Review on Tailored Carbon Dots for High‐Performance Heavy Metal Ion Sensing in Aquatic Systems

ABSTRACT With rapid industrialization, aquatic systems are increasingly contaminated by toxic heavy metal ions (HMIs) such as Fe 3+ , Pb 2+ , Cd 2+ , Hg 2+ , Cu 2+ , Cr 6+ , and As 3+ originating from mining, electroplating, and manufacturing activities. Due to their persistence and severe ecological and health impacts, efficient detection platforms are urgently required. Carbon dots (CDs) have emerged as promising nanomaterials for HMIs sensing because of their tunable photoluminescence, aqueous stability, and surface chemistry. This review critically evaluates studies (2014–2025) focusing on the synthesis, modification, and sensing performance of CDs, with emphasis on systems designed for Hg 2+ , Cu 2+ , Fe 3+ , and emerging HMIs. Tailoring approaches such as heteroatom doping (N, S, B, P, and O) and surface functionalization are highlighted for enhancing selectivity, sensitivity, and detection limits. Major sensing mechanisms include fluorescence enhancement, photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), inner filter effect (IFE), aggregation‐induced quenching (AIQ), and redox‐mediated interactions. Key findings show that heteroatom incorporation tunes electron density, defect states, and binding affinity, enabling precise ion recognition. Unlike previous reviews, this work integrates structure–property performance correlations to present a mechanism‐focused comparative assessment. Remaining challenges including multi‐ion interference, stability, and scalability are discussed, along with future directions for developing sustainable CD‐based HMIs sensors for environmental monitoring.