Ultrasensitive Ethene Detector Based on a Graphene–Copper(I) Hybrid Material

Abstract

Ethene is a highly diffusive and relatively unreactive gas that induces aging responses in plants in concentrations as low as parts per billion. Monitoring concentrations of ethene is critically important for transport and storage of food crops, necessitating the development of a new generation of ultrasensitive detectors. Here we show that by functionalizing graphene with copper complexes biologically relevant concentrations of ethene and of the spoilage marker ethanol can be detected. Importantly, in addition these sensors provide us with important insights into the interactions between molecules, a key concept in chemistry. Chemically induced dipole fluctuations in molecules as they undergo a chemical reaction are harvested in an elegant way through subtle field effects in graphene. By exploiting changes in the dipole moments of molecules that occur upon a chemical reaction we are able to track the reaction and provide mechanistic insight that was, until now, out of reach.

Ultrasensitive Field‐Effect Biosensors Enabled by the Unique Electronic Properties of Graphene

“…For example, the transfer characteristics G ( V GS ) of these GFET devices exhibit symmetric shapes and field‐effect hole carrier mobilities of ≈1500 cm 2 V −1 s −1 , which are preserved to ≈80% of their initial values upon the noncovalent surface functionalization with the copper(I) complexes via π–π and/or hydrophobic interactions. The affordable drop in the carrier mobility was ascribed to an increased scattering of the charge carriers . As it was experimentally proven recently, noncovalent functionalization can indeed deliver GFETs with fully preserved mobility .…”

“…A back‐gated GFET consists source and drain metallic electrodes bridged by a graphene conduction channel ( Figure a). To ensure a negligible contact resistance, electrodes (e.g., 5 nm Cr/50 nm Au) can be prepared directly on top of the graphene . Double contacts are found to reduce the effective contact resistance.…”

“…One possible way to avoid this unwanted doping is to transfer graphene onto surfaces treated with hexamethyldisilazane (HMDS) or octadecyltrichlorosilane to shield it from trapped charges located at the SiO 2 surface, resulting in advantageously hysteresis‐free operation and close‐to‐zero CNP point. Such high‐performance back‐gated GFETs with reliable operation have been successfully used for gas sensors . When the back‐gate is held at a fixed voltage, physisorption or chemisorption of targeted molecules on the graphene surface can induce a change in the electric field, and thus the channel current due to field effect.…”

“…Although the field‐effect mobility is reduced to ≈80% of the initial values upon the self‐assembly of the copper(I) molecules on the surface of graphene (as we discussed previously in Section ), no trend in the change of the Dirac points before and after the functionalization has been found. Therefore, it is likely that the differences in scattering rates caused by the organization of the complexes on the surface of graphene obscure the more subtle field effect of the complexes of different polarities …”

“…This field effect has been harvested to design the first generation of nanowire, carbon nanotube, and graphene‐based field‐effect transistor (GFET) . The experimental preparations and observations of the electric field effect in nanomaterials have inspired numerous experimental and theoretical works related to the application of nanoscale field‐effect transistors (FETs) for high performance label‐free biochemical sensors …”