1. Definition of a biosensor

According to Gronow [2] , a biosensor is an analytical tool or system consisting of an immobilized biological compound, called a "ligand", connected to a transducer that transforms the biochemical signal into a quantifiable physical signal. According to the International Union of Pure and Applied Chemistry (IUPAC), a biosensor must be small and compact, have a reversible signal, give precise determinations (on-off reactions) and establish a real connection between the biological material and the transducer.