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Selective Detection Of Ethylene Gas Using Carbon Nanotube-based Devices: Utility In Determination Of Fruit Ripeness.
Published 2012 · Chemistry, Materials Science, Medicine
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Ethylene, the smallest plant hormone, plays a role in many developmental processes in plants. For example, it initiates the ripening of fruit, promotes seed germination and flowering, and is responsible for the senescence of leaves and flowers. The rate-limiting step in the biosynthetic pathway to ethylene, elucidated by Yang et al., is catalyzed by 1aminocyclopropane-1-carboxylic acid (ACC) synthase. Ethylene production in plants is induced during several developmental stages as well as by external factors. The ripening process is the result of ethylene binding to the receptor ETR1, which leads to the translation of ripening genes and eventually the production of enzymes that induce the visible effects of ripening. The monitoring of the ethylene concentration is of utmost importance in the horticultural industries. The internal ethylene concentration in fruit can serve as an indicator for determining the time of harvest, while the monitoring of the atmospheric ethylene level in storage facilities and during transportation is crucial for avoiding overripening of fruit. We herein present a reversible chemoresistive sensor that is able to detect sub-ppm concentrations of ethylene. Our detection method has high selectivity towards ethylene and is simply prepared in few steps from commercially available materials. The sensing mechanism relies on the high sensitivity in resistance of single-walled carbon nanotubes (SWNTs) to changes in their electronic surroundings. These principles have been employed in a variety of sensing applications. For the selective recognition of ethylene we employ a copper(I) complex, inspired by nature, where Cu has been found to be an essential cofactor of the receptor ETR1. As a result of its small size and lack of polar chemical functionality, ethylene is generally hard to detect. Traditionally, ethylene concentrations are monitored through gas chromatography or laser acoustic spectroscopy, which both require expensive instrumentation and are not suitable for in-field measurements. Other techniques suggested are based on amperometric or electrochemical methods or rely on changes in luminescence properties. Furthermore, gas-sampling tubes based on a colorimetric reaction are available. The carbon nanotube based sensing concept we have developed is shown in Scheme 1.