Just a light salad: Glowing watercress could herald new era of sustainable lighting

Seon-Yeong Kwak from the Massachusetts Institute of Technology explains how his team's work could herald a new era of sustainable lighting

Plant nanobionics is a new research field pioneered by our Strano Research Group at the Massachusetts Institute of Technology. We previously demonstrated how nanomaterial could transform plants by giving them novel functions – we designed plants that can detect explosives and communicate that information to a smartphone, as well as plants that can monitor drought conditions.

The vision for this project is to make a plant that functions as a lamp you don’t have to plug in. The global energy consumption attributed to lighting accounts for nearly 20% of demand and more than 2 gigatonnes of CO₂ emissions per year, so we decided to create an environmentally-friendly alternative. 

To create the light-emitting plants we used luciferase, the enzyme that gives fireflies their glow. Luciferase reacts with a molecule called luciferin, causing it to emit light in the presence of adenosine triphosphate (ATP), the fuel derived from sugar. Another molecule, coenzyme A, extends the duration of the light emission by removing a reaction by-product. 

We put these three components into the plants by using nanoparticle carriers that help each component get to the right place in the plant. The plants were submerged in a pressurised chamber containing a nanoparticle suspension, allowing the particles to enter the leaves through tiny pores called stomata. We have modified watercress, rocket, spinach and kale. 

After adding the nanoparticles, we would see the plant glowing yellow-green. The nanoparticle carriers gradually release their cargo, luciferin and coenzyme A, which then enter the plant cells, where luciferase produces light. An estimate of our current lifetime is nearly four hours, although you can still observe parts of the plant emitting light after up to 8.5 hours. In a test tube, we have been able to achieve 21.5 hours but we haven’t translated that into the living plant yet. 

The light generated by one 10cm watercress plant is about one-thousandth of the amount needed to read by, but we believe we can boost the light emitted as well as the duration. These plants are not going to be searchlights or floodlights, but they could have a level of brightness and duration suitable for many important applications. The first applications will be low-intensity indoor lighting, used routinely in architecture.    

Street lighting is a challenge because a certain level of illumination is required for safety. If we rethink what we need for transport lighting, instead of high-intensity illumination spaced relatively far apart, we could substitute more densely spaced, lower-intensity lights.

The engineering of living plants for visible light emission is compelling because they have independent energy generation and storage mechanisms. Plants are doubly carbon negative, meaning they consume CO₂ in their fuel production and they are the product of carbon from the atmosphere. They could be the ultimate in bionic, sustainable illumination, relying on no human infrastructure. 

Plants are already well adapted to the outdoor environment: they self-repair, they exist in the places where we would like lamps to function, they survive bad weather, they access their own water – and they do all of this autonomously.

The next step is optimising the brightness and duration of the light coming from the plants. We’ve calculated that both can be optimised to extraordinarily high levels, and we have produced some of the brightest living organisms in existence.

Typical municipal lighting requires complex electricity grids and infrastructure, keeping many developing nations in the dark. There are no viable current solutions to address the challenges of resources for lighting, power, maintenance and disposal of batteries, bulbs, semiconductor circuits and other e-waste and hardware from traditional bulb-based grid lighting. 

Plant-based lighting would be a tremendous innovation. We envision a new platform for ambient lighting that is grown and deployed in a natural infrastructure that is safe, renewable – and eventually compostable.