Silica nanoparticles surface-decorated with Au-Ag alloy nanoparticles as highly sensitive, reproducible, and stable surface-enhanced Raman scattering (SERS) substrates

The optical properties of metal nanoparticles (NPs) are heavily influenced by their structure and composition, making them useful in surface-enhanced Raman scattering (SERS) applications. In addition, metal-embedded silica NPs have excellent plasmonic characteristics and high reproducibility that further enhance SERS measurements. Although silica NPs have been encapsulated in various metals and alloys, practical applications require strong, stable, and reproducible optical signals. Herein, we synthesized Silica nanoparticles surfacedecorated with Au-Ag alloy nanoparticles (SiO2@AuAg NPs) to perform as excellent SERS substrates. SiO2@AuAg NPs were synthesized by introducing seed Au NPs onto a spherical SiO2 NP core, followed by the addition of Au and Ag ions. From the NP characterization results, we also elucidate the growth mechanism for AuAg alloy NPs depending on the ratio of added Au to Ag ions. SiO2@AuAg NPs synthesized under optimized conditions exhibited a strong SERS signal with high stability, sensitivity, and reproducibility. Finally, SiO2@AuAg NPs successfully detected crystal violet (CV), thiram, and carbaryl at levels of 6.95 x10- 7 M, 5.56 x10- 7 M, and 7.14 x10- 6 M, respectively, which are lower than the pesticide residue limits set by the U.S. Environmental Protection Agency (EPA). The detection reproducibility was also high, with an approximate relative standard deviation (RSD) of only 8.4 % even after 3 days. The SERS substrate not only has high SERS activity and stability but can also be used to detect trace amounts of chemicals, enabling accurate SERS-based applications.