Sub-nanomolar detection of cesium with water-gated transistor

Abstract

Cesium (Cs+) cations are rare in nature, but the β− active radioisotope 137Cs can be released from nuclear accidents and find its way into the water supply, where it is harmful to humans and animals who drink it. We here report a water-gated thin film transistor (WGTFT) that allows the detection of Cs+ in drinking water at very low concentrations. The transistor channel is formed from spray-pyrolyzed tin dioxide, SnO2, which gives WGTFTs with near-zero initial threshold. When the WGTFT is sensitized with a plasticized PVC membrane containing the Cs+-selective zeolite “mordenite,” it displays a threshold shift when exposed to drinking water samples carrying traces of Cs+. The response characteristic is given by the Langmuir adsorption isotherm instead of the Nikolsky-Eisenman law commonly found for ion-sensitive WGTFTs sensitized with organic ionophores. We find a complex stability constant K = (3.9 ± 0.4) × 109 l/mol and a limit of detection (LoD) of 33 pM. Our LoD is far lower than the Cs+ potability limit of 7.5 nM, which cannot be met by organic-sensitized membranes where the LoD is typically in the order of 100 nM or more.