Marigold flower like supra structure is fabricated by growth reaction of gold nanorod incubated with methionine with two binding site, which selectively interacts with intermediate Au⁺ and Au(111) facets during nucleation and growth stage and favors the assembly and merging of nanoparticles. This observation enlightens the role of biomolecules or small molecules behind growth of novel nano-architectures.

Abstract

During morphological evolution of gold nanoparticles, amino acids play a vital role in tuning shape, introducing chirality and inducing facet selective reactivity. Herein, we report the synthesis of unique marigold like structure (MGS) via growth reaction of methionine (Met) incubated positively charged anisotropic gold nanorod (GNR). Varying three important parameters such as growth time, concentration of Met and Au³⁺ reveals the combination of freshly generated small nucleated particles (fNPs) and GNR towards fabricating the unique MGS containing disk and ray floret parts. Strong interaction between Met and (111) plane of Au⁰ controls the orientation of (111) plane parallel to the direction of growth. This preferential interaction directs the assembly of gold nanostructures through Au (200) plane and results in merging of fNPs with concave GNR (cGNR) to fabricate the external arrangement of ray floret structure. The structural selectivity is attributed to the electron donating capacity of thioether functional group of Met(S) to Au⁺, generated prior to secondary nucleation. As confirmed by XPS and ζ-potential analysis, the above interaction controls the Met concentration dependent inhibition of further Au⁺→Au⁰ reduction. The growth strategy of GNR has been further validated with a Met enriched peptide to produce disk and ray florets.