparticles into the plant to give it non-native functions," says Michael Strano, a professor of chemical engineering at MIT and the leader of the research team.
The spinach 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 is attached to a small handheld device, which then sends an email to the user.
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.
Sensors infused into the leaf
In the new study, the 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 single-walled carbon nanotubes (SWCNTs) attached to a peptide into a leaf layer known as the mesophyll, which is where most photosynthesis takes place.
They also embedded SWCNTs that emit a constant fluorescent signal that serves as a reference. This allowed 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 irradiate the leaf with laser light, causing the nanotubes in the leaf to emit near-IR fluorescent light, which is detected by a small IR camera connected to a Raspberry Pi (a $35 credit-card-sized computer). The signal could also be detected with a smartphone by removing the IR-blocking filter that most camera phones have, the researchers say.
Using the setup, the researchers can pick up a signal from about 1 meter away from the plant, and they are now working on increasing that distance.
One of the MIT researchers, Min Hao Wong, has started a company called Plantea to further develop this technology.
1. Min Hao Wong et al., Nature Materials (2016); doi: 10.1038/nmat4771