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Highly Sensitive Silicon-based Electrochemical Sensor for On-site Fluoride Ion Monitoring

Polycrystalline (poly) lanthanum fluoride (LaF3) Electrolyte-Insulator-Semiconductor (EIS) sensor, as one of silicon based electrochemical sensors, could be well suitable for promising on-site fluoride ion (F-) sensor platforms due to small size, fast response and simple fabrication method. The key to successful implementation is to optimize poly LaF3 film and total ionic strength adjustment buffer solution (TISAB). The structural and sensing characteristics of poly LaF3 EIS sensor have been investigated, which is focus on substrate temperature effects of thermal evaporation at 25°C, 150°C, 300 °C and 500°C. Poly LaF3 EIS sensors has been fabricated under the thermal evaporation at 500°C, that shows excellent sensing performances such as high sensitivity (47.9 mV /pF) and low limit of detection (3.02 ppb) caused from enhanced structural properties. In addition, the 100-times diluted TISAB gives better results such as higher sensitivity (50.2 mV/pF), lower limit of detection (1.4 ppb), smaller hysteresis voltage (0.9 mV) and lower drift rate (0.60 mV/hr). Consequently, the poly LaF3 EIS sensors with 100-times diluted TISAB show a similar detecting accuracy, which has the small difference of 6.1 % compared to commercial sensor in F- analysis of tap water.