Modeling of optical waveguide biosensor structures: Licentiate thesis

Optical biosensors have become attractive candidates for sensing immunochemical binding reactions, not only in medicine but also in environmental science and process technology monitoring applications. Fluorescence is one of the most prevalent methods to label antibodies or antigens for optical detection. Integrated optical and fiber optic sensors can help miniatyrize a conventional assay based on fluorescence and make it a cheaper and faster probe to be coupled with an economical instrument for doctor's of office, outpatient and critical care monitoring of biochemical parameters. This work presents a study of modeling, fabrication and characterization of integrated optical fluorescence sensors. Finite-difference time-domain (FDTD) modeling has been applied to the design of the device. FDTD is a numerical method for solving Maxwell's equations for electromagnetic fields in a discretized space and time grid. Benefits of the method include savings in computer memory storage and execution Limes, and the possibility to take the near field features of the model in account. The fluorescence sensor component was designed so that with correct choice of parameters, both evanescent excitation and side collection of emitted fluorescence could be maximized. The component was fabricated by sputtering quartz on a fused silica substrate in presence of nitrogen gas. The devices were characterized by various methods to get a physical picture of the properties of the sensor. Another FDTD model was subsequently developed to evaluate the performance of the component in fluorescence sensing applications. The result of the work was validation of FDTD as a tool to solve optical problems. In the characterization, a new method was developed for loss measurements of waveguides based on CCD imaging. The results of the study indicate that the fabricated components are well suited for fluorescence sensing applications.