Junhao Chen ¹ Zhengjia Chen ² Tong Liang ¹ Zhennan Zhang ¹ Dahang Cheng ¹ Shurui Liu ¹ Haiyang Liu ¹ Cuicui Liu ³ Xiaohui Song ^1*

• ¹ Hefei University of Technology, Hefei, China
• ² Chongqing Polytechnic University of Electronic Technology, chongqing, China
• ³ Nanyang Technological University, Singapore, Singapore

Surface-enhanced Raman scattering (SERS) detection holds significant promise for applications in environmental monitoring, healthcare, and the biopharmaceutical industry. Advances in technology have led to robust detection methods for certain molecules, such as 4-mercaptobenzoic acid and other thiol-and amine-containing compounds, which readily adsorb onto metal surfaces like gold and silver due to strong chemical interactions. However, there remains a paucity of research on the SERS detection of other molecular types, particularly those rich in carboxyl groups, carbon-carbon double bonds, or triple bonds, such as citric acid. In this study, we first observed distinct differences in Raman peak enhancement of Au@Ag core-shell nanoparticles in freshly prepared versus aged sodium citrate solutions. Building on this finding, we conducted a series of experiments to evaluate the SERS response of Au@Ag core-shell nanoparticles to citric acid and other carboxyl-and unsaturated bond-rich compounds in colloids. Our results demonstrate that these nanoparticles also exhibit significant SERS enhancement for this class of molecules. This research paves the way for enhanced applications in biological monitoring and the environmental and food and pharmaceutical sectors, expanding the utility of SERS technology beyond conventional analytes.