PdCo@NC-based colorimetric dual-wavelength for highly sensitive Hg ions detection

Hg 2+ ions, as one of the prevalent toxic heavy metals, are ubiquitously distributed in food and environmental systems. Consequently, there is an urgent demand to develop a convenient and reliable detection platform. In this study, heteroatom-doped PdCo@NC nanozymes were synthesized by pyrolyzing bimetallic metal-organic frameworks (MOFs) in argon, combining MOF-derived porous carbon with C/N co-doping. The resultant PdCo@NC-500 material exhibits a flower-like morphology with defects and uniform elemental distribution, demonstrating unique intrinsic peroxidase-like activity. This enables the oxidation of TMB in the absence of H₂O₂, with catalytic performance surpassing that of single-metal systems. Key reaction intermediates (•OH, 1 O₂) were verified through quenching experiments. Kinetic analysis revealed that this material possesses high catalytic efficiency ( K m  = 0.101 mM, V max  = 238.9 × 10 −3  M/s). Notably, following the distinctive REDOX reaction between H₂O₂ and Hg 2+ , the peroxidase-like activity of PdCo@NC-500 is significantly inhibited, enabling selective alteration of the reaction pathway and changing the product color from blue to yellow. This unique response characteristic provides a foundation for designing colorimetric sensors, achieving dual-wavelength colorimetric detection of Hg 2+ . Experimental results indicate that the linear range of this method is 50–1000 μM (λ = 450 nm) and 0.5–100 μM (λ = 652 nm), with a detection limit of 0.02 μM. This method has been successfully applied to highly sensitive detection of Hg 2+ in real water samples and rice, with recovery rates ranging from 94.87 % to 109.1 %.