Fluorescent sensor approaches for mercury detection: Chemosensors, carbon dots, MOFs, and nanomaterials.

Mercury (Hg2+) is a highly toxic and bio accumulative environmental pollutant, where even trace concentrations demand rapid, sensitive, and selective detection in complex media. Although traditional analytical methods offer precision, their reliance on costly infrastructure and lengthy protocols limits field deployment. Fluorescent chemo sensors, carbon dots (CDs), metal-organic frameworks (MOFs), and hybrid nanomaterials provide compelling alternatives, leveraging high sensitivity, tunable selectivity, and visual output for real-time analysis. This review critically evaluates recent advances in fluorescent Hg2+ sensor design, connecting structural and mechanistic features such as coordination chemistry, donor-atom interactions, and photo physical responses directly to analytical performance in terms of limit of detection, emission response, real-sample recovery, and solvent compatibility. A key finding is that superior sensitivity and selectivity frequently arise from integrated sensing mechanisms, in which two or more complementary processes for instance, coordination-driven quenching combined with energy transfer or nanostructure-enhanced binding operate synergistically. While CDs and hybrid materials exploit such multimodal recognition to minimize interference, MOFs offer exceptional structural programmability for environmental adaptability. Practical challenges, including matrix effects, probe stability, and reproducibility are discussed as critical barriers to real-world translation. In conclusion, we highlight how rationally engineered hybrid and nanostructured platforms, which unify multiple sensing principles within a single design, offer the most viable route to portable, sustainable, and field-ready Hg2+ monitoring systems.