Salicylaldehyde-functionalized gold-nanocluster-based Ratiometric fluorescent sensor Array for metal-ion detection

Heavy metal ions often coexist as multi-ion mixtures in aquatic environments, making their multiplex discrimination difficult for conventional fluorescent probes based on specific "lock-and-key" recognition. Herein, we report a dual-channel ratiometric fluorescent sensor array constructed from salicylaldehyde (SA)-functionalized, protein-stabilized gold nanoclusters (AuNCs) for the discrimination of ten metal ions (Zn²⁺, Hg²⁺, Co²⁺, Pb²⁺, Ag⁺, Cu²⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Mn²⁺). The two nanocluster probes generated distinct ratiometric fluorescence response patterns toward different metal ions, providing informative fingerprints for pattern recognition. Combined with principal component analysis (PCA) and linear discriminant analysis (LDA), the sensor array allowed reliable classification of ten metal ions at concentrations as low as 0.5 μM and enabled the discrimination of multicomponent heavy-metal mixtures. More importantly, the ExtraTrees model further improved concentration-independent classification and enabled satisfactory quantitative prediction. The array also remained applicable for differentiating metal ions in real water samples, highlighting its potential for practical monitoring of multiple heavy metal ions in complex aqueous environments.