An antibody-aptamer sandwich-based isothermal amplification fluorescence biosensor for the detection of <em>Salmonella</em> Typhimurium

<em>Salmonella </em>Typhimurium (<em>S. </em>Typhimurium) is an important foodborne pathogen, its harm is mainly reflected in high pathogenicity, clinical manifestations, and drug resistance. The detection technology for this pathogen is gradually shifting from traditional methods to rapid and highly sensitive molecular biological methods. In order to solve the sensitivity and specificity of Salmonella detection, we built a fluorescent biosensor with an antibody-target-aptamer sandwich structure based on immune recognition and aptamer technology for quantitative detection of<em> S. </em>Typhimurium<em>.</em> By integrating the heterogeneous recognition mode composed of antibody and aptamer with isothermal hybridization chain reaction (HCR), this approach enables highly specific detection of <em>Salmonella</em> while significantly enhancing detection sensitivity through signal amplification. In the HCR hairpin structure, site-specific labeling of the fluorophore and quencher enables fluorescence signal generation via fluorescence resonance energy transfer (FRET), thereby achieving efficient optical signal output. The results show that the proposed enzyme-free heterogeneous recognition mode sensor has a detection limit of 9 CFU/mL and a 10-10⁴ CFU/mL detection range under optimized conditions. It also has good detection performance in milk and drinking water, which are common sources of <em>S. </em>Typhimurium contamination.