Optical biosensors: Master's thesis

Optical integrated biosensors are an interesting alternative to conventional laboratory equipments in all areas concerned with biomolecule analyses. These biosensors are miniature optical configurations with a potential to be quick and simple to use, and in addition cheaper to fabricate than current laboratory devices. Optical integrated biosensors can be either direct or indirect sensors. Indirect sensors require a label, which attaches to the measured molecule and prevents the defects rising from non-specific binding. Although this improves the sensitivity of the sensor, indirect sensor needs a more complicated measuring process, because of several washing steps to remove bound from unbound label. Thus the most straightforward way is to use the direct biosensor. There are several ways to realise a direct biosensor and one of the simplest ones is a Young interferometer. We have modelled an integrated optical Young interferometer according to electromagnetic theory of propagation of light in waveguides and far fields. The designed interferometer structure should possess single mode behaviour and a sensitivity of a magnitude of 10-5. The structure is based on a 3.7µm wide and a 2.8µm thick channel waveguide with following refractive indexes nf=1.49547, nc=1.49233 and ns=1.49233. The Young interferometer has a 60m branch separation and 5mm long sensing and reference windows. According to experiments the measured and the modelled transitions of the interference pattern were in the same order of magnitude. The theoretical sensitivity obtained for the interferometer structure was . Although the interferometer functioned as expected, the sensitivity analysis was affected by the measuring configurations in such extend that neither the real sensitivity nor the comparability of the theoretical model was possible to obtain with sufficient accuracy.