Nowadays, at a time of growing concern for sustainable development and compliance with environmental standards and legislation, the detection of heavy metal contaminants in environmental matrices represents a difficult but important task. The current major limitation lies in the poor detection limits of the targeted pollutant's trace concentrations by the available conventional techniques. In order to elaborate a novel "living" self assembled electrochemical 3-D biosensor, the authors propose a new concept to overcome this shortcoming. The advantages of the properties of polyelectrolyte-functionalized NBs (nanobeads) are combined along with the use of non covalently strongly bound micro-organisms. The designed 3-D biosensor is all the more promising as it has showed a significantly improved sensitivity. In fact, the detection limits of the tested heavy metals (cadmium and mercury) were as low as 1.0 × 10-12 mol*L-1 and six to seven orders of magnitude lower than those provided by conventional 2-D biosensors. Furthermore, it is potentially applicable to a wide range of bioreceptor-pollutant detection systems.