A Mach-Zehnder interferometer based on silicon oxides for biosensor applications.

Integrated optical devices have been increasingly interested in biosensor applications including environmental pollution, biological process and medical diagnostics. Integrated optics allows high-detection sensitivity to be achieved using optical transduction techniques in a microfluidic format. Among different transduction techniques, a Mach-Zehnder interferometer (MZI) has advantage of its inherent high sensitivity and accuracy. The evanescent wave of an optical waveguide interacts with an adjacent layer, and this can be the basis of the recognition of biomolecules. In recent years, silicon dielectrics as potential materials have been attracted in an integrated optics. The refractive index of these silicon-based materials can be easily adjusted continuously over a wide range between 1.45 (SiO2) and 1.97 (SiO). This comes to be very attractive in terms of design and fabrication of single-mode waveguides. In this article, we tried to realize the Mach-Zehnder interferometer sensor based on silicon oxides, and the refractive index of the oxides was controlled by the oxygen concentration to achieve the single-mode behavior of a total internal reflection (TIR) waveguide. We have performed to verify the feasibility of the MZI sensor for the direct detection of immunoreactions.