Reversible and Precise Self-Assembly of Janus Metal-Organosilica Nanoparticles through a Linker-Free Approach.

Reversible self-assembly of nanoparticles into ordered structures is essential for both fundamental study and practical applications. Although extensive work has been conducted, the demand for simple, cheap, reversible, and versatile ordering methods is still a central issue in current nanoscience and nanotechnology. Here we report a reversible and precise self-assembly of nanoparticles through a linker-free and fast approach by manipulating the interparticle forces, e.g., van der Waals (VDW) force and electrostatic force. Because VDW force is nondirectional, an oriented interaction is achieved to induce the directional binding of nanoparticles utilizing the Janus nanostructure. An effective sol-gel approach has been developed to synthesize metal-organosilica Janus nanoparticles. Dimers and trimers can be obtained by tuning the steric hindrance. After assembly, "hot-spots" can be generated between adjacent nanoparticles, and dramatic enhancement has been observed in surface-enhanced Raman scattering. The present strategy overcomes several limitations of existing approaches and allows the controlled assembly of small particles into various structures.