Au@AuAg yolk-shell triangular nanoplates with controlled interior gap for the improved surface-enhanced Raman scattering of rhodamine 6G

In this work, a combined seed mediated and galvanic replacement strategy has been proposed to design and fabricate two unique nanostructures, including Au@AuAg yolk-shell nanostructures with tunable interior gap and Au multi-spiky nanostructures with tunable spike length. The interior gap of the Au@AuAg yolk-shell nanostructures can be controlled by varying either the amount of AgNO₃ in the first step or the amount of HAuCl₄ in the second step. The SERS activity of Au@AuAg yolk-shell nanostructures was found to increase with increase in the interior gap. Owing to the build-in electromagnetic hot spots induced by plasmonic coupling effect of the Au triangular nanoplate core and AuAg shell especially the intensive coupling between the three sharp tips of the core and the concave of the inner wall of the shell, Au@AuAg yolk-shell nanostructures exhibit significantly higher SERS enhancement compared to their original Au triangular nanoplates. The best enhancement has been achieved when the interior gap of Au@AuAg yolk-shell nanostructures is 10 nm with the enhancement factor of 3.2 × 10⁶ for rhodamine 6G, making them promising candidates for SERS-based detection.