Cyclohexanone-Responsive Networks of Polymer-Wrapped Single-Walled Carbon Nanotube Complexes

Modification of side chains on conjugated polymers used to disperse carbon nanotubes can impart function to the resulting polymer–nanotube complexes. Here, the side chains of a conjugated poly(fluorene) were functionalized with thiourea moieties using strain-promoted azide–alkyne cycloaddition (SPAAC). The polymer displayed strong supramolecular interactions with the sidewalls of single-walled carbon nanotubes (SWNTs), generating polymer-SWNT complexes that can be dispersed in THF. Analysis by 1H NMR indicated that the thiourea side chains are able to interact with cyclohexanone via hydrogen bonding. This allowed the polymer-SWNT complex to be used as a cyclohexanone sensor, providing an indirect method for the detection of Royal Demolition Explosive (RDX). A semiconducting (sc-) enriched SWNT sample was prepared and subsequently functionalized with thiourea moieties. The sensing properties of the polymer-SWNT complexes were evaluated via conductivity measurements, showing up to a 230% change in sheet resistance upon exposure to cyclohexanone vapors. This process was reversible upon washing with dichloromethane, and the sensor retained its sensitivity over multiple repeated exposures to cyclohexanone. The complex displayed sensitivity to cyclohexanone at concentrations down to 40 ppm. This polymer-SWNT complex was incorporated within electrolyte-gated field-effect transistor (EGFET) devices as the semiconducting layer, resulting in a cyclohexanone-responsive sensor. Electrolyte-gated devices showed a steady change in threshold voltage upon the addition of increasing concentrations of cyclohexanone in the aqueous electrolyte media. This work demonstrates that the preparation of sc-enriched polymer-SWNT complexes that possess sensory elements within the polymer side chain is feasible and can be used for the preparation of nanoscale EGFET sensors.