Researchers develop ultra-sensitive temperature sensor using new materials derived from plant cells

By on April 24, 2015
The researchers cultivated plant cells in a culture containing carbon nanotubes, improving the cells’ conductivity. (Credit: Francesca Cappa/CC BY 2.0)

While technology is often considered separate from nature, many of humanity’s most significant technological advancements mimic nature. Researchers at a Swiss engineering and technology institute developed a new temperature sensor that takes this concept a step forward, melding synthetic components with actual plant cells.

Using tobacco plant cells grown in a culture containing carbon nanotubes, the researchers have created an electronic sensor module that changes its conductivity in response to temperature fluctuations. The new sensor is at least 100 times more sensitive than the most advanced temperature sensors available today. A study detailing its development was published in the journal Proceedings of the National Academy of Sciences.

“In the past, materials scientists and engineers looked at biological materials and Nature as a source of inspiration, since many natural materials, even today, present properties not achievable by synthetic counterparts,” wrote Chiara Daraio, professor of mechanics and materials at Eidgenössische Technische Hochschule Zürich, in an email. “In our work, instead of being ‘inspired’ by Nature, we exploit properties found in biological systems.”

Designing the study and its experiments, Daraio worked alongside the paper’s lead author, Raffaele Di Giacomo, and Bruno Maresca, a collaborator at the University of Salerno. Di Giacomo had already conducted preliminary work examining plant and fungal cells cultivated with nanostructures, resulting in a highly conductive woody material he calls “cyberwood.” The researchers built upon that work, paying special attention to cyberwood’s thermal properties.

“Plants are known to be very sensitive to temperature variations,” Daraio wrote. “We decided to try to create materials that would ‘immortalize’ these properties, allowing them to persist after the plant cells died.”

Carbon nanotubes are used in a wide variety of modern materials for their structural durability, low weight and unique conductive properties. (Credit: NASA Goddard Space Flight Center)

Carbon nanotubes are used in a wide variety of modern materials for their structural durability, low weight and unique conductive properties. (Credit: NASA Goddard Space Flight Center)

Starting in November 2013, the researchers tested samples that Di Giacomo had prepared for prior work. He had observed drastic changes in the samples’ resistivity, apparently in response to changes in environmental temperature. Over 16 months of painstaking work involving dozens of samples, the researchers investigated the mechanisms responsible for the reaction. They found that sugar molecules known as pectins — contained in the cell walls of living plant cells and cyberwood — break apart as temperature increases, allowing calcium and magnesium ions to move more freely, thereby improving conductivity

As the researchers studied those chemical processes, they also explored potential applications for the new materials. The “most obvious application” for cyberwood, Daraio said, is in thermal sensors of unparalleled sensitivity. These could be produced en masse at very low costs for use in consumer electronics, such as touchscreen devices, or in advanced thermal cameras. Cyberwood also has some potential as a building material — it can be worked like wood, but is also more readily molded.

Developing the hybrid material and formulating its potential applications required the researchers to face challenges from both engineering and scientific perspectives. Dariao said it’s no easy task to determine the unique cellular variables behind specific responses. It was just as vexing to develop “nano-bionic” materials without any existing theoretical framework as a guide. She said the creation of these materials and others is “at the core of scientific and technological innovation,” and likened it to the development of steel or semiconductors, materials vital to the industrial and digital revolutions, respectively.

“We were able to create composite materials that preserve properties found in living systems,” Daraio wrote. “By understanding the fundamental mechanisms that govern the biological responses, we are now able to fabricate materials with unprecedented properties.”

Top image: The researchers cultivated plant cells in a culture containing carbon nanotubes, improving the cells’ conductivity. (Credit: Francesca Cappa/CC BY 2.0)

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