“…From a medical, analytical point of view, it is extremely important to work also on biosensors that allow the monitoring of fT3, as an indicator of thyroid diseases. Various ways are used to determine the level of fT3, such as radioimmunoassay (RIA), enzyme immunoassay [ 8 ], chemiluminescence, or electrochemiluminescence [ 9 ], however, they require multiple-step preparation, processing, specific laboratory equipment, are time-consuming, and do not allow continuous fT3 monitoring [ 6 ]. For instance, RIA uses a displacing agent, such as 8-anilino-1-naphthalene-sulfonic acid or salicylate, to detach the hormone [ 10 , 11 , 12 ].…”