Silver nanocubes-based bimetallic core-shell surface-enhanced Raman scattering nanoprobes for cell imaging

Silver (Ag) plays an important role in the field of surface-enhanced Raman scattering (SERS) due to its excellent plasmonic enhancement. In particular, Ag nanocubes (Ag NCs) have garnered extensive attention due to their sharp corners that are beneficial for SERS applications. However, their easy oxidation and cytotoxicity hinder their biomedical application, particularly in vivo. Comparing with Ag, gold (Au) is more stable and has good biocompatibility. Therefore, the synthesis of a bimetallic substrate with Ag as the core can effectively combine both advantages. In this work, we reported a method of introducing sodium sulfite ligand to alleviate the galvanic replacement reaction and synthesized the Ag core-Ag/Au alloy shell bimetallic nanoprobes embedded with Raman reporter molecules 1,4-benzenedithiol (BDT), named as Ag@BDT@Ag-Au NCs. These nanoprobes have a high SERS enhancement with Ag nanostructure inside and their SERS performance reach the best when the alloy shell thickness is 19 nm. Additionally, the nanoprobes exhibited improved SERS activity, higher chemical stability, and photostability than Ag@BDT. Thus, they can achieve cell SERS imaging with high signals and strong stability under 30-min long-term irradiation with a high laser power (10.36 mW). Therefore, Ag core-Raman reporter-Au/Ag alloy shell nanoprobes can combine the excellent plasmon properties of Ag and the good stability of Au, which are very suitable for SERS bioimaging in biological environment.