A membrane-free cation selective water-gated transistor.

Sensors for the detection of waterborne cations are of great practical interest, and chemistry has synthesised a formidable catalogue of cation selective complexation agents ('ionophores') as selective sensitisers. Current ionophore-based sensors separate the complexation of the cation by the ionophore, and the transduction of complexation into an electrical signal, into separate components. We here unite both functions into a single, sensitised semiconducting layer of a water-gated organic thin film transistor (OTFT).

Innate cation sensitivity in a semiconducting polymer.

Water-gated organic thin film transistors (OTFTs) using the hole transporting semiconducting polymer, poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), show an innate response of their threshold voltage to the addition of divalent metal cations to the gating water, without deliberately introducing an ion-sensitive component. A similar threshold response is shown for several divalent cations, but is absent for monovalent cations. Response is absent for transistors using the inorganic semiconductor ZnO, or the similar organic semiconductor poly(3-hexylthiophene) (rrP3HT), instead of PBTTT.

A water-gated organic thin film transistor as a sensor for water-borne amines.

The p-type semiconducting polymer Poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) displays innate sensitivity to water-borne amines. We demonstrate this with the help of water-gated PBTTT thin film transistors (TFTs). When octylamine is added to the gating water, TFTs respond with a significantly reduced saturated drain current.

Precursor-route ZnO films from a mixed casting solvent for high performance aqueous electrolyte-gated transistors.

We significantly improved the performance of precursor-route semiconducting zinc oxide (ZnO) films in electrolyte-gated thin film transistors (TFTs). We find that the organic precursor to ZnO, zinc acetate (ZnAc), dissolves more readily in a 1 : 1 mixture of ethanol (EtOH) and acetone than in pure EtOH, pure acetone, or pure isopropanol. XPS and SEM characterisation show improved morphology of ZnO films converted from a mixed solvent cast ZnAc precursor compared to the EtOH cast precursor.