Asymmetric nanoparticle assembly via simple mechanical pressing using relative hardness of materials

We report a new strategy to achieve asymmetric assembly of nanoparticles on spherical support using the relative hardness of silica particles and aluminum plate. The mechanical pressing of a two-dimensional monolayer of amine-modified silica spheres resulted in partial embedding of silica spheres in the aluminum plate as silica has higher hardness than aluminum plate. The resulting partial embedding of silica spheres provided a template for asymmetric surface decoration with gold nanoparticles. The attachment of gold nanoparticles on the exposed amine modified silica spheres and the subsequent retrieval of silica spheres resulted in asymmetric silica spheres partially decorated with gold nanoparticles. This simple approach provides a potential tool to prepare asymmetric modification of various colloidal particles with various functional nanoparticles.