
Glow-in-the-dark plants hold promise as future lighting source
The engineers embedded nanoparticles into the leaves of watercress plants, which caused the plants to give off dim light for nearly four hours. With further optimization, say the researchers, such plants may one day be able to provide low-intensity indoor lighting, or transform trees into self-powered streetlights.
“The vision is to make a plant that will function as a desk lamp – a lamp that you don’t have to plug in,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of a study on the project. “The light is ultimately powered by the energy metabolism of the plant itself.”
The goal of the researchers is to use plant nanobionics – embedding plants with different types of nanoparticles – to engineer plants that can take over many of the functions now performed by electrical devices. Having previously designed plants that can detect explosives and communicate that information to a smartphone, as well as plants that can monitor drought conditions, the researchers turned their attention to lighting, which accounts for about 20% of worldwide energy consumption.
“Plants can self-repair, they have their own energy, and they are already adapted to the outdoor environment,” says Strano. “We think this is an idea whose time has come. It’s a perfect problem for plant nanobionics.”
In this case, the researchers packaged an enzyme called luciferase – the same enzyme that enables fireflies to glow – and two enabling molecules called luciferin and co-enzyme A, each into a different type of nanoparticle carrier. The nanoparticles help each component get to the right part of the plant, as well as prevent them from reaching concentrations that could be toxic to the plants.
Silica nanoparticles about 10 nanometers in diameter were used to carry the luciferase, while slightly larger particles of the polymers PLGA and chitosan were used to carry luciferin and coenzyme A, respectively. To get the particles into the plant leaves, they were first suspended in a solution into which plants were then immersed and then exposed to high pressure, allowing the particles to enter the leaves through tiny pores in the leaves, called stomata.
Particles releasing the molecules luciferin and coenzyme A were designed to accumulate outside of the cells located in an inner layer of the leaf called the mesophyll, while the smaller particles carrying luciferase enter the cells that make up that layer. The PLGA particles gradually release luciferin, which then enters the plant cells, where luciferase performs the chemical reaction that makes luciferin glow.
According to the researchers, this initially resulted in plants that could glow for about 45 minutes, which they have since improved to three-and-a-half hours. The light generated by one 10-centimeter watercress seedling is currently about one-thousandth of the amount needed to read by, but the researchers believe they can boost both the amount of light emitted and its duration by further optimizing the concentration and release rates of the various components.
The researchers say their method could be used on any type of plant, and so far have demonstrated it with arugula, kale, and spinach, in addition to watercress. Looking ahead, they hope to develop a way to paint or spray the nanoparticles onto plant leaves, which could make it possible to transform trees and other large plants into light sources.
In addition, say the researchers, they have also demonstrated a way to turn the light off, by adding nanoparticles carrying a luciferase inhibitor. This could eventually enable plants that shut off their light emission in response to environmental conditions such as sunlight.
“Our target is to perform one treatment when the plant is a seedling or a mature plant, and have it last for the lifetime of the plant,” says Strano. “Our work very seriously opens up the doorway to streetlamps that are nothing but treated trees, and to indirect lighting around homes.”
For more, see “A Nanobionic Light-Emitting Plant.”
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