Raman based detection of Staphylococcus aureus utilizing single domain antibody coated nanoparticle labels and magnetic trapping

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.