Au–Ag bimetallic nanoparticles decorated silicon nanowires with fixed and dynamic hot spots for ultrasensitive 3D SERS sensing

Three-dimensional (3D) SERS substrates have being intensively investigated since they can afford substantial hot spots and trap targets exponentially, silicon nanowires (SiNWs) array is a promising candidate due to its facile preparation. Most often, the SiNWs based substrates were decorated with pure Ag or Au nanoparticles (NPs), Au–Ag bimetallic NPs (BMNPs) with superior plasmonic properties and stabilities are rarely studied for the fabrication of SiNWs based SERS substrates. In this work, we reported a facile method to fabricate Au-Ag BMNPs decorated SiNWs as 3D SERS substrates, the effects of Au-Ag BMNPs scale and composition ratios on SERS performance were well investigated through experiments and theoretical simulations. The vertically aligned SiNWs coated with dense Au-Ag BMNPs further improved the sensitivity by forming fixed and dynamic hot spots, and the detection limit of R6G on SiNWs-AuAg can be as low as 10-12 M by using a portable Raman spectroscopy. Meanwhile, the prepared 3D SERS substrate showed a higher SERS enhancement factor (EF) and oxidation resistance ability due to the synergistic effect of Au and Ag atoms in Au–Ag BMNPs. Considering the facile fabrication process and excellent performances, the prepared 3D SERS substrate can be potentially applied for ultrasensitive detection of trace analytes.