Fabrication of Entangled Nanowire-Based Surface-Enhanced Raman Spectroscopy Substrates

Surface-enhanced Raman spectroscopy (SERS) substrates require both strong electromagnetic enhancement and efficient access of analyte molecules to field-active hotspots. This study reports a protocol for fabricating entangled plasmonic nanowire substrates that address these requirements through an open network of wire-wire junctions. Vertically aligned carbon nanotube (VACNT) canopies and carbon nanotube buckypaper (CNTBP) provide two scaffold geometries in which numerous crossings are formed before metallization. Au deposition converts the CNT scaffolds into junction-rich plasmonic networks, while an optional alumina interlayer separates Au from the conductive CNT scaffold. Successful fabrication requires continuous metal coverage along individual fibers while preserving repeated crossings and open voids. Representative wire diameters were approximately 60 nm for the Au-coated VACNT-canopy network and approximately 25 nm for the CNTBP-based networks. Both architectures produced picomolar-level SERS responses. In the CNTBP comparison, Au/Al2O3/CNTBP showed an operational detection threshold of 50 pM, one decade lower than the 500 pM threshold of Au/CNTBP under identical acquisition conditions. At 5 pM acetaminophen, 83.1% of the responses in a 33 × 33 map of the Au-coated VACNT-canopy network remained within ±30% of the median, with most of the remaining variation arising from sparse high-response positions. The protocol provides two entangled nanowire scaffold routes for constructing open, junction-rich SERS substrates while preserving molecular access to the plasmonic surface.