Fiber-Optic Sensing System Using Polyhedral Plasmonic Nanostructures as SERS-Active Substrates

The integration of plasmonic nanostructures in an optrode sensing system holds significant promise for online and remote detection via surface-enhanced Raman scattering (SERS) method. This study focuses on the impact of the shape and composition of plasmonic materials on their ability to enhance surface-enhanced Raman scattering (SERS) signals. We compared the SERS performance of optical fiber (OF)-based sensors (OFSs) with flattened end faces, which were decorated with six mono- and bimetallic nanomaterials: Au nanoparticles (NPs), Ag NPs, Ag-coated Au NPs (Au@Ag CSNPs), Au nanostars (NSs), Ag NSs, and Ag-coated Au NSs (Au@Ag CSNSs). Among these nanomaterials, polyhedral Au@Ag CSNSs demonstrated superior SERS enhancement, mainly attributed to multifaceted hotspots on their surface and the plasmonic coupling between the Au core and Ag shell. This allowed for precise customization of the surface plasmon resonance (SPR) and distinct enhancement of the SERS efficiency by modulating the thickness of Ag shell. Our sensing system exhibited great potential, achieving the lowest detection limit of ∼5 × 10–8 M for crystal violet, which surpasses the performance of previous OF-based sensors with the same type of flattened facets.