Plasmonic Gold\nPrism Array for Digital Surface-Enhanced\nRaman Spectroscopy Sensing

While surface-enhanced Raman spectroscopy (SERS) has\nproved itself\nas a powerful tool in the analytical domain, its capability hinges\non and therefore is governed by the interaction between molecules\nand plasmonic hotspots on nanostructured metallic substrates. Yet,\nthe highly dynamic and complex molecule–metal interactions\ngive rise to pronounced SERS signal fluctuations, compromising quantitative\nanalysis at ultralow molecular concentrations. Rather than overcoming\nSERS signal fluctuations, the recently introduced digital SERS approach\ntakes full advantage of their stochastic nature and allows the digital\nvisualization of SERS events at the single pixel level based on a\npredefined signal threshold, significantly pushing down the lowest\ndetectable molecular concentration. Nevertheless, extending digital\nSERS for routine molecular analysis requires superior two-dimensional\nplasmonic substrates. Herein, we introduce a plasmonic gold prism\narray for digital SERS sensing. As opposed to nanostructured metallic\narrays with similar geometry where the vertex and edge modes dominate,\nthe gold prism array displays strong scattering as well as pronounced\nsurface roughness and nanoparticle-like surface features, thus supporting\nadditional plasmonic enhancements beyond the vertex and edge modes.\nUsing 4-aminothiophenol as a model molecule, we first verify the counterintuitive\ndistribution of SERS hotspots at the center of a gold prism instead\nof its vertices and further demonstrate digital SERS sensing at the\nfemtomolar level. We envision that the gold prism array could serve\nas a superior plasmonic platform for a wide range of digital SERS\napplications in diagnostics, environmental monitoring, and food safety.