Volume 90 Issue 19 | p. 29 | Concentrates
Issue Date: May 7, 2012

Fruit Ripeness Detected Via Nanotube

MIT researchers develop carbon nanotube-based sensor that measures concentrations of ethylene, a ripeness indicator, as low as 0.5 ppm
Department: Science & Technology
News Channels: Analytical SCENE, Biological SCENE
Keywords: chemical sensing, ethylene, fruit, ripening, carbon nanotubes, gas detection
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A fruit-ripeness sensor uses carbon nanotubes (bottom) bound to fluorinated copper(I) tris(pyrazolyl)­borates (top) to detect the plant hormone ethylene. Cu = gold, F = green, N = blue, B = pink, and C = gray.
Credit: Angew. Chem. Int. Ed.
A sensor that detects fruit ripening uses a copper-based compound attached to carbon nanotubes (bottom). When ripening indicator ethylene binds to the copper (gold), the compound detaches, causing the tube’s resistance to increase. F = green, N = blue, B = pink, C = gray.
 
A fruit-ripeness sensor uses carbon nanotubes (bottom) bound to fluorinated copper(I) tris(pyrazolyl)­borates (top) to detect the plant hormone ethylene. Cu = gold, F = green, N = blue, B = pink, and C = gray.
Credit: Angew. Chem. Int. Ed.

Rather than using expensive gas chromatography and mass spectrometry systems to monitor the freshness of their fruit, food distributors of the future might instead use low-cost carbon nanotube-based sensors. That’s because MIT researchers Timothy M. Swager, Birgit Esser, and Jan M. Schnorr have developed a device that detects fruit maturity by measuring levels of emitted ethylene, a plant hormone that initiates ripening (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201201042). The researchers make the ethylene sensor by depositing a mat of carbon nanotubes bound to fluorinated copper(I) tris(pyrazolyl)­borates onto a surface containing gold electrodes. When exposed to ethylene emitted from fruits such as pears and oranges, the copper compounds associate with the plant hormone, disrupting their interaction with the nanotubes. As a result, electrical resistance across the electrode-spanning nanotubes increases in proportion to how much ethylene is present. By adding polystyrene beads to the mat to increase its surface area, the researchers were able to detect ethylene concentrations as low as 0.5 ppm. “Food is even more important than energy,” says Swager, who has already filed a patent for the sensor. “We need to manage it, enhance production, and prevent waste.”

 
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ISSN 0009-2347
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