Biosensors are powerful tools for detecting specific molecules by leveraging biological interactions to generate measurable signals. This research focuses on the development of advanced label-free biosensors using Silicon Nitride integrated optical circuits, employing Mach-Zehnder Interferometer (MZI) structures as the sensing elements. MZIs, which combine waveguiding and interferometry, offer high sensitivity by detecting phase shifts induced by analyte binding in real time. The development process encompasses component simulation, chip design, chip fabrication, packaging, optical and electrical characterization and biological testing. Although the Silicon Nitride sensor is still under development, preliminary results from silicon waveguide-based MZI devices have demonstrated their ability to accurately monitor binding kinetics. A key advantage of Silicon Nitride is its compatibility with visible wavelengths, where optical losses are lower when using aqueous cladding, as is common in biological testing. This research holds significant potential for advancing label-free optical biosensing technologies, with applications spanning healthcare, environmental monitoring, and beyond.