Leonurus cardiaca L. Polysaccharide-Stabilized Palladium-Gold Nanoparticles and Fluorescent Carbon Dots for Selective and Dual-Mode Detection of Pesticide Glyphosate

The rapid and accurate detection of organophosphorus pesticides is crucial for food safety and environmental monitoring. Herein, we developed a palladium-gold nanoparticle/red-emissive carbon dot composite (Pd3Au-LCLP NPs/CDs) via a facile synthesis route. The composite was comprehensively characterized, confirming its structure which includes size, zeta potential and valence state of element. Pd3Au-LCLP NPs efficiently catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to generate blue oxTMB, revealing that the Pd3Au-LCLP NP component exhibits outstanding peroxidase-like activity. Notably, the fluorescence of the CDs is significantly quenched by oxTMB through an inner filter effect, establishing a synergistic colorimetric-fluorescent signal response system. Based on this mechanism, a dual-mode sensing platform was constructed for the detection of glyphosate. The assay demonstrates high sensitivity with a wide linear range from 8 × 10−4 to 1.6 × 102 mg/L and an exceptionally low detection limit of 0.015 μg/L. Recovery tests confirmed the sensor’s good accuracy, selectivity, and anti-interference ability. This work provides a robust and reliable dual-signal strategy for rapid and accurate detection of organophosphorus pesticide residues.