This thesis describes the development and evaluation of highly sensitive interferometers for permittivity measurements of biomedical materials. The objective is to engineer a sensor system enabling label-free and contactless characterization of dielectric samples. Initially,various sensing methods are discussed and compared. Subsequently, different approaches serving as read-out circuits suiting the investigated sensors are reviewed. The performance of sensors along with the respective read-out technology are compared to each other leading to the final method of choice: The interferometer is identified to be the best suited technique. It is initially realized on a printed circuit board at microwave frequencies for experimental investigations. The selected strategy to realize an extremely compact sensor that can be integrated into microfluidic systems is scaling. Subsequently, millimeter-wave frequencies are inspected on suitability for permittivity measurements. Finally, the interferometer architecture is scaled to work at 120 GHz and fabricated in a 130 nm BiCMOS process featuring an ft/fmax of 240 GHz/330 GHz. The resulting system includes a 120 GHz voltage-controlled oscillator with a tuning range of 7 GHz. It features a divide-by-64 circuit to enable external phase-locked loop stabilization. Additionally, the final chip set contains high-precision and high-resolution phase shifters based on a slow-wave transmission line approach with digital control to provide direct readout ability. The system enables automated, contactless and label-free permittivity monitoring for biomedical purposes. Hence, it represents a powerful solution for biomedical sensing applications and it provides a platform for future lab-on-chip devices.