In this paper, we introduce a charge integrator as a read-out system for piezoelectric cantilever sensors. The charge integrator is used to monitor the surface charge induced by piezoelectric materials as a function of mechanical stress. This technique improves the response of piezoelectric cantilever sensors in low-frequency measurements, which makes them suitable for chemical and biological detection. Furthermore, it is capable of real-time, portable and all-electrical detection. The detection of alkanethiols on the Au-coated piezoelectric cantilevers is demonstrated to verify the concept.