Our works aim the study of an ultra-sensitive bacteria-based biosensor for the detection of heavy metals (environmental control). They include the development of impedimetric and of Love acoustic wave devices, both associated with a microfluidic chip and functionalized with Escherichia coli immobilized on a polyelectrolyte multilayer deposited by the method "Layer by Layer." The theoretical study of physico-chemical interactions and biological phenomena involved during the steps of functionalization of the sensor surface, and during its application to the detection of cadmium and mercury, is also addressed through the real-time monitoring by the acoustic sensor and by atomic force microscopy in air or liquid medium. Detection threshold better than10-12M within only a few minutes have been observed.