Bionic spinach can detect explosives

WE HAVE had sniffer dogs and even sniffer rats, but now a new type of nanobionic spinach has been developed to detect explosives and communicate that information to a handheld device.

The specially engineered spinach (Spinacia oleracea) has been developed by chemical engineering professor Michael Strano and the team at MIT. The team first developed the technology to infuse nanosensors into Arabidopsis plants in 2014, and used it to detect nitric oxide. He suggested at the time that the technique could be used to create living explosive or chemical detectors, and has now demonstrated the “plant nanobionics” technology in spinach. When the fluorescent nanosensors in the spinach come into contact with explosive nitroaromatic compounds, the fluorescence changes, and it is this that can be detected by a small Raspberry Pi computer.

Strano and the team embed two kinds of fluorescent nanotubes into the spinach leaves, using a technique called vascular infusion. They apply a solution of the nanotubes to the underside of the leaves, which then infuse into a particular layer of the leaf called the mesophyll. The first type of nanotube is a type of single-walled carbon nanotube (SWCNT) joined to a peptide called bombolitin II, which changes its fluorescence when it comes into contact with nitroaromatics. The second type of nanotube, also a SWCNT, is bound to polyvinyl, and its fluorescence is constant.

When planted, the spinach plants take up moisture from the soil around them naturally, and the moisture, along with any chemicals in it, reaches the leaves in around eight minutes. The researchers shine a laser onto the leaves, which causes the nanomaterials in the leaves to fluoresce with near-infrared light. If there is a difference between the light emitted by the two nanomaterials, this will be picked up by the Raspberry Pi.

Strano says that a smartphone could be adapted to do the same job, after removing the infrared filter present in the camera. At present the Raspberry Pi can detect the signal from around 1 m away, but the team is working to increase this distance.

“This is a novel demonstration of how we have overcome the plant/human communication barrier,” said Strano, adding: ““Plants are very environmentally responsive. 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-signalling pathways, there is a wealth of information to access.”

The researchers have also engineered spinach which can detect dopamine, a molecule than influences root growth, and are working on other sensors for plant chemicals which could help botanists learn more about plants and potentially maximise yields from important crops, such as the Madagascar periwinkle, which produces a compound used to treat cancer. Strano’s team has previously developed nanosensors which detect hydrogen peroxide, TNT and the nerve gas sarin.