Abstract
Cesium (Cs+) cations are rare in nature, but the beta(-) active radioisotope Cs-137 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)x10(9)l/mol and a limit of detection (LoD) of 33pM. Our LoD is far lower than the Cs+ potability limit of 7.5nM, which cannot be met by organic-sensitized membranes where the LoD is typically in the order of 100nM or more.