Harnessing the collective properties of nanoparticle ensembles for cancer theranostics

Individual inorganic nanoparticles （NPs） have been widely used in the fields of drug delivery, cancer imaging and therapy. There are still many hurdles that limit the performance of individual NPs for these applications. The utilization of highly ordered NP ensembles opens a door to resolve these problems, as a result of their new or advanced collective properties. The assembled NPs show several advantages over individual NP-based systems, such as improved cell internalization and tumor targeting, enhanced multimodality imaging capability, superior combination therapy arising from synergistic effects, possible complete clearance from the whole body by degradation of assemblies into original small NP building blocks, and so on. In this review, we discuss the potential of utilizing assembled NP ensembles for cancer imaging and treatment by taking plasmonic vesicular assemblies of Au NPs as an example. We first summarize the recent developments in the self-assembly of plasmonic vesicular structures of NPs from amphiphilic polymer-tethered NP building blocks. We further review the utilization of plasmonic vesicles of NPs for cancer imaging （e.g. multi-photon induced luminescence, photothermal, and photoacoustic imaging）, and cancer therapy （e.g., photothermal therapy, and chemotherapy）. Finally, we outline current challenges and our perspectives along this line.