This research starts with a state of the art review on biosensing and applications. Then followed with the design of a structure using the advantages of carbon nanotubes (CNT) as a field effect transducer and as an interface with a biological field. Indeed CNTs are known to be very sensitive to their electrical environment and to chemical changes at close range. Moreover, CNTs, thanks to their hexagonal carbon lattice, can be used as a substrate for organic molecules deposition; allowing the creation of a selective layers.