SPP-MIM Hybridization Meta-Films for High-Sensitivity and High-Stability Biosensing at Optical Fiber End-Facets

Abstract

The specific optical dispersion of metal-insulator-metal (MIM) waveguide allows the hybridization of surface plasmon polaritons (SPPs) and the waveguide, which is not possible with dielectric waveguides. SPP-MIM hybridization creates such a meta-film that integrates the previously incompatible respective merits of SPR and LSPR, including a flat biosensing interface, a high surface sensitivity and efficient coupling with spatially confined illumination. On the other hand, to achieve stable and reproducible performance is one of the greatest but unresolved challenges for nanophotonic biosensors. Yet the underlying mechanism of instability is not well understood. We conclude, from a literature survey, that the stability of biosensing performance is strongly correlated with the flatness of the physical sensing interface. A nanostructured interface, at least, would introduce surface gas nanobubbles to interfere with the interactions between analytes in the solution and ligands on the solid substrate. Hence, the SPP-MIM meta-film provides a capable solution for sealing photonic nanostructures under a flat and stable biosensing interface. We embed the meta-film with a plasmonic crystal cavity and integrate it on a single-mode fiber's end-facet to detect biomolecular interactions. This device demonstrates highly reproducible sensorgrams and convincing detection of biotinylated proteins at down to 30 fM, with the sensorgrams following the Langmuir model. Having both high sensitivity and high stability, our device proposal provides an unprecedentedly comprehensive solution for optical fiber-tip plasmonic devices. It has immediate application values for biomolecular interaction analysis and drug discovery.

Keywords: Surface plasmon resonance, Metal-insulator-metal, Hybridization, Optical fiber end-facet, Label-free biosensing, Biomolecular interaction analysis, Stability, Surface gas nanobubble.