Nanocatalyst coupled with a latent-ratiometric electrochemical switch for label-free zero-tolerance rapid detection of live Salmonella in whole blood samples

Developing a simple and rapid analytical tool for detecting live Salmonella is urgently needed for clinical diagnosis and food surveillance. In our previous studies, an activity-based latent ratiometric electrochemical switch was successfully deployed to monitor Salmonella but it could not achieve “zero-tolerance” detection; thus, improving the detection sensitivity from that of our previous approach is needed in order to obtain a practical tool for detecting Salmonella. In this study, a latent ratiometric electrochemical switch Sal-CAF coupled with graphene quantum dots-gold nanoparticles (GQDs-AuNPs) modified electrode was developed to meet the needs of selective detection of live Salmonella. Stable and uniformly sized GQDs-AuNPs (14.25 ± 0.2 nm) were achieved by using a free of reducing agent. The Sal-CAF coupled with GQDs-AuNPs/GCE showed an enhanced current response with an extended linear Salmonella detection concentration range of 1.0 × 10³ to 1.0 × 10¹⁰ CFU/mL and a limit of detection of 35.62 × 10¹ CFU/mL within 4 h. Moreover, the detection of 10⁰ CFU/mL of the bacteria could be achieved through a dynamic monitoring method in under 12 h without sample pretreatment or enrichment. Additionally, combining GQDs-AuNPs/GCE with the Sal-CAF platform achieved excellent selectivity, serotypes of pathogenic bacteria, detection of dry-emphasized Salmonella without carrying out a pre-enrichment process, the ability to distinguish live from dead cells, and the ability to work in turbid whole blood media. The present approach constitutes a new achievement for the concept of “zero-tolerance,” as it can be used to detect bacterial pathogens ahead of infection control.