This study examined the interaction of mannose-functionalized, metal-doped magnetite@Au core@shell (MA-Mn:Fe3O4@Au) nanoparticles (NPs) with bacteria-prepared magnetically engineered multifunctional nanoplatforms for bacteria sensing and treatment. To date, there have been few reports on metal-doped magnetite@Au core@shell NPs conjugated with a bacteria-targeting moiety. Mn:Fe3O4 NPs as a core were synthesized using a thermal decomposition method. Mn:Fe3O4 NPs, 5.4 +/- 0.6 nm in mean diameter, were coated with gold in an organic solvent to produce core@shell (Mn:Fe3O4@Au) NPs, 9.5 +/- 1.5 nm in size. The estimated saturation magnetization values of the Mn:Fe3O4 and Mn:Fe3O4@Au NPs were similar to 36 and similar to 0.27 emu g(-1), respectively. Energy-dispersive X-ray spectroscopy mapping showed that the doped ions and Au ions were well distributed in the same NPs. The Mn:Fe3O4@Au NPs were transferred to water using amphiphilic polymers. The r (2) relaxivity of the aqueous Mn:Fe3O4@Au NPs was 609.6 mM(-1) s(-1) at 9.4 T. The interaction of the mannose-functionalized Mn:Fe3O4@Au NPs with bacteria was assessed by incubation with Escherichia coli to determine if the binding ability of mannose on the surface of the NPs remained. The resulting NPs may have potential applications in magnetic resonance imaging/optical imaging for the accurate detection of infectious diseases, bacteria sensing based on magnetic/optical signals, and hyper/photothermal therapy against antibiotic-resistant bacteria.