An integrated litmus test platform for low-background detection and photothermal inactivation of Salmonella typhimurium via HCR-urease signal amplification

A “Low-Background” ratiometric sensor for ultrasensitive S. typhimurium detection. • The detection limit for the platform is 2.34 CFU mL −1 , and the visual detection limit is 10 3  CFU mL −1 . • The platform enables efficient bacterial enrichment, detection, and inactivation. • Fe₃O₄@PDA@PEI is reusable and stable for sustainable reuse. Herein, we propose a novel “low-background” biosensing platform integrating magnetic separation and hybridization chain reaction (HCR) for signal amplification, enabling ratiometric colorimetric detection and visual observation of S. typhimurium . In the presence of S. typhimurium , specific aptamer recognition triggers the HCR to couple the urease-labeled DNA to the HCR reporting system, ultimately generating a ratiometric colorimetric response upon enrichment by Fe 3 O 4 @PDA@PEI and magnetic separation. The assay demonstrates excellent sensitivity, achieving a detection limit of 2.34 CFU mL −1 . Simultaneously, the ratiometric sensor enables direct visual detection of S. typhimurium at concentrations as low as 10 3  CFU mL −1 . Furthermore, leveraging the photothermal properties of Fe 3 O 4 @PDA@PEI under 808 nm NIR irradiation significantly reduced S. typhimurium viability, thereby minimizing the risk of secondary contamination. Recovery rates of 84.2%–115.3% in common spiked food samples containing S. typhimurium confirm its practicality. This integrated “detection and inactivation” strategy offers a proactive defense for food safety. Download: Download high-res image (118KB) Download: Download full-size image