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This paper describes a near-infrared quantum dot (CuInS2QD)/antibiotic (vancomycin) nanoparticle-based assay for the Staphylococcus aureusand iron(iii) detection. CuInS2QDs with good biological tissue permeability and biocompatibility are combined with vancomycin through covalent interaction to form a detection system for two harmful factors. The detection principle of Staphylococcus aureusis mainly the fluorescence quenching caused by the accumulation of CuInS2@Van QDs on the surface of Staphylococcus aureus. The detection principles of the iron(iii) ion are mainly ascribed to the aggregation of quantum dots and the transfer of charges, which cause the fluorescence signal to change. The linear range of S. aureusand the Fe3+ion is 103to 108CFU mL−1and 10–90 μM, respectively. Their detection limits are 665 CFU mL−1and 3.5 μM, respectively. The procedure was validated by the quantitation of Staphylococcus aureusand iron(iii) in spiked samples, and was found to demonstrate the feasibility of this method.

The highly efficient detection of Salmonella typhimurium(S. typhimurium), a common foodborne bacterial, is important for the safety assurance of leafy vegetables. In this study, a fluorescent sensor (FMNCs-Apt), based on Fe3O4magnetic nanoparticles and aptamer-modified carbon quantum dots, was developed for the rapid and highly sensitive detection of S. typhimuriumin lettuce. First, carbon quantum dots were covalently bonded to the surface of prepared Fe3O4@chitosan to form magnetic fluorescence composite nanoparticles (FMNCs). Then, the aptamers of S. typhimuriumwere covalently linked to the surface (and named FMNCs-Apt). Fluorescence intensity of the FMNCs-Apt probes decreased as they aggregated on the surface of the bacteria, and the aggregation was separated using a magnet. Under the optimal conditions, the fluorescence change values of the solution showed a good linear relationship with the concentration of Salmonella(103–106CFU mL−1). The detection limit of the method is 100 CFU mL−1and 138 CFU mL−1in fresh-cut vegetable washing solution and lettuce sample, respectively. Accordingly, this developed fluorescent probe became a highly sensitive and efficient sensor for the rapid detection of S. typhimuriumin lettuce.