Pathogenic bacterial infection has become a growing threat to public health; therefore, exploration of a sensitive and specific method for the identification of bacteria is very important. In this report, we fabricated a new magnetic core-shell nanocomposite with a homogenous morphology. The Fe3O4 nanoparticle core with a diameter of 15 nm was coated with a thin silica layer, and the thickness of the layer was finely adjusted to about 10 nm. Pt nanoclusters with a diameter of 2-3 nm were anchored uniformly on the surface to form Fe3O4@SiO2-Pt nanocomposites. These nanocomposites exhibited excellent peroxide enzyme activity and acted as a signal-output probe for the identification of pathogenic bacteria. This strategy was also based on using vancomycin (Van) as the capture agent in an ELISA procedure. The detection limit for S. aureus was around 1 × 101 cfu mL-1. Furthermore, Fe3O4@Si-Pt nanocomposites also show ideal bacteria separation and inhibition effects, and can act as a multifunctional platform for bacterial detection and antibacterial applications.