A real-time on-line photoelectrochemical sensor toward chemical oxygen demand determination based on field-effect transistor using an extended gate with 3D TiO2 nanotube arrays

Chemical oxygen demand (COD) is one of the most widely used parameters for water quality assessment. Quantification and detection of COD slight fluctuations is crucial for an early detection of abnormal change in the water environment. Here we report a real-time on-line photoelectrochemical method for sensitive COD detection using an extended-gate field-effect transistor (EGFET) sensor. The FET gate consists of a Ti mesh electrode with 3D TiO2 nanotube arrays modified by Pt nanoparticles. The device shows a COD detection limit down to 0.12 mg/L and a wide dynamic linear range from 1.44 mg/L to 672 mg/L at a continuous flow rate of 1.0 mL/s. The method reported also displays excellent stability, accuracy and reproducibility. More importantly, real water samples analyses with the proposed method are in a good agreement with the standard dichromate method. The results suggest that the EGFET-based photoelectrochemical sensors are potential candidates for practical COD onsite measurement.