We report a new approach to cisplatin storage and release using porous hollow nanoparticles (PHNPs) of Fe3O4. We prepared the PHNPs by controlled oxidation of Fe NPs at 250 degrees C followed by acid etching. The opening pores (similar to 2-4 nm) facilitated the cisplatin diffusion into the cavity of the hollow structure. The porous shell was stable in neutral or basic physiological conditions, and cisplatin escape from the cavity through the same pores was a diffusion-controlled slow process with t(1/2) = 16 h. However, in low pH (< 6) conditions, the pores were subject to acidic etching, resulting in wider pore gaps and faster release of cisplatin with t(1/2) < 4 h. Once coupled with Herceptin to the surface, the cisplatin-loaded hollow NPs could target to breast cancer SK-BR-3 cells with IC50 reaching 2.9 mu M, much lower than 6.8 mu M needed for free cisplatin. Our model experiments indicate that the low pH-responsive PHNPs of Fe3O4 can be exploited as a cisplatin delivery vehicle for target-specific therapeutic applications.