Fabrication of fiber-optic sensors based on plasmon resonances of metallic nanostructures
This paper describes the fabrication of portable and robust fiber optic sensors - mainly chemical and biological sensors - on standard communication grade optical fibers. Metallic nanostructures such as nanoparticles, nanopillars, nanorods, and nanoholes in optically thick metallic films were employed to precisely control the enhancement and absorption of light so as to form sensitive and specific optical sensors based on optical fibers. The fiber-optic sensors employ localized plasmon resonances (LSPRs) of metallic nanostructures formed on the fiber end-face as well as surface plasmon resonances associated with nanoholes in optically thick metallic films as a means of transducing the input optical signal. These metallic nanostructures were formed on the cleaved end-face of multimode and single mode optical fibers and were employed in both reflection and transmission modes. Metallic nanoparticles, nanorods, and nanopillars were formed on the tip or surface of the optical fiber by either employing chemical means or by first depositing a 10-200 nm layer of metallic film on the tip of the fiber and then employing focused ion beam (FIB) milling to pattern out the metallic nanoparticles and nanopillars from the film. Ordered arrays of nanoholes were formed in optically thick (150-230 nm) metallic films by employing FIB milling. Gold (Au) nanostructures are chemically stable and result in plasmon resonance related dips in the transmission spectrum in the visible spectral region. Hence, gold was selected as the material of choice for the fabrication of the plasmon resonance sensors. © The Electrochemical Society.