This thesis reports on a novel system for extracellular recordings of the activity of excitable cells, which relies on an organic, charge-modulated field-effect transistor (FET) called OCMFET. The book shows how, thanks to the intrinsic biocompatibility, lightness, and inexpensiveness of the material used, this new system is able to overcome several problems typical of of "classic" electronic and bioelectronic. It provides a full description of the system, together with a comprehensive report of the successful experimental trials carried out on both cardiac and nerve cells, and a concise yet comprehensive overview of bioelectronic interfaces and organic sensors for electrophysiological applications.