Plasma-Tunable Metasurfaces for SERS Nanosensing of Hazardous Chemicals

The demand for rapid, field-deployable detection of hazardous substances has intensified the search for plasmonic sensors with both high sensitivity and fabrication simplicity. Conventional approaches to plasmonic substrates, however, often rely on lithographic precision or complex chemistries limiting scalability and reproducibility. Here, a facile, one-step synthesis of vertically aligned 2D nanosheets composed of intergrown Cu₂O/CuO crystallites is presented, fabricated via oxygen plasma discharge on copper substrates. Decorated with a discontinuous Ag nanoparticle layer, the substrates serve as high-performance plasmonic metasurface exhibiting nanomolar sensitivity of explosive molecules, with detection limits as low as 4-5 nm for tetryl and 2-3 nm for HMX under 488 nm excitation. Importantly, the SERS (Surface enhanced Raman scattering) activity expands into a broad spectral range (488, 535, 633 nm), enabled by the formation of plasmonic "hotspots" network within nanoparticle gaps, crevices, that cumulatively boost SERS  signal. A pronounced red-shift in the symmetric NO₂ stretching mode of tetryl is further demonstrated, attributed to LUMO-mediated charge transfer from the Ag Fermi level-highlighting the need for laser- and substrate-sensitive interpretation of vibrational data. Together, these findings advance the rational design of low-cost, reproducible SERS substrates for trace chemical detection, with potential for integration into autonomous sensing platforms.