Fabrication of Ag−Au Hollow Nanoplates as SERS-Active Substrates for Ultrasensitive Detection of Hazardous Cationic Dyes

Abstract

This study reports the development of surface-enhanced Raman scattering (SERS)-active substrates based on bimetallic Ag−Au nanostructures for the ultrasensitive detection of organic dyes. Ag nanoparticles (NPs) were first synthesized using NaBH4 as a reducing agent, followed by polyvinylpyrrolidone (PVP) capping to obtain triangular plate-shaped structures termed Ag TNPs. Subsequently, Ag−Au hollow nanoplates (HNPs) were fabricated via galvanic replacement of Ag TNPs with Au precursors, combining the high Raman activity of Ag with the chemical stability of Au. The Ag−Au HNPs exhibited enhanced Raman signals attributed to plasmonic coupling within the hollow structures and the uniform distribution of Ag−Au clusters that amplify SERS responses. Solid-state SERS sensors were then fabricated by immobilizing the plasmonic Ag−Au HNPs on polydopamine/polyethyleneimine-coated glass substrates. The resultant SERS-active substrate was further optimized through electroless deposition, with reduced nanogaps between the immobilized NPs, generating uniform and abundant hotspots. The optimized SERS sensor demonstrated ultrasensitive detection of cationic organic dyes, including crystal violet, methylene blue, and rhodamine B, at ultra-trace concentrations ranging from picomolar (10−12 M) to sub-femtomolar (10−16 M) levels. The Ag−Au HNP-based substrate exhibited strong potential for stable and reliable ultra-trace detection of organic dyes, with broad applicability in environmental, medical, and biological fields.