Functionalization of Microstructured Optical Fibers by Internal Nanoparticle Mono-Layers for Plasmonic Biosensor Applications

For fully integrated next-generation plasmonic devices, microstructured optical fibers (MOFs) represent a promising platform technology. This paper describes the use of a dynamic technique to demonstrate the wet chemical deposition of gold and silver nanoparticles (NPs) within MOFs. The plasmonic structures were realized on the internal capillary walls of a three-hole suspended core fiber. Electron micrographs, taken of the inside of the fiber holes, confirm the even distribution of the NP in the MOF over a length of up to 6 m. Accordingly, this procedure is highly productive and makes the resulting MOF-based sensors potentially (very) cost efficient. In proof-of-principle experiments with liquids of different refractive indices, the dependence of the localized surface plasmon resonance (LSPR) on the surroundings was confirmed. Comparing Raman spectra of MOFs with and without NP layers, each one filled with crystal violet, a significant signal enhancement demonstrates the usability of such functionalized MOFs for surface-enhanced Raman spectroscopy (SERS) experiments.