Optical sensing techniques for iron detection in aqueous solutions: a comprehensive review

Iron (Fe) contamination in water poses a serious threat to public health and aquatic ecosystems, necessitating accurate and rapid detection technologies. This review provides an overview of optical methods for Fe pollution detection in water, emphasising the under-investigated potential of advanced techniques including ultraviolet–visible spectroscopy (UV-Vis), absorption spectroscopy, fluorescence-based sensors, surface-enhanced Raman scattering (SERS), and plasmonic sensors. Reported detection limits range from sub-ppb levels (≈0.05 ppb) to ppm-level detection for colorimetric and portable sensing platforms. While fluorescence and nanomaterial-assisted sensors offer superior sensitivity and selectivity towards specific Fe oxidation states, UV-Vis spectroscopy remains widely used for its simplicity, stability, and compatibility with reagent-based complexation. Conventional methods, though accurate, are constrained by operational complexity, cost, and lack of portability, whereas novel optical techniques offer fast, portable, and cost-effective alternatives. Key sensing mechanisms, performance trends, and practical limitations of current optical methods are critically assessed. Future directions discussed include miniaturised and low-cost optical sensors, improved discrimination between Fe oxidation states, and integration of real-time data acquisition with remote sensing for in-situ monitoring. This review is intended to serve researchers, engineers, environmental scientists, and policy makers by systematically summarising recent advances in optical Fe detection and their potential to transform environmental surveillance and water quality decision-making.