In recent years, many studies have focused on organic bioelectronics, an emerging technology that employs organic transistors for biosensing applications. Compared to their inorganic counterparts, organic transistors exhibit several advantages, such as biocompatibility, low cost, high sensitivity, flexible substrate compatibility, easy fabrication and low-temperature processability. A specific category of organic transistors, the subject of this thesis, is the organic electrochemical transistor (OECT). In this device, the channel is typically made of a conductive polymer, such as Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), in contact with an electrolyte in which the gate is immersed. OECTs act as a transducer and amplifier of an ionic signal into an electrical one, operating at low voltages and providing significant amplification; this characteristic makes them highly pertinent in biosensing applications, such as medicine and biology.