Zeolites as sensitizers in water-gated thin film transistors sensors

Thin film transistor TFT technology has emerged in several applications including in sensing
applications. The discovery of water gated thin film transistors (WGTFTs) in 2010 made possible a new technique of sensing waterborne analytes, where the test solution is the gating water and the sensitizer is integrated into the WGTFT architecture. The work presented in this thesis is toward improving the performance of WGTFTs sensors.
The solution processing of semiconductors offers a simple manufacturing method to produce good performance in TFTs using metal oxide semiconductors in particular. In this work, aiming to improve the stability of the WGTFTs sensors, solution processed SnO2 thin films prepared by spray pyrolysis were used as the semiconductor in WGTFTs. SnO2 transistors show good stability under water gating, especially when compared to other metal oxide semiconductors (here compared to ZnO). Another favorable property of SnO2 WGTFTs is the very low threshold voltage Vth. Therefore, the SnO2 WGTFT is adopted for the sensing experiments in this thesis.
Also, very sensitive WGTFTs sensors were achieved here by incorporating zeolites as sensitizers in the WGTFT architecture. Zeolites are porous aluminumsilicate minerals with different sizes of cages and channels that analytes are trapped in. As a first attempt, a PVC (Polyvinylchloride) membrane was sensitized with mordenite zeolite to detect the radioactive isotope of cesium 137Cs+ in the drinking water where this sensitized membrane is included in the WGTFT sensor. Such a sensor for Cs+ shows very good performance with a very low limit of detection of sub-nanomolar and also a very high binding constant K of 109 L/mole. In a similar way and to investigate further this finding with zeolites sensitizers, a different zeolite ‘clinoptilolite’ was used to sense the existence of heavy metals in water, in particular here lead Pb2+ and copper Cu2+ cations. Very similar behavior was obtained confirming the success of such a new family of sensitizers in the WGTFTs sensors field.
Another type of zeolite is the catalytic zeolites where these zeolites are modified to be catalysts. As the first step in the catalytic reaction is the adhesion of the analyte onto the surface of the
catalyst, so we used this fact to build a sensor from catalytic zeolites as sensitizers to the analyte that is meant to be catalyzed in water, where hydrocarbons are usually the analytes. The finding that a good catalyst is also a good sensitizer is approved here with benzyl alcohol as an analyte. Also, this work shows that a specific type of analyte can be detected by our sensors which is hydrocarbons with a free dipole.