Durable gold-coated coral-like Ag and AgO substrates for high-performance SERS sensors: experimental validation and electromagnetic modeling

We present a novel and versatile strategy for fabricating high-performance surface-enhanced Raman scattering (SERS) substrates by depositing thin gold films onto coral-like silver (Ag) or silver oxide (AgO) nanostructured templates. These porous architectures, produced via a cold plasma-assisted process, exhibit broad plasmonic responses and a large fractal surface area conducive to molecular adsorption. By varying the gold coating thickness between 2 and 55 nm, we identify an optimal enhancement factor (EF) of ∼ 5.7 × 107 at a thickness of ∼ 40 nm under 785 nm excitation. Finite element method simulations—parametrized by SEM and AFM-derived geometries—reveal that this enhancement originates from a synergistic combination of lightning rod effects and enhanced optical backscattering. The fabrication protocol enables both Ag- and Au-coated substrates within a unified process. Notably, gold coatings impart superior chemical stability and biocompatibility, with durability tested over more than two weeks of continuous exposure to air and immersion in water. These properties, along with structural robustness, make the proposed substrates ideally suited for integration into microfluidic platforms for real-time biosensing of proteins, DNA, and living cells. Furthermore, the proposed fabrication process is well-suited for sustainable, high-throughput, and cost-effective industrial-scale production.