Is it ripe? Carbon nanotube-based ethylene sensor establishes fruit ripeness

May 19, 2012

( -- The term ethylene (ethene) generally brings to mind polyethylene plastics, not fruit. However, ethylene is more than just a feedstock for chemical industry, it is also the smallest plant hormone, and it controls physiological processes, such as the ripening of fruit, seed germination, and the blooming and wilting of blossoms. In the journal Angewandte Chemie, American researchers have now introduced a highly sensitive ethylene sensor that could be used to determine the ripeness of fruit.

The ripening process of many fruits is triggered when ethylene binds to a specific receptor. Bananas, for example, are usually unripe when they are harvested. They are transported under a atmosphere to stop the ripening process and are then exposed to ethylene gas in a ripening facility before delivery. However, they must not be ripened too much because bananas become “overripe” very fast. It is thus important to precisely control the ethylene concentration in storage facilities. It is also interesting to know how much ethylene fruits release at any given point in their development because this could help determine the ideal time for harvest.

As a small, nonpolar molecule, ethylene (C2H4) is difficult to detect. Conventional methods are mainly based on expensive, complex instruments that are not well suited for use in the field or in an orchard. Timothy M. Swager and his team at the Massachusetts Institute of Technology (MIT) in Cambridge (USA) have now developed a portable sensor that can reliably measure tiny concentrations of ethylene, such as those released when fruit ripens. Their device is also easy and inexpensive to produce.

The sensory element consists of a small glass plate with two gold electrodes. A mixture of single-walled carbon nanotubes and a special copper complex is deposited between the electrodes. The copper complexes bind tightly to the carbon nanotubes. When the sensor comes into contact with ethylene, the ethylene binds to the copper complex, weakening the bond between the copper complex and the carbon nanotube. The electronic properties of carbon nanotubes are very sensitive to the strength of their interaction with the copper complexes. Their electrical resistance changes in relation to the ethylene concentration.

The researchers placed different fruit in an airtight chamber and allowed nitrogen to flow through the chamber and over the sensor. This made it possible for them to compare the ethylene emissions of different fruit and to follow the amount of ethylene reduced by a single fruit as it ripened. This revealed a clear ethylene peak during storage of fruits that ripen after harvest, such as , pears, and avocados. The maximum is reached when the fruit is ripe. In contrast, fruit that do not ripen after harvest, such as oranges, release uniformly low amounts of ethylene.

Explore further: Comparing apples and oranges

More information: Timothy M. Swager, et al. Selective Detection of Ethylene Gas Using Carbon Nanotube-based Devices: Utility in Determination of Fruit Ripeness, Angewandte Chemie International Edition,

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not rated yet May 19, 2012
So the question now becomes, is it a one shot detector? Does the detector recover after a detection? Also, I WANT ONE!
1 / 5 (3) May 19, 2012
Hmmm, nice to have one in the fridge, would be curious to see if there could be enough to build up to a stoichiometric mixture ;-)

Well if it got closer to that, it would make a nice murder plot, though I'd rather vent the gas to a fuel cell or one of those oldie kerosene type coolers of last century to run the fridge itself, that way the ethylene is consumed to offset electricity consumption, I just love recursion :-)
not rated yet May 19, 2012
It wouldn't be much of a murder weapon. Ethylene is the gas the Oracle sniffed to go into their trances. It might make someone dizzy but that would be about it.
1 / 5 (1) May 19, 2012
Indeed, next on the list will be to make a fart detecting device. Capable not only of alerting one to the presence of a fart but determining who supplied it as well.

But in reality maybe it will be nice if it reduces waste, I have worked in a produce department and am well aware of how many starving people can be fed by wasted food, which is not allowed to be fed to starving people, only thrown in the trash.

So maybe after the corporations are able to save millions of dollars from this invention the standards of work and pay will accomadate the people who would have otherwise been starving in the first place. Of course that's the Republican/Tea-bagger way to do it, why don't we just feed it too them now and let them risk getting poisoned at least there's a chance they will live.
not rated yet May 20, 2012
So maybe after the corporations are able to save millions of dollars from this invention the standards of work and pay will accomadate the people who would have otherwise been starving in the first place. Of course that's the Republican/Tea-bagger way to do it, why don't we just feed it too them now and let them risk getting poisoned at least there's a chance they will live.

Not really.

Giving someone food these days is a risky endeavor, since if they get sick they can sue you for tens of millions of dollars, even if they already know there's a risk involved.

"The coffee was HOT. I'm suing!"

Also, if produce is bad enough to be thrown out, then getting it to a charity or other distribution place in time for it to be useful to anyone willing to do "culls" will often be impossible or impractical. You'd spend more money and resources than the food is worth, and would be better served making a cash donation.
1 / 5 (2) May 20, 2012
Sonhouse didnt notice I said stoichiometric
It wouldn't be much of a murder weapon...
I was referring to the chance of ignition with a stoichiometric mixture, enough for a fully combustible mixture (sufficient O2 & C2H4 for them both to be fully consumed) ie a BanG.

I know of pensioners who stuff their fridges full of fruits and veges and sometimes don't open them for days !

Say 60% of the available fridge volume is taken up with solid matter, the remainder air mixed with ethylene and assuming the seals will be more likely to pass the smaller molecules, will there be enough C2H4 to build up a flammable mixture over a few days ?

I have this image of the classic bogan pensioner waking up, walking naked to the fridge, lighting a smoke when he opens the door looking for milk for his coffee and getting a rather nasty surprise...

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