The ripening process of many fruits is triggered when ethylene binds to a specific receptor. Bananas, for example, are usually unripe when they are harvested. They are transported under a nitrogen atmosphere to stop the ripening process and are then exposed to ethylene gas in a ripening facility before delivery. However, they must not be ripened too much because bananas become “overripe” very fast. It is thus important to precisely control the ethylene concentration in storage facilities. It is also interesting to know how much ethylene fruits release at any given point in their development because this could help determine the ideal time for harvest.

As a small, nonpolar molecule, ethylene (C2H4) is difficult to detect. Conventional methods are mainly based on expensive, complex instruments that are not well suited for use in the field or in an orchard. Timothy M. Swager and his team at the Massachusetts Institute of Technology (MIT) in Cambridge (USA) have now developed a portable sensor that can reliably measure tiny concentrations of ethylene, such as those released when fruit ripens. Their device is also easy and inexpensive to produce.