Plasmonic nanoparticle-functionalized exposed-core fiber—an optofluidic refractive index sensing platform

Here, we show that immobilizing ensembles of gold nanospheres within tailored areas on the open side of an exposed-core microstructured fiber yields a monolithic, highly sensitive plasmon-based refractive index sensor. The nanoparticle densities (average nanoparticle diameter: 45 nm) on the small-core fiber (core diameter: 2.5 μm) are controlled electrostatically, yielding densities of 4  nanoparticles/μm2. Refractive index sensitivities of 200 nm/RIU for aqueous analytes at high fringe contrast levels (−20  dB) have been observed. Our concept presents an easy-to-use, efficient, and multiplex-compatible sensing platform for rapid small-volume detection with the capacity for integration into a bioanalytic, optofluidic, or microfluidic system.