Zinc Oxide-Coated Tapered Plastic Optical Fiber for Saline Sensing Applications

Accurate and real-time measurement of saline concentration is vital across healthcare, environmental monitoring and industrial sectors. However, traditional detection methods often suffer from being intrusive, expensive and having limited sensitivity. This study presents the development and validation of a portable, non-invasive and cost-effective saline detection system designed to overcome these challenges. The core of this system is a novel sensor created from a tapered plastic optical fiber (POF) coated with Zinc Oxide (ZnO) nanorods, integrated with a NodeMCU ESP8266 for data transmission and real - time monitoring. To optimize the interaction between light and the surrounding saline solution, POFs were tapered to various waist diameters (500 µm, 550 µm, 600 µm, 650 µm, and 700 µm) using a combination of chemical and mechanical etching techniques. Subsequently, ZnO nanorods were grown on the tapered fiber surface via the hydrothermal method - a critical step for enhancing the sensor’s sensitivity. The sensor’s performance was evaluated using a saline concentration ranging from 2 g to 10 g. A consistent and predictable inverse relationship was observed, where the output voltage decreased as saline concentration increased. The configuration with a 550 µm waist diameter demonstrated the highest sensitivity of 0.256 V/%g. Furthermore, the sensor exhibited excellent linearity, with correlation coefficient values consistently above 99%, confirming its high precision. The successful integration of the NodeMCU ESP8266 facilitates a practical solution for remote monitoring through data transmission. This work validates the ZnO-coated tapered POF sensor as a reliable and efficient alternative for diverse applications - including biomedical diagnostics and water quality analysis.

Plastic optical fiber, Humidity sensor, tapered fiber, Zinc Oxide Nanorods

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