Fluorescent hydrogel materials for heavy metal ion detection: design strategies, sensing mechanisms, and applications

Heavy metal ion pollution has become a major global environmental and health challenge due to its persistence, bioaccumulation, and strong toxicity. In recent years, fluorescent hydrogel materials have become a research hotspot for the detection of heavy metal ions due to their high sensitivity, fast response, visualization, and designability. Although several reviews have separately addressed hydrogels (including classification, preparation, and applications) or heavy metal ions detection (including detection methods and functional materials), they often discuss components or applications in isolation or fail to provide a detailed exploration of the detection mechanisms. Unlike previous studies, this review uniquely focuses on the design strategies, sensing mechanisms, and applications of fluorescent hydrogel materials for heavy metal ions detection. A comprehensive and critical evaluation has been conducted. Furthermore, compared to previous reviews that focused on hydrogels (including classification, preparation, and applications) or heavy metal ion detection (including detection methods and functional materials), this review provides an outlook on sensitivity, selectivity, multifunctionality, stability, and practical applications. This review focuses specifically on fluorescent hydrogels for heavy metal ion sensing. It further highlights future opportunities in areas such as hydrogel network engineering, stimulus-responsive regeneration, machine learning-assisted intelligent sensing, biomonitoring of heavy metal toxicity, and commercialization-oriented development. Consequently, it provides a more targeted perspective for advancing fluorescent hydrogel-based sensing systems.