Nanotubes detect ripeness of fruits

MIT researchers Dr. Birgit Esser and Professor Timothy Swager have demonstrated an unexpected use for carbon nanotubes: helping grocers determine when fruit is going to spoil. Ethylene is a plant hormone that controls the ripening of fruits and vegetables; plants secrete it at various stages of the ripening process. Fruit distributors and mass vendors closely monitor ethylene levels to best understand the ripeness of their products, typically using mass spectrometry or similar technologies to detect minute levels of ethylene gas in air. Esser and Swager have demonstrated that with a little modification, carbon nanotubes can be made to detect very small concentrations of ethylene in air using simple and relatively inexpensive materials. The researchers add copper atoms to the carbon nanotubes which, when binding with ethylene gas molecules that are present in the air, change how easily electrons flow across the nanotubes. By passing a current across the modified nanotubes, they are able to determine if and how much ethylene is present by measuring their resistance.