Asymmetric Silica–Gold Nano/Microparticles: Eccentric, Janus, Tadpole Structures, and Their Applications

Asymmetric particles, characterized by asymmetries in composition, topology, or surface properties, have attracted increased attention due to their unique advantages, enabling versatile applications across a broad range of fields. Herein, we employ gold nanoparticles as cores and deposit silica to form a series of asymmetric structures, including eccentric, Janus, and tadpole morphologies. Polyacrylic acid (Mw: 1800 Da) and 4-mercaptophenylacetic acid are used for functionalizing the surface of gold nanoparticles prior to silica coating. We systematically investigate the role of ligands in directing silica shell formation and demonstrate that the position of the gold core within the silica shell can be precisely controlled by tuning the total ligand amount while maintaining a fixed ligand ratio. In addition, by adjusting the ligand ratio, a Janus structure can be obtained, which is then used as seeds for site-selective nucleation and growth of a second metal on the exposed Au surface, further breaking the structural symmetry. Through lowering the reaction pH from 10 to 8 and extending the aging time, tadpole structures with tails ranging from tens of nanometers to over one micrometer are fabricated. Finally, we briefly demonstrate potential applications of the asymmetric Janus and tadpole structures in a catalysis and liquid crystal system study.