A Plant-Based Self-Powered Sensor Could Provide an Eco-Friendly Approach for Future Electronics

Researchers at the University of Groningen's Zernike Institute for Advanced Materials have come up with an eco-friendly, self-powered sensor — built using a material derived from the soft rush plant, Juncus effusus L.

"The structure of the soft rush stem consists of layers of interconnected stars, a bit like tiny snowflakes," explains first author Qi Chen explains. "My samples were ultra-lightweight. Once, I left the samples uncovered and as I opened the lab door, the samples were blown away. It looked like it had snowed in the hallway."

Those samples came about serendipitously: Chen had been casually discussing research topics with friends in the Zernike campus, with one absentmindedly stripping the outer layer from a grass-like stem. As Chen explained the focus of her research on foam-like materials, the friend joked that the plant's airy structure might make it suitable for study — so Chen put the reed in her backpack and promptly forget all about it for two years.

That airy inner, though, proved ideal for Chen's work on generating electricity using bacteria. "The plant needs this open structure to breathe," the scientist explains, "because with their roots in a wet environment, they need to take oxygen from the air and transport it through the stem." The bacteria, too, needs to breathe — and thus the plant's inner structure became a key part of Chen's work.

Chen and colleagues used the soft rush stem to produce a triboelectric nanogenerator, roughly the size of a postage stamp, which doubles as a motion sensor. "You can put it in your shoe," explains co-author Dina Manair, "and when you walk, jump, or run, it releases a distinct signal that we can recognize" — generating energy through static discharge as two layers rub together while the wearer walks, and doing away with the need for the bacteria altogether.

"We can really call it sustainable," Chen claims of the sensor's production process: the soft rush stems are peeled and then dissolved in a simple mixture, requiring very little energy and no oil-based fossil materials. The material may have applications beyond triboelectric sensors, too, including forming part of a battery for more complex electronic creations or for clearing pollutants from water.

The team's work has been published in the journal Advanced Functional Materials under open-access terms.

Main article image courtesy of Leoni von Ristok/University of Griningen.