We introduce a facile and robust methodology for the aggregation-free aqueous-phase synthesis of hierarchically complex metal-semiconductor heterostructures. By encapsulating semiconductor nanostructures within a porous SiO(2) shell with a hollow interior, we can isolate each individual particle while allowing it access to metal precursors for subsequent metal growth. We illustrate this by Pt deposition on CdSe-seeded CdS tetrapods, which we found to be facilitated via the surprising formation of a thin interfacial layer of PtS coated onto the original CdS surface. We took advantage of this unique architecture to perform cation exchange reactions with Ag(+) and Pd(2+), thus demonstrating the feasibility of achieving such transformations in complex metal-semiconductor nanoparticle systems.