Selective Detection of Ethylene by MoS₂–Carbon Nanotube Networks Coated with Cu(I)–Pincer Complexes

Abstract

The plant hormone ethylene (C2) can induce premature fruit ripening and flower senescence at levels below 1 ppm, which has motivated efforts to develop cost-effective methods for C2 monitoring during the transport and storage of climacteric fruits. Here, we describe a nanocomposite film composed of exfoliated MoS₂, single-walled carbon nanotubes (SCNTs), and Cu(I)-tris(mercaptoimidazolyl)borate complexes (Cu-Tm) for real-time detection of C2 at levels down to 100 ppb. A copercolation network of MoS₂ and SCNTs was deposited onto interdigitated Ag electrodes printed on plastic substrates and then coated with Cu-Tm with a final conductance in the 0.5 mS range. Reversible changes in relative conductance (-Δ<i>G</i>/<i>G</i>₀) were measured upon C2 exposure with a linear response at sub-ppm levels. The thin-film sensors were highly selective toward C2, and they responded weakly to other volatile organic compounds or water at similar partial pressures. A mechanism is proposed in which Cu-Tm behaves as a chemically sensitive <i>n</i>-type dopant for MoS₂, based on spectroscopic characterization and density functional theory modeling. Cu-Tm-coated MoS₂/SCNT sensors were also connected to a battery-powered wireless transmitter and used to monitor C2 production from various fruit samples, validating their utility as practical, field-deployable sensors.