Gold-Stabilized Gold–Silver Alloy Nanostructures as High-Performance SERS Substrate

Abstract

Surface-enhanced Raman scattering (SERS) is a molecule-specific ultra-sensitive spectroscopic technique. With the development of portable Raman equipment, it has become possible to apply the SERS technique for rapid on-site detection. Therefore, the search for materials with excellent surface plasmon resonance (SPR) activity and high stability has become an important research focus in recent years. In this study, we successfully prepared plasmonic nanostructures with a large number of SERS “hotspots” using alloy nanoparticles (NPs) with tunable gold–silver mole ratios. These structures were composed of numerous narrow gapped gold–silver alloy NPs with diameters ranging from 10 to 100 nm. SERS property evaluation showed that the prepared alloy SERS substrates had good uniformity, and the performance of the substrates rapidly improved as the Ag content increased. Gold-stabilized Au–Ag alloy SERS substrates combine the high performance of the Ag SERS substrate and the excellent stability of Au. In addition, the wavelength of the SPR can be tuned by adjusting the mole ratio of Au and Ag to satisfy different excitation wavelengths. Thus, the Au–Ag alloy SERS substrates we prepared show good comprehensive performance. The lowest concentration of rhodamine 6G that can be homogeneously detected by the prepared Au1Ag8 alloy substrate is 5 × 10−12 M, and the enhancement factor is 5.1 × 108. Finite-difference time-domain (FDTD) theoretical calculations further confirmed our experimental results and theoretically demonstrated the unique properties of the Au–Ag alloy SERS substrates.