Synergistic selectivity carbon-dot-embedded imprinted fluorescence sensor with decision tree for intelligent on-site detection of hexavalent chromium.

A novel synergistic selectivity carbon dot-embedded ion-imprinted fluorescence sensor was fabricated for intelligent on-site detection of hexavalent chromium (Cr(Ⅵ)). One-pot hydrothermal method synthesis yielded CDs that preferentially fluoresce toward Cr(VI) owing to surface amino, hydroxyl, and thiol groups. To further enhance the recognition selectivity, CDs were embedded into an ion-imprinted polymer via inverse microemulsion polymerization using 4-vinylpyridine as the functional monomer and ethylene glycol dimethacrylate as the cross-linker. The resulting carbon-dot-embedded ion-imprinted polymers (CDs@IIPs) combine the intrinsic selectivity of CDs with the specific recognition capability of the imprinted cavities, achieving a synergistic selectivity sensing platform. Mechanistic studies reveal that fluorescence quenching in the presence of Cr(Ⅵ) is primarily governed by an inner filter effect (IFE), while the imprinted sites ensure the exclusive recognition of Cr(Ⅵ) even in complex matrices. Under optimal conditions, the sensor exhibits a broad linear range of 0.01-50.0 mg/L and a low limit of detection of 0.012 mg/L. Its practical applicability is successfully validated in complex matrices (including seawater, fish, shrimp, and mussels), yielding robust recoveries of 95.3%-106.2%, with RSDs below 3.8%. Furthermore, a decision tree machine learning model was integrated to directly correlate the RGB image features with the Cr(Ⅵ) concentrations, enabling instrument-free, real-time visual quantification with a 95.5% accuracy. This study presents a cost-effective, intelligent, and field-deployable strategy for reliable trace Cr(Ⅵ) monitoring for environmental and food safety.