Electrochemical detection of S. typhimurium based on peroxidase-like activity of gold nanoparticle-doped CuZr-MOF nanozyme.

An electrochemical biosensor using gold nanoparticles (AuNPs)-doped bimetallic-organic framework (BMOF) with enhanced peroxidase-like activity was constructed to detect Salmonella Typhimurium (S. typhimurium). The BMOF of CuZr-MOF was synthesized via a two-step method and used as carrier to in situ immobilize AuNPs. Due to the stability of Zr-MOF, the good electrocatalytic ability of Cu (II), and the synergetic effects of AuNPs, Cu (II) and Zr (IV), the prepared AuNPs@CuZr-MOF nanozyme showed improved stability and catalytic activity to HO oxidation. The oxidation reaction was found to be a surface-controlled process of electron transfer and a pH-dependent electron transfer process of oxidation reaction involving two electrons. Further, AuNPs@CuZr-MOF was biofunctionalized with signal DNA probe, forming sDNA-AuNPs@CuZr-MOF nanotags. The biosensing platform was constructed on a glassy carbon electrode modified sequentially with electrodeposited AuNPs, capture DNA probe (cDNA), and BSA. Finally, a sandwich-type detection structure was formed by hybridization reactions between cDNA and target invA gene of S. typhimurium, as well as between invA gene and the sDNA of sDNA@AuNPs@CuZr-MOF nanotags. Under optimized experimental conditions, the biosensor achieved a linear range of 1 × 10 to 1 × 10 mol L for the target invA gene with a detection limit (LOD) of 6.2 × 10 mol L using differential pulse voltammetry measurement (DPV). It was successfully applied to the direct and quantitative detection of invA gene segments in total DNA extracts of S. typhimurium, showing a linear range from 3.5 to 3.5 × 10 CFU mL and a LOD of 0.82 CFU mL. The fabricated biosensor exhibited good selectivity, reproducibility, and storage stability, enabling its use for the detection of invA gene segments in contaminated milk, with recoveries between 95.9% and 103.1%.