Seedless synthesis and SERS characterization of multi-branched gold nanoflowers using water soluble polymers

We report for the first time, the aqueous-based synthesis of multibranched, monodispersed gold nanoflowers (AuNFs) using pyromellitic dianhydride-p-phenylene diamine - PPDDs at room temperature. AuNF synthesis was achieved using PPDDs that converts Au precursor (Au³⁺) into AuNFs while serving as both the reducing and directional agent. The resulting branched AuNFs exhibited different degrees of anisotropy and protuberance lengths obtained by modulating the ratio of PPDDs and HAuCl₄·3H₂O. The surface roughness obtained ranged from small bud-like protuberances to elongated spikes, which enabled the tuning of the optical properties of the nanoparticles from ∼450 to 1100 nm. Systematic analysis revealed that the generation of urchin-like particles as well as their size depended on the PPDDs/HAuCl₄·3H₂O ratio. At a medium concentration of the precursor, spherical nanoparticles were formed. Whereas at lower precursor concentrations, urchin-like nanoparticles were obtained with their size and protuberances length increasing at even lower HAuCl₄·3H₂O concentration. Increasing the temperature to 100 °C resulted in the enhancement of the anisotropy of the AuNFs. The resulting gold nanoflowers exhibited an enhanced performance in surface-enhanced Raman scattering (SERS). This work provides a unique approach for anisotropic particle synthesis using water soluble polymer and greener approaches. The fabricated AuNFs exhibited variable UV-vis absorption and SERS enhancement as a function of branch morphology, indicating their potential application in biolabeling, biosensing, imaging, and therapeutic applications.