The sensor can detect concentrations of ethylene as low as 0.5 parts per million (PPM) with the usual levels required for fruit ripening between 0.1 and 1PPM, making it suitable for warehouse use.
Timothy Swager, the John D. MacArthur professor of Chemistry at the Massachusetts Institute of Technology (MIT), invented the patented device which can be attached to produce crates and shipping containers. He said there were sensors in the market but they were more costly and a number of shipping businesses said the technology sometimes didn’t work as advertised.
A radio frequency identification (RFID) chip is added to the sensor so it can communicate wirelessly with a handheld device that would display ethylene levels.
Swager said the price could be as low as 25 cents for the carbon nanotube sensor plus 75 cents for the RFID chip.
Ethylene is a gaseous plant hormone which is responsible for fruit ripening.
How it works
The sensor consists of tens of thousands of carbon nanotubes, which are sheets of carbon atoms rolled into cylinders that act as “superhighways” for electron flow.
The researchers added copper atoms to modify the tubes to detect ethylene gas which serve as “speed bumps” to slow the flowing electrons. Ethylene binds to the copper atoms to slow the electrons further.
By measuring how much the electrons slow down the researchers can determine the presence of ethylene.
The team added tiny beads of polystyrene, which absorbs ethylene and concentrates it near the carbon nanotubes to make the device more sensitive.
Swager said the ethylene can be detected by real-time constant read out or in dosage measures.
“I started work in this field about five years ago heavily on ethylene methods but they weren’t sensitive enough so it was all about building it up. RFID tags were always part of the motivation.
“It will minimise spoilage and manage the distribution chain to ensure that food is not over ripe or under ripe.
Moving forward
“We hope to make it so inexpensive that there can be systems in every refrigerator to help keep the ethylene levels down or letting you know when the fruit is ripe.”
Swager said team had recently received a grant for more research and have formed a start-up company.
“We are going to work on refining the process in our laboratory by making it more robust in the next nine months and then we can move to start-up, it isn’t just something we can chuck over the wall for anyone to use.
“We hope by 2013 we will be able to support prototypes and be up to full scale production six months after that but we will have to get feedback and see how it’s working in terms of temperature, humidity and range.”
