The year is 2021, you open your preferred email application to find spam mail sent by… a field of spinach? Although the actual paper was published in Nature back in 2016 , social media has recently brought MIT’s Strano Group’s research to light. While the salacious headlines claim that the group was able to “teach” spinach plants how to send emails, their research actually focuses on nanobionics, where extremely tiny sensors are implanted into the spinach leaves so that they’ll fluoresce when the plant roots comes into contact with nitroaromatic (found in explosives) compounds.
“Plants are very good analytical chemists. 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.”
MIT’s Michael Strano to Euronews
Although detecting compounds used in explosives may not play a big role in our everyday lives, the potential to build on this technology to detect future droughts or pollutants in farmland soil has immense applications.
“Plant nanobionics aims to embed non-native functions to plants by interfacing them with specifically designed nanoparticles.” – Says the original 2016 paper in their abstract. It goes on to illustrate how said nanoparticles need to be around 10 nanometers in dimension to be comparable in size to typical proteins and macromolecules that embody the plant matter. As plants continuously exchange fluids and gases with their environment, using them as naturally occurring “devices” to sample soil and air quality as well as capitalizing on their natural ability to draw in and concentrate contaminants may just be the next big thing for nano-technology.
Typical work in detecting airborne and soil/water bound pollutants involves on site human sampling, followed by transportation of the samples to an environmental lab nearby. The pollutants must then be manually extracted and concentrated before being analyzed by expensive machines such as gas chromatographs and mass spectrometers.
The Strano Group, however, were able to engineer a specifically designed nanoparticle and introduce it into the leaves of spinach plants. Direct uptake of their target pollutant, in this case Picric acid, through both the leaves and the roots of the plants were able to illicit a chain reaction that results in the nanoparticles fluorescing. A nearby sensor is then able to pick up on the specific wavelength of the induced photoluminescence and alert the researchers via email. Astoundingly, the group was able to use a slightly modified cell phone camera (Raspberry Pi CCD detector with IR filters removed) to detect the nanoparticle signal, allowing for portable and inexpensive methods of detection.
The group isn’t exactly the first one to utilize plants as detectors and samplers for pollutants, but are the first to employ non-genetically modified plants to do so. Recently, they’ve pivoted towards a new and more ambitious project titled “The Light Emitting Plant Project”. The goal is to transform living plants and trees into autonomous light sources, capable of generating visible light for human use. Seemingly a concept out of fantasy, they aim to create a world where street lamps are replaced with vibrant glowing trees, and your backyard patio can be lit by shining flowers. With the emphasis that direct and indirect lighting accounts for around 20% of global energy consumption, plants, which are able to generate energy independently, possess a negative carbon footprint, and are able to self repair, offer a compelling alternative to conventional lighting. Once again, the group targets this problem from a non-GMO perspective, using instead “a collection of chemically interacting nanoparticles that are able to convert the plant’s stored chemical energy into light emission.”
Plant nanobiotics are just the tip of the iceberg for the novel work being done by this group at MIT and I encourage those curious to read more for themselves at https://srg.mit.edu/research/.
 M.S., Strano et al, Nature Mater 16, 264–272 (2017). https://doi.org/10.1038/nmat4771