Development of a Multi-Mode Optical Fiber Sensor for Cadmium Detection in Contaminated Water

Abstract

Liquid waste contamination poses a significant risk to ecosystems and human health, particularly owing to heavy metals such as cadmium (Cd). Traditional detection techniques like ICP-MS, AAS, and spectrophotometry exhibit excellent precision but are limited by their expense, complexity, and time efficiency. This study established a multi-mode optical fiber sensor system for the detection of cadmium levels in polluted water. The sensor was developed utilizing FD 620-10 multi-mode optical fiber, incorporating a chitosan-dithizone material as the immobilized cladding layer via an evanescent wave absorption method. A diode laser (KY-008) served as the light source, while an OPT101 photodiode measured the transmitted light intensity. The signals were processed with an ESP32 microcontroller, displayed in real-time on an LCD, and transmitted to a database for monitoring purposes. The experiment's results indicated that the system possesses a high sensitivity of 7.65 V/ppm, with a coefficient of determination (R2 = 0.995), signifying a strong linear correlation between cadmium content and sensor response. Prototype testing was conducted with water samples from the Pesanggrahan River. The research indicated that water samples from South Kebayoran Lama exhibited the lowest cadmium levels, whilst those from Ulujami displayed the highest. Nevertheless, the system exhibited cross-sensitivity to additional metals (Fe, Pb, Zn, and Cu), indicating that its selectivity for Cd remains insufficiently specific. This system has the potential to serve as an effective, cost-efficient, and real-time solution for monitoring water quality.