An advanced plasmonic bimetallic nanostar composite for ultra-sensitive SERS detection of crystal violet

The controlled synthesis of Ag/Au nanocomposite particles has remained a significant challenge in nanomaterial research. This study presents the synthesis, characterization, and surface-enhanced Raman scattering (SERS) performance of silver (Ag) and gold (Au) nanostar composites. The structural and plasmonic properties of these nanocomposites were optimized by varying the molar ratios of silver nanostars (AgNSs) and gold nanostars (AuNSs). By synthesizing composite nanostars with differing AgNS/AuNS ratios, we systematically compared their optical and spectroscopic behaviors. The results demonstrated that Ag/Au nanostar composites function as highly effective SERS substrates for the detection of rhodamine 6G (R6G), with solutions tested at concentrations from 10⁻¹⁵ to 10⁻⁶ M. Compared to individual AgNS or AuNS substrates, the Ag/Au nanocomposites exhibited significantly enhanced SERS signals, with superior consistency and sensitivity. Notably, the nanostar composite with a 75 : 25 Ag/Au ratio showed the highest SERS performance, achieving an enhancement factor of 8.9 × 10⁶ and a detection limit of 10⁻¹⁵ M for R6G. Additionally, this composite demonstrated excellent long-term stability, maintaining performance until ten weeks of storage. To our knowledge, this represents the highest sensitivity reported for R6G detection using label-free SERS. The study further provides a detailed analysis of the composition-dependent SERS activity, underscoring the potential of Ag/Au nanocomposites as advanced SERS substrates for applications in chemical and biological sensing, as well as environmental monitoring.