Zainuddin, N.A.M. et al. 2026. Solution-Based Fertilizer Detection Using Guided-Mode Resonance Optical Sensors: A Comparative Study with a Commercial Multispectral Sensor. Engineering Journal. 30, 8 (Aug. 2026), 81–101. DOI:https://doi.org/10.4186/ej.2026.30.8.81.