Most piezoelectric biosensors normally use crystals, as in the quartz crystal microbalances or surface acoustic wave devices. A new system is described in which piezoelectric polymer films (made of polyvinylidene fluoride, PVDF, and Immobilon, a porous type of PVDF) are used to produce a mass sensitive oscillatory resonant device. Recent results demonstrated that this system successfully detects the binding between bovine IgG (immunoglobulin G) and anti bovine IgG. In order to improve the performance of the biosensor the electromechanical behaviour of such film-membrane is being studied. Miniaturization is also a desirable trend which will be pursued. Thus reports on the dependence on the electrical, mechanical and biological properties with the size of the film will be presented.