Selective Detection of Ethylene Gas Using Carbon Nanotube-based Devices: Utility in Determination of Fruit Ripeness

Sensing concept we have developed is shown schematically in Scheme 1

Birgit Esser; Jan M. Schnorr; Timothy M. Swager

2012

Ethylene as the smallest plant hormone plays a role in many developmental processes in plants
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 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 over ripening of fruit
The ethylene sensitive material is an intimate mixture of singlewalled carbon nanotubes with a copper(I) complex 1 based upon a fluorinated tris(pyrazolyl) borate ligand, which is able to interact with the surface of carbon nanotubes, thereby influencing their conductivity
Employing the ethylene complex 2 resulted in device sensitivity towards 20 ppm ethylene, the response amounts to only ~25% of that of 1-SWNT devices
In order to assess the selectivity of our sensory system, we measured the responses of 1-SWNT devices to several solvents as representatives of functional groups as well as to ethanol and acetaldehyde, which occur as fruit metabolites
A 1.3-2.2 fold increase in sensitivity was observed, which we attribute to an increased surface area of the singlewalled carbon nanotubes network and possibly an increase in the local ethylene concentration in the device by partitioning into the polystyrene beads

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