Nanoparticle labels were used to detect the pathogenic bacteria Staphylococcus aureus. Two different labels were employed. These consisted of nanoparticles based on iron-oxide for magnetic trapping and isolation of the bacteria and surface enhanced Raman spectroscopy (SERS) active gold nanoparticles (AuNPs) coated with 4-mercaptobenzoic acid for the detection and quantification of the bacteria. Both types of nanoparticles were conjugated with single domain antibodies that selectively bind to protein A on the surface of S. aureus. Transmission electron microscopy (TEM) image analysis showed the iron-oxide nanoparticles to have magnetic core diameters of 20 nm +/- 3 nm and the gold nanoparticles to be 51 nm +/- 2 nm in diameter. A response curve was obtained displaying a logarithmic dependency between the 1073 cm(-1) peak intensity in the SERS spectra of the AuNPs and the concentration of S. aureus cells in the initial sample. The overall detection limit was estimated to be 1 S. aureus cell mL(-1) in less than 10 min without culturing.
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