Multiplex interferometric biosensor based on photonic crystal microdisks

In this thesis, an optical multiplex biosensor approach based on multi-pinhole and multi-microdisk interferometry is introduced for the parallel screening of multiple biomarkers at the point of care. The compact biosensor system is based on one-dimensional photonic crystal slabs (1D-PCS) as signal transducer. It is designed for simultaneous intensity and phase measurements of the guided mode resonance. The approach provides inherent differential referencing that results in an improved signal to noise ratio compared to non-interferometric photonic crystal based sensors. Furthermore, the combination of intensity and phase measurements increases the reliability due to the redundancy produced by the two different measurement approaches of the same biorecognition signal. The advantage of the method is the combination of low cost 1D-PCS signal transducers with the low detection limit interferometric measurement approach while the biosensor system is compact and simple. The performance of the microdisk biosensor system is validated by simulations and measurements using human α-thrombine and streptavidin as test biomarkers. For multiplex interferometric phase sensing based on photonic crystal microdisks, an unambiguous interference pattern with unique spatial frequencies is required. Hence, different pattern designs of circular diffractor elements that produce unique spatial frequencies are investigated. Design algorithms are introduced, whereby their optimization criteria are the uniqueness of the spatial frequencies and the density of the microdisk pattern. Theoretically designed patterns are validated through fabrication of photonic crystal microdisk elements and characterized optically.
The thesis starts with an introduction to the basic theory of label-free optical biosensors, one dimensional photonic crystal slabs, interferometry and Fourier optics. 


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