SERS Activity in Gold Particles Obtained via a Modified Seeded-Growth Method

Precise control over nanoparticle morphology and spatial arrangement is fundamental for optimizing plasmonic performance. This study investigates the role of the HAuCl₄/NaBH₄ molar ratio in governing the formation kinetics, structure and Surface-Enhanced Raman Scattering (SERS) response of gold nanoparticles (AuNPs) synthesized via seed-mediated approach in which triangular gold nanoparticles (T-AuNPs) account for an increased fraction. Real-time ultraviolet-visible (UV-Vis) spectroscopy reveals a direct correlation between absorbance evolution and precursor consumption, consistent with the Beer-Lambert law, and identifies distinct kinetic regimes controlled by reductant concentration. At low NaBH4 content (1:12), nucleation proceeds under diffusion-limited conditions, yielding small and relatively uniform nanoparticles. Intermediate ratios (1:6) promote chemically controlled growth, while equimolar (1:1) conditions induce delayed nucleation followed by rapid growth, resulting in larger triangular nanoplates with broader size distributions. Electron microscopy (scanning electron microscope (SEM) and HR-transmission electron microscopy (TEM)) confirms that these structures enhance plasmonic coupling at sharp edges and interparticle junctions, generating intense electromagnetic hot spots. Consequently, the equimolar (1:1) system exhibits up to a 9-fold increase in SERS intensity compared to more dispersed nanoparticle assemblies. These findings demonstrate that kinetic regulation provides an effective bottom-up strategy to direct anisotropic growth and tune plasmonic properties without postsynthetic modification, enabling the development of highly sensitive SERS substrates for molecular detection and plasmonic sensing.