TAGRA 2025

Salinity detection plays a vital role in environmental monitoring, the food industry, and healthcare. Traditional methods such as conductivity meters or titration often involve bulky equipment, high costs, and limited sensitivity, making them less suitable for compact or cost-effective applications. This project focuses on the development of a zinc oxide (ZnO) coated tapered D-shape Plastic Optical Fiber (POF) sensor for saline concentration detection. The POF was fabricated with waist diameters of 500 µm, 550 µm, 600 µm, 650 µm, and 700 µm using a combination of chemical etching with acetone and deionized water, and mechanical polishing with sandpaper to enhance light interaction through the evanescent field. ZnO nanorods were grown on the tapered surface using the hydrothermal method, serving as a sensitive layer due to their high surface area and excellent optical properties. The sensors were tested with saline concentrations ranging from 0 g to 10 g, and a noticeable decrease in output voltage was observed as concentration increased. Among all samples, the ZnO-coated POF with a waist diameter of 600 µm showed the highest sensitivity at 0.1279 V/%, while the uncoated POF with a 700 µm diameter exhibited a sensitivity of 0.1127 V/%. The linearity of the ZnO-coated sensor was 95.46%, while the uncoated sensor reached 97.37%. These results demonstrate that ZnO coating significantly enhances sensor performance in terms of sensitivity, indicating the potential of ZnO-coated tapered POFs as a reliable, efficient, and cost-effective solution for accurate saline concentration monitoring in real-world applications.