How often does this happen to you? You bite into an apple only to find that it isn't quite ripe yet. Or you peel open a banana to find that it's already browning inside and past its prime.


A new device developed at MIT could help avoid these unwelcome fruity discoveries and save grocery stores millions of dollars in spoiled produce.


The device, which is still in the concept phase, uses carbon nanotubes to detect the gas ethylene, which fruits emit as they mature, causing them to ripen. Produce warehouses already monitor ethylene with current technologies such as gas chromatography or mass spectroscopy, but those devices are large and expensive: they can cost upwards of $1,200 each.


Looking for a more affordable solution, MIT professor Timothy Swager developed a small sensor coated with thousands of nanotubes that contain copper atoms. Ethylene bonds to the carbon atoms, impeding the flow of electrons through the nanotubes. The sensor can then determine how much the rate of electron flow has slowed — and the slower the flow, the more ethylene is present. The more ethylene is present, the riper the fruit.


Swager says he envisions a day when this technology could be employed in small devices that could be attached to produce packing crates. The devices would contain RFID chips, which would transmit the ripeness of each crate's contents to handheld devices that shopkeepers could use to determine which produce in their storerooms is ready to sell.


According to the U.S. Department of Agriculture, American grocery stores lose about 10 percent of fruits and vegetables to spoilage every year. "If we can create equipment that will help grocery stores manage things more precisely, and maybe lower their losses by 30 percent, that would be huge," Swager said in a prepared statement.


The total cost for the sensors would be a fraction of current ethylene-detecting technologies: just 25 cents for the sensor and another 75 cents for the RFID chip.


Research on the process was published April 19 in the journal Angewandte Chemie.


Funding for the research came from an interesting source: MIT's Institute for Soldier Nanotechnologies, which is funded by the U.S. Army Office of Research. Swager's previous research focused on sensors to detect explosives or chemical and biological warfare agents.


Also on MNN: The secret of low-tech food preservation at home


MNN tease photo of fruit: Shutterstock

Want the freshest fruit? New sensor improves on the human nose
Carbon nanotubes could provide an easy, inexpensive method of determining fruit ripeness.