Highly integrated biosensors based on fiber optics

• Main Author: Zhang, Mengying
• Other Authors: Shum Ping
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Science::Physics::Optics and light; DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: https://hdl.handle.net/10356/89954; http://hdl.handle.net/10220/47180
• Institution: Nanyang Technological University

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 highly-sensitive, 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 magnetic-fluid-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 both reducing and stabilizing agent during synthesis and also biocompatible selective surface functionalization for target molecule recognition. Benefited from the highly efficient host-guest interaction between CDs and cholesterol molecules, we achieve an ultra-sensitive microfiber based cholesterol biosensor with good biocompatibility, specific selectivity and LOD as low as 5 aM. Lastly, we propose a highly-birefringent microstructured optical fiber (MOF) based plasmonic biosensor. Birefringence commonly exists in fiber-optic platforms and external perturbations would induce polarization crosstalk thereby destabilize the sensor output. We theoretically prove that the output instability due to polarization crosstalk can be effectively suppressed when the birefringence of MOF is larger than 2 × 10-4. Here, we design a polarization maintaining MOF with birefringence as large as 4 × 10-4, which can suppress the impact of polarization crosstalk to be negligible. Meanwhile, our proposed highly-birefringent MOF based plasmonic sensor also provides a high sensitivity of 3100 nm/RIU. In the studies we conducted so far, it is shown that the vast possibilities of optical fiber design and the breakthroughs of functional nanomaterials facilitate promising potentials in achieving highly sensitive and highly integrated biosensors. Further improvements in the specificity, sensitivity, biocompatibility and integration of fiber-optic biosensors will be carried out in the near future.