Green and Controllable Synthesis of Au-Ag Bimetal Nanoparticles by Xylan for Surface-Enhanced Raman Scattering

In surface-enhanced Raman scattering, Ag nanoparticles are broadly employed. However, their lack of oxidation resistance means that their performance diminishes and is difficult to repeat. In this study, with addition of xylan, Au-Ag core-shell and alloy nanoparticles were prepared. Besides functioning as a reducing and stabilizing agent for Au-Ag bimetal nanoparticles, xylan protected them from oxidation and aggregation and created hot spots between interconnected nanoparticles. By seed-mediated methods, Au-Ag hollow alloy and Au@Ag core-shell nanoparticles with different shell thicknesses were prepared. More spherical and larger core-shell nanoparticles were prepared by an optimized dosage of xylan without the generation of excess Ag nanoparticles. Furthermore, the Au@Ag nanoparticles showed enhanced stability against oxidation and corrosion by H2O2 with the packing of xylan. The Raman enhancement performance of xylan-capped Au@Ag nanoparticles with optimized shell thickness to 4-mercaptobenzoic acid was better than that of Au-Ag alloy, neat Au and Ag nanoparticles. The Au@Ag nanoparticles could detect 4-mercaptobenzoic acid with a greater sensitivity and its limit of detection was 1 nM. Moreover, xylan-capped Au@Ag nanoparticles could detect food contaminant like Sudan I with a limit of detection as low as 0.126 ppm. Therefore, this work not only offers a new method for high-value utilization of xylan but also presents a simple, green, and ultrasensitive surface detection technique for the assessment of food/environmental safety.