In this work QCM technologies were used to set up a DNA based biosensor dedicated to the detection of toxic micro-algae in the environment. Up to now, appropriate detection were not achieved for different reasons as the possibility of regeneration, the capability of multidetection or the detection of very low DNA target concentration. For these reasons different configurations were examined based on in-situ and fast regeneration, supramolecular chemistry of DNA and high sensitive gravimetric devices. In a first step an OligoDesoxyRibonucleotide 5’ tailed with a disulfide group (SH-ODN) designed to be a specific molecular probe for the toxic micro-algae Alexandrium minutum was grafted on the quartz surface resonators. Kinetics of probe immobilization and of hybridization reactions with different targets were followed by monitoring the microbalance frequency changes of QCM working at 27 MHz and 50 MHz. These first experiments also showed that regeneration of this disulfide DNA QCM biosensor was possible as the target could be removed by alkaline dehybridization. Finally, to design a reversible QCM-DNA-biosensor in order to detect successively different targets, a modification of the grafted probe was attempted based on a complex structure of DNA assemblies.