Seed-Mediated Growth of Anisotropic Au Nanostructures: Mechanistic Insights and Application Possibilities

Abstract

Anisotropic gold nanocrystals (Au NCs) have attracted a great deal of attention from the scientific community in recent years. One of the main reasons behind this intense interest stems from the shape dependent surface plasmon resonance (SPR) property, apart from the fact that the composition, size, and shape of nanocrystals not only define their overall physicochemical properties but also determine their effectiveness in practical applications. In this regard, seed-mediated growth has been acknowledged as a powerful and versatile method for the synthesis of colloidal metal nanocrystals.

First, the general strategies for synthetic control of anisotropic Au NCs are discussed, emphasizing key factors that result in the generation of high-index facet (HIF) Au concave cuboid (CCB) NCs. The role of the cationic and anionic counterpart of a quaternaryammonium halide surfactant which constitutes as key chemical parameters in the above-stated synthesis. Furthermore, the role of another key chemical parameter, silver nitrate (AgNO3), has been investigated in the same synthesis from the perspective of time, to generate Au CCB NCs with tunable aspect ratios (AR). Next, the unusual behaviour of AgNO3 is discussed in dictating the Pt deposition on Au CCB NCs. The generality of which is extended to another HIF Au NC, elongated tetrahexahedra (ETHH). Finally, by manipulating a quaternaryammonium chloride-based binary surfactant mixture and modulating the AgNO3 amount, we were able to introduce a new morphology to the existing library of anisotropic 1D Au nanostructures, Au nano-earbud (NEB). Au NEBs exhibit three plasmonic peaks, analysed theoretically, with the longitudinal SPR tuned beyond 1200 nm, while maintaining the dimension well below 100 nm, a challenging accomplishment in the realm of one-dimensional (1D) Au nanostructures.

In summary, some key chemical parameters have been extensively studied to expand their understanding in the seed-mediated synthesis, offering new mechanistic insights into the growth of anisotropic Au NCs, which were additionally explored for various applications.