Glowing Plants Created by MIT Engineers

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Imagine that instead of switching on a lamp when it gets dark, you can read by the light of a luminous plant on your desk.

MIT engineers have taken a critical first step toward making that vision a reality. By integrating specialized nanoparticles into the leaves of a watercress plant, then inducing the plants to give off dim mild for nearly four hours. They believe that, with further optimization, such crops will one day be bright enough to light up a workspace.

“The vision is to make a plant that will be a desk lamp–a lamp that you don’t have to plug in. The light is ultimately powered by the energy metabolism of the plant itself,” states Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the study.

This technology could also be used to provide low-intensity indoor Lighting, or to transform trees to self-powered streetlights.

MIT postdoc Seon-Yeong Kwak is the lead author of the research, which appears in the journal Nano Letters.

Nanobionic plants

Plant nanobionics, a new research area pioneered by Strano’s lab, Aims to provide plants novel features by embedding them with various types of nanoparticles. The team’s target is to engineer plants to take a lot of the functions now performed by electric devices. The researchers have previously designed plants which can detect explosives and convey that data to a smartphone, in addition to plants that may track drought conditions.

Lighting, which accounts for about 20 percent of global energy intake, appeared like a logical next target. “Plants can self-repair, they have their own power, and they are already adapted to the outdoor surroundings,” Strano states. “We believe that is an idea whose time has arrived. It is the ideal problem for plant nanobionics.”

To make their luminous plants, the MIT team turned to luciferase, The receptor which gives fireflies their glow. Luciferase acts on a molecule known as luciferin, causing it to emit light. Another molecule called co-enzyme A helps the process along by removing a reaction byproduct that can inhibit luciferase activity.

The MIT team packaged each of these three components into another kind of nanoparticle carrier. The nanoparticles, which are all made of materials that the U.S. Food and Drug Administration classifies as “generally regarded as safe,” assist each element get to the perfect part of the plant. They also prevent the components from reaching concentrations which could be toxic to the plants.

The researchers used silica nanoparticles about 10 nanometers in diameter to carry Luciferase, and they used slightly bigger particles of the polymers PLGA and chitosan to carry Luciferin and Coenzyme A, respectively. To get the particles into plant leaves, the investigators first suspended the particles at a solution. Plants were immersed in the solution and then subjected to elevated pressure, allowing the particles to go into the leaves via tiny pores called stomata.

Particles releasing Luciferin and Coenzyme A were created to accumulate in the extracellular space of the mesophyll, an interior layer of the leaf, while the smaller particles carrying luciferase input the cells which compose the mesophyll. The PLGA particles slowly release luciferin, which then enters the plant cells, where luciferase plays the chemical reaction that produces luciferin glow.

The investigators’ early attempts at the start of the project yielded plants that could glow for about 45 minutes, which they’ve since improved to 3.5 hours. The light generated by one 10-centimeter watercress seedling is currently roughly one-thousandth of the amount required to read by, but the investigators believe they can raise the light emitted, as well as the length of light, by further optimizing the concentration and discharge rates of the components.

Plant transformation

Previous attempts to create multi-colored plants have relied on genetically engineering crops to express the gene for Luciferase, but that is a laborious process which yields exceptionally dim light. These studies were performed on tobacco plants and Arabidopsis thaliana, which are widely used for plant genetic research. However, the method created by Strano’s lab could be used on any kind of plant. So far, they’ve demonstrated it with arugula, kale, and spinach, in addition to watercress.

For future versions of this technology, the investigators expect to develop a means to spray or paint on the nanoparticles onto plant leaves, which could make it possible to change trees and other big plants to light sources.

“Our target is to do one treatment when the plant is really a seedling or a mature plant, and have it last for the duration of the plant,” Strano says. “Our work very seriously opens up the doorway to streetlamps that are nothing but treated trees, and also to indirect lighting around homes.”

The researchers have also demonstrated that they can turn the light Off by incorporating nanoparticles carrying a luciferase inhibitor. This could enable them to finally produce plants that closed off their light emission in response to environmental conditions like sunlight, according to the engineers.