Exploring the Slab : Pathways Towards Advanced Refractive Index Sensor Systems Using Photonic Crystal Slabs
Waveguide gratings commonly known as photonic crystal slabs have been studied as refractive index sensors. Their ability to act as optical transducer in biosensing applications and cheap nano-replication methods make photonic crystal sensors a promising technological platform for decentralized, point-of-care diagnostics. In this thesis two domains of these sensor systems are investigated, the readout system and the geometry as a basis for the optical transducer. A multi-spot time-resolved measurement setup is introduced and the in-situ binding of human thrombine is shown. To overcome the necessity of expensive laboratory equipment, intensity-based read-out of photonic crystal sensors has been proposed and shown in literature. Here different approaches for future read-out systems were studied. Multiperiodic and deterministic aperiodic nanostructures are investigated for refractive index sensing applications. While multi-resonance human thrombine binding measurements show that no benefit is achieved compared to better resolved single-resonance measurements, the use of eight different resonance positions made is possible to measure spatially resolved refractive index dispersion. It is shown that localized fields of aperiodic structures may offer higher sensitivity. Here laser ablation experiments and the resonant, photocatalytic growth of gold nanoclusters are shown, that might open a door to access localized fields for sensing applications. A 2D finite-element COMSOL Multiphysics® model, with simple MATLAB® control, was created and validated that computes spectral responses as well as the electric near-fields of the photonic crystal structures used in this work.
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