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.