Electrolyte-Gated Organic Field-Effect Transistor for Ultra-Sensitive Cs Ion Sensor

A main purpose of this work is to develop a new ultra-highly sensitive sensor in particular for the detection of Cs+ ions in natural water. The radioactivity of Cs+ ions produced in nuclear power stations (NPSs) causes serious impact on the health condition of humans, as well as aquatic plants and animals. Therefore, it should be strictly controlled. However, a large amount of radioactive Cs+ had been distributed from Fukushima NPS due to the tragic accident after the great earthquake in Japan. Because of these reasons, the detection and monitoring of Cs+ ions in natural water are necessary. To tackle this issue, we developed an organic field-effect transistor (OFET)-based ion sensor. The sensor is composed of three main components: (1) organic semiconducting channel with high stability in working with natural water, (2) monolayer lipid membrane working as ultra-thin dielectric layer to allow low operating voltage and high sensitivity, and (3) novel calixarene-crown ether probe for high selectivity to Cs+ , which is grafted with lipid layer. Here, gate bias voltage is applied through electrolyte solution, in which the target ion and other competing ions are simultaneously contained. Once ion probes form metal-complex with Cs+, the electrical signal from the ion, the concentration of which is even on the ppb order, can be detected as a shift of threshold voltage. This is owing to the large electrical capacitance of monolayer lipid membrane. In comparison with other conventional methods like ICP-MS, our new sensor has many advantages: high sensitivity and selectivity, high-throughputs, integration and portability associated to real-time and on-site monitoring capabilities. In this presentation, we demonstrate a label-free sensor operation with the sensitivity of femtomolar (pg/l) concentrations of Cs+ ion with high selectivity.