Quartz crystal is generally used in some applications as a microbalance taking advantage of its capacity to change the resonance frequency according to any surface mass change on the resonator. In this way a quartz crystal can be used as a transducer in a piezoelectric inmunosensor system in order to detect antigen-antibody bonds. An interface for Quartz Crystal Microbalances, QCM, based on an improved version of an oscillator in balanced differential configuration and its respective validation as a biosensor characterization system is introduced in this paper. The system was successfully tested in a piezoelectric inmunosensor for detecting the pesticide Carbaryl.