It’s Strong to the Finich, this Bomb-Sniffing Spinach

SCIENCE

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Discussion Ideas

The great Forbes article reports that nanoparticles embedded in spinach can signal if molecules found in common explosives are present in the soil. What are nanoparticles?
- A nanoparticle is simply any material that has an average particle size of 1-100 nanometers. (How small is a nanometer? Use this activity to find out.)
- The “bionic spinach” actually has two types of nanoparticles.
  - The first set of nanoparticles is made of polyvinyl alcohol (PVA), a type of plastic. These tiny pieces of plastic are coated with bombolitins. Bombolitins are molecules naturally found in bee venom, “and by coincidence they bind nicely to molecules called nitroaromatics. You’re probably familiar with at least one of these: 2,4,6-trinitrotoluene or TNT.”
  - The second set of nanoparticles is composed of SWCNTs, or single-walled carbon nanotubes. These nanotubes are hollow cylinders about 100,000 times thinner than a human hair. The bombolitin-coated nanoparticles sit on top of the carbon nanotubes. As the plant transpires, water and the chemicals in it flow through the nanotube and interact with the bombolitin-coated PVA.

How are the plastic and carbon nanoparticles attached to three-week-old spinach plants?
- The bombolitin-decorated nanotubes are injected into the spinach leaves with a needle-less syringe.

How does the treated spinach detect explosives?
- The carbon nanotubes fluoresce in infrared light. “But when the bombolitin picks up a nitroaromatic molecule, changes in the electronic character of the whole package reduce the amount of light the nanotube emits.”
  - So, when a laser shines on the spinach, the unaffected spinach will fluoresce, while spinach that has absorbed nitroaromatics will only emit near-infrared radiation.
- Scientists tested the spinach using picric acid, a nitroaromatic. The picric acid was applied to the spinach in two ways: directly to the leaves and into the material absorbed by the roots. In both cases, scientists “saw the fluorescence from the bombolitin-modified nanotubes drop in the presence of picric acid. The researchers even found a way to detect those changes in fluorescence using a smartphone with some basic hardware added. That could make it relatively easy for people with basic training to use [chemical engineer Michale Strano’s] technology in remote places.”
  - Learn more about that amazing “basic hardware,” Raspberry Pi, here.

What types of explosives might the treated spinach detect?
- Buried bombs and land mines. “Countries like Cambodia, Croatia, Rwanda and Afghanistan have millions of land mines or unexploded bombs left from past conflicts. In some of these places people are routinely injured or killed by these explosives. Strano’s spinach plants could be a passive, low-tech way to find them so they can be removed safely.”

Can we eat the nanobiotic spinach?
- We would think not, but we here at NG aren’t entirely sure. We’ve read articles on this from Forbes, Christian Science Monitor, Washington Post, Salon, and others. None of them explicitly say consuming the nanoparticles is dangerous.

What factor might slow the development of “bomb-sniffing” spinach?
- “One potential complicating factor is pesticides, some of which are also nitroaromatics … one possible solution is adding more different types of nanoparticles that could give a more complete picture of what molecules the plants are taking up.”

How else might the application of nanotechnology be used?
- “The group is already looking beyond explosives to other types of compounds plants could detect. Strano says his lab is working on nanoparticles to detect dozens of different molecules like pharmaceuticals or pollutants in the same way these spinach plants sense nitroaromatics.”