Exposed Core Microstructured Optical Fiber Surface Plasmon Resonance Biosensor

Surface Plasmon Resonance (SPR) scattering offers significant advantages compared to traditional reflectivity measurements, essentially turning a non-radiative process into a radiative one. Recently, we have shown that SPR scattering can be used in an optical fiber, enabling higher signal to noise ratio, reduced dependence on the metallic thickness as well as the unique capability of multiplexed detection with a single fiber. Here we report a novel SPR scattering based sensor fabricated based on an exposed-core silica Microstructured Optical Fiber (MOF). This MOF presents a structure with a relatively small core (empty set = 10 mu m), exposed along the whole fiber length. This exposed core MOF allows for fabrication of SPR supporting metallic thin films directly onto the fiber core offering the new prospect of exploiting SPR in a waveguide structure that supports only a relatively small number of guided optical modes, with a structure that offers ease of fabrication and handling. A thin silver film of 50 nm thickness was deposited onto the fiber core by thermal evaporation. The significant surface roughness of the prepared metallic coatings facilitates strong scattering of the light wave coupled into the surface plasmon. Performance characteristics of the new exposed core fiber sensor were compared to those of a large bare core silica fiber (empty set = 140 mu m). Although sensitivity of both sensors was comparable (around 2500 nm/RIU), full width at half maximum (FWHM) of the SPR peaks for the new exposed core fiber sensor decreased by a factor of 3 offering an significant enhancement in the detection limit of the new sensing platform in addition to the prospect of a sensor with a lower detection volume.