Improved performance of nitrate extended gate field effect transistor sensor through deposition of polymer layer at various withdrawal speeds using dip coating method

In this study, a nitrate Extended Gate Field Effect Transistor (EGFET) sensor has been deposited with polyaniline (PANI) using a dip coating method by varying the withdrawal speed parameter at a range of 1 to 7 mm/s to improve the detection and stability of the sensor that uses zinc oxide (ZnO) as a sensing material, which lacks sensitivity and stability in detecting nitrate. The sensor was characterized by analysing its surface morphology, light absorption, and wettability level. The sensitivity and linearity of the sensors were evaluated using EGFET measurements, which showed that the threshold voltage changes when the sensor interacts with the analyte. The results obtained by comparing ZnO/indium tin oxide film and PANI/ZnO film show that PANI helps to improve sensor performance, and the best parameter setup to deposit PANI was at 2 mm/s withdrawal speed, resulting in a super-Nernstian response with a high sensitivity of 78.90 mV/dec and close to 1 linearity. The film showed excellent long-term stability in detecting nitrate in a 50-ppm nitrate solution, with the lowest drift rate at 0.1278 V/h. The dip coating method, using a 2 mm/s withdrawal speed, appears to be effective for fabricating PANI as a polymer layer for nitrate sensors.