Two-Step Synthesis of Narrow Size Distribution Nanoflowers Using a Tree-Type Multi-Amine-Head Surfactant as a Template

Unique, narrow polydispersity, hierarchical gold nanoflowers were synthesized by a two-step method using a tree-type multi-amine surfactant (C18N3) as the template and ascorbic acid (AA) as the reductant. Upon the addition of a stronger reductant AA, the C18N3–HAuCl₄ composite changed to a black color, due to the gold nanoflower formation. Under a specific concentration ratio of C18N3, HAuCl₄, and AA, narrow polydispersity flower-like gold structures were obtained. These nanoflowers were stable as an aqueous solution for months, with no deformation to particle size and no obvious change in the surface morphology. The experimental results demonstrated that the complexation between C18N3 and HAuCl₄ is essential for the formation of gold nanoflowers with a narrow size distribution. The morphology and size of the composites can be easily adjusted by changing the concentration of C18N3, HAuCl₄, and AA. The growth of nanoflowers is discussed in terms of two steps: the formation of complexes between C18N3 and HAuCl₄, which determines the core size of the nanoflowers, and the surface nanocrystal growth, due to the reduction of HAuCl₄ by AA, which determines the thickness and morphology of nanoflower surface layers. In the measurement of surface-enhanced Raman scattering (SERS) using rhodamine 6G, the gold nanoflowers exhibited a significant enhancement factor, indicating their potential in biosensing and nanodevice applications.