Self-Assembled Bimetallic Au-Ag Nanorod Vertical Array for Single-Molecule Plasmonic Sensing

Ordered plasmonic nanoparticle arrays are highly desirable for optical sensing as they provide uniformly distributed plasmonic hotspots due to their periodic order and near-field coupling. Anisotropic-shaped bimetallic nanoparticles are of particular interest, as their hybridized plasmonic modes enable precise tuning of plasmonic resonance and optical responses. However, the controlled assembly of large-scale arrays of bimetallic nanoparticles with uniformly distributed hotspots remains a challenge. In this study, we present a highly robust and reproducible method for creating large-area vertically aligned arrays of bimetallic Au-Ag nanorods by epitaxially growing Ag over preassembled Au nanorods. Structural characterization using electron microscopy and X-ray photoelectron spectroscopy confirms the formation of a uniform thin layer of Ag, creating a bimetallic Au-Ag nanorod array. We also demonstrate the efficacy of the designed nanoarrays for surface-enhanced Raman scattering (SERS) spectroscopy. Our experimental and computational studies show considerably enhanced optical responses of bimetallic Au-Ag nanorods compared to their monometallic counterparts. The scalability, cost-effectiveness, and reproducibility of this method make it a versatile platform for creating various structures by varying guest nanoparticles in suspensions with broad applications in biomedical research, food safety surveillance, and environmental monitoring.