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By using carbon nanotubes, this innovative technology detects the release of ethylene gas in flowers, fruits, and vegetables when they are about to spoil.
Even though environmental awareness is on the increase, food waste figures are still staggering. Some estimates put annual food spoilage in the European Union around 173 kilos per capita, which amounts to 88 million tons every year. Likewise, in the USA, 12% of fruits and vegetables go to waste in shops and supermarkets. Finding new ways to prevent food wastage is an ethical and environmental obligation. One of the tell-tale signs of ripening vegetables is the release of a phytohormone known as ethylene, which could hold the key to monitor the life cycle of food. An innovative technology project developed at MIT can detect this type of emissions at extremely low concentrations of 15 parts per million. To achieve this, they have used a carbon nanotubes grid with palladium as a catalyst.
In their experiment, the researchers deposited the new generation of sensors onto a glass slide. Then, in the following five days, they measured the release of ethylene by two types of flowers — carnations and purple lisianthus. After detecting an ethylene spike in the first day of the experiment, they witnessed the blooming of the flowers within one or two days. Purple lisianthus flowers showed a more gradual increase in ethylene, throughout four days. This, as expected, led to a slower blooming, with some of them not blooming at all throughout the experiment.
According to the researchers, so far, no ethylene sensors have been developed. The same team created a similar sensor back in 2012, based on a grid of thousands of carbon nanotubes and copper atoms. In this prototype, ethylene atoms bonded to copper atoms, which slowed down their movement. Thus, the slowdown levels marked the presence of ethylene. The model, however, was less accurate, and copper tended to oxidize and lose its efficiency over time.
Now, with the new generation of nanotubes, the research team has opted for palladium as a catalyst. This metal adds oxygen to ethylene in a process known as Wacker oxidation. Oxidation, in turn, transfers electrons temporarily to palladium, which then are passed to the carbon nanotubes. The process increases the overall conductivity, and ethylene levels can be established once the electric current has been measured. One of the advantages of this new sensor is that it can detect ethylene in a matter of seconds. Once the ethylene disappears, the grid quickly recovers its average conductivity.
The researchers believe that the patent-pending sensors will have exciting applications in the food industry, especially with vegetables, fruits, and flowers, as reducing ethylene levels can slow down the ripening process. Moreover, as ethylene is the most widely manufactured organic compound in the world, the sensor could also be used to monitor production across a range of industries.