Dual-mode of magnetic assisted Au@Ag SERS tags and cationic conjugated UCNPs for qualitative and quantitative analysis of multiple foodborne pathogens

A new dual-mode optical-nano-sensor was designed to effectively isolate, discriminate and inactivate multiple foodborne pathogens through the combined effort of magnetic SERS tags and functionalized upconversion nanoparticles. The positively charged quaternary ammonium salt (QAS) functionalized upconversion nanoparticles (UCNPs@QAS) were used as a fluorescent probe for the analysis of total bacteria count and inactivation of bacteria, and 4-mercaptophenylboronic acid (4-MPBA) modified magnetic Au@Ag NPs (MAu@Ag@MPBA) were applied as a SERS tag for isolation and classification of bacteria. Various types of bacteria can be captured by UCNPs@QAS through electrostatic interactions and by MAu@Ag@MPBA via the reversible recognition interaction of a boronic acid group of 4-MPBA and peptidoglycan from bacteria simultaneously. And then the formed complex structural assemblies were isolated rapidly from the sample matrix by employing the magnetic force for fast and simple dual-model optical detection. In addition, the novel biosensor was successfully applied to discriminate and detect Escherichia coli , Salmonella , Staphylococcus aureus, and their mixture in contaminated milk with the classification rate of 97.2–100 %. The proposed multi-functional nano-platform was able to sensitively capture, detect, and kill foodborne pathogens in a complex system, which could be deployed successfully towards the monitoring of food safety.