Label-free HCR-facilitated nanozyme catalysis and fluorescence simultaneous amplification for ultrasensitive dual-signal sensing of foodborne Salmonella typhimurium.

A label-free hybridization chain reaction (HCR)-facilitated nanozyme catalysis and fluorescence simultaneous amplification strategy is proposed for the ultrasensitive fluorescence-colorimetric dual-mode detection of S. typhimurium in complex food matrices. In the approach, aptamer-functionalized magnetic beads specifically captured S. typhimurium, and the cDNA triggered HCR to generate long and rigid double-stranded DNAs (dsDNAs), which could be inserted with SYBR Green I (SGI) and regulate the surface charge and spatial distribution of gold nanoparticles (AuNPs). Consequently, the produced dsDNAs simultaneously enhanced the fluorescence intensity of SYBR Green I and the enzyme-like activity of AuNPs catalyzing the 3,3',5,5'-tetramethylbenzidine chromogenic reaction, yielding robust dual-signal outputs for quantification. With the label-free HCR-facilitated nanozyme catalysis and fluorescence simultaneous amplification feature, the detection Limit of our dual-mode system is as low as 1 CFU/mL, and its analytical application in real food samples was also verified with satisfactory accuracy. The proposed HCR-enabled sensing system furnishes an ultrasensitive and precise method for the detection of foodborne pathogens, holding great application potential in food safety analysis and other fields.