Nano-engineered surface-enhanced Raman scattering (SERS) substrates with patterned structures on the distal end of optical fibers
This paper describes the development of fiber optic sensor probes and planar substrates containing patterned nanostructures such as nanoholes in gold films, as well as gold nanoparticles, nano-pillars, nanorods, and nano-islands. Several methods of producing gold nanofeatures on fiber tips and planar substrates were investigated such as annealing of thin gold films and focused ion beam (FIB) milling. A Hitachi FB-2100 FIB milling machine with a gallium ion source was employed to form the nanoparticles from 20-100 nm gold films deposited on the fiber tip. Nano-engineered gold features were also formed by coating planar substrates and fiber tips with thin gold films (4-10 nm) and annealing these thin films. Excitation of surface plasmons in gold nanostructures leads to substantial enhancement in the Raman scattering signal obtained from molecules attached to the nanostructure surface. In this work, a comparison was made between the SERS signals obtained from the gold substrates developed by employing the different procedures mentioned above. Fiber samples and planar substrates with these nanostructures were coated with SERS active dyes such as p-mercaptobenzoic acid (pMBA) and cresyl fast violet (CFV). It was observed that the SERS signal obtained from these gold nanofeatures was much higher than that obtained from a continuous gold film and that the SERS enhancement was shape and size dependent.
