Self-Assembly Mechanism of Spiky Magnetoplasmonic Supraparticles

Concave nanoparticles (NPs) with complex angled and non‐Platonic geometries have unique optical, magnetic, catalytic, and biological properties originating from the singularities of the electrical field in apexes and craters. Preparation of such particles with a uniform size/shape and core–shell morphology represents a significant challenge, largely because of the poor knowledge of their formation mechanism. Here, this challenge is addressed and a study of the mechanism of their formation is presented for a case of complex spiky morphologies that led us to the conclusion that NPs with concave geometries can be, in fact, supraparticles (SPs) produced via the self‐assembly of smaller convex integrants. This mechanism is exemplified by the vivid case of spiky SPs formed via the attachment of small and faceted Au NPs on smooth Au‐coated iron oxide (Fe3O4@Au) seeds. The theoretical calculations of energies of primary interactions—electrostatic repulsion and van‐der Waals repulsion, elaborated for this complex case—confirm experimental observation and the self‐limiting mechanism of SP formation. Besides demonstrating the mechanistic aspects of synthesis of NPs with complex geometries, this work also uncovers a facile approach for preparation of concave magnetoplasmonic particles. When combined with a spiky geometry, such bi‐functional magnetoplasmonic SPs can serve as a unique platform for optoelectronic devices and biomedical applications. Synthesis of nanoparticles with uncommon non‐Platonic shapes is only vaguely understood, however, such particles with concave shapes demonstrate a variety of unique chemical, optical, and biological properties. In this work, the spiky colloidal particles can be successfully made by self‐assembly. This makes it possible to combine different materials and results in the first example of spiky magnetoplasmonic supraparticles.