WHEN ILLUMINATED by magenta and blue grow lights, Harpreet Sareen’s mini greenhouse looks like almost any other indoor gardening setup in New York City. But when the interaction designer switches the bulbs off to pitch the lab into darkness, a soft red glow persists. Nanosensors flow through the veins of a peace lily, allowing its broad leaf to fluoresce. The beacon fades over the course of a couple of hours, but this is by design: The dying light signals that its host is taking in toxic lead.

The glowing lily is one of Sareen’s botanical “cyborgs”—vegetation he biohacks to serve as environmental watchdogs. Plants, he explains, are natural sentinels. When they absorb nutrients through their roots, they also sop up low concentrations of pollutants. “They are automatic absorbers or scrubbers of [contaminants] in the environment,” he says. Sareen—a biodesigner and director of the Synthetic Ecosystems Lab at Parsons School of Design, where he’s also an assistant professor—hopes to harness those qualities to sound the alarm on factory spills, tainted soil, and bacteria-​infested water.

This idea first took root during his childhood in the 1990s in Punjab, where Indian mustard, Brassica juncea, is a staple crop grown for cooking and oilseed production. The yellow-petaled plant is also well known for its usefulness in purifying sullied earth, or phytoremediation. After studying engineering in India, Sareen blended his technical skills with art at the MIT Media Lab in 2015, where he began to think back to the metal-sucking abilities of his local flora. He soon learned that a plethora of plants were capable of drawing up mercury, lead, cadmium, and other potentially toxic compounds. “Many of the things that we call weeds are actually phytoremediators,” he says.

Sareen also realized that the same suction power that helps them cleanse the soil means these crops can reveal the level of toxicity in it. But, he points out, there isn’t a quick way to read how much of a substance a sprout has taken in. So he decided to try to give the plants a voice—by turning them into cyborgs.

In 2018, he created his first bit of bionic flora: a wheeled, motorized plant called Elowan. Sensors attached to the stem, leaves, and soil looked for the cascade of calcium that comes with a surge in sun and signaled the motors to roll the foliage toward nearby light. “You’re not used to seeing a plant on a robot, but I think the intention behind this work is to make people a little bit uncomfortable with such a thing,” Sareen says. “They might pay more attention to the fact that something is indeed happening inside this plant.”

Sareen crafted his bionic peace lily (named Argus, Latin for “guardian”) at Parsons in 2020. He and his team fashioned sensors—small enough to flow through the intercellular channels of a leaf—that turn red when hit with a laser. When the plant takes in water contaminated with lead, the metal slowly dims that glow. Inspired by environmental catastrophes like the Flint water crisis in Michigan, Sareen hopes that such a biosensing botanical could one day reveal toxicity in household taps in a more hands-off fashion than current options like dipsticks. “If we had mechanisms that could give us output in real time, as well as tell us how much damage has happened, then we will be able to take rapid actions against these things,” he says.

This story originally ran in the Summer 2022 Metal issue of PopSci. Read more PopSci+ stories.