Engineering carbon dots with ligand-rich architectures for coordination chemistry-driven fluorescent sensing of metal ions

Anthropogenic emissions of metal ions from human activities pose significant environmental and health risks. Fluorescence optical detection is an effective approach for monitoring these ions to offer rapid response, high sensitivity, and cost-effectiveness. Consequently, carbon dots (CDs) have emerged as promising nanomaterials for this purpose due to their excellent luminescence, tunable emission profiles, and biocompatibility. The utility of CDs for metal ion monitoring is fundamentally governed by coordination chemistry and can be substantially enhanced through targeted design, including (i) surface ligand engineering (incorporating chelating groups like − COOH or − NH2 to establish strong, selective metal-binding sites), (ii) elemental doping (e.g., metal, nonmetal, and dual co-doping), and (iii) integration into hybrid coordination architectures (e.g., CDs combined with metal-organic frameworks (MOFs) or metal clusters). The core sensing mechanism relies on the chelation-induced change in the CD photophysics, leading to high-efficiency fluorescence quenching or enhancement upon ligand-metal coordination. The effects of these coordination-based modifications on CD sensing performance are systematically evaluated using key analytical metrics, particularly the limit of detection (LOD). Furthermore, current challenges and future prospects for CD-based metal ion sensors are critically examined to advance the control over surface coordination sites for their scalable manufacturing and operational performance in real-world conditions.