As fruit matures, it releases ethylene which is a gas that initiates the ripening process. Once the ripening process begins, more ethylene is released and the process accelerates. Currently produce warehouses that store and ripen fruit make use of gas chromatography and mass spectroscopy systems that cost about $1,200 to measure the levels of ethylene which in turn reveals the ripeness of the fruits in storage.
A scientist from MIT has reportedly been working on something that might change that soon. His name is Timothy Swager and he is in the midst of developing small and inexpensive ethylene sensors that could even be used in commercial outlets like supermarkets or greengrocers. His experiment which utilizes an array of tens of thousands of carbon nanotubes in each sensor could be used to let shopkeepers know which batches of fruit need to be sold soonest in order to maintain the ripest fruit to be consumed immediately and the less ripe ones that can last a bit longer.
All the carbon nanotubes in each sensor have had copper atoms attached to them and while electrons can flow freely through the nanotubes, any ethylene present around the sensor will bond with the copper atoms and effectively block the flow of the electrons. To centralize where the ethylene is concentrated, the simple additions of polystyrene beads which absorb ethylene are used.
By measuring how much the electron flow has either slowed down or sped up, the sensors can determine the correct ethylene level surrounding the device. The sensors thus far have been tested on a few fruits and accurately gauged the ripeness of all of them. Swager’s vision for the invention is to incorporate it into storage boxes for fruit along with a radio-frequency identification chip that would transmit ripeness related data to a handheld device kept by the shopkeeper in question. By his estimate, instead of the $1,200 needed for the alternative method such as gas chromatography, the sensor along with the radio chip should incur a combined cost of about $1.