For drug delivery applications, drug carrying polymeric nanoparticles formed by the self-assembly of polymeric blocks have been studied by different groups. Such systems facilitate the delivery of hydrophobic drugs to the target cells by encapsulation of the drug in a hydrophobic core surrounded by a hydrophilic shell. In a similar way, nanoparticle assemblies can also encapsulate drug molecules to be delivered and released in the target cells. As shown by Wang et al., ligand-capped 4 nm Au nanoparticles can efficiently encapsulate poorly water soluble molecules from the dispersing solvent with high uptake. Considerable uptake of different molecules such as bisphenol A (BPA), azulene, para-dichlorobenzene (p-DCB), Alachlor, etc. is demonstrated in this procedure. The molecules could also be released easily by the dissolution of the nanoparticle clusters in CD2Cl2 environment, Figure . The release of the drug can similarly be triggered by for instance changing the pH of the solvent. Song et al. showed that Au nanoparticle assemblies forming vesicles can be used as drug carriers for controlled drug release inside cells by changing the pH from 7.4 to 5.0, Figure ). Nanoparticle clusters can further facilitate the incorporation of multiple functionalities. For example, the encapsulation of photosensitizer Ce6 in Au nanoparticle clusters enables three functionalities: strong fluorescence, photoacoustic signal and photothermal effect, for imaging-guided synergistic photothermal/photodynamic therapy (PTT/PDT).