On-Demand Electromagnetic Hotspot Generation in Surface-Enhanced Raman Scattering Substrates via "Add-On" Plasmonic Patch.

Electromagnetic hotspots at the interstices of plasmonic assemblies are recognized to be the most potent sites for surface-enhanced Raman scattering (SERS). We demonstrate a novel "add-on" electromagnetic hotspot formation technique, which significantly improves the sensitivity of conventional SERS substrates composed of individual plasmonic nanostructures. The novel approach demonstrated here involves the transfer of "plasmonic patch", a transparent, flexible, and conformal elastomeric film adsorbed with plasmonic nanostructures, onto a conventional SERS substrate. The addition of the plasmonic patch onto a conventional SERS substrate following the analyte capture results in the formation of electromagnetic hotspots and hence a large SERS enhancement. The application of the plasmonic patch improves the sensitivity and limit of detection of conventional SERS substrates by up to ∼100-fold. The transfer of the plasmonic patch also effectively transforms the SERS-inactive gold mirror to a highly SERS-active "particle-on-mirror" system. Furthermore, we demonstrate that the "add-on" technique can be effectively utilized for the vapor-phase detection of explosives such as trinitrotoluene (TNT) using peptide recognition elements. We believe that the on-demand hotspot formation approach presented here represents a highly versatile and ubiquitously applicable technology readily expandable to any existing SERS substrate without employing complicated modification.