Rigid and Flexible Photonic Crystal Slabs for Label-Free Biosensing of Biological Liquids as a Basis for Wearable and Point-of-Care Sensing

The use of wearable and point-of-care testing devices promises great benefits for individual health monitoring. For health monitoring affinity-based biosensors are often used and in this work an optical transducer based on photonic crystal slabs is employed. Photonic crystal slabs have commonly been processed on rigid substrates, which renders an application as a wearable component difficult. Further, limited research has been done on rigid photonic crystal slabs when sensing directly from liquids of biological origin, such as unprocessed whole blood. The sensing of unprocessed whole blood is of great interest, as it is the most information abundant biological liquid and is quite easily obtained. The first part of this work introduces two new fabrication techniques for flexible photonic crystal slabs. The first one is based on an exfoliation method. The effect of the fabrication process on the quality factor (Q-factor) as well as refractive index and biomolecular sensing properties are investigated. The second type of fabrication technique uses the direct deposition of waveguiding layers onto a nanostructured polydimethylsiloxane (PDMS) substrate. Its mechano-optical properties are analyzed and found to suppress mechanochromatic effects. Due to these properties, they are named stabilized photonic crystal slabs (sPCS). The second part of the thesis investigates camera-assisted readout approaches for point-of-care analysis. First, an intensity-based camera setup (IBCS) is introduced, which uses the sharp edge of a cut-off filter to enhance the sensitivity. Further it shows the concept of an autonomous microfluidic biochip as a single-use consumable for point-of-care applications. In addition, a second setup is introduced, which uses an angle-tuning of an optical interference filter to sample the surface of a photonic crystal slab. Both setups are able to sense from unfiltered whole blood. This is of great interest for a potential use as point-of-care device.

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