A Multivalent Aptamer-Driven “4 + 1” Nanozyme Platform for Ultrasensitive Detection and Synergistic Inactivation of <i>Salmonella typhimurium</i>

Herein, we developed a novel "4 + 1" biosensing platform based on cascaded nucleic acid amplification and nanozyme activity, enabling fluorescence-colorimetric dual-mode detection and efficient inactivation of <i>Salmonella Typhimurium</i> (<i>S. typhimurium</i>). The "4 + 1" system incorporates a multi-component strategy featuring multivalent aptamers for enhanced target recognition, coupled with a quadruple signal amplification strategy involving exponential amplification reaction (EXPAR), hybridization chain reaction (HCR), multivalent aptamers, and functional nanozymes (Fe₃O₄ and Fe-PDs), thereby achieving synergistic antibacterial effects. It achieves a wide linear range of 3 × 10¹-3 × 10⁷ CFU/mL, with detection limits of 7.7 CFU/mL for fluorescence and 8.7 CFU/mL for colorimetry. Furthermore, the system exhibits antibacterial capability by catalytically generating reactive oxygen species (ROS), reducing the risk of secondary contamination. When applied to spiked milk samples, the biosensor showed satisfactory recovery rates and reproducibility. The study provides a high-precision, low-cost analytical solution for detecting and inactivating foodborne pathogens, demonstrating significant potential for rapid on-site food safety monitoring.