Recent Advances in Alginate-Based Functional Materials for Colorimetric and Fluorescent Detection of Environmental and Biological Targets

Alginate-based functional materials have emerged as versatile platforms for the development of sensitive and selective sensors for environmental and biological monitoring. Owing to their excellent biocompatibility, tunable mechanical properties, and facile functionalization, alginate hydrogels, beads, and composite systems have been extensively explored for colorimetric and fluorescent detection applications. This review highlights recent advances in the design and fabrication of alginate-based sensors for the detection of metal ions, drugs, biological molecules, and pathogenic bacteria. For metal ion detection, alginate hydrogels integrated with fluorescent nanomaterials, quantum dots, or rare-earth phosphors demonstrate high selectivity and sensitivity, enabling rapid and reversible visual or fluorescence-based monitoring of metal ions. In the context of biological molecules, alginate matrices functionalized with enzymes, fluorophores, or perovskite quantum dots allow for the detection of small biomolecules, providing both colorimetric and ratiometric fluorescent outputs with low detection limits and robust performance in complex biological samples. Furthermore, the incorporation of metal ions, cationic crosslinkers, or antimicrobial agents into alginate-based hydrogels has enabled the development of multifunctional platforms capable of detecting pathogenic bacteria, such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), through fluorescence activation, pH-responsive color changes, or combined antibacterial-sensing strategies. Smartphone-assisted colorimetric analysis, microfluidic integration, and visual readout techniques enhance the portability and real-world applicability of these sensors.