Medical science and biology take a prominent part in our age. Today, the knowledge and application of biological mechanisms are getting more and more important. Science has already had numerous achievements in this field so far. However, there are still several essential processes we miss. In my opinion, it is one of the greatest scientific challenges to develop better sensors, the so-called biosensors, in order to experimentally investigate the relevant physiological processes more accurately. I have been working with a label-free biosensor, the Optical Waveguide Lightmode Spectroscopy (OWLS). This device is specialized for examining surface adhesion processes of biological and chemical materials. An evanescent field is produced at the surface of the OWLS waveguide sensor by the illumination light, which is coupled into the waveguide film through an optical grating. The coupling angle of the light is changed due to the presence of the sample entering into this evanescent field.
We can obtain the refractive index and layer thickness of the layers deposited on the waveguide chip using electromagnetic field simulation, which is known as the equation of the four-layered model in the scientific literature. This model usually assumes homogeneity and isotropy for the examined sample. But, in most practical situations the analyte layer is neither homogeneous nor isotropic, therefore the simplest optical model cannot be employed.
In this work I construct the electromagnetic model of the OWLS sensor in CST Microwave Studio and implement this structure in a MATLAB algorithm which is developed by myself. The MATLAB algorithm was created by using the Maxwell’s equations and taking into account the optical parameters of the sample. I determine the OWLS coupling angle in both simulation environments in the function of the parameters of the sensor and the biological sample. The results of these two simulation environments will be compared with two real measurements on homogeneous glycerol solutions and on an inhomogeneous film formed by the F40 protein. The Maxwell-Garnett mixing rule will be applied to determine the filling factor in case of the inhomogeneous protein layer. I will also employ microtechnological tools to fabricate a working OWLS waveguide sensor and present the steps of the OWLS measurement.