Nanofabrication of surface-enhanced Raman scattering substrates for optical fiber sensors

Surface-enhanced Raman scattering (SERS) allows the detection of sub-monolayer adsorbates on nanostructured metal surfaces (typically gold or silver). The technique has generated interest for applications in biosensing, high-resolution chemical mapping and surface science. SERS is generated by the localized surface plasmon resonance that occurs when the nano-metal is exposed to laser light. These plasmonic effects rely on features as small as ∼1 nm, which poses a challenge for the fabrication of sensitive and reproducible substrates. Consequently a wide range of nanofabrication techniques have been used to make SERS substrates. Further challenges are encountered when transferring wafer-scale techniques to the tips of optical fibers in order to produce devices for in vivo SERS sensing. Here we describe fiber tip substrates based on miniaturization by fiber drawing, physical vapor deposition and nanoimprint lithography. Despite recent progress, the fabrication of sensitive, reproducible and affordable SERS fiber sensors remains an unresolved problem.