U.S.: MIT scientists building mobile fruit ripening sensor
Researchers from the Massachusetts Institute of Technology (MIT) are developing portable sensors to monitor the ripeness of fruit and vegetables. 
MIT chemistry professor Timothy Swager hopes the ethylene-detecting sensors could be attached to cardboard boxes of produce and scanned with a handheld device, letting grocers know when to put certain items on sale to boost rotation before they are overripe.
"If we can create equipment that will help grocery stores manage things more precisely, and maybe lower their losses by 30%, that would be huge," he says
"Food is something that is really important to create sensors around, and we’re going after food in a broad sense."
An MIT release said monitors already exist that use gas chromatography or mass spectroscopy, seperating gases and analyzing their composition, but these systems cost around US$1,200.
"Right now, the only time people monitor ethylene is in these huge facilities, because the equipment’s very expensive," Swager said.
The sensor consists of an array of tens of thousands of carbon nanotubes, which have been modified to detect ethylene gas through the addition of copper atoms, which serve as 'speed bumps' to slow the flowing electrons.
When ethylene is present it binds to these copper atoms and slows down the flow of electrons even more. To detect the presence of ethylene, the sensors need only see by how much the electrons slow down, which is also known as resistance.
To make the device even more sensitive, the researchers added tiny beads of polystyrene, which absorbs ethylene and concentrates it near the carbon nanotubes.
Swager has filed for a patent on the technology and hopes to start a company to commercialize the sensors, while he also plans to develop a radio-frequency identification (RFID) chip so that the sensor can communicate wirelessly with a handheld device that would display ethylene levels.
He estimates the carbon nanotube sensor would cost US$0.25 while each RFID chip would cost US$0.75.
"This could be done with absolutely dirt-cheap electronics, with almost no power."
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