Made from semiconducting carbon nanotubes, the sensor can detect ethylene - a colorless, sweet-smelling gas that is emitted when flowers bloom and fruits ripen - in concentrations as low as 15 parts per billion. The sensor, say the researchers, could be used to monitor fruit and vegetables as they are shipped and stored, helping to reduce food waste.
“There is a persistent need for better food management and reduction of food waste,” says Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT. “People who transport fruit around would like to know how it’s doing during transit, and whether they need to take measures to keep ethylene down while they’re transporting it.”
In addition to being a plant hormone, ethylene is also the world’s most widely manufactured organic compound and is used to manufacture products such as plastics and clothing. A detector for ethylene could also be useful for monitoring this kind of industrial ethylene manufacturing, say the researchers.
Ethylene is produced by most plants, which use it as a hormone to stimulate growth, ripening, and other key stages of their life cycle. Produce and flowers under stress can overproduce ethylene, leading them to ripen or wilt prematurely. It is estimated that every year U.S. supermarkets lose about 12% of their fruits and vegetables to spoilage, according to the U.S. Department of Agriculture.
“There still is not a good commercial sensor for ethylene,” says Swager. “To manage any kind of produce that’s stored long-term, like apples or potatoes, people would like to be able to measure its ethylene to determine if it’s in a stasis mode or if it’s ripening.”
The new ethylene sensor works via a mechanism known as Wacker oxidation , where a palladium metal catalyst is used that adds oxygen to ethylene during oxidation. As the palladium catalyst performs this oxidation, the catalyst temporarily gains electrons. Palladium then passes these extra electrons to carbon nanotubes, making