Fluorescent probes for heavy metal detection: A review of emerging trends and advances in sensing zinc, cadmium, and mercury ions

Heavy metal ions present a significant threat to human health and the environment, making their detection critical for public safety and water quality. Organic fluorescent sensors have emerged as a powerful tool for this purpose. These sensors are built from easily synthesized organic molecules incorporated with heteroatoms (N, O, S) that can bind to metal ions. This review focuses on recent progress in using these sensors to detect transition metal ions from the zinc group: Zn 2+ , Cd 2+ , and Hg 2+ . A major challenge for this purpose is the difficulty of selective detection due to the similar properties of these ions. We classify organic fluorescent sensors into single-ion and dual/multi-ion systems and provide a critical comparison of their chemical structures, sensing mechanisms, detection limits, and binding ratios. Our analysis offers valuable insights for designing more effective future sensors. We also discuss how integrating organic fluorescent probes with advanced support materials—such as paper strips, MOFs, and nanostructures—along with techniques like chemometric analysis, can significantly improve sensor sensitivity, selectivity, and practicality for real-world environmental applications. • This review focuses on recent developments in organic fluorescent probes for the selective detection of Zn 2+ , Cd 2+ , and Hg 2+ ions. • We provide an in-depth discussion and comparison of the molecular designs, sensing mechanisms, and the sensitivity and selectivity of each probe. • Sensing probes are classified for improved readability as single-, dual-, or multi-metal ion detection systems, with further subcategorization based on their structural classes. • Recent advancements in sensing applications, with a special emphasis on enhancing sensing efficiency and portability, are also highlighted.