Synthesis and Optimization of Highly Bright Silver-Coated Au Nanostars with Tunable Plasmonic Properties

Silver-coated gold nanostars (AuNSt@Ag) offer a powerful platform for plasmon-enhanced sensing, yet their fabrication often compromises structural sharpness and spectral tunability. Here, we report a robust and flexible method for synthesizing AuNSt@Ag with precisely controlled localized surface plasmon resonance (LSPR) across a broad spectral range, achieved by systematically optimizing multiple synthetic parameters. Strikingly, surface-enhanced Raman scattering (SERS) performance reached a maximum for bimetallic nanostars with LSPR maxima near 605-615 nm, regardless of excitation wavelength (633 or 785 nm). This reveals that local near-field enhancement at Ag-coated tips, rather than spectral overlap, governs SERS efficiency in these AuNSt@Ag systems. The optimized AuNSt@Ag structures outperform previously reported analogues, exhibiting significantly enhanced SERS capabilities, including an 80-fold increase in signal compared to optimized monometallic AuNSt resonant with the 785 nm laser line. These findings establish a new design paradigm for highly tunable and high-performance plasmonic substrates for analytical sensing applications.