Highly integrated biosensors based on fiber optics

Abstract

Benefited from the advantages of flexibility, miniaturization, immunity to electromagnetic interference and compatibility with today's well-developed optical fiber based telecommunication system, fiber-optic sensors show huge potentials with the increasing demand of comprehensive perception in every aspect of life. Especially in the practices of biosensing, optical fibers are prevailing platforms for highlysensitive, real-time, label-free and in vivo detection due to their high degree of integration, dielectric nature, non-toxicity and chemical inertness. In this thesis, we investigate several approaches focusing on the proper design of optical fiber structure and the efficient integrations with functional materials to enhance the effectiveness of light-matter interaction and the reliability of biosensing output. Firstly, we develop a highly sensitive magnetic field sensor based on magneticfluid-coated long period fiber grating (LPG). The emergence of optomagnetic biosensors in recent years brings the needs of all-optical, integrated and flexible magnetic field sensors. Benefited from the acute response of LPG to ambient medium and the remarkable magneto-optic properties of magnetic fluid, our proposed magnetic field sensor provides a superior sensitivity of 0.154 dB/Gauss. Secondly, we investigate the possibility of improving conventional fiber-optic plasmonic biosensors by employing a graphene/gold hybrid plasmonic structure. Introducing a graphene layer not only strengthens the surface plasmons but also acts as an excellent replacement of surface functionalization. We construct a biosensor that integrates such hybrid plasmonic architecture with a side-polished optical fiber and achieves a limit of detection (LOD) of ssDNA as low as 1 pM. Thirdly, we explore the potentials of adopting transition metal oxides as an alternative class of plasmonic 2D materials for biosensing in well-developed visible and near-infrared (NIR) optical windows, since plasmonics of common 2D materials locate intrinsically at mid-infrared range. Here we demonstrate the feasibility of integrating heavily-doped 2D MoO3 with fiber-optic platform and achieving strong surface plasmons in NIR range, which facilities low LOD of biomolecules. Fourthly, we realize one-step green synthesis of -cyclodextrin (-CD) capped gold nanoparticles. The macrocyclic supramolecular -CD serves as