Direct assembly of hydrophobic nanoparticles to multifunctional structures

We present a general process that allows convenient production of multifunctional composite particles by direct self-assembly of hydrophobic nanoparticles on host nanostructures containing high-density surface thiol groups. Hydrophobic nanoparticles of various compositions and combinations can be directly assembled onto the host surface through the strong coordination interactions between metal cations and thiol groups. The resulting structures can be further conveniently overcoated with a layer of normal silica to stabilize the assemblies and render them highly dispersible in water for biomedical applications. As the entire fabrication process does not involve complicated surface modification procedures, the hydrophobic ligands on the nanoparticles are not disturbed significantly so that they retain their original properties such as highly efficient luminescence. Many complex composite nanostructures with tailored functions can be efficiently produced by using this versatile approach. For example, multifunctional nonspherical nanostructures can be efficiently produced by using mercapto-silica coated nano-objects of arbitrary shapes as hosts for immobilizing functional nanoparticles. Multilayer structures can also be achieved by repeating the mercapto-silica coating and nanoparticle immobilization processes. Such assembly approach will provide the research community a highly versatile, configurable, scalable, and reproducible process for the preparation of various multifunctional structures.