Researchers have developed what appears to be ‘by far’ the world’s most sensitive temperature sensor using chemicals present in tobacco plants.
Essentially an electronic module that changes its conductivity as a function of temperature, the sensor is at least 100 times more sensitive than any existing device, the researchers claim.
"No other sensor can respond to such small temperature fluctuations with such large changes in conductivity,” said Raffaele Di Giacomo, a post-doc researcher at the Department of Mechanical and Process Engineering of ETH Zurich.
The researchers were inspired by the well-documented ability of plants to register the tiniest temperature differences and respond to them through changes in conductivity of their cells. Instead of trying to mimic plant behaviour, the team sought to develop an innovative hybrid material that would include temperature-sensitive components taken directly from the plants. Tobacco suggested itself as a suitable candidate.
"We asked ourselves how we might transfer these cells into a lifeless, dry material in such a way that their temperature-sensitive properties are preserved," Di Giacomo explained.
The scientists grew tobacco cells in a medium containing tiny tubes of electrically conductive carbon. The nanotubes created a network between the tobacco cells, penetrating the cell walls.
After drying out the culture, the researchers discovered a firm wood-like material. On closer examination, they found that this substance maintained its conductive properties as well as superb temperature sensitivity.
Having dubbed the material ‘cyberwood’, the researchers conducted several experiments, demonstrating that the material can detect warm subjects even from a distance, such as an approaching hand.
Further analysis revealed that chemicals known as pectins, the molecules of sugar found in plant cell walls, are the key to the temperature-sensing properties.
Depending on the surrounding temperature, the pectins can be cross-linked, forming a gel that also contains calcium and magnesium ions.
"As the temperature rises, the links of the pectin break apart, the gel becomes softer and the ions can move about more freely," Di Giacomo explained, adding that as a result, the material conducts electricity better when temperature increases.
The patented invention could be used to make temperature-sensitive, touch-less screens capable of reacting to nearby gestures. The tobacco-based sensors could also be used in innovative heat-sensitive cameras or night-vision devices.
The researchers are now trying to mimic the properties of the plant-based pectins with a synthetic material. Eventually, they hope to create a low-cost, flexible, transparent and bio-compatible sensor that could be moulded into arbitrary shapes.