Dumbbeil-like Au-Fe3O4 nanoparticles (NPs) were made and coupled with Herceptin and a platin complex. The ptatin-Au-Fe3O4-Herceptin NPs act as a target-specific nanocarriers for delivery of platin into Her2-positive breast cancer cells (Sk-Br3) with strong therapeutic effects. The conjugate has a half-maximal inhibitory concentration (IC50) toward Sk-Br3 cells of 1.76 mu g of Pt/mL, which is lower than that needed for cisplatin (3.5 mu g/mL). The work demonstrates that the dumbbell-like Au-Fe3O4 NPs are promising nanocarriers for highly sensitive diagnostic and therapeutic applications.